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But, what if an object travels so close to the speed of light that it travels across the entire observable universe in femtoseconds of proper time? Would the object continue on its trajectory until it hits into another object? Or would it wrap around the universe infinitely or stay in place in empty space as the universe expands so that the object HAS TO experience time?
So when I'm playing chess with my computer and our kings wind up next to each other, and im pissed because the computer wont let me take its king saying its an illegal move but it's king takes mine‽ I shouldn't be learning chess from a computer.
This has nothing to do with scientific analysis, this is a video/channel analysis. He always sets himself up as the ignorant foil asking the questions. Einstein or whatever author he’s read is always correcting him, even though he’s the guy who understands what he’s teaching us. This is what makes him charming and charismatic and approachable from our point of view as learners: let’s learn together. That’s the literal definition of a good teacher.
Veritasium did a video on this teaching technique as well. It’s more important to explain what something is not / incorrect than it is to simply list truths
Yes, this channel is amazing for all the reasons you just said, not to mention how excited he is about all the information, it's impossible to be bored watching him 😂
I'm with that line of thinking, but then if equations are allowed to be blown up do we assume that singularities exist?! Perhaps time not moving and singularities are connected in some way, at least in telling us that we're missing something major in our knowledge!
If an object travels almost at c, from its reference frame the universe is traveling at almost c and is extremely contracted in the direction of the movement. So, from its perspective, it would traverse the entire universe almost instantaneously. I think looking this way we could say this object experiences almost no time, meaning it does not see the universe evolve in the very short time (from its perpective) it took to traverse the universe. If you think regular objects do not traverse the entire universe, but a smaller distance between object creation and destruction, for this object it existed during almost no time and was almost instantly destroyed
That is also how I see light, it's as if the photon was using a wormhole through space-but-not-time, and that wormhole is called the EM-field, but it's an imperfect wormhole due to redshift..
I view light in the sense of limits and infinities, that blow up equations. Like singularities. We're clearly missing something significant in our understanding.
You're absolutely right. As every point in the universe sees light traveling at the speed of light relative to it, then light in turn sees every point in the universe moving at the speed of light relative to it self and hence the whole universe is length contracted to be infinitely thin in the direction of travel. The universe becomes an infinitely thin but very wide pancake. This means that the point in space where it starts its journey is the same point in space where it ends its journey and it take zero time from its perspective to travel from start to finish. So does light experience time, well its life is over before it has a chance to experience anything. We see light moving but for it, it all happened and finished it's journey before time even moved.
@@DABmonger Nope, photons are just the exchange particles, there exist no photons on the path of light, just electromagnetic waves, the photons are only created from those electromagnetic fields by interactions with matter.
I'm two minutes in and you are already blowing my mind about concepts I thought I understood. I absolutely love your videos, you are by FAR the best physics presenter and explainer since Feynman. Keep up the great work, I'm hanging on your every word now!
I love it when people actually believe that they can really KNOW this stuff. They really have convinced themselves that they have actually understood what we can never possibly understand. Understanding what does light experience, is a classic case of over confidence. google the free ebooks, "Dave vs Hal 9001" for more information. You may change your mind about what you think is real and true.
@@Mahesh_Shenoy it's true my man, I look forward to seeing your presentations when they drop in my notifications. They're actually fun dude, you make science what it's supposed to be, awesome 👍
I read somewhere how we could imagine photon 'perspective'. From it's 'point of view' there is only act of creation and then instantaneous act of annihilation (when it interacts with some object). There is nothing in between for photon, it does not 'experience' time.
Well as far as it (the photon) is concerned, it might as well be instantaneous, even if it took 13.8 billion years in reference to me? Zero time experience is pretty well instant right? Kinda baffles the logic of normal intuition when you realize that time is truly based around the fastest thing in the universe, that's how it ought to be reasoned at least, if you want to truly understand what time is. Base your reference at the fastest thing known, kind of like temperatures and zero. There's a limit and we reference from there in science, hence Kelvin. Why not do the same with light\photons\emr? I'm not trying to turn our time reference understanding on it's head, Just like we don't use Kelvin in everyday life. But for scientific matters, yeah 👍 I think it would simplify the problem of medium speeds not matching to do that way, cause it's all light speed, just different frames of reference right? I'm not gonna even attempt to address the things that would happen sub-planck though, haha, not qualified. It'd be weird for sure, in case this isn't weird enough for you. I am in no way certain there's anything meaningful below Planck pixel, but I'm certainly not opposed to it being more than not meaningful, so what if the Schwartzchild radius = black hole. Another thing we don't really know anything about other than they're there and they're doing something deeply interesting.
@@G0ldbl4e They do not. The math for time dilation/length contraction doesn't work for things moving at c. They don't have reference frames, so special relativity doesn't apply.
The very idea that the photon does not experience time, as far as it's concerned it's just sitting there, good Lord man what a concept. I mean really if you think about it 🤯 trillions of trillions of trillions of photons, all different amplitudes and wavelengths, interacting with different interferences to form stuff, all infinitely small and large at the same time, this is weird stuff seriously. It makes me pull back to the holographic model, you know what I mean, if it's just there then not, everything else around it being what's in motion... Which is also a bunch of other photons at rest, blipping on and off here and there. Kind of leads to the idea that maybe it is in some way intricately holographic. I mean it's pretty much all electrical\em. I learned that some years ago during a heroic experience that I did not plan on taking but accidentally did anyway. Idk I think a lot about stuff but this one I think is above human thinking. I'm definitely not smart enough to grapple with that one, but I'd be willing to bet my life that it's so ridiculously elegant and simple that we're just looking right over it. It's probably right in front of us 😅
05:40 f _Looking from s.o.'s perspective basically means looking from s.o.'s reference frame._ I'd put it differently: By "looking from s.o.'s perspective" physicists mean *describing the scenario from a rest frame of her/ his.* ▪︎A frame in this context is a coordinate system which basically maps all of spacetime, so you can't really looking _out of_ it. Rather you express physical quantities in those coordinates. ▪︎Everything kind of has infinitely many rest frames with different orientations or origins. ▪︎Your reference frame is the frame you use to describe a scenario. This _might_ be a rest frame of yours but it _doesn't have to._ And in everyday life, it seldom is. Mostly we implicitly use a frame bound to Earth; otherwise, if I went to Cologne by train, I'd have to say "the train has come to rest (a very active rest like that of someone running on a treadmill) and lets Cologne approach it".
I also asked myself this question, and, hopefully, i have a similar answer to what Einstein would have given. I phrased the question like this: If I approach the speed of light relative to the centre of mass of the Milky Way, I see the Milky Way's length along my direction of travel as approaching 0. So I should cross the Milky Way in a length of my proper time that approaches 0. But an external observer (who is at rest with the Milky Way's centre of mass) will see my velocity as approaching c, and hence my length will approach 0, while the galaxy's stays "normal". So the external observer would see me cross the galaxy in a long amount of time, nowhere near 0.000...01 seconds. So whats the solution to this paradox? After 0.00..01 seconds have i, or have i not, crossed the galaxy? Who's right - me or the external observer? The answer i could come up with is this- There is no shared definition of "right now" between me, and the external observer "B". So while my journey takes 0.00...1s in my time, it takes some years in B's time. B and I, however, are using different standards to measure the distance between two events - me setting off, and me crossing the galaxy. That's why we don't agree on the time between those events. As you can see, until now, the situation is perfectly symmetrical and both of us are equally "right". So we just don't agree on the time between two events. But thats ok, it happens all the time in special relativity. Also B would agree on the length of *my* time it would take me to cross the galaxy because he sees my clock as very slow, approaching not ticking at all. So he would agree that it takes me less than a second of *my* time for me to cross the galaxy. I think it's beautiful how this fits so nicely - i measure so little time due to velocity which manifests as length contraction, while B measures the same length of *my* time, again, due to velocity, but this time it manifests as time dilation. And the result is exactly the same in both measurements. Maybe this shows the deep similarities between space and time, and why one can't be without the other, why we speak about spacetime together, not separately. But what if i turned around and came back to B, and we compared our ages? This is called the twin paradox. To come back, I'd have to accelerate. Time, space and simultaneity are relative but acceleration is absolute. So the moment i accelerate towards B, i break the symmetry. Now both of us have traveled thru spacetime, between two events - me leaving and me coming back. However my path was more thru my space and less thru my time, B's was more thru B's time and not at all thru B's space. So B has aged more than me when we meet again. And this comparison is only valid if and when we do meet up, otherwise you can't ask both of us how old we are right "now" because there is no meaningful way to define a shared right "now" for both of us.
Supposing you were to introduce a third perspective into the twin paradox scenario. One in which a spaceship is always manoevred to be halfway between the two. Putting myself in this third perspective, I find it implausible that two people, always equidistant to myself, could be ageing at such dramatically different rates. Similarly, consider the graphics at 0:53 to depict time slowing down for a moving clock. The inverse would also be true, from the top clocks perspective, the lower clock would be ticking slower. Then consider a third perspective 'C' where the top clock 'A' travels west-east at the same speed that the lower clock 'B' travels east-west. A and B would see each other ticking slower. But C would calculate A to be ticking at the same rate as B. Logically, it would seem, this is truly a profound 'paradox' - or these presentations are a little muddleheaded.
@@bobpower9189 you are correct - the middle clock, C, will see both A (who is at rest with the Milky Way) and B (who is crossing the Milky Way) as aging both slower than C and at the same rate as each other, as they are moving away from C at equal but opposite velocities. As you pointed out near the bottom of your comment, this situation is 100% symmetric. *If A and B are in relative motion, A sees B slow and B sees A slow.* That is, until acceleration happens, or more specifically, until one of these observer assumes a distinct inertial frame, and abandons his initial inertial frame. Everyone would agree on who changed their inertial frame and he would be found to have aged less when all three observers meet up again. This is consistent with the time animation you provided a timestamp to. Try drawing out a spacetime diagram for this accelerating observer. Initially, in the first inertial state, the light bounces off between two lines parallel to the proper time. But when the proper time changes direction, the light suddenly starts bouncing off much less frequently than before. So when your three observers meet up again, we can assert that B accelerated the least (didn't accelerate at all), C accelerated a little bit (less than A) and A, who travelled at nearly c, accelerated the most. Hence A ages the least, C a bit more and B the most.
@@Krokodil986The effects of acceleration breaking time symmetry seem credible enough, but I could not imagine putting the 'pedal to the metal' for a duration of half an hour could result in years of age disparity, as is often presented. Presumably, different rates of acceleration yield different results. Also, have you ever come across any explanation whereby the effects of deceleration cancel, to any extent, the effects of acceleration. Just a thought - I've never come across it. How would this configure in a spacetime diagram.
@@bobpower9189 amazing question So rate of acceleration is how much you are accelerating per second, "jerk". The lower the jerk, the slower the change to the new inertial frame, but also the more time spent in acceleration. So I think it cancels out (to be honest I'm not too sure about this) Deceleration is the same as acceleration, but viewed from a different perspective. Imagine me walking along the street. I can start running. I think I'll be accelerating, right? Well someone who is already running will think I'm decelerating, because I'll be decreasing the relative velocity between me and that person. But for me I'm still accelerating - so the effects of acceleration and deceleration must be the same, time dilates. Put in other words, the direction of acceleration does not matter because the universe is fair - it treats all directions equally. In a spacetime diagram, deceleration may be shown as acceleration to the left instead of to the right. Directions are equal, the universe is fair so it doesn't matter. The only thing that may change is simultaneity lines may bunch up or spread out depending if you're accelerating toward or away from an observer onto his world line But the only meaning of this spreading or bunching is it changes from what point in time causal action propagating from this observer can reach you in your own "right now". I didn't explain this last point very well, if you don't get it I'll try to explain it better, let me know
@@bobpower9189 I've done some digging around... also let's define two velocities u and f let's say u -> c And f -> -c If you go from v = u to v = f, even if your change in velocity is instantaneous, ie delta t = 0, the age disparity will still approach infinity. In fact the quicker you get the acceleration part over, the quicker your two two inertial frames will reach their maximum difference. The quicker this happens, the longer they will be maximally different from each other. And the age disparity comes from this difference. So the longer the difference exists for, the larger the age disparity. So rate of acceleration does play a small part, but what's more important is the difference between the two inertial frames - ie the difference in initial and final velocity, rather than the time spend in transition.
The beauty of this format is that we leave with two amazing takeaways: a better understanding of physics and for me is a new way of thinking about hard subjects like physics.
"There comes a point in every man, woman, and child's life that they wonder - Does light experience time?" See, that's the mindset of a great theoretical physicist..
OK, fine. I can't help noticing the animations all say "length contraction ignored". So let's talk length contraction. Suppose we have three objects: P, Q, and R. P and Q are at rest with respect to each other, while R is moving with respect to both. P and Q can be road signs and R can be a car, or something. In P and Q's reference frame, they are some distance d apart. Due to length contraction, in R's reference frame they are some smaller distance d*k apart, where 0 < k < 1. As the speed of R with respect to P and Q approaches c, the factor k approaches what number? In R's reference frame, after P has gone past, it takes some time t for Q to reach it (since in R's reference frame it is P and Q that are moving). What happens to the time t as R's speed with respect to P and Q approaches c?
@silverrahul The thought experiment I started this comment thread with. Did you watch the video? Mohesh says that "does light experience time?" isn't a meaningful question, because it can't be framed in a way that has an answer within the laws of special relativity. I'm querying that.
@silverrahul Calculating what happens as one _approaches_ an unreachable limit, as a proxy for what happens _at_ that limit, is a routinely used and uncontroversial method in calculus. Mahesh himself discusses it in this very video (9:39--11:48).
@silverrahul I know that an object with mass cannot reach c. If you were concerned that I didn't understand that, you can rest easy. Thought experiments, in physics just as in mathematics and philosophy, reach out into the impossible, if only to understand _why_ it is impossible. We wouldn't say to Einstein "But you can't accelerate a train to half the speed of light, you'll kill all the passengers." We can turn my question around, if you like. Let's suppose again that we have objects P and Q, stationary with respect to each other, and object R, moving at speed v with respect to P and Q. P and Q are a distance d apart in their own reference frame, and a shorter distance d*k apart in R's reference frame due to length contraction. Let's ask now: what would v have to be to make k = 0? Now, is there any _other_ value of k that would yield the answer v = c? (There are certainly other impossible values of k. k can't be negative, or >1, or an imaginary or complex number. If you plugged _those_ values into the equation and solved for v, what answers would you get? Not c. v = c is associated with k = 0 and only 0.)
I always just thought about it like: If you're nearly at the speed of light (c) others would see your time go very, very slow. But for you in this reference frame your time goes "normal" but everything around you seems to be very, very fast. So if you would be at the speed of light for the others your time stands still (∞ slow) but for you everything around you would be ∞ fast. So for you the whole age of the universe would be over in 0 seconds. So you can't experience anything outside of your reference frame. And that's the problem that arises like you described the problem in another way.
That's not how it works as you're skipping relativity. You see the universe moving slowly too as it is also moving relative to you, therefore your clocks would agree. Only when you accelerate or spend time in a gravitational field will your clock slow down relative to everything else.
I think the more intriguing point with the "experience" of something moving "almost" at the speed of light is that it would experience ending up at any destination "almost" instantaneously. If it keep going without any destination it would experience ending up infinitely far into the future (whatever that means) "almost" instantaneously. If it could do this indefinitely it would for sure experience the clock ticking as usually. But that it would even have time to experience one tick of the clock before either smashing into something or getting to the end of times is not likely.
I was literally looking for a person who could explain things that comprehensively. The way you crack things, like the scientists who are much more eager to break apart the subatomic particles in the Large Hadron Collider to understand the behavior or laws of this Universe. The power of visualization and the interpretation you have mastered is just Astonishing. I don't have words for you, you are just limitless. Keep continuing the series I am learning a lot by opening different ways to visualize things for Better interpretation. My regards to you.
I asked myself this when I was young. Like late teens early 20's. I would mention it to people and they would have no idea what I was talking about. My friends weren't physics geeks. lol. Thanks for sharing. Love this videos
I studied this subject some decades ago. My interpretation of this question was somewhat different. You are focusing on time for the photon and the photons rest frame. You don’t have to do that. Instead think of travelling ‘almost at the speed of light’ and what you will see is that your own time passes normally, but the entire rest of the universe is Lorentz contracted in distance. In other words, you will (due to length contraction) arrive almost immediately after you leave - as the distance to travel is minuscule - even light years would (if you go fast enough) shrink to millimetres. The reason light does not experience time is nothing to do with rest frames, but rather that at the speed of light it arrives at the same instance it leaves / because the ‘length’ of its travel has shrunk to zero. This is in a perfect Vacuum. If the vacuum is not perfect, then the light will experience some minuscule time.
Excellent... Also, I think the video would better serve viewers by comparing clocks. If a photon were to look at its wristwatch, it would observe the hands moving in proper time. Sure, but an observer watching the photon go by would observe that the photon's wristwatch has hands that aren't moving at all. As you point out, this is explained by the photon observing that all the points through which it travels at the speed of light have contracted into one infinitesimal. I'm super curious how this topic relates to entanglement. Could it be that entangled pairs, despite potentially being separated by light years, "think" that they continue to occupy the same point because per their observation, zero time/space has passed between before they were split and when they become disentangled?
In a reference frame the observer is at rest; not the photon is at rest. The photon needs to travel at the speed c with respect to any observer - even if the observer would himself travel at c with respect to some other observer . . .
Time cannot be applied to a null curve, that is, for a photon. Light in a medium will travel along a world-line (time-like curve) so there's no difference between us and light as far as time goes.
