SpaceTime is definitively the best channel on UA-cam I have come across. It's amazing how excited they've been able to get me over watching a video about physics. I love how much better I'm able to understand properties of physics I've been hearing and learning about all of my life by watching these episodes.
"The flow of time depends fundamentally on motion" Oh snap. Did I just catch my first real glimpse at understanding why they (physicists) say that time didn't even exist before the Big Bang?
Yeah if there's no matter, time is irrelevant. Also, 'time not existing before the Big Bang' is only a consequence of using general relativity to rewind the universe to a single point ( which is at a hypothetical time "t=0") and then saying that's that. We do not yet know what was happening close to (let along *at* or before) time t=0 because our current theories break down. So there very well may have been matter/ time/ energy before the Big Bang, we just do not know what was going on then.
awesome mindblowing video, as usual. Furthermore, these videos are really interlinked, maybe it would be better to do the question answer from the previous episode first, and then proceed to the new lesson ?
+François A I disagree. His mind-blowing explanations with the accompanying animations are the real attention grabbers. It's usually a good idea to showcase your best material first to keep people hooked when you have videos at these lengths.
+Tim E I see your point, but really, if you didn't see the previous video, I don't think that a beautiful animation over something you *really* don't understand is sufficient to keep someone. Whereas answering questions first, could allow the viewer to check the skill required to understand the video, then really put an emphasis on the need to check out previous episode, and also positively reintroduce the subject to the loyal audience. At least, I think its worth to try, and see how it's working out :-)
+Tim E I thought this channel focuses on trying to actually teach people, more than being attention grabber. If they agree that showing answers first will help with that, I'm sure they wil do it.
Maybe I should have said conceptually challenging? Hell, I have an Associates Degree in Physics, while my Bachelors is in a different field, and I think the concepts in this video are still difficult even though I have some understanding/knowledge in Physics.
Thoughtful, entertaining, with impressive visuals? It cuts right to the core of the subject matter without being boring or dull. Thank you for making this!
Although I suffer from a brain that tends to forget, from an injury, I still regularly watch these vids. I know I won't retain it. But, it sets my imagination afire as I watch. I don't mind being the dumbest kid in the smart kids table. I'd rather that than be the smartest kid in the meatheads table.
Do you reread books/rewatch movies, to experience the same hit the plot twists hit you with originally? I know I sometimes hope I could forget a certain plot line so that I could experience it again afresh.
@@Mernom all the time. Its even wierder than that sometimes. I'll reread books that I don't even know I've read before. Its like...that looks like a good book, than I buy it. I go home, and found i already own the damn book and it has dog ears and a book mark in it.
I am almost 70 and my memory is awful but I love the feeling of trying to understand something that is mind boggling. Still waiting for an ‘aha’ moment regarding much of this.
I have a brain that can't retain this any more than yours but it's still fun. And I get to hear it all over again the next time I forget I saw it earlier
My brain is stuck in a recursive loop. We're explaining time using motion, but what even is motion in the absence of time? If the photon experiences no time, how does it experience its changing location in space? From the photon's perspective, is it everywhere it will ever be? And if its location is uncertain, is it everywhere it could potentially be?
+Kevin Colwell pardon my interruption inside your recursive loop but location is uncertain for photon the particle not for photon the field, it does not require motion to exist but it changes with time. time is objectively a measure of change and nothing changes for the particle photon
+Kevin Colwell Time is the way we experience the 4th spatial dimension. The photon experiences no time, from it's point of view it is an immobile 4 spatial dimension line. Since we can't "see" the fourth dimension, we experience photons as 3 dimensional particles moving at the ultimate speed. It's location in time from our point of view is never uncertain because we know it's speed and the path it travels along (a straight line), so by knowing it's source and emission angle we can determine it's position at any point in time.
+Kevin Colwell Because of length contraction, to the photon space is compressed to a 2D plane and the direction of its motion doesn't exist. Not only does it experience itself emitted and absorbed at the same time, but also at the same location. Though this isn't really accurate since to the photon both time and what we would call the direction of it's motion are meaningless.
+Kevin Colwell From what I've gotten the last few episodes, as motion increases, mass increases, and the speed of 'time' decreases from the perspective of the thing in motion. So once motion reaches a high enough level (light speed) time would stop around you. So the photon isn't necessarily everywhere at once. But it travels it's given path so quickly that in that instant every potential observer can experience it as if it were everywhere at once. From an observer's perspective you could argue that it's everywhere it will ever be, but from the photon's perspective, time would be flowing normally and it would travel it's given path the same as it always would.
PBS Space Time is a _godsend_ for visual learners, myself very much included! Some of us just can't effectively grasp difficult concepts without visual aids, and the Space Time team is here to save the day!!! Thank you, guys 😎🤜🤛
These videos are fantastic. I love how difficult physics theories are explained in a way not using complex math. I can actually share these videos with my friends who haven't spend years studying calculus and physics.
These are fantastic videos. I can feel myself trailing behind in understanding, but after a couple of viewings, and a bunch more videos on similar topics, I catch enough to be astounded at the utter complexity of the fundamentals of the universe, and that people like Matt and all the other geniuses who do this research and develop the mathematical models even exist. The human brain....Whoa!
+Fluxquark It's rather sad but a lot, especially school books are written by cheaply paid writers. Proper scientists are busy, and expensive, are often not the best writers and can have ideological differences with you. (Especially if you're Texas, which is responsible for most textbooks and doesn't like evolution or talk of slavery.) Then there are those that just write what's popular, not what's true.
Man, I love this channel but please, turn on the options for users to upload captions for then, it will be nice for u and for the others if it reaches another languages... see what "in a nutshell" channel does, they upload a video and the next 3 days someone already did captions for then in various languages.... please consider this.... keep the good work! Thanks for the videos!!! the way u guys explain this is veeeery nice, i wish had teaches like u guys!!
... Normal persons don't speak English, Def. They speak some version of Chinese. --Dave, English is widely spoken as a SECOND language, not a birth tongue
@@daviddelaney2407 Well said. There are 800+ Portuguese-based creoles around the world. The English-based ones are in third or fourth place. And then there's Churchill's good crack about England and America, "two countries separated by a common tongue."
@Definitely a George Soros funded bot I do speak English, but many don't, I wonder how many languages u speak, must be awesome to watch all videos from the internet without needing subtitles.
So if an accelerating clock ticks slower than a non accelerating one then would a clock tied to a spinning wheel tick slower? how much slower if say the wheel was 1M wide and spinning at 6000 rpm?
+Kahandran No velocity isn't categorized as a type of acceleration. If the wheel was spinning at a constant rate of 6000 rpm it's not acceleration. Initially speeding up the wheel to a point of 6000 rpm would then be acceleration.
+Clarkzor Acceleration is a change in velocity, which is directional. So a spinning wheel is experiencing acceleration even if it's rotational speed is constant.
As far as I know time dilation is affected by speed not acceleration necessarily. The faster you're moving, regardless of acceleration, the slower you're clock moves in relation to someone moving slower.