Bhai re addict ho jata hu teri video ka Mat banaya kar aisi itni badhiya video Subah 5 baje teri video ko play kar diya dekhna nhi tha bas yuhi save karne ka irada tha Ab nahane nhi ja paa rha. Teri wajah se school jane me late ho jaunga😢 BTW I am physics teacher Feynman lecture ki book kharid ke rakhi thi padhne ka time nikalana bhul gya tha Ab tu aisi aisi chije lata hai to padhna padga😅
Okay, firstly, I can not get enough of your excitement and energy. I am always glad to see another one of your videos uploaded. Now onto the fun part. I think the better question is "what IS time for light?" I have thought about this a lot, and here is what I came up with. Light doesn't "experience anything except the start and stop of its travel. Say it is emitted from a lightbulb, travels to the surface of the moon, and gets absorbed by an atom in the moon rock. From the point of emission to the point of absorbtion, there is no interaction. As such, there is no "time". Time requires change, and for the photon, there is no change. So what does this "look like" for the photon? Nothing more than the series of interactions; emission, absorbtion, emission, absorbtion, over and over, with no "time" (change) to speak of in between. Thus, for the photon, time is nothing more than the series of interactions it has. To us there may be hundreds of years of travel in between, or a millisecond, but to the photon it is just event, event, event.... Does this perspective still seem to jive with special/general reletivity?
No, the start and stop are the same instant i.e. the spacetime interval is zero, so there is no meaningful attribution of "time" to a photon (or along any null curve).
@@kylelochlann5053 if they are the same instant, does that mean all instants for a photon, from the start if the universe to the end, happen simultaneously? Parmenides is pleased! But in all seriousness, I dont think your statement is any different than mine. There is no "time" between each event for the photon. "Time" for the photon is just the list of events that occur. So you could only ask "how many events back did it get emitted from that atom?" But you couldnt ask "how many seconds ago was that".
@@klosnj11 No, there is no list of events for a photon. In essence there isn't a photon, just an exchange between emitter and absorber that instantaneous in spacetime. If you can, see if you can find a paper by Willis Lamb (of Lamb effect fame) called "Anti-Photon."
Hypothetically, if I make a phone call to my friend who is near the sun, than he would recieve it after more than 8 mins 16 secs and we will have conversation at each interval of more than 8 mins 16 secs?
The Interval would be double that. You Record your message and send it away. After 8min 16 sec your friend will recive it. He Records an answer and sends its back. After another 8min and 16 sec the answer has reaced you. So for you the time it takes from sening your message and getting an answer is 16min and 32 seconds. + the time he has used to reply to your message. Thus the interval is at 16mins and 32 seconds at a minimum.
Light is a null vector of space time which mean that is proper time is always 0 . This is can be seen from the equation of proper time `dtau^2 = dt^2 - 1/c^2 dx^2' which is always 0 for a photon whatever is the reference frame. So saying that light as zero proper time is perfectly legit, and this in all reference frames.
Well... not exactly. The equation you should have is general flat-space metric: ds^2=-dt^2+dx^2. It is only in the special case of a time-like curve that ds^2=-dτ^2. The proper time along a null curve is not 0, it is undefined.
@@kylelochlann5053 Thanks for your comment. If I understand well your point, you agree that light is a null vector of space time and has 0 norm, but you point that this norm can not be called `proper time` but should only stick to `norm`. How is this more that a play on word ?
@@stephanevernede8107 Given a spacetime curve, S, in arbitrary spacetime coordinates with tangent vector, U, the "norm" is then the inner product on the tangent space, g(U,U). This would have nothing to do per se with how the curve is parameterized. For a time-like curve, the norm is a constant, g(U,U)=1, we can use a clock to measure off the distance along any time-like curve (if measurement shows that all identical clocks tick at the same rate, everywhere in the universe, and under all circumstance of motion and orientation). A null curve has no spacetime length, so in what sense can a clock be used to define time as a parameter to measure length along a length-less curve?
@@kylelochlann5053proper time is by definition the length of the spacetime interval measured in the rest frame. However due to Lorentz invariance this number is always the same regardless of the reference frame. So we can just choose a different one to perform the calculations. We can choose any so it doesn't matter. The photon will always travel with spacial velocity c which means that Δs = 0 for all reference frames and hence Δτ = 0.
I really liked how you presented your understanding step by step emerging from your confessed confusion. Also loved how you made it a conversation between Mahesh, Einstein and Feynman chipped in, that made it both interesting and funny. A honest presentation full of excitement. Liked and subscribed!
I'd love to see a video where you focus on the reference frame more, with more than one observer. Observer 1 at rest, observer 2 moving at almost the speed of light relative to observer 1. Observer 3 accelerating at 1000 m/s/s relative to observer 2. Do this and show each observers perspective and how they experience light. I think it would make a fascinating video.
Awesome video Mahesh. I wish you pointed out that when an object approaches speed of light although it would experience proper time, if it eventually stops, its time would be behind the proper time for the non moving reference frame. That’s an important bit of info. Yes ?
@@Mahesh_Shenoy According to relativity it is equally valid to claim photon is travelling at the speed of light or photon is stationary and everything else is travelling at speed of light relative to a photon. Photon's perspective exist but it is not included in special relativity. If photon's perspective is not important is like claiming it is not important what happens to photons at the event horizon of a black hole. General relativity breaks down at the event horizon the same way as special relativity breaks at the speed of light. Einstein's theories break down at the speed of light which results in infinities that show up in physics when you are doing something wrong.
It's not important as at no point are any clocks actually ticking slower. It is fundamental to relativity that all identical clocks tick away at the same rate, everywhere, and under all circumstances of motion and orientation. What you're alluding is that the integral over the accelerating clock's world-line is simply shorter (wrt the global coordinates) which is not meaningful here in any obvious way.
There is another counter-attack: how much time does an observer experience between photon emission and photon absorption, if he is tracing the same path as the light, travelling with a speed limiting to the speed of light? In that sense, you do get that the events (emission and absorption) happen basically immediately one after the other, leading to a loose statement that a photon doesn't experience any proper time. In "photon's frame", it is born and dies at the same time - by definition, because the space-time interval is 0 on a light-cone.
That’s because, from that frame, the emission and absorption locations were infinitesimally close to each other. If my neighbors house is infinitesimally close to my own, the moment I step out of my house, I would have stepped into the neighbor’s almost instantly. That doesn’t mean I don’t experience time, right?
@@Mahesh_Shenoy If you only exist while traveling from your house to your neighbour's house, and the threshold is infinitesimally narrow, you could say that you only exist for a single moment, not any finite interval of proper time during which you could experience anything. I'm thinking of neutrinos here, who do have "time" to oscillate during their flight. Again, of course, Einstein's argument holds that the limit c→∞ isn't strictly reasonable. p.s. Just keeping the back-and-forth discussion with Einstein here, the conclusion in the video is of course correct :)
Photon experienced time but unfortunately nothing happens in that time as the space outside is not changing. It's as if it went out of the universe and popped right back in just before annihilation.
Isn't that just sophistry? You've just used different words to suggest the same thing as an imagined frame of reference that is travelling in equality to light.. The logical conclusion of SR is that there is no, "basically immediately, one after the other", by Light's terms - that is is fudge the conclusion for the convenience of human interpretation. The natural consequence must be that Light does _not_ perceived Time - because by Light's terms, there is no such thing as, "Time": and there is no such thing as, "Space". Those attributes only mean anything, to us and other entities of those dimensions... For Light, there is absolutely nothing. That is: Time and Space are emergent properties - dimensions in a Universe that Light, by nature, has no access to: because they and that Universe are, by nature, coiled up to zero and contracted out of existence. Every single thing, is beyond Lights event horizon - where Light, is it's own event horizon. That's why the question makes no sense - but to say that the question makes no sense isn't necessarily a mature or complete answer to be shared among adults. The simple answer is that no, Light doesn't experience Time. The expanded answer is that Light cannot experience Time l, even if it wanted to - because neither Time nor anything else actually exist on Light's side of Light's own event horizon. That is to say: if Light could communicate, it couldn't process a question on whether it experiences Time? It wouldn't - couldn't - even have any single idea, whatsoever, of what you were even talking about: "Time", and, "Space"?..... Utterly meaningless.
@@lewis7515 i don't realy get this. Why shouldnt light experience time if we see time as the change happening to matter in space . it should in my opinion. Giving light a perspectiv as a human doesnt make sense to me but looking at it from the outside its clear that change is happenig while it moves so how could it be different from the inside perspektiv of light? is it just a hypothetikal question that doesent realy apply to the real world?
You are absolutely right - that kind of question uses lots of words with imprecise meaning. What I found talking about light not experiencing time is a person I talk to has in mind is what other reference frames look like from a reference frame approaching speed of light.
Dumb question perhaps.. if an object is traveling close to C does it appear colder to a stationary observer? My thinking is if time slows for that object including all particle momentum, average kinetic would appear lower. And I suppose all stationary objects would appear colder to the moving object too?
I think “colder” is a very lose word here. If you are specifically thinking about the temperature, then you will have to measure it in its rest frame, no? (I mean you need to stick a thermometer in there somewhere, and now the thermometer is in the rest frame of that object). But, the average thermal energy should slow down. So, that’s an interesting question. Let me add it to my list of topics to research more. Thanks for the question. It’s anything BUT DUMB.
@@Mahesh_Shenoy thank you for the reply. To expand on this.. remote observation of temperature is possible (we measure temperature of everything in space remotely). Also colder == more red shifted.. what if part of the red shift we observe from distant objects is because they are at relativistic speeds from our reference frame due to expansion? Obviously Doppler shift is still relevant. If we see their “clock” moving slower, we should also detect the temperature as lower; all time based events are affected, and temperature is time based. I just solved dark energy (Kidding).
@@amaze2708 Well , Temperature is time based as it measures total kinetic energy of molecule and kinetic energy is dependent upon velocity which depends upon time and as time is relative , temperature is also relative . I am not a physicist but I think a way to measure temperature can be thermal radiation, as thermal radiation is electomagnetic radiation it's speed is not relative but it's total power should as no of photon emitted in some time is different for both of them
When light goes from A to B, we can compute the spacetime interval and corresponding "proper time" - for a photon it will be zero and it will be a valid computation. This is enough to say that time doesn't tick for a photon, and thus it "doesn't experience time". And it's an idea with practical measurable consequences: particles moving at light speed must not change along the way, they must be "frozen in time". That's why we now think neutrinos must move a bit slower than light, as they do change during their travel.
😂 This is the funniest comedy show I have seen in ages. Is this really what passes for logic in the minds of humans? 😂 Thank you very much. I needed that. There is nothing better than a good chuckle to break the melancholy of a dull, winter's day.
@@godfreypigott That depends entirely on how you define the word "god". I could easily say that humans are gods over this planet, and that the laws of physics are a god over humans. I could even say that alcohol is god to a drunkard. I don't see how any of those statements could be deemed illogical in a sincere manner.
@@godfreypigott You see, presumptive statements like that are inherently illogical. I could guess at what god you are referring to, but there is an extensive list of possibilities. I could never know "precisely" what is knocking around inside the head of a human. I could hazard an educated guess, based on my experience with your species, and say that it is highly improbable that you, yourself, know what god you are referring to.
I think I should cover this in a separate video. Adding it to the list. Short answer is, it doens’t make sense to think of “speed of photons” inside a medium
@@Mahesh_ShenoyI would look forward to that video. Some points of interest for me would be, is causality slowed in a medium? When you say vacuum do you just mean free from baryonic matter? Also how does the light accelerate¿ when entering vacuum from a medium? I don't know enough to ask the questions correctly but it is very interesting to me and the way you explain mathematics to us laypeople is some of the best I've seen.
@@Mahesh_Shenoy I also look forward to this video. Can you also include in that video an explanation of what's going on in the experiment where Hau and Harris "stopped" light in a cloud of ultra-cold sodium atoms? I'm having trouble understanding how the photon wouldn't see its own velocity as 0 instead of c.
I think some of the confusion comes in trying to understand length contraction in this context. Traveling very close to the speed of light, you experience proper time, yes. But the distance between the start and end points would be much shorter and take less time than it would for an observer watching you or for a traveler going at non-relativistic speeds. That makes it sound like you'd experience "no time".
Could you say that the faster you are moving, that the objects approaching you from the front seem to have their time speeding up (like a Doppler effect with a sound pitch getting higher)? And could you say that as you get arbitrarily closer to the speed of light, the passing of time of objects in front of you gets arbitrarily closer to infinitely fast? Or am I off base here?
_"Could you say that the faster you are moving, that the objects approaching you from the front seem to have their time speeding up"_ - if you are asking about the light that you see from the objects that approach you, then that is fully correct, yes. That is mostly due to the Doppler shift of the light. If you asking about what you would conclude about the clocks of the others, then your conclusion would be that they tick slower than yours. That is due to the relativistic time dilation.
@@renedekker9806I think you are saying opposite , if we are moving near speed of light our clock tick slower than theirs and other object appear travelling faster as they are moving fast in time relative to us
@@FocusingOnStudy _"if we are moving near speed of light our clock tick slower"_ - our clock never ticks slower or faster. It always ticks at the same rate. It's that rate that is called proper time. It is always our perception of OTHER clocks that appear to tick slower (or faster in some circumstances). _"other object appear travelling faster"_ - other objects always appear to travel at the speed that they travel relative to us.
@@renedekker9806 If time is relative how can we say that clock ticks at same rate ,proper time should not exist even if proper time exist , then it is different for everybody If we are moving with speed near speed of light then other thing at rest only does not appear moving faster in time they are actually faster, and in this situation clocks at rest will always tick faster than our clock (if both clock have same mechanism)
Light doesn't experience time... in a different way. For the following I am considering "approaching to" everywhere, ok? I am just not saying it for brevity. I will use a * instead. The thing is... length contraction. But lets start with this: There are things that don't depend on the frame of reference. Simultaneous things that happen in the same place, are simultaneous for everybody. If when a spaceship flies by the moon its clock was indicating 3:17, it was indicating 3:17 for everybody. For the guys on the moon, the guys in the spaceship, and everybody else. Not all with agree that they flew by the moon at 3:17, but everybody will agree that the spaceship's clock was indicating 3:17. Say that you have something traveling at the speed of light* in a straight line and flies right by the Earth first and then right by the Moon. Form us on Earth or Moon (that will be "us"), due to time dilation, their clock will be stopped*. Let's say that for us we observe that the clock of the fast thing's guys (them) was indicating 0:00 when they fly by the Earth. Then their clock would have advanced 0* seconds by when they fly by the Moon and it will be still indicating 0:00*. Now, from our perspective the trip didn't take 0* seconds. It took d/c*. A very finite and measurable amount of time (we use the time the light takes to go to the Moon and back to measure the distance to the Moon). It is just that, from our perspective, the "fast guys'" time (i.e. the rate at which their clock ticks) was dilated to oblivion. But what from their perspective? What do they observe? Or, more correctly, how do we explain this from their frame of reference? Well, we all MUST agree that their clock was indicating exactly 0:00 when they flew by the Earth and it was still indicating 0:00* when they flew by the Moon. That means that, from them, flying by the Earth and by the Moon are simultaneous events*, it took no time to go ron Earth to the Moon (remember * = approaching to). Wait a second (pun not intended). How did they get from the Earth to the Moon so fast (basically in zero time)? Were they going faster than light from their perspective? Absolutely not. What happens is that from the reference frames, the length of the moving frame contract in the direction of motion. If they guys are going in a rocket, the rocket will look extremely short for us, 0 length*. And looked from their frame of reference, the distance from the Earth to the moon will be extremely contracted, the distance would be zero* So they would perceive that they are still flying at the speed of light*, and their time will pass at a normal rate. It is just that they will take zero* time to cover the zero* distance. So, even when time itself passes at a normal rate, they don't have any time to "enjoy" the trim from the Earth to the Moon. Now say "they" are not people in a rocket but a small particle (a muon or a neutrino) that is created in the Earth and that it travels to the Moon at the speed of light*, and when it gets there it hits another particle and "dies". For us, it would take a couple of seconds for the particle to get there. But how will the particle experience it? For the particle, time will pass at the normal rate, but the trip will be extremely short, with a duration approaching to zero. The particle would be born on Earth, experience the trip with a normal-pace passage of time, and die, at the same time*, so it will experience the normal-pace passage of time for no time. Take it to the extreme, and everything breaks down. But unlike the black hole singularity where a lot of things explode to infinity, here it breaks down in a nice way. While you cannot do the calculation of what happens exactly when v=c, you can take the mathematical the limit with v approaching c and you will have no infinites. Rather you will have a zero. A photon, now traveling at exactly the speed of light (no asterisks anymore), would not experience time. But NOT because time would pass at a different pace for it. Oh no no no... Time would pass at the same pace, if only it had a moment to experience that time. The photon will be born and will die at the exact spacetime coordinates in its reference system. Will be born and die at the same place and same time. Yes, it will be born on Earth and die on the Moon, but the distance between them would be zero. It didn't have time to experience the passage of time.
Excellent argument, your logic is very sound - it brings to mind constructor theory. Also love the chess analogy reminds me of Feynman's use of a chess analogy. Thanks very thought provoking.
But you can have two kings next to each other in chess. That would have required an illegal move though but it can still happen. There has even been a real chess game where the judge ruled that the one who played a move after an illegal move lost, because it was illegal to to continue after this illegal position and create a new illegal position. When the player who made the first illegal move pointed that out the judge concluded that the last player who made an illegal move lost! ;) Not sure what conclusion we can draw about lights perspective from this though lol
First, why are you so good at incorporating your sponsors in your videos? You're simply too good. Secondly, I totally agree with correcting people's understanding about certain subjects and misconceptions. Though, I would totally commend them for thinking about these things and being curious. I also can understand others telling others "click bait" concepts. I feel it is to get then intrigued and interested to learn more. Promoting education, critical thinking and scientific literacy is definitely a great thing to do.😊
If you and I travel very close to c in opposite directions, the speeds will add up to be more than c (as it is numerically close to c). So for you, I travel faster than c.
Mahesh I have a doubt ... Why pair annihilation doesn't takes place in mesons ? I surf the internet and found some answers..i know charged pi mesons don't annihilate because the quark and anti quark are different flavours but what about the neutral pi mesons? Some of them said annihilation is not a instantaneous process..we know that mesons are unstable so before annihilate..it's starts to decay into other subatomic particle...is that right explanation ? Which property differentiate the lambda -0 and Sigma -0 in elementary particle because both are made of up quark-1 down quark -1 and strange quark - 1 ? If anyone have the answer let's start discussion 😅😊
Good video! The whole answer to this is that light neither experiences time nor distance. The concept of a 'physical wave' between emission and absorption of light is not real. The 'wave' is only a mathematical conception which informs us where and when the light energy packet is "transmitted" to. There is Nothing in between the emission and absorption points, either in time or in space..
Good point and so many seems to not understand that part of the physical properties (or lack of that) in light. It explains a lot of what we think of as strange behavior like "spooky action at a distance" and the many strange things with quantum physics.
Light takes up physical space (wavelength) based on the number of oscillations in its E-field per unit of time (frequency). It's energy (E=hv) is based on these physical properties. Photons have to physically change to be measured, so I don't know how those concepts would make sense if light didn't interact with time or space.
@@Vexas345 No, light itself does not energy/frequency as per E=m. Given some world-line, we can assign a photon an energy/frequency, which are frame dependent values.
@@kylelochlann5053 how do you define a photon then? Our interactions with photons are based entirely by the transfer of energy. A photon with zero energy essentially doesn't exist, since it can't interact. Sure, its energy may change depending on the observer's frame, but that also applies to real objects. Real particles have relativistic momentum and so their measured energy is frame dependent.
@@Vexas345 We define a photon as an excitation of the free electromagnetic field that couples to electric charge and associated with the quantum state of some system. Let's say we have a hydrogen atom in state A that transitions to A', that then is coupled to a detector (which also undergoes a state transition) at light-like separation. The "photon" is the exchange between the systems. Keep in mind that energy is a description of matter, specifically being the Noether charge of time-translation symmetry, and not something that exists. Or to put it more leisurely, energy is an arbitrary number assigned to a system that represents a constraint on the dynamics. The equation E=m is a statement about the internal dynamics of a system. We say an electron has an intrinsic energy because there's an internal interaction between the electron matter field and the Higgs field. Given an arbitrary time-like curve we can assign the electron a coordinate energy/momentum: E=γm and p=γmu, constructed in terms of the internal dynamics represented by m. We can do no such thing with a photon - there are no internal dynamics. The energy of a photon is zero (intrinsically), E=m=0. However, as the photon couples to the electric charge, and the electromagnetic interaction is constant over spacetime, we can associate the photon with conserved quantities with regards to the space and time components of some observer, E=p=ω.
Can you constantly accelerate to closer to the speed of light such that, from an outside perspective, the light never reaches the top of the clock and ticks? I suspect from inside the vehicle, you would just see space continually contract such that you would arrive at any destination point before light had a chance to tick the clock.
Or, as we say in mathematics: You can't divide by zero, but you can take the limit as the denominator approaches zero. At v = c, you're literally dividing by 0 to get quantities like γ, length contraction, time dilation etc. So those quantities are no longer well-defined. This is where the next genius wonders what happens if one were to allow division by zero, and thereby revolutionizes math as we know it.
that segway to the sponsor segment is crazyyyyy good 😂 anyways, I have a question, if the speed of light is the speed of causality is the speed of time, shouldn't light be time?
I needed this channel for so long and didn’t even know 😱 Finally instead of just knowing the right answer I can understand what is going on. TY so much, great work! 👍🏻👍🏻👍🏻
Love watching floatHead Physics! Your enthusiasm is infectious and I will be showing my teen daughter your videos to help her intuition of physics. Thanks, Mahesh!
That asterisk "ignoring length contraction" is doing a lot of work here, since in "light's reference frame" the universe is 2-dimensional, and its velocity is zero in what we would call its direction of travel (because for a photon, that direction doesn't exist). But real photons don't travel in only one direction, they propagate with a probability cone. Might be some insightful math to be done there...
How have you concluded with such certainty that Light's universe is 2-Dimensional?..... Light's velocity is zero in its, "direction of travel" - purely from our, practically-useful, perspective, of Light's perspective. However, surely, Light only has a, "direction of travel", at all, from our perspective, of Light's perspective? That is: isn't it the case that Light's, "travel", is only perceived? Light doesn't travel, it cannot - we call how it presents in our Dimensions, "travelling", because it's intuitive and helpful. Meanwhile, isn't it actually the case that Light only simply _propagates_ - from the point that it manifests? If that is the case, then Light must propagate, at the speed of Light. If that is so, then Light simply propagates, from wherever it manifests, in every Dimension, in every direction, equally - which is: at the speed of Light. Wouldn't that then mean that every direction and every Dimension: is zero? Isn't the conclusion, then, that while there is no, "direction of travel", from Lights perspective - the exact same terms apply to all other, "directions": that it could only move to, at the speed of Light....So, wouldn't there, equally, be, no, "Direction" - in any non-direction it could move to?.. Must it not then be the case that there are no, "Directions", whatsoever - and, by that token, no, "Dimensions", in any non-direction, for Light to not, "travel", to? Isn't it the ultimate conclusion that, for Light, there is no, "Direction", at all, that it could travel to at anything less than the speed of Light - meaning there is no, "Dimension", whatsoever, to not, "traverse": with the result that there is no, "Space"; no, "Time"; no, "Thing"; no, "Where" - and there was not, is not, and never could be... Would it not be that, for Light, _all_ is simply null - and moot?
Does Time experience Light? is the question i get asked the most. Right behind Do you know what time it is? And How are you doing? Thank the good Lord i have the answer now.
Now that the "experience" part is ingeniously taken care of, Shall we move to the next innocent but tricky term i.e, "Time"?. What is it? is there any intuitive sense of this term? Is it universal or it's just an emergent phenomenon as a statistical byproduct of entropy? I thought I almost got it from the Arvin Ash's video on the topic but would really love to have it reimagined with your enthusiasm and care. Great work brother, I absolutely admire your explanations. ❤
Great & thought provoking video. However, one of the major problems I have with SOME scientific "conclusions" is the unprovable "fact". For example; if we cannot experience light's perspective, then we cannot say that it does or does not experience time. But on the other hand, special relativity is only relevant INSIDE of time & depends on the perspective of two or more subjects. Therefore, if we cannot use light as a subject in special relativity, then it is more likely that light does NOT experience time, and we must use quantum principles to determine its nature. ***I LOVE YOUR CHANNEL!*** Keep up the great content.
1.Being at rest is the same as moving at a constant speed. 2. To "experience time" means to experience change. 3. Only an observer of change can experience change. 4. The changing things themselves do not experience any “time”, they simply “change.” 5. The concept of “time” refers only to the observer who is aware of himself.
Naturally, inside a reference frame, the speed of light remains c, regardless the reference frame's speed in relation to any other reference frame. The speed of light is actually the speed of causality. Inside any reference frame, it is constant. If we sit inside a space ship that travels very fast, approaching c, we still experience everything inside the space ship as normal. The issue is the relationship with other reference frames that are not traveling that fast. The imaginary photon that is bouncing up and down the cart, is indeed perceived as traveling at c inside that cart, constituting a reference frame. But, if we could somehow register that photon's movement from outside the cart, standing still, events inside the cart would seem to freeze. An imaginary particle that was moving at the speed of light inside the cart could not be perceived on one spot, moving laterally "up" and "down" with regard to the non-moving observer. That movement would be extended along the vector of the cart's trajectory. It's Special Relativity's space contraction that does the trick here. If the cart was moving very fast, approaching c, the imaginary particle at the speed of c inside the cart would actually not traverse the same distance anymore, as it would at a low speed. It's forced to traverse a much larger distance, as seen from the outside observer, whereas the inside observer in the cart still perceives the particle to move at c. This is exactly the core concept of Special Relativity. What an inside observer sees , while moving very fast, is not the same as what an outside observer sees, when standing still. So, light that travels through the Universe experiences space contraction so that all of Space becomes contracted into one point. Time dilation is stating the same mechanism here: to traverse a point does not take any time at all. A hypothetical space ship that approaches the speed of light is seeing the Universe as contracted into almost one point, a distance that takes almost no time to traverse. And that while inside the space ship, light still travels at the speed of c, without any contradiction.
You all need to talk more about proper time as I think many people believe that your experience would be different and you'd see things going slower or faster in your reference frame, but that's not the case. Your faucet would still drip at the same rate and clocks would still be 1 second per second. Are GPS satellites not in our reference frame? I know they have to take into account time dilation, but as I understand there is no real boundary for time dilation. So, the answer would be no, those satellites are not in my reference frame. But then, where does that stop? Are my head and feet while standing in the same reference frame? So, how can a human be in rest and in a inertial reference frame if there is always space and/or time dilation. Or do I need to be in the middle of space away from gravity? Great stuff.
1. I think "light does not experience time" is a good description of "proper time for light is meaningless". 2. There is still an affine parameter along any light-like geodesic, but there is no way to fix its unit (as we have fixed the second for proper time). 3. When gravitational lensing happens, you can connect two events by a family of time-like curves approaching a light-like curve in limit. In that case, proper time measured along those curves goes to zero as the curves approach the light. 4. Existence of singularities is proven using light-like geodesics, so even without proper time, the light can experience "something". 5. Not to mention interference and various electromagnetic interactions light can participate in.
This highlights an important distinction between pure mathematics and physics. Math is an excellent tool for describing the reality (maybe the best tool we have?) but still will never "be" reality itself. The hard part is knowing where the math diverges from the physics.
The more I learn about special relativity, the more I think that our movement is just an illusion, rather we all stay in place and only light is truly moving.
I think you are confused by what a frame of reference is in physics. A frame of reference is a set of coordinates to describe a velocities of objects in that frame. A key feature of an INERTIAL frame of reference (the one we use in physics, which you are describing) is the frame is not accelerating, which does not mean that the speed is zero (which is also a “loose” term as describing velocity in respect to something, like the ground or earth)
Exactly. At rest also extends to straight line, non-accelerated motion which is exactly how photons travel through the vacuum of Space. I think this explanation is inconsistent with the very foundational basis on which it claims to sit. In another video, he explains why everything at rest in the universe is moving through Time at the speed of light. Using that thought experiment, he goes on to agree that the faster one travels, the greater their displacement through Space and the less their displacement through Time, till, eventually, the particle in the thought experiment reaches c and employs all its speed in the spatial dimension with nothing left over for Time hence, objects travelling at c experience no time. This video appears to contradict that. 🤷🏾♂️
@@ToyyinnAuslander Yes, I agree. To be honest, I always had a problem with the proverbial 'light-clock' being used in these thought experiments. I never understood how it was possible for the path-length between the reflector and detector to be altered by the velocity of the clock as it travels through space. These experiments seem to assume that the motion of the clock provides some forward momentum to the photon being emitted and detected in the clock but doesn't that contradict the postulate that all observers experience the same 'c'? I mean, if the clock is traveling along the x-axis and the photon is emitted along the y-axis then the photon would travel along a path that is perpendicular to the direction along which the clock is traveling, right? The photon would have traveled in a straight line but the location of the detector would have changed during the time of the photon's journey. Also, one would assume that each photon can be detected only once but in the model used here, the photon is depicted as a wave travelling from the emitter to the reflector. The fact is, according to the postulate, when the clock is at rest, the experiment is set up so that the photon travels the path between the emitter, the reflector and the detector. When the clock is in motion however, we can see that 'at rest' is a 'special case' since from the photon's point of view, the positions of the clock-parts are arbitrary. As soon as we put the clock in motion, the photon is no longer traveling the path between emitter/reflector/detector; it travels from point 'a' on the y-axis to point 'b' on the y-axis and arrives back at point 'a' on the y-axis. Right? The photon _never_ deviates from the y-axis but the emitter of the photon does. It's not the photon traveling along a path that is 45° to the direction of travel, it's the emitter that has moved to a new position on the x-axis that is at a 45° angle with respect to the photon's position along the y-axis; the photon is 45° _behind_ the emitter. The length of the photon's journey however remains constant. In other words, if you had a photon emitter firing photons between two parallel plates, the top one is uniformly reflective and will reflect any photon back the way it came; the bottom one will detect and register any photon that interacts with any point on its surface and we can have the plates spaced at some arbitrarily small distance so that even at light-speed, no photons will be lost to the system. There is a tiny hole at the centre of the detector where the emitter injects photons between the plates. With a clock like this, no matter how fast you travel, the clock will tick at a rate that is proportional to the distance between the two plates and the speed of light, both of which remain constant in all frames. And even assuming that 'length contraction' is an actual thing, that would not change the rate at which the clock ticks either. One might argue that the length of the clock becomes so contracted that its displacement along the x-axis takes the reflector out of the space occupied by the photon which is never detected. In that case, the clock simply stops but until then, the rate at which it ticked remained constant. So yeah, these thought experiments make it appear that the velocity of the clock alters the path of the photon somehow but how, no-one ever explain that to me.
I have a rebuttal. To invent an idea that breaks rules does not necessarily mean all rules must be thrown out. A clear example: sqrt(-1) used to be thought of as a meaningless question that broke foundational rules, until certain mavericks said, "Let's do it anyway and see where it takes us!" They didn't have to reinvent all of math, they didn't have to get rid of "a negative times a negative equals a positive," they just invented a new abstract concept that turned out to not break math when implemented. A tweak to the rules (i.e. overturning the rule that there's no sqrt to a negative) was enough. Likewise, tweaking the postulate to say "all *sub-c* inertial reference frames" (it already has "inertial" as a qualifier, after all) allows for everything special relativity claims to remain the same (since it's already assuming all reference frames are sub-c), while allowing for mavericks to break the rules beyond the limits and see what happens. So I don't think you can really say (at least as it was presented here) that you can't tweak the postulate while retaining all its current predictions, just like the introduction of the seemingly-nonsensical *i* didn't undermine the math of real numbers in any way.
I love the way you break these concepts down in ways an average person can understand. I was a little bit disappointed in this video when I saw the asterisk though: *length contraction ignored. I have always been so fascinated by imagining what the universe might look like from lights perspective, and in my mind, I always assumed light (sorry Einstein, *an object moving *almost* the speed of light) would experience the universe as (almost) two dimensional in the direction of travel. Even if the clock is moving at normal speeds from that perspective, the way space dilates is still fundamentally different from our usual 3D perspective. I was really hoping to see an animated view where the cart was bouncing up and down while the light particle was stationary so we could see how the cart contracted in both the X and Y directions.
I'm a bit confused. Any object traveling near the speed of light would experience proper time from it's perspective, and almost stopped from the stationary observer perspective. So light will experience time proper time, and from the external frame of reference it has stopped. So I don't see the difference between light and any other object. > So time dilation does not apply to a photon as shown in 2:45? Because in this example time has stopped for the photon :/ So is the example wrong?
It's because for a photon reality is vastly different than ours. I can imagine that length contraction causes whole universe to be contracted to 2D plane. So from it's perspective it does not 'travel' like a regular matter, it does not 'experience' time nor distance. It's existence is only to be created and to be annihilated, with no time in between. The regular matter will never reach the speed of light because it would require infinite amount of energy, so we are stuck to be always different than elementary particles which travel at the speed of light.
@@kriiistofel Hi, thanks for the reply, but isn't what you are saying contradictory to the assertion in this video :/ " *So from it's perspective it does not 'travel'* like a regular matter, it *does not 'experience' time nor distance.* It's existence is only to be created and to be annihilated, with *no time in between.* " > This is where I am confused. Massless particles etc travel at the speed of light always. As such from an outside observer (us, not moving) zero time passes (time dilation). For us it's clock does not move. (The presenter says first this is correct (The train) and then says this is incorrect) Regular objects with mass can never reach the speed of light so so some small amount of time always passes observing from our not moving frame. So light is a bit special because it does travel AT 'c'. If from "our" perspective it experiences "zero time" we have a weird paradox where it both exists and does not exist. There is a big step between an object with small dilated time and zero dilated time :/ Albert knows this and say the solution to this paradox is don't ever ask about it lol > So, I am completely lost as to what the assertion of the video is. From what I can tell the assertion is never ask about the photon problem because it breaks SR and GR. So, does a photon exist? The answer is "We don't know" or "Don't ask that question" lol Which is a bit weird as the photon is a central study used for most physics requiring 'c' as a perimeter lol
@@axle.studentIsn't the, "big step", your conclusion that, because a photon experiences zero time, it does not exist. Why? Just because you can't fathom the terms of its existence, from your perspective, why would that mean it doesn't exist, from its perspective? How would you know? Walk it through: you surmise it experiences zero Time. If that's correct, on what basis do you determine that effects its existence? On what terms? That's number 1. Number 2, is that you cannot directly observe Light's perspective - you can only determine that it must experience zero Time... That's quite reasonable and seems intellectually sound - but, it is possible that there's more than one way to resolve any, "zero Time", dilemma at Number 1 - if there actually is a dilemma. Once you cross the threshold of Light's perspective, "zero Time", might mean not only that Light can experience no proper time, and no Time as a dimension: it could equally mean that Light has no facility for a temporal dimension, whatsoever? Perhaps, Time, itself, as a tangible Dimension, does not exist, for Light? Perhaps, equally, on Lights side of the threshold, it exists quite perfectly well - and, from that perspective, what does not exist, is _you?_
@@lewis7515 Thank you. What you say is very close to what I am attempting to work out. Maybe no answer currently exists. > What is the relationship between the photon and time? > "Perhaps, Time, itself, as a tangible Dimension, does not exist, for Light?" Can I suggest that light does not have any experience of time (0 time) or as you say for light time does not exist. It's a matter of semantics and interpretation here :) > "Perhaps, Time, itself, as a tangible Dimension, does not exist, for Light?" Yet, for us it can appear to exist for billions of years. "Perhaps, equally, on Lights side of the threshold, it exists quite perfectly well - and, from that perspective, what does not exist, is you?" yet light can interact with us even though we don't exist to light? > So, I am left with saying that light both exists and does not exist. "Does not exist" is akin to saying that Zero does not exist or that Zero is the absence of anything tangible, yet we use zero in a tangible way > *So, this is 100% on point to what I am attempting to work out/understand. What is the photons place (relationship) with the 3D and 'c'.* If for the photon time does not exist, then causality can not exist? Yet if it hits a photovoltaic plate it can transfer it's potential to the plate.