I'm actually serious. I want to know more about this. We're told only things with mass experience time and space. Mass is only confined energy, and energy is only an accounting system. Counting what? It seems like the whole thing is built on nothing. I'm totally lost.
dude.. i'm not sure why i hesitated at first.. you are legit one of the best educators i've ever heard. incredible. deep thoughts made highly accessible. well done and keep it up!
wow, this is the absolute best explanation of time dilation I've ever seen. Even channels like Minute Physics seem incomprehensible, whereas this is very clear.
After three and a half years of desperate online searching to find an animation that would help me understand relativity, PBS Space Time gave us the best intuition. Your animation of Einstein's thought experiment is priceless. Thank you so much....
ahhh how I hate that feeling when I discover a new great channel and I just finish listening to the last episode made so far! I can't say I understand everything (in fact I can say that I don't understand everything at all...) but this is very entertraining and episodes are very well made with great visuals and explanations! Can't wait for the next ones!
Isn't there a paradox here? Thought experiment: Two people set off on rockets in oposite directions, but observe eachother. They will each see time slow for the other person relative to them. They now simultaniously stop their rockets relative to eachother. They will each claim that they have experienced more time than the other person, because they have observed both their own and the other persons clock, and the other persons clock would always apear slower than their own. Obviously they must have experienced the same amount of time, so when they meet up and compare clock it is the same, but that seems incompatible with the observations each person has made, where the other persons clock slowed down. Where are the missing seconds for each person? Basically: How can time slow down only for the observed person, when both claim that it's the other guys clock slowing down. Who actually experiences more time?
+CPG VonC I have a similar thought experiment. Let's say I start orbiting Earth in a spaceship near the speed of light. I'd see the clocks (and time) on Earth to slow down and vice versa, but in actual reality it's my clock that runs slower. What would I see if I suddenly came to a stop? At first i thought they'd see my clock slow down by a bigger amount than I'd see theirs, but I realized, I'd still see the Earth in slow motion instead of fast forward. Would I stop seeing Earth's past in an instance and start seeing the present?
Essentially relativity says simultaneity is relative. One person will insist that the two rockets stopped simultaneously and the other that one stopped before the other. It works out in such a way as to exactly account for the time disparity.
+CPG VonC Yeah, same thing when people always say: A space ship flying away from earth has a slower clock and experiences 1 year, while on earth 100 years go by. But the space ships just says that the earth is flying away, which means 1 year goes by on the earth, while on the spaceship 100 years go by. Spaceship comes back, so who is older? Both can't be right. Reality has to converge and reconcile somewhere that is always left out of these explanations.
+CPG VonC There's absolutely nothing wrong with the use of the word "simultaneously" since it was clear in the example that you meant simultaneously in the center of mass frame. There is nothing to do with acceleration either. In fact your problem is very closely related to the twins paradox, except that instead of one twin remaining on Earth, he sets off on a spaceship in the opposite direction. The solution is still the same: you have to calculate the length of time experienced by each twin by carefully considering each leg of the journey. Add up the proper times for each leg and you get the total time.
+Szap Pan No, you would continue to see the Earth's past from the point you decelerated, except now the clocks would seem to continue at a normal rate. This happens because the photons (coming from Earth) that you were essentially "running away" from are now catching up to you, and you are now seeing the past because of the distance you have covered.
I've recently seen Interstellar and it got me thinking about a scenario that wish you could clarify for me (sorry if i miss spell something, i'm not english). First let's assume that our civilization gets to master interstellar travel. Based on relativity wouldn't it be possible for people to go inhabit planets near black holes, so that time outside those plannets would run faster and people in the "normal time" wuold get technologically advanced much much faster relative to the black hole's planets (a sort of einsteinien cryogenic sleep in this sense, so that people near black holes can sort of "freeze" time and wait for humanity to "cure" death ). What would happen also if we invented the following rule: at each person is given a very precise clock and every time a year of their time passes they move a certain distance towards the black hole and they stay there for another year, then they repeat the process, so that as they get older they get closer and closer to the black hole, so that time on the planet they were born on wuold have passed faster and faster relative to them. What wuold they see happening behind them, since as gravity gets stronger the only ones that rest in sync with their time are the ones that on the same circle (or sphere) with them aruond the black hole; all the others have times that pass incrementaly faster. Also if you get closer to the black hole, do the people in the concetric circles behind you get closer and closer to your circle since their time moves faster and faster relative to yours? Last question: When you are very close to the black hole (assuming that you are not close enouth so that your atoms get ripped appart) is the time of the part of your body that is facing the black hole slower than the opposite side? If so could one side of you die before the other one does? And if so would the part in front know that the part behind is dead, since information travels more slowly(or i think it does, i dont know)? Also how wuold it be for you if a person standing one meter behind you were to shuot or say something (assuming there is air), what wuold you hear? Thank you for your time,i'll be waiting for your answer near a black hole so it reaches me faster :).
+Non ho nome I believe it would. Ever since I first learned about time dilation a few years ago I've dreamt (not actual dreams just wishing I could) of doing this!
+Non ho nome 1) Yes, it would be possible to "wait" near black holes. Not sure how orbiting would change the results though. 2) Yes, there would be more and more people the closer you are to the black hole. 3) Yes. The closer you are, the slower the clock ticks for you. 4) I think you would not be ripped apart, because the part of your body that is closer to the black hole moves relatively slower and the more distant part would always push you faster, keeping you roughly the same. So unless there is any significant difference between these two aspects, you should not end up squished nor stretched. 5) I think the information in your brain will travel roughly normal speed as always, as the electrical pulses and chemical reactions IS how you experience time. 6) If close enough, you would hear nothing. Interesting questions, hope I helped :)
+Non ho nome Try to keep in mind that in your reference frame in the gravity well, time passes normally for you. It's only everyone else outside of the gravity well that sees your clock moving slower. For gravitational time dilation, I believe you will also see their clocks moving faster than yours, but for normal constant-velocity time dilation you would see their clocks moving slower than yours even though they still see your clock moving slower than theirs for both cases. So anyway, according to your reference frame, your time passes normally, so you wouldn't experience these weird effects. Someone outside would see them, but you wouldn't. And for really massive black holes, spaghettification doesn't happen until a while after you cross the event horizon (I think).
+Non ho nome Some mistakes here - 1) Inhabiting planets around a black hole is actually quite dangerous, especially due to something called the accretion disk (the big shiny ring on interstellar) which could shoot out electromagnetic waves. 2) Being close to a black hole enough to slow time down sufficiently would prove difficult without the black hole sucking you in (not to mention the EM waves). 3) You would only get ripped apart by the black hole when getting extremely close (usually past the event horizon/entering the black hole), as for aging at different rates, no. Gravitational time distortion is just not that extreme, you would only see changes in time over long distances. 4) Sound would reach you at normal speed (relative to you), but so would light - so you'd actually see the people "behind" you moving at normal speed and not in fast forward. Hope that cleared things up for you (:
s1lverbullet1234 1) Don't accretion disks only form when the black hole is pulling stuff in? If it's a lonely black hole with nothing to gobble, the accretion disk wouldn't be something to worry about. 2) He said in a previous episode that block holes don't suck everything in, that you can orbit them just fine without worrying about that. (Stable circular orbits outside of 3 Schwarzschild radii.)