@@axle.studentI'd suggest, no: Light certainly _does_ exist. What's significant is that Light can have no tangible experience of its own existence - nor that of anything else. There's no dilemma - it's a matter of perspective. Meanwhile, it doesn't seem quite analogous to, "Zero" - as zero is just a definition, of a certain state. There is no definition for Lights state. Its state, is no state - that perspective doesn't exist: in anywhen, nor anywhere. Light, just is, from one perspective - and is, not, from another. A photon doesn't have a relationship to 3D, and a photon doesn't have a relationship to C - because a photon doesn't go anywhere. That has no bearing on casualty, because the realm of causality and photovoltaic plates is a realm a photon has no access to and which is totally meaningless to a photon - it transfer potential it cannot be aware of, in a transaction it cannot perceive, within a Universe that is beyond its nature. However, the fact that the realm is invisible, intangible and practically meaningless, to a photon, doesn't mean that realm does not exist? That's not the same thing at all.... To the interior of a black hole, we, are on the one side of an horizon that means we are invisible, intangible, and practically meaningless, from that interior...we still do very much exist?. Its just a matter of _perspective,_ and the limitations of horizons.
If you measure time as clock hands from a tower. If you rush away at speed of c, the hands are moving but you can’t “see” them moving. They are frozen. If you stop they start catching up or moving normal. If move toward the clock accelerating toward c the hands will speed up as you experience all the time or hand movements that you out ran before. When you reach c the spin is so fast it stops again. So not being able to tell time, or frozen clock hands is the same as not experiencing time.
This might be slightly off track? My understanding is this: that, nothing, actually, freezes? It just _appears_ to, depending on who's looking, from where. Rush away from the clock, and it appears to freeze, to _you:_ somebody at the clock doesn't see any freezing going on. They will see that _your_ watch appears to have frozen - but it hasn't as far as _you're_ concerned. When you stop and look back at the clock, it will obviously state the time you read on your watch: as you will be looking at the equivalent to your Present - the same Present you left at the clock, but only from a new _location._ A location that, comparitively, would have been in your temporal Future, _if_ you'd stayed at the clock? By travelling at the speed of Light, you will have made a shortcut in Time and Space, across that distance to where you now are - a distance it would have taken Light time to reach: you have simply kept pace with that future expectation. So, you could look back from there, and see yourself preparing to leave... IF you had a special telescope that could reverse that shortcut [by operating faster than the speed of Light] you could look at the clock in _its,_ relative, Present - and only then could you see that, actually, much more time has passed, _there,_ than what your watch reads and what your eyes tell you, in your Present - you just couldn't see that without your special telescope. Without that device, you'd just have to wait for the Light you have shortcut, to catch up to you: and even more time would pass at the clock, while you wait... If you decide not to wait and lose even more decades, and immediately rush back towards the clock, it, again, appears _to you,_ to freeze - but, again, it doesn't actually freeze. It doesn't speed up, either - the image you're receiving is not a video in a player? It is Light. For the image you receive to "speed up", it would have to travel faster than Light, and it cannot?... Time at the clock passes quite normally, as far as it is concerned - you appear _to the clock_ to freeze and, meanwhile, you see what you see of the clock - which is, again, the Present that you left. Only when you do finally arrive back, will the two shortcuts you made, instantly, resolve - at the speed of Light. That, is how you will step from your ship, look around, and see that you are now in your home reference frame again, experience a shared Present: but, while only minutes have passed on your watch, decades, or centuries, have passed at the clock. Not being able to tell time, and frozen clock hands, are nothing to do with this.
BOTTOM LINE: An object moving at "Nearly" the "Speed of Light" is experiencing "Proper Time" in its own "Frame of Reference," which measures "Time" when the object is "At Rest." An object "Constantly" (c) moving at the "Speed of Light" is not "At Rest" and therefore has no "Reference Frame" at all to measure "Time."
Great show! I suppose that one could make the argument, that light doesn't experience time precisely because photons going at the speed of light don't experience reference frames, so they couldn't experience time either. The only way they could experience time in the first place would be through a reference frame.
I like to think of it in terms of definitions. In special relativity, time is defined by measuring how “fast” light travels. When a car moving at 90% speed of light relative to the ground sends out a light beam, to an observer on the ground, either the light beam is traveling at 1.90c (wrong) relative to the ground or the light beam is traveling c relative to the ground and the relative time is dilated and relative length is contracted (as well as simultaneity differences for the two observers). Both observers say “I must use c as my basis for time since it is actually the speed of causality / electric field changes etc” Thus we see why it makes no sense. How does a perturbation in electric field “experience” itself? It’s like asking a gust of wind how it feels to hit itself.. if electric field perturbations are how we measure rate of causality - eg how many times an block of radium decays in a period depends on rate of electric field flow C - then we can’t ask how does electric field disturbance measures itself. How many electric field disturbances did the electric field disturbance feel? Going in the same direction. It just doesn’t make sense. An electric field ripple in a direction can’t experience other electric field ripples in the same direction. It can’t measure time because it is how time is defined
I reached the same conclusion following this thought experiment: consider a massless observer, accelerating along a beam of light. Since it is massless, it can accelerate to C. Now what does it observe? As it accelerates, the speed increases, and it sees the beam of light redshifting. From the observer perspective, the beam of light loses energy. When he reaches C, the beam of light he was following practically lost all of its energy and is not detectable, ceases to exist. A photon does not exist from it's own perspective, nothing exists from the photon perspective. A photon that traveled since the big bang,13.8 billion years, traveled 13.8 billion light-years. Form the photon perspective that is meaningless, he has travelled 0 attoseconds, 0 attometers. Maybe here is the next physics breakthrough, since this does not make sense from the quantum perspective as well.
An inertial frame of reference is not at rest (as asserted), it is moving at constant speed, undergoing no acceleration. So light is always in an inertial reference frame because it always travels at the speed of light, never accelerating or decelerating. You can say the question of whether light experiences time is moot. However, consider a massive object that continues to accelerate closer and closer to the speed of light. As it does so it experiences ever-increasing time dilation and length contraction according to GR, the limit of which is the state, mass, energy, and speed of light. Massive things cannot reach the speed of light but they can get infinitely close, and time for them can approach "not passing". For example a massive object could in principle travel fast enough to reach anywhere in the universe in one second (its time). Muon decay proves this. I don't see the downside of thinking light does not experience time even if the real case is that time does not exist for light.
It's fundamental to relativity that all identical clocks tick at the same rate, everywhere, and under all circumstance of motion and orientation (LPI and LLI, respectively). The downside of thinking that light does not experience time is that it makes understanding the theory rather difficult, e.g. understanding the causal structure.
Please explain this hypothetical case: Let’s say we have a particle at almost the speed of light. According to my understanding, applying the length contraction would mean, that the distance until the particle collides with something, would shrink. In the lim(v -> c) the distance would shrink to zero. Meaning, that the time of flight would become zero. For a hypothetical particle identical to a photon, except with a minimal mass. This would mean, that in the outside frame of reference, in the limit, the particle would be created, move at a speed indistinguishable from c and finally interact with something and get destroyed. In the reference frame of our hypothetical particle, it would be created and, in the limit, after a short time indistinguishable from 0, interact with something and get destroyed. So the particle would experience time in the sense, that a hypothetical clock in it‘s time frame would tick normally. But on the other hand it wouldn‘t experience time in the sense, that the time between creation and destruction would become zero.
@@MaxStephandurchpiquer of course I did mean, that the distance from the point of creation to the point of destruction shrinks in the reference frame of the particle. And with „in the limit“ I always meant „in the limit of v->c“, not „in the limit of mass->0“. I intentionally did try to avoid the case of a massless particle.
1. My hypothetical particular has a very small, but non-zero mass. So I see no problem here. (See 2) 2. My limit does not change the rest mass. The limit doesn’t say the particle reaches c, it only sais it approaches c (In the reference frame of point of creation/destruction). (The limit of 1/(x²) for x-> 0 is +∞, even from both sides. But that doesn’t mean I would ever dare to say „1/(0²) = +∞“. 1/(0²) remains undefined.) 3. Misunderstanding on my side. 4. see 2. The limit doesn‘t mean, that one just plugs in that value (which would be invalid here). And so I don’t see, where I have ever tried to apply something to a massless object. 5. That was an implicit assumption. Should have been that precise. Like in an experiment, where a LASER-analog, which produces our hypothetical particle instead of photons, is pointed at a black body. 5 (again). But wouldn‘t it be possible to weaken this assumption to this point?: The point of creation and destruction move relative to each other with a small speed, small enough, that the edge case of relativity called newtonian mechanics is precise enough to describe their relative behavior.
@silverrahul I know, that I can’t plug in „v=c“ for a particle with non-zero mass. But that‘s the whole point of a mathematical limit: Approaching an undefined value infinitesimally close WITHOUT really reaching it. Same example as above: lim(x->0) 1/(x²) = ∞ (even from both sides), but 1/(0²) ≠ ∞. Instead 1/(0²) is undefined.
@silverrahul Then please explain to me, why the mathematical tool of a limit cannot be applied here! In principle we can accelerate a particle arbitrarily close to c. So the limit is applicable here. Since the particle can’t reach c, the limit doesn‘t say anything about particles moving at c, but I DIDN‘T TRY TO DO THAT. I just said, that by increasing the speed arbitrarily close to c, the lifetime of the particle gets arbitrarily small, to a point where it gets indistinguishable from (BUT NOT ACTUALLY) zero.
@silverrahul 1. I know that it would require infinite energy to actually reach c, but as I pointed out, this is a hypothetical case. So right now I don’t care about energy constraints except that it has to be finite. It’s a thought experiment. Nothing more. 2. I never said the lifetime actually gets to zero. Here the „in the limit“ as part of the sentence is important! As I pointed out multiple times, the value of the limit (v->c) DOESN‘T say anything about the case (v=c), but about the behavior close to that. So saying that the limit (v->c) of the lifetime is zero, is the same as saying „for v close to c, lifetime is close to zero“. Again: This is not making any statement about behavior AT v=c. When I said indistinguishable from zero, I was talking about a case CLOSE TO C since a statement about a case AT C would be invalid.
I feel I should add that the "almost c" reference frame does have some special properties. While yes, it experiences time normally, it needs to be said that from that perspective, the universe will be going by so quickly that you'll reach the extents of space _and time_ itself in the blink of an eye. If we assume that at some point, time ends -- as time had a beginning, it should have an end -- you will reach it extremely quickly by going super close to c. Therefore, a photon essentially _skips_ to the end of the universe instantly. Thus, it experiences no time at all because by definition, whatever the universe's maximum time limit is, you'll reach it immediately.
How about the question: How much time would an object going 0.999C experience if it was traveling a certain distance? It would experience time normally, but the amount of time to go a specific distance would, from its perspective, be severely shortened. Like, how fast would you have to go for your experience of a trip from the Andromeda Galaxy to the Milky Way to only be one second long from your perspective? I feel like this phrasing better gets to the heart of the question without breaking relativity.
If Andromeda (M31) is 2.537 million light years away, then _from Earth_ an object going 0.999999999999999999999999999922 C should arrive at Andromeda after experiencing 1 second of proper time.
That's 28 nines, so from Earth's perspective (or I guess the Milky Way) you're only going 7.8×10⁻²⁷ percent slower than light. You will arrive at the Andromeda galaxy one second after light/radio from Earth arrives. I'm not taking into account that the Andromeda galaxy is actually "falling" towards the Milky Way galaxy and will collide will us in about four or five billion years. This calculation I did assumes that these two galaxies are not moving relative to each other.
_"It would experience time normally, but the amount of time to go a specific distance would, from its perspective, be severely shortened."_ You appear to be referring to time in one reference frame and distance in another.
@@lewis7515 Yes he is. When he says "a specific distance", he is referring to distance measured in a "stationary" frame. Ignoring the relative motion of the earth and Sirius as it is insignificant compared to the speed of light : Sirius is 8.6 light years away as measured in the reference frame in which the earth and Sirius are stationary. So an object travelling at 0.5c will take 17.2 years to travel to Sirius as measured in our reference frame. In the reference frame of the moving object, it will still take 17.2 years to move *that specific distance,* but it will take it WAY past Sirius. Instead of saying "to go a specific distance" he should have said "to travel between two specific objects".
When we say that something experiences little to no time when reaching relativistic speeds, we are saying that in relation to our own time. All things in the universe experience time flowing normally in their own frame of reference. But it is closer to true than to false to say that light or other things reaching the speed of light experience no time. The way that it all ends up working is that when they reach light speed, the very next instant in their consciousness is them going below light speed. From the point of view of everyone else, they are frozen in time the entire time they are at light speed, but for whoever that is, reaching and leaving light speed are adjacent moments. So yes, from their own reference frame, time is flowing normally, but it is still true that no time passed for them in all of that time. It’s just that they weren’t conscious of any of that passage of time, and the transition back into time unfreezing is truly seamless from their frame of reference. But definitely going say 95% of light speed, even though they look nearly frozen in time to everyone else, to them, in their own reference frame, time is passing totally normally.
I was ready to angrily type away in the comment section, defending the idea that light experiences no time. But you made such a compelling argument, now I have nothing to say but thank you for the informative video. 😂
Go to ground.news/floathead to stay fully informed and access reliable information. Subscribe through my link to get 30% off unlimited access this month only.
Also, first :D!
Minor correction. Fact. Tu. Ality. Not Faculty. :)
But, what if an object travels so close to the speed of light that it travels across the entire observable universe in femtoseconds of proper time? Would the object continue on its trajectory until it hits into another object? Or would it wrap around the universe infinitely or stay in place in empty space as the universe expands so that the object HAS TO experience time?
where to get that t-shirt? XL size
So when I'm playing chess with my computer and our kings wind up next to each other, and im pissed because the computer wont let me take its king saying its an illegal move but it's king takes mine‽
I shouldn't be learning chess from a computer.
I think your explanation is better, and it proves Tyson's experiment wrong:
ua-cam.com/video/B2dCvxpKWFk/v-deo.html
This has nothing to do with scientific analysis, this is a video/channel analysis. He always sets himself up as the ignorant foil asking the questions. Einstein or whatever author he’s read is always correcting him, even though he’s the guy who understands what he’s teaching us. This is what makes him charming and charismatic and approachable from our point of view as learners: let’s learn together. That’s the literal definition of a good teacher.
Veritasium did a video on this teaching technique as well. It’s more important to explain what something is not / incorrect than it is to simply list truths
Yes, this channel is amazing for all the reasons you just said, not to mention how excited he is about all the information, it's impossible to be bored watching him 😂
I love the hypothetical conversations with Einstein and Feinman. A great vehicle for explanations.
This addition to his explanations are what made me subscribe immediately. 💯
man your topics are always so interesting i just have to watch
Thank you :)
Do you have girl friend?@@Mahesh_Shenoy
No.
At the speed of light…the time stops. According to Gödel's interpretation of Relativity.
I'm with that line of thinking, but then if equations are allowed to be blown up do we assume that singularities exist?!
Perhaps time not moving and singularities are connected in some way, at least in telling us that we're missing something major in our knowledge!
You don't understand inertial reference frames
I have a masters in Math, and your videos have allowed me to appreciate axioms, postulates, and modeling so much more.
If an object travels almost at c, from its reference frame the universe is traveling at almost c and is extremely contracted in the direction of the movement. So, from its perspective, it would traverse the entire universe almost instantaneously. I think looking this way we could say this object experiences almost no time, meaning it does not see the universe evolve in the very short time (from its perpective) it took to traverse the universe. If you think regular objects do not traverse the entire universe, but a smaller distance between object creation and destruction, for this object it existed during almost no time and was almost instantly destroyed
That is also how I see light, it's as if the photon was using a wormhole through space-but-not-time, and that wormhole is called the EM-field, but it's an imperfect wormhole due to redshift..
I view light in the sense of limits and infinities, that blow up equations. Like singularities.
We're clearly missing something significant in our understanding.
You're absolutely right. As every point in the universe sees light traveling at the speed of light relative to it, then light in turn sees every point in the universe moving at the speed of light relative to it self and hence the whole universe is length contracted to be infinitely thin in the direction of travel. The universe becomes an infinitely thin but very wide pancake. This means that the point in space where it starts its journey is the same point in space where it ends its journey and it take zero time from its perspective to travel from start to finish. So does light experience time, well its life is over before it has a chance to experience anything. We see light moving but for it, it all happened and finished it's journey before time even moved.
@@petejohnston5880It can be argued that light does not experience time, and a photon is in all places on its path at the same time.
@@DABmonger Nope, photons are just the exchange particles, there exist no photons on the path of light, just electromagnetic waves, the photons are only created from those electromagnetic fields by interactions with matter.