I'm hoping you address the connection between time and temperature. I love these videos. It's refreshing to find difficult topics explained without dumbing them down, as many pop-science documentaries and articles tend to do.
WTF MAN?! Every time I watch these videos I realize how unstable the universe is & now you're telling me not even time is absolute?! How wonderfully terrifying!
Absolute is just another word for static. Just because something isn't static doesn't mean it is not stable. For example planet orbits are not static, however there are stable. Don't fear change, it's what allows life to happen.
psst: planetary orbits AREN'T stable in the long run. we do not actually have a general solution to the two-body problem in general relativity, let alone three or more. --Dave, but don't worry, it's on a timescale of millions of years or more. ...usually.
So you brought up another question for me. If you could slow down an electron (in a black hole for example) could you then pinpoint its location in spacetime?
+skykid Here Heisenberg's inequality is going to come in to play. If you slow down the electron so much that you would know it's velocity with an almost absolute certainty, you wont be able to pinpoint it's position with any reasonable uncertainty and vice-versa.
A couple of moths ago scientists pinpointed locations of e- to if I am not wrong 10^-18 seconds. But you cannot know the location and the velocity at the same time. I could be wrong
+skykid The problem with that would be that is that slowing it using gravity isn't actually slowing but rather slow it's time relative to you. If you got it to a point where relative to you it was motionless then you would know exactly where it was but because it's not actually stopped, just it's time relative to you, then you would be unable to measure it's velocity. Outside of practically stopping it's time relative to you there is no way to stop a particle. Even if you were to somehow remove all of it's energy so that it has no energy with which to move, not even vibrate, then you would have effectively erased the particle all together.
+skykid no, Ix times Ip has to be bigger than h/4pi (I is for standard deviation, imprecision in other words for position and momentum). that means that none can be zero at any time and the smaller one is, bigger the other. so in your case, you would know even less of its position
Before, at the end of 2022, I started to cry 😢 😭 about time, flies fast, and every day was going super fast and I want to be a little boy again and time travel back to the 2000's.
When you drive slower than another vehicle that is passing you, you can observe the difference of speed. But if you drive at the same speed than another car, let's 100mph, and you are next to eachother, when you take a look at the other car, it seems like time "stopped". Although, inside your car, time seems to always run at the same speed no matter what. You experience that everytime you are driving. So, if you could travel at the speed of light, time would stop. But on earth you are not traveling at the speed of light. So time goes on...etc.
What'll really boggle your mind is, what if we already are? Speed is only relevant when measured relative to another point in space. Even now, you're sitting still relative to your desk in front of you, but you're actually travelling up to (depending on the distance from the equator) 465 meters/second relative to the center of the Earth - just from the Earth rotating on its axis. What if the entire universe is moving in some direction that we cannot measure, because we have no frame of reference to measure it towards? We would have to locate another universe outside of our own to make that measurement - and then, how would we know whether we're the ones moving, or they are? Maybe both are? In the same manner, time is only relevant when relative to time measured in another speed. Assume we accelerated up towards c. In our near vicinity, nothing would have changed. From our perspective, time wouldn't slow - rather, time would appear to speed up for everything NOT in there with us. In what would have appeared as just the blink of an eye for us, the universe would have evolved, lived out its life, and died off. In respect to the universe expanding faster than the speed of light, that's again measured relatively. Relative to us, there are galaxies that are moving away from us (and we from them) such that the speed of one galaxy measured relative to the other is greater than c. Imagine taking two guns and shooting them in 90 degree angles away. Lets say they leave the barrel at approximately 800 m/s and (for some reason) never lose any of their speed. In relation to us, each would maintain that velocity ad infinitum, but in relation to each other, their speeds would be closer to 1130 m/s (classic pythagoras). Now assume those bullets are photons. Suddenly you have a photon traveling faster than the speed of light relative to the other photon. This is usually what's meant by saying that the universe is expanding faster than the speed of light. It's all about relativity. Nothing with any mass can travel faster than the speed of light, because the faster something moves, the more energy it accumulates. The more energy it accumulates the more mass it accumulates (E=mc^2, or m = E/c^2). The more mass something has, the harder it is to accelerate (compare rolling an empty can of beer vs rolling a full one - now multiply that with billions). At some point, you accumulate so much mass that it's literally impossible to move it faster. It just so happens that that point is c.
You bring up some very interesting ideas to ponder! Even though we may not have some absolutely static frame of reference, we, thanks to relativity, can determine that nothing can move faster than the speed of light. Just think about it. Relativity guarantees that an observer can call their frame of reference inert and still make perfectly valid measurements. Even if observers in different frames of reference don't agree on some values, they will all come to the conclusion that the speed of light is a constant which cannot be exceeded. Your analogy as to why the universe can expand faster than light is certainly unique, but flawed. Applying the Pythagorean theorem directly speeds wouldn't work; instead, you have to invoke some calculus. Work it out and you will find that the rate at which the distance of separation between the two photons is given by c*(x+y)*(x^2+y^2)^-1/2, where c is the speed of light, and x and y are the distances of the first and second photons from the origins, respectively. Note that x+y is always greater than sqrt(x^2+y^2), because the sum of the lengths of the legs of a triangle is always greater than the length of the hypotenuse. This indicates that the rate of change in the distance of separation between the two photons is actually increasing--the photons are accelerating away from each other! Now that we are dealing with accelerations, special relativity breaks down and we have to bring in Einstein's theory of general relativity. There will be effects in the space time between the two particles, but I don't know exactly what kinds. However, the universe can expand faster than the speed of light. More specifically, space can. As far as I know, there is no speed limit on the rate at which space can expand. Going back to the original question. If it were possible to move faster than the speed of light, one would not experience negative time. Time dilation involves the gamma function, (1-(v^2/c^2))^-1/2. As can be seen from this equation, if v surpasses c, then the radical becomes imaginary and one would be experiencing "imaginary" time, whatever that may be.
you dont hear a super sonic jet as it flys by, until its sonic boom catches up. particles with no mass(?) going faster than the speed of light would be undetectable in our universe, i think.
Well, yes, to a point. More precisely, if you had a particle moving faster than the speed of light, then from the point of view of another observer (depending on his speed relative to you) the particle would travel back in time, also faster than light. You'd also have another observer according to whom the particle's speed is infinite and it would take no time at all to travel from point A to point B. Such a particle - tachyon - would have an imaginary rest mass and would be impossible to slow down to the speed of light or below. (And yes, if you had a way to produce and detect tachyons, it would have been possible to violate causality.) There's a deeper meaning to this. Take events A and B separated - from your point of view - by a particular distance and interval of time. If the distance between them is smaller than the interval, i.e. it is possible for light or a massive particle to travel between the two events, then it is possible for one event to have caused the other; all observers will agree on the order of the two events (but from the point of view of some observer the distance is zero). Conversely, if the distance is greater than the interval (scaled by the speed of light), then two observers travelling at a particular velocity relative to each other may not agree in what order the two event occurred; it is not possible for the two events to influence each other, because neither a massive particle nor light could travel from point A and reach point B in time (or vice versa). This is the separation of space-time intervals into time-like, space-like, and light-like intervals.