I'm two minutes in and you are already blowing my mind about concepts I thought I understood. I absolutely love your videos, you are by FAR the best physics presenter and explainer since Feynman. Keep up the great work, I'm hanging on your every word now!
Wow, that’s super encouraging to hear. Thank you :)
I love it when people actually believe that they can really KNOW this stuff. They really have convinced themselves that they have actually understood what we can never possibly understand. Understanding what does light experience, is a classic case of over confidence. google the free ebooks, "Dave vs Hal 9001" for more information. You may change your mind about what you think is real and true.
@@Mahesh_Shenoy it's true my man, I look forward to seeing your presentations when they drop in my notifications. They're actually fun dude, you make science what it's supposed to be, awesome 👍
@@Mahesh_Shenoy, you help us to have some glimpses from the shoulder of science giants. That's the POV worth to achieve. Many thanks 🙏👍
Because it's not correct
I read somewhere how we could imagine photon 'perspective'. From it's 'point of view' there is only act of creation and then instantaneous act of annihilation (when it interacts with some object). There is nothing in between for photon, it does not 'experience' time.
But why assume it's instantaneous?
@@Vexas345 They experience infinite time and length contraction as per special relativity
Well as far as it (the photon) is concerned, it might as well be instantaneous, even if it took 13.8 billion years in reference to me? Zero time experience is pretty well instant right?
Kinda baffles the logic of normal intuition when you realize that time is truly based around the fastest thing in the universe, that's how it ought to be reasoned at least, if you want to truly understand what time is. Base your reference at the fastest thing known, kind of like temperatures and zero. There's a limit and we reference from there in science, hence Kelvin.
Why not do the same with light\photons\emr? I'm not trying to turn our time reference understanding on it's head, Just like we don't use Kelvin in everyday life. But for scientific matters, yeah 👍 I think it would simplify the problem of medium speeds not matching to do that way, cause it's all light speed, just different frames of reference right?
I'm not gonna even attempt to address the things that would happen sub-planck though, haha, not qualified. It'd be weird for sure, in case this isn't weird enough for you. I am in no way certain there's anything meaningful below Planck pixel, but I'm certainly not opposed to it being more than not meaningful, so what if the Schwartzchild radius = black hole. Another thing we don't really know anything about other than they're there and they're doing something deeply interesting.
@@G0ldbl4e They do not. The math for time dilation/length contraction doesn't work for things moving at c. They don't have reference frames, so special relativity doesn't apply.
The very idea that the photon does not experience time, as far as it's concerned it's just sitting there, good Lord man what a concept. I mean really if you think about it 🤯 trillions of trillions of trillions of photons, all different amplitudes and wavelengths, interacting with different interferences to form stuff, all infinitely small and large at the same time, this is weird stuff seriously.
It makes me pull back to the holographic model, you know what I mean, if it's just there then not, everything else around it being what's in motion... Which is also a bunch of other photons at rest, blipping on and off here and there. Kind of leads to the idea that maybe it is in some way intricately holographic. I mean it's pretty much all electrical\em. I learned that some years ago during a heroic experience that I did not plan on taking but accidentally did anyway.
Idk I think a lot about stuff but this one I think is above human thinking. I'm definitely not smart enough to grapple with that one, but I'd be willing to bet my life that it's so ridiculously elegant and simple that we're just looking right over it. It's probably right in front of us 😅
05:40 f
_Looking from s.o.'s perspective basically means looking from s.o.'s reference frame._
I'd put it differently: By "looking from s.o.'s perspective" physicists mean *describing the scenario from a rest frame of her/ his.*
▪︎A frame in this context is a coordinate system which basically maps all of spacetime, so you can't really looking _out of_ it. Rather you express physical quantities in those coordinates.
▪︎Everything kind of has infinitely many rest frames with different orientations or origins.
▪︎Your reference frame is the frame you use to describe a scenario. This _might_ be a rest frame of yours but it _doesn't have to._ And in everyday life, it seldom is. Mostly we implicitly use a frame bound to Earth; otherwise, if I went to Cologne by train, I'd have to say "the train has come to rest (a very active rest like that of someone running on a treadmill) and lets Cologne approach it".
google the free ebooks "dave vs Hal 9001" you will be surprised what you will discover.
I followed your recommendation in a party, and the dude telling the story punched me in the face!!!
What recommendation? :D
@@Mahesh_Shenoy probably saying "you're breaking the rules, you cannot use SR to conclude anything once you've broken SR"
I also asked myself this question, and, hopefully, i have a similar answer to what Einstein would have given.
I phrased the question like this:
If I approach the speed of light relative to the centre of mass of the Milky Way, I see the Milky Way's length along my direction of travel as approaching 0. So I should cross the Milky Way in a length of my proper time that approaches 0.
But an external observer (who is at rest with the Milky Way's centre of mass) will see my velocity as approaching c, and hence my length will approach 0, while the galaxy's stays "normal". So the external observer would see me cross the galaxy in a long amount of time, nowhere near 0.000...01 seconds.
So whats the solution to this paradox? After 0.00..01 seconds have i, or have i not, crossed the galaxy? Who's right - me or the external observer?
The answer i could come up with is this-
There is no shared definition of "right now" between me, and the external observer "B". So while my journey takes 0.00...1s in my time, it takes some years in B's time.
B and I, however, are using different standards to measure the distance between two events - me setting off, and me crossing the galaxy. That's why we don't agree on the time between those events.
As you can see, until now, the situation is perfectly symmetrical and both of us are equally "right".
So we just don't agree on the time between two events. But thats ok, it happens all the time in special relativity.
Also B would agree on the length of *my* time it would take me to cross the galaxy because he sees my clock as very slow, approaching not ticking at all. So he would agree that it takes me less than a second of *my* time for me to cross the galaxy. I think it's beautiful how this fits so nicely - i measure so little time due to velocity which manifests as length contraction, while B measures the same length of *my* time, again, due to velocity, but this time it manifests as time dilation. And the result is exactly the same in both measurements. Maybe this shows the deep similarities between space and time, and why one can't be without the other, why we speak about spacetime together, not separately.
But what if i turned around and came back to B, and we compared our ages? This is called the twin paradox.
To come back, I'd have to accelerate. Time, space and simultaneity are relative but acceleration is absolute. So the moment i accelerate towards B, i break the symmetry. Now both of us have traveled thru spacetime, between two events - me leaving and me coming back. However my path was more thru my space and less thru my time, B's was more thru B's time and not at all thru B's space. So B has aged more than me when we meet again. And this comparison is only valid if and when we do meet up, otherwise you can't ask both of us how old we are right "now" because there is no meaningful way to define a shared right "now" for both of us.
Supposing you were to introduce a third perspective into the twin paradox scenario. One in which a spaceship is always manoevred to be halfway between the two.
Putting myself in this third perspective, I find it implausible that two people, always equidistant to myself, could be ageing at such dramatically different rates.
Similarly, consider the graphics at 0:53 to depict time slowing down for a moving clock. The inverse would also be true, from the top clocks perspective, the lower clock would be ticking slower.
Then consider a third perspective 'C' where the top clock 'A' travels west-east at the same speed that the lower clock 'B' travels east-west.
A and B would see each other ticking slower.
But C would calculate A to be ticking at the same rate as B.
Logically, it would seem, this is truly a profound 'paradox' - or these presentations are a little muddleheaded.
@@bobpower9189 you are correct - the middle clock, C, will see both A (who is at rest with the Milky Way) and B (who is crossing the Milky Way) as aging both slower than C and at the same rate as each other, as they are moving away from C at equal but opposite velocities. As you pointed out near the bottom of your comment, this situation is 100% symmetric.
*If A and B are in relative motion, A sees B slow and B sees A slow.*
That is, until acceleration happens, or more specifically, until one of these observer assumes a distinct inertial frame, and abandons his initial inertial frame. Everyone would agree on who changed their inertial frame and he would be found to have aged less when all three observers meet up again.
This is consistent with the time animation you provided a timestamp to. Try drawing out a spacetime diagram for this accelerating observer. Initially, in the first inertial state, the light bounces off between two lines parallel to the proper time. But when the proper time changes direction, the light suddenly starts bouncing off much less frequently than before.
So when your three observers meet up again, we can assert that B accelerated the least (didn't accelerate at all), C accelerated a little bit (less than A) and A, who travelled at nearly c, accelerated the most. Hence A ages the least, C a bit more and B the most.
@@Krokodil986The effects of acceleration breaking time symmetry seem credible enough, but I could not imagine putting the 'pedal to the metal' for a duration of half an hour could result in years of age disparity, as is often presented. Presumably, different rates of acceleration yield different results.
Also, have you ever come across any explanation whereby the effects of deceleration cancel, to any extent, the effects of acceleration. Just a thought - I've never come across it. How would this configure in a spacetime diagram.
@@bobpower9189 amazing question
So rate of acceleration is how much you are accelerating per second, "jerk". The lower the jerk, the slower the change to the new inertial frame, but also the more time spent in acceleration. So I think it cancels out (to be honest I'm not too sure about this)
Deceleration is the same as acceleration, but viewed from a different perspective. Imagine me walking along the street. I can start running. I think I'll be accelerating, right? Well someone who is already running will think I'm decelerating, because I'll be decreasing the relative velocity between me and that person. But for me I'm still accelerating - so the effects of acceleration and deceleration must be the same, time dilates.
Put in other words, the direction of acceleration does not matter because the universe is fair - it treats all directions equally.
In a spacetime diagram, deceleration may be shown as acceleration to the left instead of to the right. Directions are equal, the universe is fair so it doesn't matter. The only thing that may change is simultaneity lines may bunch up or spread out depending if you're accelerating toward or away from an observer onto his world line
But the only meaning of this spreading or bunching is it changes from what point in time causal action propagating from this observer can reach you in your own "right now".
I didn't explain this last point very well, if you don't get it I'll try to explain it better, let me know
@@bobpower9189 I've done some digging around...
also let's define two velocities u and f
let's say u -> c
And f -> -c
If you go from v = u to v = f, even if your change in velocity is instantaneous, ie delta t = 0, the age disparity will still approach infinity.
In fact the quicker you get the acceleration part over, the quicker your two two inertial frames will reach their maximum difference. The quicker this happens, the longer they will be maximally different from each other. And the age disparity comes from this difference. So the longer the difference exists for, the larger the age disparity. So rate of acceleration does play a small part, but what's more important is the difference between the two inertial frames - ie the difference in initial and final velocity, rather than the time spend in transition.
I learn more from you in a 14 minute video than all my years of high school. Thank you sir!!
The beauty of this format is that we leave with two amazing takeaways: a better understanding of physics and for me is a new way of thinking about hard subjects like physics.
"There comes a point in every man, woman, and child's life that they wonder - Does light experience time?" See, that's the mindset of a great theoretical physicist..
who does not know normal people 🙃
OK, fine. I can't help noticing the animations all say "length contraction ignored". So let's talk length contraction.
Suppose we have three objects: P, Q, and R. P and Q are at rest with respect to each other, while R is moving with respect to both. P and Q can be road signs and R can be a car, or something.
In P and Q's reference frame, they are some distance d apart. Due to length contraction, in R's reference frame they are some smaller distance d*k apart, where 0 < k < 1.
As the speed of R with respect to P and Q approaches c, the factor k approaches what number?
In R's reference frame, after P has gone past, it takes some time t for Q to reach it (since in R's reference frame it is P and Q that are moving). What happens to the time t as R's speed with respect to P and Q approaches c?
@silverrahul Then isn't that a meaningful way of framing the question?
@silverrahul ...the question in the title of the video? "Does light experience time?"
@silverrahul The thought experiment I started this comment thread with. Did you watch the video? Mohesh says that "does light experience time?" isn't a meaningful question, because it can't be framed in a way that has an answer within the laws of special relativity. I'm querying that.
@silverrahul Calculating what happens as one _approaches_ an unreachable limit, as a proxy for what happens _at_ that limit, is a routinely used and uncontroversial method in calculus. Mahesh himself discusses it in this very video (9:39--11:48).
@silverrahul I know that an object with mass cannot reach c. If you were concerned that I didn't understand that, you can rest easy.
Thought experiments, in physics just as in mathematics and philosophy, reach out into the impossible, if only to understand _why_ it is impossible. We wouldn't say to Einstein "But you can't accelerate a train to half the speed of light, you'll kill all the passengers."
We can turn my question around, if you like. Let's suppose again that we have objects P and Q, stationary with respect to each other, and object R, moving at speed v with respect to P and Q. P and Q are a distance d apart in their own reference frame, and a shorter distance d*k apart in R's reference frame due to length contraction. Let's ask now: what would v have to be to make k = 0? Now, is there any _other_ value of k that would yield the answer v = c?
(There are certainly other impossible values of k. k can't be negative, or >1, or an imaginary or complex number. If you plugged _those_ values into the equation and solved for v, what answers would you get? Not c. v = c is associated with k = 0 and only 0.)
What a video! I think this series is one of the greatest assistant to understand special theory of relativity
Wonderful to hear that :)
Mind duly blown. I had never considered that consequence of the second postulate. Wonderful. Thank you.
I always just thought about it like: If you're nearly at the speed of light (c) others would see your time go very, very slow. But for you in this reference frame your time goes "normal" but everything around you seems to be very, very fast. So if you would be at the speed of light for the others your time stands still (∞ slow) but for you everything around you would be ∞ fast. So for you the whole age of the universe would be over in 0 seconds. So you can't experience anything outside of your reference frame. And that's the problem that arises like you described the problem in another way.
That's not how it works as you're skipping relativity. You see the universe moving slowly too as it is also moving relative to you, therefore your clocks would agree. Only when you accelerate or spend time in a gravitational field will your clock slow down relative to everything else.
I think the more intriguing point with the "experience" of something moving "almost" at the speed of light is that it would experience ending up at any destination "almost" instantaneously.
If it keep going without any destination it would experience ending up infinitely far into the future (whatever that means) "almost" instantaneously.
If it could do this indefinitely it would for sure experience the clock ticking as usually. But that it would even have time to experience one tick of the clock before either smashing into something or getting to the end of times is not likely.
I was literally looking for a person who could explain things that comprehensively. The way you crack things, like the scientists who are much more eager to break apart the subatomic particles in the Large Hadron Collider to understand the behavior or laws of this Universe. The power of visualization and the interpretation you have mastered is just Astonishing. I don't have words for you, you are just limitless.
Keep continuing the series I am learning a lot by opening different ways to visualize things for Better interpretation.
My regards to you.
I asked myself this when I was young. Like late teens early 20's. I would mention it to people and they would have no idea what I was talking about. My friends weren't physics geeks. lol. Thanks for sharing. Love this videos
I studied this subject some decades ago. My interpretation of this question was somewhat different.
You are focusing on time for the photon and the photons rest frame.
You don’t have to do that. Instead think of travelling ‘almost at the speed of light’ and what you will see is that your own time passes normally, but the entire rest of the universe is Lorentz contracted in distance. In other words, you will (due to length contraction) arrive almost immediately after you leave - as the distance to travel is minuscule - even light years would (if you go fast enough) shrink to millimetres.
The reason light does not experience time is nothing to do with rest frames, but rather that at the speed of light it arrives at the same instance it leaves / because the ‘length’ of its travel has shrunk to zero. This is in a perfect
Vacuum. If the vacuum is not perfect, then the light will experience some minuscule time.
Excellent... Also, I think the video would better serve viewers by comparing clocks. If a photon were to look at its wristwatch, it would observe the hands moving in proper time. Sure, but an observer watching the photon go by would observe that the photon's wristwatch has hands that aren't moving at all. As you point out, this is explained by the photon observing that all the points through which it travels at the speed of light have contracted into one infinitesimal.
I'm super curious how this topic relates to entanglement. Could it be that entangled pairs, despite potentially being separated by light years, "think" that they continue to occupy the same point because per their observation, zero time/space has passed between before they were split and when they become disentangled?
In a reference frame the observer is at rest; not the photon is at rest. The photon needs to travel at the speed c with respect to any observer - even if the observer would himself travel at c with respect to some other observer . . .
@@Jim-uq1mc two photons moving at the same direction: do they travel at c from each others' perspective?
@@Jim-uq1mc In my comment I make the photon the observer. "If a photon were to look at its wristwatch..."
Time cannot be applied to a null curve, that is, for a photon. Light in a medium will travel along a world-line (time-like curve) so there's no difference between us and light as far as time goes.
To be honest, I hadn't wondered until clicking on this video.
As always these videos are amazing! By far the best most easily digestible explanations of physics concepts I’ve ever seen.
Hear hear
Or is it "Here, here?"
Bhai re addict ho jata hu teri video ka
Mat banaya kar aisi itni badhiya video
Subah 5 baje teri video ko play kar diya dekhna nhi tha bas yuhi save karne ka irada tha
Ab nahane nhi ja paa rha.
Teri wajah se school jane me late ho jaunga😢
BTW I am physics teacher
Feynman lecture ki book kharid ke rakhi thi padhne ka time nikalana bhul gya tha
Ab tu aisi aisi chije lata hai to padhna padga😅
Ab bas bi Karo bhai. Rulayega kya?
And you might say, mahesh - i always wondered if we could have a beer together. But einstein says yes, of course you can have a beer with mahesh.
Okay, firstly, I can not get enough of your excitement and energy. I am always glad to see another one of your videos uploaded.
Now onto the fun part. I think the better question is "what IS time for light?"
I have thought about this a lot, and here is what I came up with. Light doesn't "experience anything except the start and stop of its travel. Say it is emitted from a lightbulb, travels to the surface of the moon, and gets absorbed by an atom in the moon rock.