If atomic clocks are the most accurate clocks we can make, how can we know that they drift by a billionth of a second in a day? As in, we'd have nothing more accurate to compare it to and know that it drifted
So I'm re-watching this video for the hell of it a year later, came up with an answer and then noticed I made the comment. I'm thinking the drift figure is what you get when you compare the results of multiple atomic clocks, it's never been seen to drift off more than that. If I'm right, I'm disappointed no-one answered my question, but given that I'm the original asker of this question, I suck even more so bleh
@@delespai5592 I guess if you have 100 clocks & your superaccurate caesium clock is the only 1 out by a millionth of a second & all 99 other clocks are in sync, you'd probably think oh the caesium 1 got hit by a cosmic ray or a g wave rather than doubt the 99?
IKR. When I look at stars I imagine those particles crossing millions of years of emptiness just to suddenly bump in my retina. I guess that's an analogy for death. I'm gonna take my antidepressants, excuse me.
@@WillMauer Everything you see is just a hallucination inside your mind created by your brains. It's not like there's projectors or anything, so it's kinda cool.
How can the clocks of both observers slow down relative to each other? When we put atomic clocks in orbit, those clocks slow down relative to us. Doesn't that mean that our clock speeds up relative to them?
+Virtuously .Selfish It works like that for the same reason that a rod will look shorter if you incline it by 45 degrees. Lorentz transformations are hyperbolic rotations and work similarily. You should think of the system as the time directions for the two observers being rotated relative to each other, and neither one is "special".
***** But neither of them is "special". Both look like they slow down to the other. There is no absolute time in relativity like you have in Newtonian physics. Velocity is relative, the only thing that is absolute is acceleration(i.e. in the accelerated clock case, everyone will agree that the accelerated clock slows down).
+BosonCollider now your answering a different question. or rather the correct one. in +Virtuously .Selfish original question atomic clocks would NOT see each others clock be slower because one of them is "accelerating" (experiencing more gravity) the ground clocks would see the space clocks time travel faster your first reply was related to the constant speed case, not this one.
+Virtuously .Selfish It does mean that. Imagine that we both have a clock each, both perfectly synced. Then imagine that I get into a space ship and accelerate away from you on the ground, you look into the window of my spaceship and see my clocks are moving slower, I look at you and see your clock is slower too. We both think that we're the normal one and you're the slow one. Then I stop, turn around, accelerate down, slow down and land. Your clock will be ahead of mine. Why? Because I was the one who accelerated. And it was when I was accelerating back to you that I saw you speed up instead of slowing down.
Hi PBS Space Time! First of all, congratulations for your UA-cam video series, you're doing a great job of explaining science and getting more people involved in it. In the series of videos about time ("When time breaks down", "The origin of matter and time"), you spoke about a very interesting idea about passing of time depending on the internal structure and evolution of particles and atoms, and ultimately on motion. I got particularly curious about the idea, and I was looking for some more precise reference about it (I am a physics PhD, so it would be wonderful if you could point me to some paper or book). Thank you very much in advance, for the references and for your awesome job!
If one could ride on a photon, or strap a gopro camera to it, or something similar, and take a ride from let's say the Sun to the Earth, how long would that journey take you if you timed it? About 8 minutes for an earthbound observer, but what about the guy on the photon? Would it take no time, i. e. an instantaneous journey, or would it be an eternal journey? I think it would be instantaneous, right? A journey to the edge of the observable universe would be instantaneous on a photon. Right?
+Joe Brown If you could build a massless clock and strap it to a photon, you could send it across the universe before the first tick. You could send it infinitely far without it ever ticking.
Best explanation of time, and lorentz transformation-time dilation,, matter and mass that I've ever seen/heard. So many physicists and physics educators have attempted to explain the relationship between velocity and time yet do a bad job of it. in not explaining the question everyone wants answered, WHY? Why does it do that? Well done. It does raise a point, and that is the approach of Heisenberg, author of the Heisenberg uncertainty principle in quantum mechanics. He took a non reductionist approach to reality, unlike the trying to find smaller and smaller fundamental building blocks of the universe. The block universe concept is not based on reductionist fundamental particles and/or forces/fields. Reality's secret may not rest in the smallest, but in the largest structures.
Question: You mentioned that a photon experiences no time. Let's say i'm a photon, and time is standing still for me. I get emitted from a star lightyears away and got absorbed in some lucky observers eyeball. This happens then instantaneously ? So in a photons reference frame, speed doesn't seem to make sense anymore (speed=distance/time and time=0)
+MrHighvolt Yes. Remember that speed also causes length contraction. To the photon the eyeball isn't light years away, it's infinitely close. No matter what speed it traveled at it'd arrive instantly, from its perspective anyway. The fact that time, distance and speed break down when you travel at light speed inspired the title of this episode.
+Feynstein100 Photons *don't* evolve, from their point of view anyway. Everything they do and experience happens all at once for them. It's only us, massive systems who see it evolve. In a way we're just limited to seeing part of it at a time. Right now I cannot see the sun, but it is still there, the evolving nature of night and day is just me being limited in when I can interact with the sun.
+Gareth Dean So when the distance is infinitely close, the universe looks like a singularity ? I rewatched the video a couple of times and I still find it confusing since in the video at 4:24 he says that from an observer standing still, the moving clock seems to slow down. However, from the reference frame of the moving clock, time is experienced as normal, and it's everything else that slows down (time dilation). I get that, but it also means that in that saying, a photon DOES experience time as normal, doesn't it ? I think my brain just rebooted
+Code Slinger Ever see a video like this and then youtube suggest you might also want to see something about Planet X or the spiritual universe? People who get sent here from those videos dislike it.
There's a big loophole in the time dilation concept. At least as it comes to me. Time should run fastest if I sit statically on a borring algebra lecture. But it's other way round. It's ticking fastest when I'm running back and forth from table to the blackboard on a calculus classes. It's very well tested. But seriously, this is the best show on youtube. I know 300k of subscriptions and views is not much compared to mainstream shit. But what you're doing is really outstanding. Giving inspiration to people to seek and keep on overcoming hard times with algebra and calculus for the bigger goal - the beauty of science ^^. You're doing great job. It's even more awesome that you're not begging for subscriptions which would be totally reasonable based on the amount of work put into preparing of each episode. I'd be happy to donate some $$ every now and then, given the promise it would be distributed among the people preparing the show (not the money people behind the scenes, if there're any ;)). I'm pretty sure there're others like me, feeling gratitude for great stuff you're making. Thanks!
All this depends on a perceiver. Conscious attention creates the false perception of the passing of time. Creating any device to measure time is just us bolstering that false perception.
1 question here that has been on my mind for quite some time! HELP If space and time are linked (spacetime) and 'space' is thought to be expanding, shouldn't its linked property (time) also expand at a directly proportionate rate? wouldn't the implications of this be quite large? (just to name one, s=d/t. the speed of light is just a distance light travels over a certain period of time... if space expands say by a factor 10 (extreme, i know), time would also have to expand by a factor of 10 to maintain the same overall magnitude of speed: ~3.0x10^8m/s (increase in time would serve to increase the denominator in proportion to the numerator). and furthermore, if we didn't take into account this expansion of time and failed to adjust our own measurement of the second proportionately, we would most definitely perceive light's speed to be increasing. now clearly, its not increasing... so therefore im led to believe that the properties of spacetime, although 'linked', are separable.
+James Corbett Let's imagine light travelling from A to B. Let's say it takes 10 years for it to travel that distance. So now it's been a million years since that data was true. The distance now between A and B is now greater. Light would still travel the same distance, at the same velocity, but it wouldn't reach B this time, only where it used to be. So it would than have to travel a larger distance thus taking longer. So no. It doesn't have to be considered. Since it's the space *between* matter expanding and not matter itself.
+s1lverbullet1234 ok i understand this supposedly... however i believe the expansion of the universe is a 'homogenous' expansion, meaning the expansion of space between ur two ears is the same as the expansion of space between galaxies. but the reason we dont see the effects is due to the strong and weak nuclear force, which is far stronger than the strength of the expansion of space. but i think that if the expansion continues to accelerate, there will someday come a time when the force is so great everything will literally rip apart...
+s1lverbullet1234 also think about this for a second. when space is warped by gravity, so is time. essentially, when the fabric of 3d spacetime is manipulated, u get time dilation effects as well as gravitational effects... so wouldnt u then be led to believe that ANY warping of spacetime would affect its time property associated with it?
James Corbett you're *completely* right, actually there's some really cool vids on this topic. Space eventually going poof. Kinda interesting but depressing. :/
Could someone explain me how they tested that the speed of light is constant? I never really understood why we cant say that time is constant and the speed of light is dependent on the speed of the movement
+Gunar Kroeger This was first observed by looking at a binary star system aka two stars rotating around the same point. It was seen that the wavelength of the light coming from both stars was the same despite one of the stars heading away from Earth and one star heading towards Earth. If the wavelength/speed of light depended on the velocity of the emitter there would have been interference effects from the light as it was observed on Earth. However, there was none, so the speed of light is independent of the velocity of the emitter and is therefore constant.
***** I suppose I worded that poorly, but remove wavelength from that and it's all logically sound. There would be weird effects happening if one path of light was travelling faster than the other, and this was not observed in the experiment. The binary star system "experiment" was very real, and I believe it predated the Michelson-Morley experiment and the discovery of stellar aberration.
I'll have to watch this a few more times to fully absorb it, but it's still the best explanation of time dilation and the relationship between matter and time that I've seen.
That's what I've been trying to tell people, but they don't take it seriously. Time is just a system of measuring motion. Events always occur in the present.
They occur at the space-time points they're at, Steve. Because of this, you NEVER see an event as occuring in YOUR present; there's always the travel time to you of the light, involved, so that your senses always report to you on events slightly past. (Or greatly, if you look up at the stars at night.) This is why, in even special relativity, let alone general, "simultaneously" is meaningless; closest you can get is "space-time interval of zero"... because the t axis slopes at different angles when two inertial frames are moving relative to each other, so it's not particularly useful to say whether two events are "really at the same time". "The present", as in "everything happening when my t = 0", is different slices of spacetime in differently-moving frames of references. There's no unique consistent "the present" covering everywhere. Time's a variable just like space; it acts differently cuz it has a minus sign attached. Our perception of time is quite possibly completely erroneous; the universe CAN be described in a way where no motion or change ever exists, just particular sets of connections between various space-time events, which happen to always follow the "laws of motion" when interpreted in x,y,z,t terms. --Dave, sorry dude
Time is a human illusion. It does not exist at all. Its just events occuring at a faster vs slower rate due to the reasons described in many of these videos.. Just imagine. If humans were immortal would the concept of time ever be invented ?
Question. I'm in a rocket in space flying past my friend who is also in space. If there's NO such thing as absolute motion or absolute rest, then why don't we both experience the same degree of time dilation? Ie to me it appears as though he's in motion, but to him it appears as though I'm the one in motion. If we both observe that we are in motion relative to each other, who experiences the time dilation? Shouldn't it cancel out, because we each observe the others photon beam clock to be moving? P.S best channel on UA-cam, thanks for all the vids
+Manveer Singh The time dilation in case of objects at constant speed is just apparent effect - you observe each other as being time-dilated. However, time dilation caused by acceleration is absolute - because only one of you experiences the acceleration. If I remember correctly, PBSspace time made a video about this some time ago...
i really love your vids, they delve deeper into physics than most on youtube. Could you please make a video about entropy and thermodynamics in the same thorough manner? Would be awesome to learn something new about these subjects.
If as you approach the speed of light time starts to move slower at at the speed of light it freezes, if you could go faster than the speed of light you would go back in time?
If you could jump over the speed of light, you'd SEE the rest frame as moving backwards in time ... because your trajectory FTL goes OUTSIDE its own light cone, so the further you went from point B, the further back in the past light emitted from stationary B would have had to have been emitted to get to your location. (Remember that in a spacetime diagram, light always travels at 45 degrees to the x and t axes.) If you suddenly reversed direction, now you'd be moving TOWARDS stationary B faster than light, so you'd be catching up with its light-cones on your side, and you'd see B living its point life FASTER than normal until you got back to it, at which point you'd've caught up to t=0 and passed it enough for t to be 2 * (distance you went) / (your speed) and the light from your furthest point away couldn't reach B until 2 * (distance you went) / c . --Dave, and you COULD go back in time and arrive back at B before you left it, but doing so involves stopping, then changing your velocity correctly at your furthest point, to move your location in Elsewhere relative to B =below= the t=0 axis - and in the process getting B to appear to be living more slowly enough, THEN heading back towards B at your same FTL speed from that frame
Dang, those mass questions about the thought experiments were good! I particularly liked the question about compression of a spring being related to momentum. That’s sharp!
How can I determine whether the speed that I'm traveling with is close to the speed of light or not? I think I'm standing still on the chair, but if you add up the speed that the Earth is spinning me around its axis and around the Sun and speed of the solar system within the galaxy, I'm moving quite fast. So how can I determine what fraction of speed of light (v/c) I'm traveling with?
One half of the cosmic background radiation should be slightly cooler on average than the other. You could use this to estimate your "absolute" direction and velocity relative to the universe as a whole.
The question to answer your question, maereanm, is "... relative to what?". You're never "just moving" - any time you say you're moving, it's always in relation to something else. ("But I can FEEL when I start to move!" Because you are at that time moving relative to the fluid in your semicircular canals, in your ears, and to some extent relative to the fluids in your body, which don't catch up quite immediately when some outside force presses part of your skin to make you change velocity.) --Dave, as Chris notes, "relative to the CMB" is the usual answer, but you still need that answer to make the original question make sense at all
So, you covered a very nice, intuitive explanation of the physical source of time dilation caused from motion and acceleration. I was hoping you could explain the same thing for length contraction. I've never understood why we must have length contraction when time dilation seems to have us covered.