From the point of emission to the point of absorbtion, there is no interaction. As such, there is no "time". Time requires change, and for the photon, there is no change.
So what does this "look like" for the photon? Nothing more than the series of interactions; emission, absorbtion, emission, absorbtion, over and over, with no "time" (change) to speak of in between.
Thus, for the photon, time is nothing more than the series of interactions it has. To us there may be hundreds of years of travel in between, or a millisecond, but to the photon it is just event, event, event....
Does this perspective still seem to jive with special/general reletivity?
No, the start and stop are the same instant i.e. the spacetime interval is zero, so there is no meaningful attribution of "time" to a photon (or along any null curve).
@@kylelochlann5053 if they are the same instant, does that mean all instants for a photon, from the start if the universe to the end, happen simultaneously? Parmenides is pleased!
But in all seriousness, I dont think your statement is any different than mine. There is no "time" between each event for the photon. "Time" for the photon is just the list of events that occur. So you could only ask "how many events back did it get emitted from that atom?" But you couldnt ask "how many seconds ago was that".
@@klosnj11 No, there is no list of events for a photon. In essence there isn't a photon, just an exchange between emitter and absorber that instantaneous in spacetime. If you can, see if you can find a paper by Willis Lamb (of Lamb effect fame) called "Anti-Photon."
@@kylelochlann5053 an interesting perspective. I will look into that.
Hypothetically, if I make a phone call to my friend who is near the sun, than he would recieve it after more than 8 mins 16 secs and we will have conversation at each interval of more than 8 mins 16 secs?
Duh
I'd check with your mobile provider first to see if interplanetary calling is included in your package. Could be expensive 🤠
He is toasted.
The Interval would be double that.
You Record your message and send it away. After 8min 16 sec your friend will recive it. He Records an answer and sends its back. After another 8min and 16 sec the answer has reaced you. So for you the time it takes from sening your message and getting an answer is 16min and 32 seconds. + the time he has used to reply to your message.
Thus the interval is at 16mins and 32 seconds at a minimum.
@@Fluxikator It means if I say "Hello", I would hear his reply "Hi" after around 17 mins?
I watch a lot of these types of videos, and you just make things so much easier to understand than pretty much any other channel or there.
Light is a null vector of space time which mean that is proper time is always 0 . This is can be seen from the equation of proper time
`dtau^2 = dt^2 - 1/c^2 dx^2' which is always 0 for a photon whatever is the reference frame.
So saying that light as zero proper time is perfectly legit, and this in all reference frames.
Well... not exactly. The equation you should have is general flat-space metric: ds^2=-dt^2+dx^2. It is only in the special case of a time-like curve that ds^2=-dτ^2. The proper time along a null curve is not 0, it is undefined.
@@kylelochlann5053 Thanks for your comment. If I understand well your point, you agree that light is a null vector of space time and has 0 norm, but you point that this norm can not be called `proper time` but should only stick to `norm`.
How is this more that a play on word ?
@@stephanevernede8107 Given a spacetime curve, S, in arbitrary spacetime coordinates with tangent vector, U, the "norm" is then the inner product on the tangent space, g(U,U). This would have nothing to do per se with how the curve is parameterized.
For a time-like curve, the norm is a constant, g(U,U)=1, we can use a clock to measure off the distance along any time-like curve (if measurement shows that all identical clocks tick at the same rate, everywhere in the universe, and under all circumstance of motion and orientation).
A null curve has no spacetime length, so in what sense can a clock be used to define time as a parameter to measure length along a length-less curve?
@@stephanevernede8107 you are correct in your original argument. He is just writing word salads.
@@kylelochlann5053proper time is by definition the length of the spacetime interval measured in the rest frame. However due to Lorentz invariance this number is always the same regardless of the reference frame. So we can just choose a different one to perform the calculations. We can choose any so it doesn't matter. The photon will always travel with spacial velocity c which means that Δs = 0 for all reference frames and hence Δτ = 0.
I really liked how you presented your understanding step by step emerging from your confessed confusion. Also loved how you made it a conversation between Mahesh, Einstein and Feynman chipped in, that made it both interesting and funny. A honest presentation full of excitement. Liked and subscribed!
Oh god I recognize your voice from khan academy
Thanks again great videos as usual. Love the energy!
Thanks, Donny :)
I'd love to see a video where you focus on the reference frame more, with more than one observer.
Observer 1 at rest, observer 2 moving at almost the speed of light relative to observer 1. Observer 3 accelerating at 1000 m/s/s relative to observer 2.
Do this and show each observers perspective and how they experience light. I think it would make a fascinating video.
Awesome video Mahesh. I wish you pointed out that when an object approaches speed of light although it would experience proper time, if it eventually stops, its time would be behind the proper time for the non moving reference frame. That’s an important bit of info. Yes ?
Not sure how it would be relevant. If folks don’t already know it, it’s not that easy to make sense of it without diving deeper into it. I think.
Well you have the other awesome videos. So it makes sense that you didn’t specify it. There is nothing wrong with my understanding tough right?
@@Mahesh_Shenoy According to relativity it is equally valid to claim photon is travelling at the speed of light or photon is stationary and everything else is travelling at speed of light relative to a photon. Photon's perspective exist but it is not included in special relativity. If photon's perspective is not important is like claiming it is not important what happens to photons at the event horizon of a black hole. General relativity breaks down at the event horizon the same way as special relativity breaks at the speed of light. Einstein's theories break down at the speed of light which results in infinities that show up in physics when you are doing something wrong.
It's not important as at no point are any clocks actually ticking slower.
It is fundamental to relativity that all identical clocks tick away at the same rate, everywhere, and under all circumstances of motion and orientation.
What you're alluding is that the integral over the accelerating clock's world-line is simply shorter (wrt the global coordinates) which is not meaningful here in any obvious way.
Man, my physics teacher is going to LOVE these videos. Thanks for explaining all of these things so well!!
There is another counter-attack: how much time does an observer experience between photon emission and photon absorption, if he is tracing the same path as the light, travelling with a speed limiting to the speed of light? In that sense, you do get that the events (emission and absorption) happen basically immediately one after the other, leading to a loose statement that a photon doesn't experience any proper time. In "photon's frame", it is born and dies at the same time - by definition, because the space-time interval is 0 on a light-cone.
That’s because, from that frame, the emission and absorption locations were infinitesimally close to each other.
If my neighbors house is infinitesimally close to my own, the moment I step out of my house, I would have stepped into the neighbor’s almost instantly. That doesn’t mean I don’t experience time, right?
@@Mahesh_Shenoy If you only exist while traveling from your house to your neighbour's house, and the threshold is infinitesimally narrow, you could say that you only exist for a single moment, not any finite interval of proper time during which you could experience anything.
I'm thinking of neutrinos here, who do have "time" to oscillate during their flight. Again, of course, Einstein's argument holds that the limit c→∞ isn't strictly reasonable.
p.s. Just keeping the back-and-forth discussion with Einstein here, the conclusion in the video is of course correct :)
Photon experienced time but unfortunately nothing happens in that time as the space outside is not changing. It's as if it went out of the universe and popped right back in just before annihilation.
Isn't that just sophistry?
You've just used different words to suggest the same thing as an imagined frame of reference that is travelling in equality to light..
The logical conclusion of SR is that there is no, "basically immediately, one after the other", by Light's terms - that is is fudge the conclusion for the convenience of human interpretation.
The natural consequence must be that Light does _not_ perceived Time - because by Light's terms, there is no such thing as, "Time": and there is no such thing as, "Space".
Those attributes only mean anything, to us and other entities of those dimensions... For Light, there is absolutely nothing.
That is: Time and Space are emergent properties - dimensions in a Universe that Light, by nature, has no access to: because they and that Universe are, by nature, coiled up to zero and contracted out of existence. Every single thing, is beyond Lights event horizon - where Light, is it's own event horizon.
That's why the question makes no sense - but to say that the question makes no sense isn't necessarily a mature or complete answer to be shared among adults.
The simple answer is that no, Light doesn't experience Time.
The expanded answer is that Light cannot experience Time l, even if it wanted to - because neither Time nor anything else actually exist on Light's side of Light's own event horizon.
That is to say: if Light could communicate, it couldn't process a question on whether it experiences Time? It wouldn't - couldn't - even have any single idea, whatsoever, of what you were even talking about: "Time", and, "Space"?..... Utterly meaningless.
@@lewis7515 i don't realy get this. Why shouldnt light experience time if we see time as the change happening to matter in space . it should in my opinion. Giving light a perspectiv as a human doesnt make sense to me but looking at it from the outside its clear that change is happenig while it moves so how could it be different from the inside perspektiv of light? is it just a hypothetikal question that doesent realy apply to the real world?
You are absolutely right - that kind of question uses lots of words with imprecise meaning. What I found talking about light not experiencing time is a person I talk to has in mind is what other reference frames look like from a reference frame approaching speed of light.
Dumb question perhaps.. if an object is traveling close to C does it appear colder to a stationary observer? My thinking is if time slows for that object including all particle momentum, average kinetic would appear lower. And I suppose all stationary objects would appear colder to the moving object too?
I think “colder” is a very lose word here. If you are specifically thinking about the temperature, then you will have to measure it in its rest frame, no? (I mean you need to stick a thermometer in there somewhere, and now the thermometer is in the rest frame of that object). But, the average thermal energy should slow down. So, that’s an interesting question. Let me add it to my list of topics to research more. Thanks for the question. It’s anything BUT DUMB.
That is actually a very interesting question...
@@Mahesh_Shenoy thank you for the reply. To expand on this.. remote observation of temperature is possible (we measure temperature of everything in space remotely). Also colder == more red shifted.. what if part of the red shift we observe from distant objects is because they are at relativistic speeds from our reference frame due to expansion? Obviously Doppler shift is still relevant. If we see their “clock” moving slower, we should also detect the temperature as lower; all time based events are affected, and temperature is time based. I just solved dark energy (Kidding).
@@amaze2708 Well , Temperature is time based as it measures total kinetic energy of molecule and kinetic energy is dependent upon velocity which depends upon time and as time is relative , temperature is also relative .
I am not a physicist but I think a way to measure temperature can be thermal radiation, as thermal radiation is electomagnetic radiation it's speed is not relative but it's total power should as no of photon emitted in some time is different for both of them
This was so much fun. I laughed all the way through. "That question is meaningless" but delightful!
When light goes from A to B, we can compute the spacetime interval and corresponding "proper time" - for a photon it will be zero and it will be a valid computation. This is enough to say that time doesn't tick for a photon, and thus it "doesn't experience time". And it's an idea with practical measurable consequences: particles moving at light speed must not change along the way, they must be "frozen in time". That's why we now think neutrinos must move a bit slower than light, as they do change during their travel.
Photons also change, their wavelength gets longer as they travel through spacetime
@@kriiistofel Not in special relativity ;) In GR yes, but there the topic gets more nuanced.
No, the proper time for a photon is not zero - it's undefined.
@@kriiistofel No, it is impossible for a photon to change, or have any intrinsic frequency/wavelength.
@@thedeemon No, there is no distinction between SR and GR (SR is simply describes the ground state gravitational field).
😂 This is the funniest comedy show I have seen in ages. Is this really what passes for logic in the minds of humans? 😂
Thank you very much. I needed that. There is nothing better than a good chuckle to break the melancholy of a dull, winter's day.
Almost as funny as the "logic" of a "god".
@@godfreypigott That depends entirely on how you define the word "god". I could easily say that humans are gods over this planet, and that the laws of physics are a god over humans. I could even say that alcohol is god to a drunkard. I don't see how any of those statements could be deemed illogical in a sincere manner.
@@Naomi_Boyd You know precisely what "god" I am referring to.
@@godfreypigott You see, presumptive statements like that are inherently illogical. I could guess at what god you are referring to, but there is an extensive list of possibilities. I could never know "precisely" what is knocking around inside the head of a human. I could hazard an educated guess, based on my experience with your species, and say that it is highly improbable that you, yourself, know what god you are referring to.
@@Naomi_Boyd In that case it is also presumptive to assume that there is only one definition for each of the words you have used.
Sir another question why the speed of light is less in water if the speed of light is always same for all observer? Love your videos
And also if the speed of light is less than the speed of light then Photons will have mass. As you said in that video.
I think I should cover this in a separate video. Adding it to the list. Short answer is, it doens’t make sense to think of “speed of photons” inside a medium
@@Mahesh_ShenoySir it will be very helpful for me because I can't find the answer. Love you and your videos from West Bengal ❤❤❤
@@Mahesh_ShenoyI would look forward to that video. Some points of interest for me would be, is causality slowed in a medium? When you say vacuum do you just mean free from baryonic matter? Also how does the light accelerate¿ when entering vacuum from a medium?
I don't know enough to ask the questions correctly but it is very interesting to me and the way you explain mathematics to us laypeople is some of the best I've seen.
@@Mahesh_Shenoy I also look forward to this video. Can you also include in that video an explanation of what's going on in the experiment where Hau and Harris "stopped" light in a cloud of ultra-cold sodium atoms? I'm having trouble understanding how the photon wouldn't see its own velocity as 0 instead of c.
I think some of the confusion comes in trying to understand length contraction in this context. Traveling very close to the speed of light, you experience proper time, yes. But the distance between the start and end points would be much shorter and take less time than it would for an observer watching you or for a traveler going at non-relativistic speeds. That makes it sound like you'd experience "no time".
Could you say that the faster you are moving, that the objects approaching you from the front seem to have their time speeding up (like a Doppler effect with a sound pitch getting higher)? And could you say that as you get arbitrarily closer to the speed of light, the passing of time of objects in front of you gets arbitrarily closer to infinitely fast? Or am I off base here?
_"Could you say that the faster you are moving, that the objects approaching you from the front seem to have their time speeding up"_ - if you are asking about the light that you see from the objects that approach you, then that is fully correct, yes. That is mostly due to the Doppler shift of the light. If you asking about what you would conclude about the clocks of the others, then your conclusion would be that they tick slower than yours. That is due to the relativistic time dilation.
@@renedekker9806 I see... Thanks for the reply!
@@renedekker9806I think you are saying opposite , if we are moving near speed of light our clock tick slower than theirs and other object appear travelling faster as they are moving fast in time relative to us
@@FocusingOnStudy _"if we are moving near speed of light our clock tick slower"_ - our clock never ticks slower or faster. It always ticks at the same rate. It's that rate that is called proper time.
It is always our perception of OTHER clocks that appear to tick slower (or faster in some circumstances).
_"other object appear travelling faster"_ - other objects always appear to travel at the speed that they travel relative to us.
@@renedekker9806 If time is relative how can we say that clock ticks at same rate ,proper time should not exist even if proper time exist , then it is different for everybody
If we are moving with speed near speed of light then other thing at rest only does not appear moving faster in time they are actually faster, and in this situation clocks at rest will always tick faster than our clock (if both clock have same mechanism)
Light doesn't experience time... in a different way. For the following I am considering "approaching to" everywhere, ok? I am just not saying it for brevity. I will use a * instead.
The thing is... length contraction. But lets start with this:
There are things that don't depend on the frame of reference. Simultaneous things that happen in the same place, are simultaneous for everybody. If when a spaceship flies by the moon its clock was indicating 3:17, it was indicating 3:17 for everybody. For the guys on the moon, the guys in the spaceship, and everybody else. Not all with agree that they flew by the moon at 3:17, but everybody will agree that the spaceship's clock was indicating 3:17.
Say that you have something traveling at the speed of light* in a straight line and flies right by the Earth first and then right by the Moon. Form us on Earth or Moon (that will be "us"), due to time dilation, their clock will be stopped*. Let's say that for us we observe that the clock of the fast thing's guys (them) was indicating 0:00 when they fly by the Earth. Then their clock would have advanced 0* seconds by when they fly by the Moon and it will be still indicating 0:00*. Now, from our perspective the trip didn't take 0* seconds. It took d/c*. A very finite and measurable amount of time (we use the time the light takes to go to the Moon and back to measure the distance to the Moon). It is just that, from our perspective, the "fast guys'" time (i.e. the rate at which their clock ticks) was dilated to oblivion. But what from their perspective? What do they observe? Or, more correctly, how do we explain this from their frame of reference?
Well, we all MUST agree that their clock was indicating exactly 0:00 when they flew by the Earth and it was still indicating 0:00* when they flew by the Moon. That means that, from them, flying by the Earth and by the Moon are simultaneous events*, it took no time to go ron Earth to the Moon (remember * = approaching to).
Wait a second (pun not intended). How did they get from the Earth to the Moon so fast (basically in zero time)? Were they going faster than light from their perspective?
Absolutely not. What happens is that from the reference frames, the length of the moving frame contract in the direction of motion. If they guys are going in a rocket, the rocket will look extremely short for us, 0 length*. And looked from their frame of reference, the distance from the Earth to the moon will be extremely contracted, the distance would be zero*
So they would perceive that they are still flying at the speed of light*, and their time will pass at a normal rate. It is just that they will take zero* time to cover the zero* distance. So, even when time itself passes at a normal rate, they don't have any time to "enjoy" the trim from the Earth to the Moon.
Now say "they" are not people in a rocket but a small particle (a muon or a neutrino) that is created in the Earth and that it travels to the Moon at the speed of light*, and when it gets there it hits another particle and "dies". For us, it would take a couple of seconds for the particle to get there. But how will the particle experience it? For the particle, time will pass at the normal rate, but the trip will be extremely short, with a duration approaching to zero. The particle would be born on Earth, experience the trip with a normal-pace passage of time, and die, at the same time*, so it will experience the normal-pace passage of time for no time.