I've been watching a lot of the videos on this channel for a few weeks now. I'd say I understand very very little of it most of the time, but in find it fascinating nonetheless so I keep going. As I keep looping around through different topics I understand a little more. This is the first time I've actually kind of sort of understood time dilation in the theory of general relativity and this is the first that I'm kind of sort of wrapping my mind around e=mc2. In short, great videos, not easy(for me at least)... but great.
one of the best channels on UA-cam
+Alejandro Jimenez The best channel on UA-cam.
+Alejandro Jimenez CatBug!
+Alejandro Jimenez Best comment section on youtube
This is the best explanation of time dilation in general relativity I've heard. I've always struggled with understanding it until now. Thanks.
Yeah, now it just seems obvious. Matt is a great explainer
SpaceTime is definitively the best channel on UA-cam I have come across. It's amazing how excited they've been able to get me over watching a video about physics. I love how much better I'm able to understand properties of physics I've been hearing and learning about all of my life by watching these episodes.
"The flow of time depends fundamentally on motion"
Oh snap. Did I just catch my first real glimpse at understanding why they (physicists) say that time didn't even exist before the Big Bang?
DUde
No
Yeah if there's no matter, time is irrelevant.
Also, 'time not existing before the Big Bang' is only a consequence of using general relativity to rewind the universe to a single point ( which is at a hypothetical time "t=0") and then saying that's that. We do not yet know what was happening close to (let along *at* or before) time t=0 because our current theories break down. So there very well may have been matter/ time/ energy before the Big Bang, we just do not know what was going on then.
Motion isn't but an illusion.
This channel has done so much for me over the years. Sometimes I am brought to tears at the beauty of this…thank you.
awesome mindblowing video, as usual. Furthermore, these videos are really interlinked, maybe it would be better to do the question answer from the previous episode first, and then proceed to the new lesson ?
+François A I agree, hopefully they notice this comment
+François A I disagree. His mind-blowing explanations with the accompanying animations are the real attention grabbers. It's usually a good idea to showcase your best material first to keep people hooked when you have videos at these lengths.
I agree with Tim
+Tim E I see your point, but really, if you didn't see the previous video, I don't think that a beautiful animation over something you *really* don't understand is sufficient to keep someone.
Whereas answering questions first, could allow the viewer to check the skill required to understand the video, then really put an emphasis on the need to check out previous episode, and also positively reintroduce the subject to the loyal audience.
At least, I think its worth to try, and see how it's working out :-)
+Tim E I thought this channel focuses on trying to actually teach people, more than being attention grabber. If they agree that showing answers first will help with that, I'm sure they wil do it.
I love the fact that you guys stay away from the normal silly analogies and stick more to the issue. Great going.
These are easily the most intellectually challenging videos on UA-cam.
These are the most intellectually challenging videos for a layman audience. There are definitely more challenging videos.
+Kahandran examples?
Maybe I should have said conceptually challenging? Hell, I have an Associates Degree in Physics, while my Bachelors is in a different field, and I think the concepts in this video are still difficult even though I have some understanding/knowledge in Physics.
+enriqueDFTL check out +gavinwince it probably the roughest channel, I'm subscribed to when it comes to theoretical, quantum, and astrophysics.
+Brendan Haran sorry my grammar was shit in that comment.
Thoughtful, entertaining, with impressive visuals? It cuts right to the core of the subject matter without being boring or dull. Thank you for making this!
Although I suffer from a brain that tends to forget, from an injury, I still regularly watch these vids. I know I won't retain it. But, it sets my imagination afire as I watch. I don't mind being the dumbest kid in the smart kids table. I'd rather that than be the smartest kid in the meatheads table.
Do you reread books/rewatch movies, to experience the same hit the plot twists hit you with originally?
I know I sometimes hope I could forget a certain plot line so that I could experience it again afresh.
@@Mernom all the time. Its even wierder than that sometimes. I'll reread books that I don't even know I've read before. Its like...that looks like a good book, than I buy it. I go home, and found i already own the damn book and it has dog ears and a book mark in it.
I am almost 70 and my memory is awful but I love the feeling of trying to understand something that is mind boggling. Still waiting for an ‘aha’ moment regarding much of this.
I have a brain that can't retain this any more than yours but it's still fun. And I get to hear it all over again the next time I forget I saw it earlier
My brain is stuck in a recursive loop. We're explaining time using motion, but what even is motion in the absence of time? If the photon experiences no time, how does it experience its changing location in space? From the photon's perspective, is it everywhere it will ever be? And if its location is uncertain, is it everywhere it could potentially be?
+Kevin Colwell perhaps there is some kind of universal "Deep time" that is separate from the time we experience through the motion of particles?
+Kevin Colwell pardon my interruption inside your recursive loop but location is uncertain for photon the particle not for photon the field, it does not require motion to exist but it changes with time. time is objectively a measure of change and nothing changes for the particle photon
+Kevin Colwell Time is the way we experience the 4th spatial dimension. The photon experiences no time, from it's point of view it is an immobile 4 spatial dimension line. Since we can't "see" the fourth dimension, we experience photons as 3 dimensional particles moving at the ultimate speed. It's location in time from our point of view is never uncertain because we know it's speed and the path it travels along (a straight line), so by knowing it's source and emission angle we can determine it's position at any point in time.
+Kevin Colwell Because of length contraction, to the photon space is compressed to a 2D plane and the direction of its motion doesn't exist. Not only does it experience itself emitted and absorbed at the same time, but also at the same location. Though this isn't really accurate since to the photon both time and what we would call the direction of it's motion are meaningless.
+Kevin Colwell From what I've gotten the last few episodes, as motion increases, mass increases, and the speed of 'time' decreases from the perspective of the thing in motion. So once motion reaches a high enough level (light speed) time would stop around you. So the photon isn't necessarily everywhere at once. But it travels it's given path so quickly that in that instant every potential observer can experience it as if it were everywhere at once. From an observer's perspective you could argue that it's everywhere it will ever be, but from the photon's perspective, time would be flowing normally and it would travel it's given path the same as it always would.
I usually watch these videos, understand abt 2% of the whole content, then continue to move on with my life. I like my 2% tho, don't knw abt u guys.
Exactly..
I love my 2% !!!!!!!!!!!!1
Dude, you're so dumb! I can easily understand twice as much! u.u
yeah my head hurts lol
Sounds like me in a algebra class.
PBS Space Time is a _godsend_ for visual learners, myself very much included! Some of us just can't effectively grasp difficult concepts without visual aids, and the Space Time team is here to save the day!!! Thank you, guys 😎🤜🤛
These videos are fantastic. I love how difficult physics theories are explained in a way not using complex math. I can actually share these videos with my friends who haven't spend years studying calculus and physics.
These are fantastic videos. I can feel myself trailing behind in understanding, but after a couple of viewings, and a bunch more videos on similar topics, I catch enough to be astounded at the utter complexity of the fundamentals of the universe, and that people like Matt and all the other geniuses who do this research and develop the mathematical models even exist. The human brain....Whoa!
That moment when you correct your science textbook with stuff you learn from PBS Space Time :D
+Melon Cooler sciene textbooks are written by writers, not scientists. To be fair, it's really hard to read most scientific papers.
OceanFlex Gamer True, and the mistake was minor, but its still funny to have corrected it.
+OceanFlex Gamer ??? All physics books I have are written by physicists. And all my math books are written by mathematicians.
+OceanFlex Gamer They are written by scientists usually, unless you are talking about some middle school (and maybe high school) text.
+Fluxquark It's rather sad but a lot, especially school books are written by cheaply paid writers. Proper scientists are busy, and expensive, are often not the best writers and can have ideological differences with you. (Especially if you're Texas, which is responsible for most textbooks and doesn't like evolution or talk of slavery.) Then there are those that just write what's popular, not what's true.
Matter, motion, and the nature of my brain melting while it tries to soak this all in.
This show is such a tease.
one of the most amazing and beneficial videos I have seen on the youtube, every time I re-watch it I discover and grasp something New.
Man, I love this channel but please, turn on the options for users to upload captions for then, it will be nice for u and for the others if it reaches another languages... see what "in a nutshell" channel does, they upload a video and the next 3 days someone already did captions for then in various languages.... please consider this.... keep the good work! Thanks for the videos!!! the way u guys explain this is veeeery nice, i wish had teaches like u guys!!
... Normal persons don't speak English, Def. They speak some version of Chinese.
--Dave, English is widely spoken as a SECOND language, not a birth tongue
@@daviddelaney2407 Well said.
There are 800+ Portuguese-based creoles around the world. The English-based ones are in third or fourth place. And then there's Churchill's good crack about England and America, "two countries separated by a common tongue."
Definitely a George Soros funded bot wtf? Such arrogance! How many languages do you speak?
Unfortunately, it seems like user captions are dead soon.
@Definitely a George Soros funded bot I do speak English, but many don't, I wonder how many languages u speak, must be awesome to watch all videos from the internet without needing subtitles.
So if an accelerating clock ticks slower than a non accelerating one then would a clock tied to a spinning wheel tick slower? how much slower if say the wheel was 1M wide and spinning at 6000 rpm?
Interesting. I guess that it would, since it's categorized as a type of acceleration...
+Kahandran No velocity isn't categorized as a type of acceleration. If the wheel was spinning at a constant rate of 6000 rpm it's not acceleration. Initially speeding up the wheel to a point of 6000 rpm would then be acceleration.
+Clarkzor it's not accelerating*****
+Clarkzor Acceleration is a change in velocity, which is directional. So a spinning wheel is experiencing acceleration even if it's rotational speed is constant.
As far as I know time dilation is affected by speed not acceleration necessarily. The faster you're moving, regardless of acceleration, the slower you're clock moves in relation to someone moving slower.
_"Time is an illusion. Lunchtime doubly so."_ -- Douglas Adams
"Is time even a real dimension? ... We'll have time for all of this, in a future episode..." Which episode???
Great. Relatively speaking an absolutely genius remark! 👌👍
No time like the present
It’s time for y’all to stop with the puns
I'm actually serious. I want to know more about this. We're told only things with mass experience time and space. Mass is only confined energy, and energy is only an accounting system. Counting what? It seems like the whole thing is built on nothing. I'm totally lost.
polanve ehheeemmmlsdehheeemmm
dude.. i'm not sure why i hesitated at first.. you are legit one of the best educators i've ever heard. incredible. deep thoughts made highly accessible. well done and keep it up!
The section immediately before and after the 4:00 mark is the clearest description of why time appears the way it does, that I have ever seen. Kudos!
Found this channel by accident. Love it!
wow, this is the absolute best explanation of time dilation I've ever seen. Even channels like Minute Physics seem incomprehensible, whereas this is very clear.
i was watching interstellar when i got notification..what the coincidence...
No way! Me too lol!
+Ronsito Platano
i think we both love physics of time.....
+Vaibhav Jain Its no coincidence. Its us, the 5th dimensional civilization.
+Adhiraj Sharma
ohh...u just referred to the movie plot....but u are right....
I think not!
After three and a half years of desperate online searching to find an animation that would help me understand relativity, PBS Space Time gave us the best intuition. Your animation of Einstein's thought experiment is priceless. Thank you so much....
ahhh how I hate that feeling when I discover a new great channel and I just finish listening to the last episode made so far! I can't say I understand everything (in fact I can say that I don't understand everything at all...) but this is very entertraining and episodes are very well made with great visuals and explanations! Can't wait for the next ones!
Isn't there a paradox here? Thought experiment:
Two people set off on rockets in oposite directions, but observe eachother. They will each see time slow for the other person relative to them. They now simultaniously stop their rockets relative to eachother. They will each claim that they have experienced more time than the other person, because they have observed both their own and the other persons clock, and the other persons clock would always apear slower than their own.
Obviously they must have experienced the same amount of time, so when they meet up and compare clock it is the same, but that seems incompatible with the observations each person has made, where the other persons clock slowed down. Where are the missing seconds for each person?
Basically: How can time slow down only for the observed person, when both claim that it's the other guys clock slowing down. Who actually experiences more time?
+CPG VonC I have a similar thought experiment. Let's say I start orbiting Earth in a spaceship near the speed of light. I'd see the clocks (and time) on Earth to slow down and vice versa, but in actual reality it's my clock that runs slower. What would I see if I suddenly came to a stop?
At first i thought they'd see my clock slow down by a bigger amount than I'd see theirs, but I realized, I'd still see the Earth in slow motion instead of fast forward. Would I stop seeing Earth's past in an instance and start seeing the present?
Essentially relativity says simultaneity is relative. One person will insist that the two rockets stopped simultaneously and the other that one stopped before the other. It works out in such a way as to exactly account for the time disparity.
+CPG VonC Yeah, same thing when people always say: A space ship flying away from earth has a slower clock and experiences 1 year, while on earth 100 years go by. But the space ships just says that the earth is flying away, which means 1 year goes by on the earth, while on the spaceship 100 years go by.
Spaceship comes back, so who is older? Both can't be right. Reality has to converge and reconcile somewhere that is always left out of these explanations.
+CPG VonC There's absolutely nothing wrong with the use of the word "simultaneously" since it was clear in the example that you meant simultaneously in the center of mass frame. There is nothing to do with acceleration either.
In fact your problem is very closely related to the twins paradox, except that instead of one twin remaining on Earth, he sets off on a spaceship in the opposite direction. The solution is still the same: you have to calculate the length of time experienced by each twin by carefully considering each leg of the journey. Add up the proper times for each leg and you get the total time.
+Szap Pan No, you would continue to see the Earth's past from the point you decelerated, except now the clocks would seem to continue at a normal rate. This happens because the photons (coming from Earth) that you were essentially "running away" from are now catching up to you, and you are now seeing the past because of the distance you have covered.