Take it to the extreme, and everything breaks down. But unlike the black hole singularity where a lot of things explode to infinity, here it breaks down in a nice way. While you cannot do the calculation of what happens exactly when v=c, you can take the mathematical the limit with v approaching c and you will have no infinites. Rather you will have a zero. A photon, now traveling at exactly the speed of light (no asterisks anymore), would not experience time. But NOT because time would pass at a different pace for it. Oh no no no... Time would pass at the same pace, if only it had a moment to experience that time. The photon will be born and will die at the exact spacetime coordinates in its reference system. Will be born and die at the same place and same time. Yes, it will be born on Earth and die on the Moon, but the distance between them would be zero. It didn't have time to experience the passage of time.
Excellent argument, your logic is very sound - it brings to mind constructor theory. Also love the chess analogy reminds me of Feynman's use of a chess analogy. Thanks very thought provoking.
Thanks, Jonathan. :)
But you can have two kings next to each other in chess. That would have required an illegal move though but it can still happen.
There has even been a real chess game where the judge ruled that the one who played a move after an illegal move lost, because it was illegal to to continue after this illegal position and create a new illegal position.
When the player who made the first illegal move pointed that out the judge concluded that the last player who made an illegal move lost! ;)
Not sure what conclusion we can draw about lights perspective from this though lol
First, why are you so good at incorporating your sponsors in your videos? You're simply too good. Secondly, I totally agree with correcting people's understanding about certain subjects and misconceptions. Though, I would totally commend them for thinking about these things and being curious. I also can understand others telling others "click bait" concepts. I feel it is to get then intrigued and interested to learn more. Promoting education, critical thinking and scientific literacy is definitely a great thing to do.😊
Mahesh sir please cover quantum mechanics stuff also......
Yes, yes! On my ever growing backlog of videos.
If you and I travel very close to c in opposite directions, the speeds will add up to be more than c (as it is numerically close to c). So for you, I travel faster than c.
Mahesh I have a doubt ...
Why pair annihilation doesn't takes place in mesons ? I surf the internet and found some answers..i know charged pi mesons don't annihilate because the quark and anti quark are different flavours but what about the neutral pi mesons? Some of them said annihilation is not a instantaneous process..we know that mesons are unstable so before annihilate..it's starts to decay into other subatomic particle...is that right explanation ?
Which property differentiate the lambda -0 and Sigma -0 in elementary particle because both are made of up quark-1 down quark -1 and strange quark - 1 ?
If anyone have the answer let's start discussion 😅😊
I have no clue about this. List most stuff in my life! But adding it to a list of my research topics
Good video! The whole answer to this is that light neither experiences time nor distance. The concept of a 'physical wave' between emission and absorption of light is not real. The 'wave' is only a mathematical conception which informs us where and when the light energy packet is "transmitted" to. There is Nothing in between the emission and absorption points, either in time or in space..
Good point and so many seems to not understand that part of the physical properties (or lack of that) in light. It explains a lot of what we think of as strange behavior like "spooky action at a distance" and the many strange things with quantum physics.
Light takes up physical space (wavelength) based on the number of oscillations in its E-field per unit of time (frequency). It's energy (E=hv) is based on these physical properties. Photons have to physically change to be measured, so I don't know how those concepts would make sense if light didn't interact with time or space.
@@Vexas345 No, light itself does not energy/frequency as per E=m. Given some world-line, we can assign a photon an energy/frequency, which are frame dependent values.
@@kylelochlann5053 how do you define a photon then? Our interactions with photons are based entirely by the transfer of energy. A photon with zero energy essentially doesn't exist, since it can't interact. Sure, its energy may change depending on the observer's frame, but that also applies to real objects. Real particles have relativistic momentum and so their measured energy is frame dependent.
@@Vexas345 We define a photon as an excitation of the free electromagnetic field that couples to electric charge and associated with the quantum state of some system. Let's say we have a hydrogen atom in state A that transitions to A', that then is coupled to a detector (which also undergoes a state transition) at light-like separation. The "photon" is the exchange between the systems.
Keep in mind that energy is a description of matter, specifically being the Noether charge of time-translation symmetry, and not something that exists. Or to put it more leisurely, energy is an arbitrary number assigned to a system that represents a constraint on the dynamics.
The equation E=m is a statement about the internal dynamics of a system. We say an electron has an intrinsic energy because there's an internal interaction between the electron matter field and the Higgs field. Given an arbitrary time-like curve we can assign the electron a coordinate energy/momentum: E=γm and p=γmu, constructed in terms of the internal dynamics represented by m.
We can do no such thing with a photon - there are no internal dynamics. The energy of a photon is zero (intrinsically), E=m=0. However, as the photon couples to the electric charge, and the electromagnetic interaction is constant over spacetime, we can associate the photon with conserved quantities with regards to the space and time components of some observer, E=p=ω.
Can you constantly accelerate to closer to the speed of light such that, from an outside perspective, the light never reaches the top of the clock and ticks?
I suspect from inside the vehicle, you would just see space continually contract such that you would arrive at any destination point before light had a chance to tick the clock.
I like this question. I think you are right
I thought this was gonna talk about how light oscillates and if something changes throughout it's existence it must have time or something.
Nice content! The moving clock ticking slower points directly to the twins paradox which has one of the hardest wikipedia pages I've ever seen lol
Or, as we say in mathematics: You can't divide by zero, but you can take the limit as the denominator approaches zero. At v = c, you're literally dividing by 0 to get quantities like γ, length contraction, time dilation etc. So those quantities are no longer well-defined.
This is where the next genius wonders what happens if one were to allow division by zero, and thereby revolutionizes math as we know it.
that segway to the sponsor segment is crazyyyyy good 😂
anyways, I have a question, if the speed of light is the speed of causality is the speed of time, shouldn't light be time?
I needed this channel for so long and didn’t even know 😱 Finally instead of just knowing the right answer I can understand what is going on. TY so much, great work! 👍🏻👍🏻👍🏻
Love watching floatHead Physics! Your enthusiasm is infectious and I will be showing my teen daughter your videos to help her intuition of physics. Thanks, Mahesh!
That asterisk "ignoring length contraction" is doing a lot of work here, since in "light's reference frame" the universe is 2-dimensional, and its velocity is zero in what we would call
its direction of travel (because for a photon, that direction doesn't exist). But real photons don't travel in only one direction, they propagate with a probability cone. Might be some insightful math to be done there...
How have you concluded with such certainty that Light's universe is 2-Dimensional?.....
Light's velocity is zero in its, "direction of travel" - purely from our, practically-useful, perspective, of Light's perspective.
However, surely, Light only has a, "direction of travel", at all, from our perspective, of Light's perspective?
That is: isn't it the case that Light's, "travel", is only perceived?
Light doesn't travel, it cannot - we call how it presents in our Dimensions, "travelling", because it's intuitive and helpful. Meanwhile, isn't it actually the case that Light only simply _propagates_ - from the point that it manifests?
If that is the case, then Light must propagate, at the speed of Light.
If that is so, then Light simply propagates, from wherever it manifests, in every Dimension, in every direction, equally - which is: at the speed of Light.
Wouldn't that then mean that every direction and every Dimension: is zero?
Isn't the conclusion, then, that while there is no, "direction of travel", from Lights perspective - the exact same terms apply to all other, "directions": that it could only move to, at the speed of Light....So, wouldn't there, equally, be, no, "Direction" - in any non-direction it could move to?..
Must it not then be the case that there are no, "Directions", whatsoever - and, by that token, no, "Dimensions", in any non-direction, for Light to not, "travel", to?
Isn't it the ultimate conclusion that, for Light, there is no, "Direction", at all, that it could travel to at anything less than the speed of Light - meaning there is no, "Dimension", whatsoever, to not, "traverse": with the result that there is no, "Space"; no, "Time"; no, "Thing"; no, "Where" - and there was not, is not, and never could be...
Would it not be that, for Light, _all_ is simply null - and moot?
Does Time experience Light? is the question i get asked the most. Right behind Do you know what time it is? And How are you doing? Thank the good Lord i have the answer now.
Now that the "experience" part is ingeniously taken care of, Shall we move to the next innocent but tricky term i.e, "Time"?. What is it? is there any intuitive sense of this term? Is it universal or it's just an emergent phenomenon as a statistical byproduct of entropy? I thought I almost got it from the Arvin Ash's video on the topic but would really love to have it reimagined with your enthusiasm and care. Great work brother, I absolutely admire your explanations. ❤
Amazing video Mahesh. The production values are going up too. Nice!
Great & thought provoking video. However, one of the major problems I have with SOME scientific "conclusions" is the unprovable "fact". For example; if we cannot experience light's perspective, then we cannot say that it does or does not experience time. But on the other hand, special relativity is only relevant INSIDE of time & depends on the perspective of two or more subjects. Therefore, if we cannot use light as a subject in special relativity, then it is more likely that light does NOT experience time, and we must use quantum principles to determine its nature. ***I LOVE YOUR CHANNEL!*** Keep up the great content.
Using quantum principles doesn't change anything. Quantum Field Theory is based on special relativity.
1.Being at rest is the same as moving at a constant speed. 2. To "experience time" means to experience change. 3. Only an observer of change can experience change. 4. The changing things themselves do not experience any “time”, they simply “change.” 5. The concept of “time” refers only to the observer who is aware of himself.
Naturally, inside a reference frame, the speed of light remains c, regardless the reference frame's speed in relation to any other reference frame. The speed of light is actually the speed of causality. Inside any reference frame, it is constant.
If we sit inside a space ship that travels very fast, approaching c, we still experience everything inside the space ship as normal. The issue is the relationship with other reference frames that are not traveling that fast.
The imaginary photon that is bouncing up and down the cart, is indeed perceived as traveling at c inside that cart, constituting a reference frame. But, if we could somehow register that photon's movement from outside the cart, standing still, events inside the cart would seem to freeze.
An imaginary particle that was moving at the speed of light inside the cart could not be perceived on one spot, moving laterally "up" and "down" with regard to the non-moving observer. That movement would be extended along the vector of the cart's trajectory.
It's Special Relativity's space contraction that does the trick here. If the cart was moving very fast, approaching c, the imaginary particle at the speed of c inside the cart would actually not traverse the same distance anymore, as it would at a low speed. It's forced to traverse a much larger distance, as seen from the outside observer, whereas the inside observer in the cart still perceives the particle to move at c.
This is exactly the core concept of Special Relativity. What an inside observer sees , while moving very fast, is not the same as what an outside observer sees, when standing still. So, light that travels through the Universe experiences space contraction so that all of Space becomes contracted into one point. Time dilation is stating the same mechanism here: to traverse a point does not take any time at all.
A hypothetical space ship that approaches the speed of light is seeing the Universe as contracted into almost one point, a distance that takes almost no time to traverse. And that while inside the space ship, light still travels at the speed of c, without any contradiction.
I'm loving your vids, currently binge watching, thanks!
Your more then a teacher, you make our heads float in to physics ;) Enjoyed it so much!
You all need to talk more about proper time as I think many people believe that your experience would be different and you'd see things going slower or faster in your reference frame, but that's not the case. Your faucet would still drip at the same rate and clocks would still be 1 second per second. Are GPS satellites not in our reference frame? I know they have to take into account time dilation, but as I understand there is no real boundary for time dilation. So, the answer would be no, those satellites are not in my reference frame. But then, where does that stop? Are my head and feet while standing in the same reference frame? So, how can a human be in rest and in a inertial reference frame if there is always space and/or time dilation. Or do I need to be in the middle of space away from gravity? Great stuff.
1. I think "light does not experience time" is a good description of "proper time for light is meaningless".
2. There is still an affine parameter along any light-like geodesic, but there is no way to fix its unit (as we have fixed the second for proper time).
3. When gravitational lensing happens, you can connect two events by a family of time-like curves approaching a light-like curve in limit. In that case, proper time measured along those curves goes to zero as the curves approach the light.
4. Existence of singularities is proven using light-like geodesics, so even without proper time, the light can experience "something".
5. Not to mention interference and various electromagnetic interactions light can participate in.
This highlights an important distinction between pure mathematics and physics. Math is an excellent tool for describing the reality (maybe the best tool we have?) but still will never "be" reality itself. The hard part is knowing where the math diverges from the physics.
Your channel is incredible. I really cant wait to see you at 1 million subscribers. I have little doubt.
The more I learn about special relativity, the more I think that our movement is just an illusion, rather we all stay in place and only light is truly moving.
Lemme guess-still working from home? 😁😂🤣
You have an amazing ability to clarify complex topics. Salut!
I think you are confused by what a frame of reference is in physics. A frame of reference is a set of coordinates to describe a velocities of objects in that frame. A key feature of an INERTIAL frame of reference (the one we use in physics, which you are describing) is the frame is not accelerating, which does not mean that the speed is zero (which is also a “loose” term as describing velocity in respect to something, like the ground or earth)
Exactly. At rest also extends to straight line, non-accelerated motion which is exactly how photons travel through the vacuum of Space. I think this explanation is inconsistent with the very foundational basis on which it claims to sit.
In another video, he explains why everything at rest in the universe is moving through Time at the speed of light. Using that thought experiment, he goes on to agree that the faster one travels, the greater their displacement through Space and the less their displacement through Time, till, eventually, the particle in the thought experiment reaches c and employs all its speed in the spatial dimension with nothing left over for Time hence, objects travelling at c experience no time.
This video appears to contradict that.
🤷🏾♂️
@@ToyyinnAuslander Yes, I agree. To be honest, I always had a problem with the proverbial 'light-clock' being used in these thought experiments. I never understood how it was possible for the path-length between the reflector and detector to be altered by the velocity of the clock as it travels through space. These experiments seem to assume that the motion of the clock provides some forward momentum to the photon being emitted and detected in the clock but doesn't that contradict the postulate that all observers experience the same 'c'? I mean, if the clock is traveling along the x-axis and the photon is emitted along the y-axis then the photon would travel along a path that is perpendicular to the direction along which the clock is traveling, right? The photon would have traveled in a straight line but the location of the detector would have changed during the time of the photon's journey.
Also, one would assume that each photon can be detected only once but in the model used here, the photon is depicted as a wave travelling from the emitter to the reflector. The fact is, according to the postulate, when the clock is at rest, the experiment is set up so that the photon travels the path between the emitter, the reflector and the detector. When the clock is in motion however, we can see that 'at rest' is a 'special case' since from the photon's point of view, the positions of the clock-parts are arbitrary. As soon as we put the clock in motion, the photon is no longer traveling the path between emitter/reflector/detector; it travels from point 'a' on the y-axis to point 'b' on the y-axis and arrives back at point 'a' on the y-axis. Right? The photon _never_ deviates from the y-axis but the emitter of the photon does. It's not the photon traveling along a path that is 45° to the direction of travel, it's the emitter that has moved to a new position on the x-axis that is at a 45° angle with respect to the photon's position along the y-axis; the photon is 45° _behind_ the emitter. The length of the photon's journey however remains constant.
In other words, if you had a photon emitter firing photons between two parallel plates, the top one is uniformly reflective and will reflect any photon back the way it came; the bottom one will detect and register any photon that interacts with any point on its surface and we can have the plates spaced at some arbitrarily small distance so that even at light-speed, no photons will be lost to the system. There is a tiny hole at the centre of the detector where the emitter injects photons between the plates. With a clock like this, no matter how fast you travel, the clock will tick at a rate that is proportional to the distance between the two plates and the speed of light, both of which remain constant in all frames.
And even assuming that 'length contraction' is an actual thing, that would not change the rate at which the clock ticks either. One might argue that the length of the clock becomes so contracted that its displacement along the x-axis takes the reflector out of the space occupied by the photon which is never detected. In that case, the clock simply stops but until then, the rate at which it ticked remained constant.
So yeah, these thought experiments make it appear that the velocity of the clock alters the path of the photon somehow but how, no-one ever explain that to me.
I have a rebuttal. To invent an idea that breaks rules does not necessarily mean all rules must be thrown out. A clear example: sqrt(-1) used to be thought of as a meaningless question that broke foundational rules, until certain mavericks said, "Let's do it anyway and see where it takes us!" They didn't have to reinvent all of math, they didn't have to get rid of "a negative times a negative equals a positive," they just invented a new abstract concept that turned out to not break math when implemented. A tweak to the rules (i.e. overturning the rule that there's no sqrt to a negative) was enough.
Likewise, tweaking the postulate to say "all *sub-c* inertial reference frames" (it already has "inertial" as a qualifier, after all) allows for everything special relativity claims to remain the same (since it's already assuming all reference frames are sub-c), while allowing for mavericks to break the rules beyond the limits and see what happens.
So I don't think you can really say (at least as it was presented here) that you can't tweak the postulate while retaining all its current predictions, just like the introduction of the seemingly-nonsensical *i* didn't undermine the math of real numbers in any way.
so interesting man, my mind is blown after every video you release
I love the way you break these concepts down in ways an average person can understand. I was a little bit disappointed in this video when I saw the asterisk though: *length contraction ignored.
I have always been so fascinated by imagining what the universe might look like from lights perspective, and in my mind, I always assumed light (sorry Einstein, *an object moving *almost* the speed of light) would experience the universe as (almost) two dimensional in the direction of travel. Even if the clock is moving at normal speeds from that perspective, the way space dilates is still fundamentally different from our usual 3D perspective. I was really hoping to see an animated view where the cart was bouncing up and down while the light particle was stationary so we could see how the cart contracted in both the X and Y directions.
I'm a bit confused. Any object traveling near the speed of light would experience proper time from it's perspective, and almost stopped from the stationary observer perspective.
So light will experience time proper time, and from the external frame of reference it has stopped. So I don't see the difference between light and any other object.
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So time dilation does not apply to a photon as shown in 2:45? Because in this example time has stopped for the photon :/ So is the example wrong?
It's because for a photon reality is vastly different than ours. I can imagine that length contraction causes whole universe to be contracted to 2D plane. So from it's perspective it does not 'travel' like a regular matter, it does not 'experience' time nor distance. It's existence is only to be created and to be annihilated, with no time in between. The regular matter will never reach the speed of light because it would require infinite amount of energy, so we are stuck to be always different than elementary particles which travel at the speed of light.
@@kriiistofel Hi, thanks for the reply, but isn't what you are saying contradictory to the assertion in this video :/
" *So from it's perspective it does not 'travel'* like a regular matter, it *does not 'experience' time nor distance.* It's existence is only to be created and to be annihilated, with *no time in between.* "
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This is where I am confused. Massless particles etc travel at the speed of light always. As such from an outside observer (us, not moving) zero time passes (time dilation). For us it's clock does not move.
(The presenter says first this is correct (The train) and then says this is incorrect)
Regular objects with mass can never reach the speed of light so so some small amount of time always passes observing from our not moving frame.
So light is a bit special because it does travel AT 'c'. If from "our" perspective it experiences "zero time" we have a weird paradox where it both exists and does not exist. There is a big step between an object with small dilated time and zero dilated time :/
Albert knows this and say the solution to this paradox is don't ever ask about it lol
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So, I am completely lost as to what the assertion of the video is. From what I can tell the assertion is never ask about the photon problem because it breaks SR and GR.
So, does a photon exist? The answer is "We don't know" or "Don't ask that question" lol
Which is a bit weird as the photon is a central study used for most physics requiring 'c' as a perimeter lol
@@axle.studentIsn't the, "big step", your conclusion that, because a photon experiences zero time, it does not exist. Why?
Just because you can't fathom the terms of its existence, from your perspective, why would that mean it doesn't exist, from its perspective? How would you know?
Walk it through: you surmise it experiences zero Time.
If that's correct, on what basis do you determine that effects its existence? On what terms? That's number 1.
Number 2, is that you cannot directly observe Light's perspective - you can only determine that it must experience zero Time... That's quite reasonable and seems intellectually sound - but, it is possible that there's more than one way to resolve any, "zero Time", dilemma at Number 1 - if there actually is a dilemma.
Once you cross the threshold of Light's perspective, "zero Time", might mean not only that Light can experience no proper time, and no Time as a dimension: it could equally mean that Light has no facility for a temporal dimension, whatsoever?
Perhaps, Time, itself, as a tangible Dimension, does not exist, for Light?
Perhaps, equally, on Lights side of the threshold, it exists quite perfectly well - and, from that perspective, what does not exist, is _you?_
@@lewis7515 Thank you. What you say is very close to what I am attempting to work out. Maybe no answer currently exists.
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What is the relationship between the photon and time?
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"Perhaps, Time, itself, as a tangible Dimension, does not exist, for Light?"
Can I suggest that light does not have any experience of time (0 time) or as you say for light time does not exist. It's a matter of semantics and interpretation here :)
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"Perhaps, Time, itself, as a tangible Dimension, does not exist, for Light?"
Yet, for us it can appear to exist for billions of years.
"Perhaps, equally, on Lights side of the threshold, it exists quite perfectly well - and, from that perspective, what does not exist, is you?"
yet light can interact with us even though we don't exist to light?
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So, I am left with saying that light both exists and does not exist. "Does not exist" is akin to saying that Zero does not exist or that Zero is the absence of anything tangible, yet we use zero in a tangible way
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*So, this is 100% on point to what I am attempting to work out/understand. What is the photons place (relationship) with the 3D and 'c'.*
If for the photon time does not exist, then causality can not exist? Yet if it hits a photovoltaic plate it can transfer it's potential to the plate.
@@axle.studentI'd suggest, no: Light certainly _does_ exist.
What's significant is that Light can have no tangible experience of its own existence - nor that of anything else.
There's no dilemma - it's a matter of perspective.
Meanwhile, it doesn't seem quite analogous to, "Zero" - as zero is just a definition, of a certain state.
There is no definition for Lights state. Its state, is no state - that perspective doesn't exist: in anywhen, nor anywhere. Light, just is, from one perspective - and is, not, from another.
A photon doesn't have a relationship to 3D, and a photon doesn't have a relationship to C - because a photon doesn't go anywhere.
That has no bearing on casualty, because the realm of causality and photovoltaic plates is a realm a photon has no access to and which is totally meaningless to a photon - it transfer potential it cannot be aware of, in a transaction it cannot perceive, within a Universe that is beyond its nature.
However, the fact that the realm is invisible, intangible and practically meaningless, to a photon, doesn't mean that realm does not exist? That's not the same thing at all....
To the interior of a black hole, we, are on the one side of an horizon that means we are invisible, intangible, and practically meaningless, from that interior...we still do very much exist?. Its just a matter of _perspective,_ and the limitations of horizons.
The way You explaining things is just mind blowing. Keep up the good work.❤❤❤😊
If you measure time as clock hands from a tower. If you rush away at speed of c, the hands are moving but you can’t “see” them moving. They are frozen. If you stop they start catching up or moving normal. If move toward the clock accelerating toward c the hands will speed up as you experience all the time or hand movements that you out ran before. When you reach c the spin is so fast it stops again. So not being able to tell time, or frozen clock hands is the same as not experiencing time.
This might be slightly off track?
My understanding is this: that, nothing, actually, freezes? It just _appears_ to, depending on who's looking, from where.
Rush away from the clock, and it appears to freeze, to _you:_ somebody at the clock doesn't see any freezing going on. They will see that _your_ watch appears to have frozen - but it hasn't as far as _you're_ concerned.
When you stop and look back at the clock, it will obviously state the time you read on your watch: as you will be looking at the equivalent to your Present - the same Present you left at the clock, but only from a new _location._ A location that, comparitively, would have been in your temporal Future, _if_ you'd stayed at the clock? By travelling at the speed of Light, you will have made a shortcut in Time and Space, across that distance to where you now are - a distance it would have taken Light time to reach: you have simply kept pace with that future expectation. So, you could look back from there, and see yourself preparing to leave...
IF you had a special telescope that could reverse that shortcut [by operating faster than the speed of Light] you could look at the clock in _its,_ relative, Present - and only then could you see that, actually, much more time has passed, _there,_ than what your watch reads and what your eyes tell you, in your Present - you just couldn't see that without your special telescope. Without that device, you'd just have to wait for the Light you have shortcut, to catch up to you: and even more time would pass at the clock, while you wait...
If you decide not to wait and lose even more decades, and immediately rush back towards the clock, it, again, appears _to you,_ to freeze - but, again, it doesn't actually freeze. It doesn't speed up, either - the image you're receiving is not a video in a player? It is Light. For the image you receive to "speed up", it would have to travel faster than Light, and it cannot?... Time at the clock passes quite normally, as far as it is concerned - you appear _to the clock_ to freeze and, meanwhile, you see what you see of the clock - which is, again, the Present that you left.
Only when you do finally arrive back, will the two shortcuts you made, instantly, resolve - at the speed of Light. That, is how you will step from your ship, look around, and see that you are now in your home reference frame again, experience a shared Present: but, while only minutes have passed on your watch, decades, or centuries, have passed at the clock.
Not being able to tell time, and frozen clock hands, are nothing to do with this.
[*correction: not see yourself, preparing to leave; see, just after - the gathered crowd, looking up, watching you go].
BOTTOM LINE: An object moving at "Nearly" the "Speed of Light" is experiencing "Proper Time" in its own "Frame of Reference," which measures "Time" when the object is "At Rest." An object "Constantly" (c) moving at the "Speed of Light" is not "At Rest" and therefore has no "Reference Frame" at all to measure "Time."
Great show! I suppose that one could make the argument, that light doesn't experience time precisely because photons going at the speed of light don't experience reference frames, so they couldn't experience time either. The only way they could experience time in the first place would be through a reference frame.
The cart illustration is amazing
I really like your videos as a physics student. Especially the dialogue between you and Einstein etc. Keep up the great work!
This is an awesome video, very well explained, thank you…
I like to think of it in terms of definitions. In special relativity, time is defined by measuring how “fast” light travels.
When a car moving at 90% speed of light relative to the ground sends out a light beam, to an observer on the ground, either the light beam is traveling at 1.90c (wrong) relative to the ground or the light beam is traveling c relative to the ground and the relative time is dilated and relative length is contracted (as well as simultaneity differences for the two observers).
Both observers say “I must use c as my basis for time since it is actually the speed of causality / electric field changes etc”
Thus we see why it makes no sense. How does a perturbation in electric field “experience” itself? It’s like asking a gust of wind how it feels to hit itself.. if electric field perturbations are how we measure rate of causality - eg how many times an block of radium decays in a period depends on rate of electric field flow C - then we can’t ask how does electric field disturbance measures itself.
How many electric field disturbances did the electric field disturbance feel? Going in the same direction. It just doesn’t make sense.
An electric field ripple in a direction can’t experience other electric field ripples in the same direction. It can’t measure time because it is how time is defined
I woke up saw your video and now I am dead😂😂
I can see light reference frame now😂😂
By the way awesome video ❤❤
You are the chosen one!
Thanks Einstein 💓
Dude taught me Relatively in 10 min than my entire high school. 🔥
I reached the same conclusion following this thought experiment: consider a massless observer, accelerating along a beam of light. Since it is massless, it can accelerate to C. Now what does it observe? As it accelerates, the speed increases, and it sees the beam of light redshifting. From the observer perspective, the beam of light loses energy. When he reaches C, the beam of light he was following practically lost all of its energy and is not detectable, ceases to exist. A photon does not exist from it's own perspective, nothing exists from the photon perspective. A photon that traveled since the big bang,13.8 billion years, traveled 13.8 billion light-years. Form the photon perspective that is meaningless, he has travelled 0 attoseconds, 0 attometers. Maybe here is the next physics breakthrough, since this does not make sense from the quantum perspective as well.
Wow... i have seen many videos but no one explained like you did...hats off
Your explanations and animations are fantastic. Best I've ever seen.
An inertial frame of reference is not at rest (as asserted), it is moving at constant speed, undergoing no acceleration. So light is always in an inertial reference frame because it always travels at the speed of light, never accelerating or decelerating. You can say the question of whether light experiences time is moot. However, consider a massive object that continues to accelerate closer and closer to the speed of light. As it does so it experiences ever-increasing time dilation and length contraction according to GR, the limit of which is the state, mass, energy, and speed of light. Massive things cannot reach the speed of light but they can get infinitely close, and time for them can approach "not passing". For example a massive object could in principle travel fast enough to reach anywhere in the universe in one second (its time). Muon decay proves this. I don't see the downside of thinking light does not experience time even if the real case is that time does not exist for light.
It's fundamental to relativity that all identical clocks tick at the same rate, everywhere, and under all circumstance of motion and orientation (LPI and LLI, respectively). The downside of thinking that light does not experience time is that it makes understanding the theory rather difficult, e.g. understanding the causal structure.
Please explain this hypothetical case:
Let’s say we have a particle at almost the speed of light. According to my understanding, applying the length contraction would mean, that the distance until the particle collides with something, would shrink. In the lim(v -> c) the distance would shrink to zero. Meaning, that the time of flight would become zero. For a hypothetical particle identical to a photon, except with a minimal mass. This would mean, that in the outside frame of reference, in the limit, the particle would be created, move at a speed indistinguishable from c and finally interact with something and get destroyed. In the reference frame of our hypothetical particle, it would be created and, in the limit, after a short time indistinguishable from 0, interact with something and get destroyed.
So the particle would experience time in the sense, that a hypothetical clock in it‘s time frame would tick normally. But on the other hand it wouldn‘t experience time in the sense, that the time between creation and destruction would become zero.
@@MaxStephandurchpiquer of course I did mean, that the distance from the point of creation to the point of destruction shrinks in the reference frame of the particle. And with „in the limit“ I always meant „in the limit of v->c“, not „in the limit of mass->0“. I intentionally did try to avoid the case of a massless particle.
1. My hypothetical particular has a very small, but non-zero mass. So I see no problem here. (See 2)
2. My limit does not change the rest mass. The limit doesn’t say the particle reaches c, it only sais it approaches c (In the reference frame of point of creation/destruction). (The limit of 1/(x²) for x-> 0 is +∞, even from both sides. But that doesn’t mean I would ever dare to say „1/(0²) = +∞“. 1/(0²) remains undefined.)
3. Misunderstanding on my side.
4. see 2. The limit doesn‘t mean, that one just plugs in that value (which would be invalid here). And so I don’t see, where I have ever tried to apply something to a massless object.
5. That was an implicit assumption. Should have been that precise. Like in an experiment, where a LASER-analog, which produces our hypothetical particle instead of photons, is pointed at a black body.
5 (again). But wouldn‘t it be possible to weaken this assumption to this point?:
The point of creation and destruction move relative to each other with a small speed, small enough, that the edge case of relativity called newtonian mechanics is precise enough to describe their relative behavior.
@silverrahul I know, that I can’t plug in „v=c“ for a particle with non-zero mass. But that‘s the whole point of a mathematical limit: Approaching an undefined value infinitesimally close WITHOUT really reaching it.
Same example as above:
lim(x->0) 1/(x²) = ∞
(even from both sides), but
1/(0²) ≠ ∞.
Instead 1/(0²) is undefined.
@silverrahul Then please explain to me, why the mathematical tool of a limit cannot be applied here!
In principle we can accelerate a particle arbitrarily close to c. So the limit is applicable here.
Since the particle can’t reach c, the limit doesn‘t say anything about particles moving at c, but I DIDN‘T TRY TO DO THAT.
I just said, that by increasing the speed arbitrarily close to c, the lifetime of the particle gets arbitrarily small, to a point where it gets indistinguishable from (BUT NOT ACTUALLY) zero.
@silverrahul 1. I know that it would require infinite energy to actually reach c, but as I pointed out, this is a hypothetical case. So right now I don’t care about energy constraints except that it has to be finite. It’s a thought experiment. Nothing more.
2. I never said the lifetime actually gets to zero. Here the „in the limit“ as part of the sentence is important! As I pointed out multiple times, the value of the limit (v->c) DOESN‘T say anything about the case (v=c), but about the behavior close to that. So saying that the limit (v->c) of the lifetime is zero, is the same as saying „for v close to c, lifetime is close to zero“. Again: This is not making any statement about behavior AT v=c. When I said indistinguishable from zero, I was talking about a case CLOSE TO C since a statement about a case AT C would be invalid.
I feel I should add that the "almost c" reference frame does have some special properties. While yes, it experiences time normally, it needs to be said that from that perspective, the universe will be going by so quickly that you'll reach the extents of space _and time_ itself in the blink of an eye. If we assume that at some point, time ends -- as time had a beginning, it should have an end -- you will reach it extremely quickly by going super close to c. Therefore, a photon essentially _skips_ to the end of the universe instantly. Thus, it experiences no time at all because by definition, whatever the universe's maximum time limit is, you'll reach it immediately.
How about the question: How much time would an object going 0.999C experience if it was traveling a certain distance? It would experience time normally, but the amount of time to go a specific distance would, from its perspective, be severely shortened. Like, how fast would you have to go for your experience of a trip from the Andromeda Galaxy to the Milky Way to only be one second long from your perspective? I feel like this phrasing better gets to the heart of the question without breaking relativity.
If Andromeda (M31) is 2.537 million light years away, then _from Earth_ an object going 0.999999999999999999999999999922 C should arrive at Andromeda after experiencing 1 second of proper time.
That's 28 nines, so from Earth's perspective (or I guess the Milky Way) you're only going 7.8×10⁻²⁷ percent slower than light. You will arrive at the Andromeda galaxy one second after light/radio from Earth arrives. I'm not taking into account that the Andromeda galaxy is actually "falling" towards the Milky Way galaxy and will collide will us in about four or five billion years. This calculation I did assumes that these two galaxies are not moving relative to each other.
_"It would experience time normally, but the amount of time to go a specific distance would, from its perspective, be severely shortened."_
You appear to be referring to time in one reference frame and distance in another.
@@godfreypigott No, he isn't - he describes effects perceived by the subject in motion, and he is correct.
@@lewis7515 Yes he is. When he says "a specific distance", he is referring to distance measured in a "stationary" frame.
Ignoring the relative motion of the earth and Sirius as it is insignificant compared to the speed of light :
Sirius is 8.6 light years away as measured in the reference frame in which the earth and Sirius are stationary.
So an object travelling at 0.5c will take 17.2 years to travel to Sirius as measured in our reference frame.
In the reference frame of the moving object, it will still take 17.2 years to move *that specific distance,* but it will take it WAY past Sirius.
Instead of saying "to go a specific distance" he should have said "to travel between two specific objects".
you mate are fantastic at explaining things that I have had difficulty with over the years understanding
When we say that something experiences little to no time when reaching relativistic speeds, we are saying that in relation to our own time.
All things in the universe experience time flowing normally in their own frame of reference. But it is closer to true than to false to say that light or other things reaching the speed of light experience no time.
The way that it all ends up working is that when they reach light speed, the very next instant in their consciousness is them going below light speed.
From the point of view of everyone else, they are frozen in time the entire time they are at light speed, but for whoever that is, reaching and leaving light speed are adjacent moments.
So yes, from their own reference frame, time is flowing normally, but it is still true that no time passed for them in all of that time. It’s just that they weren’t conscious of any of that passage of time, and the transition back into time unfreezing is truly seamless from their frame of reference.
But definitely going say 95% of light speed, even though they look nearly frozen in time to everyone else, to them, in their own reference frame, time is passing totally normally.
Man you are the best. The concept best thing is that you use intuition for everything. Thanks man , helped me clear my curiosity
I was ready to angrily type away in the comment section, defending the idea that light experiences no time. But you made such a compelling argument, now I have nothing to say but thank you for the informative video. 😂
most other videos say it doesnt...