Why does PBS Space Time teach me more about the universe in one 10-minute video than I've learned in all my 10 years of school
Cause school sucks
I've recently seen Interstellar and it got me thinking about a scenario that wish you could clarify for me (sorry if i miss spell something, i'm not english). First let's assume that our civilization gets to master interstellar travel. Based on relativity wouldn't it be possible for people to go inhabit planets near black holes, so that time outside those plannets would run faster and people in the "normal time" wuold get technologically advanced much much faster relative to the black hole's planets (a sort of einsteinien cryogenic sleep in this sense, so that people near black holes can sort of "freeze" time and wait for humanity to "cure" death ). What would happen also if we invented the following rule: at each person is given a very precise clock and every time a year of their time passes they move a certain distance towards the black hole and they stay there for another year, then they repeat the process, so that as they get older they get closer and closer to the black hole, so that time on the planet they were born on wuold have passed faster and faster relative to them. What wuold they see happening behind them, since as gravity gets stronger the only ones that rest in sync with their time are the ones that on the same circle (or sphere) with them aruond the black hole; all the others have times that pass incrementaly faster. Also if you get closer to the black hole, do the people in the concetric circles behind you get closer and closer to your circle since their time moves faster and faster relative to yours? Last question: When you are very close to the black hole (assuming that you are not close enouth so that your atoms get ripped appart) is the time of the part of your body that is facing the black hole slower than the opposite side? If so could one side of you die before the other one does? And if so would the part in front know that the part behind is dead, since information travels more slowly(or i think it does, i dont know)? Also how wuold it be for you if a person standing one meter behind you were to shuot or say something (assuming there is air), what wuold you hear? Thank you for your time,i'll be waiting for your answer near a black hole so it reaches me faster :).
+Non ho nome I believe it would. Ever since I first learned about time dilation a few years ago I've dreamt (not actual dreams just wishing I could) of doing this!
+Non ho nome
1) Yes, it would be possible to "wait" near black holes. Not sure how orbiting would change the results though.
2) Yes, there would be more and more people the closer you are to the black hole.
3) Yes. The closer you are, the slower the clock ticks for you.
4) I think you would not be ripped apart, because the part of your body that is closer to the black hole moves relatively slower and the more distant part would always push you faster, keeping you roughly the same. So unless there is any significant difference between these two aspects, you should not end up squished nor stretched.
5) I think the information in your brain will travel roughly normal speed as always, as the electrical pulses and chemical reactions IS how you experience time.
6) If close enough, you would hear nothing.
Interesting questions, hope I helped :)
+Non ho nome
Try to keep in mind that in your reference frame in the gravity well, time passes normally for you. It's only everyone else outside of the gravity well that sees your clock moving slower.
For gravitational time dilation, I believe you will also see their clocks moving faster than yours, but for normal constant-velocity time dilation you would see their clocks moving slower than yours even though they still see your clock moving slower than theirs for both cases.
So anyway, according to your reference frame, your time passes normally, so you wouldn't experience these weird effects. Someone outside would see them, but you wouldn't. And for really massive black holes, spaghettification doesn't happen until a while after you cross the event horizon (I think).
+Non ho nome Some mistakes here -
1) Inhabiting planets around a black hole is actually quite dangerous, especially due to something called the accretion disk (the big shiny ring on interstellar) which could shoot out electromagnetic waves.
2) Being close to a black hole enough to slow time down sufficiently would prove difficult without the black hole sucking you in (not to mention the EM waves).
3) You would only get ripped apart by the black hole when getting extremely close (usually past the event horizon/entering the black hole), as for aging at different rates, no. Gravitational time distortion is just not that extreme, you would only see changes in time over long distances.
4) Sound would reach you at normal speed (relative to you), but so would light - so you'd actually see the people "behind" you moving at normal speed and not in fast forward.
Hope that cleared things up for you (:
s1lverbullet1234
1) Don't accretion disks only form when the black hole is pulling stuff in? If it's a lonely black hole with nothing to gobble, the accretion disk wouldn't be something to worry about.
2) He said in a previous episode that block holes don't suck everything in, that you can orbit them just fine without worrying about that. (Stable circular orbits outside of 3 Schwarzschild radii.)
I'm hoping you address the connection between time and temperature.
I love these videos. It's refreshing to find difficult topics explained without dumbing them down, as many pop-science documentaries and articles tend to do.
This is such a great video series. I really appreciate the effort that has gone into making these.
Extremely close to getting my armchair physics degree im so excited.
WTF MAN?! Every time I watch these videos I realize how unstable the universe is & now you're telling me not even time is absolute?! How wonderfully terrifying!
If all things are relative, yet possess structure, certainly something stable must provide the structure. There is much more for mankind to learn.
Only Sith deal in absolutes.
Absolute is just another word for static. Just because something isn't static doesn't mean it is not stable. For example planet orbits are not static, however there are stable. Don't fear change, it's what allows life to happen.
You’re 100+ years behind. Catch up.
psst: planetary orbits AREN'T stable in the long run. we do not actually have a general solution to the two-body problem in general relativity, let alone three or more.
--Dave, but don't worry, it's on a timescale of millions of years or more. ...usually.
So you brought up another question for me. If you could slow down an electron (in a black hole for example) could you then pinpoint its location in spacetime?
+skykid Here Heisenberg's inequality is going to come in to play. If you slow down the electron so much that you would know it's velocity with an almost absolute certainty, you wont be able to pinpoint it's position with any reasonable uncertainty and vice-versa.
A couple of moths ago scientists pinpointed locations of e- to if I am not wrong 10^-18 seconds. But you cannot know the location and the velocity at the same time. I could be wrong
+skykid The problem with that would be that is that slowing it using gravity isn't actually slowing but rather slow it's time relative to you. If you got it to a point where relative to you it was motionless then you would know exactly where it was but because it's not actually stopped, just it's time relative to you, then you would be unable to measure it's velocity. Outside of practically stopping it's time relative to you there is no way to stop a particle. Even if you were to somehow remove all of it's energy so that it has no energy with which to move, not even vibrate, then you would have effectively erased the particle all together.
+skykid no, Ix times Ip has to be bigger than h/4pi (I is for standard deviation, imprecision in other words for position and momentum). that means that none can be zero at any time and the smaller one is, bigger the other. so in your case, you would know even less of its position
you cant know both the velocity and position at the same time.
so you might know it's position, but the you won't know it's velocity
Electrons in atomic orbitals have v
Going back through these now...you really do an incredible job presenting this information.
Before, at the end of 2022, I started to cry 😢 😭 about time, flies fast, and every day was going super fast and I want to be a little boy again and time travel back to the 2000's.
This is killing my brain cells trying to understand this
That's just growing pains ;)
James Gifford IV dem feels
it needs focused and opened brains I agree with you on its complicated futuristics but that's how life is
Patrick Bateman Luckily I'm quite comfortable with these concepts :p
When you drive slower than another vehicle that is passing you, you can observe the difference of speed. But if you drive at the same speed than another car, let's 100mph, and you are next to eachother, when you take a look at the other car, it seems like time "stopped". Although, inside your car, time seems to always run at the same speed no matter what. You experience that everytime you are driving. So, if you could travel at the speed of light, time would stop. But on earth you are not traveling at the speed of light. So time goes on...etc.
this episode is tough
+Yao Zong Tay Time is hard =/
so then... if it were possible, what if you went faster then C? Would time go backwards? Just simple pattern skills, not sure if this is true or not.
Baashaal Baashaal The expansion of space is faster than light at times, right? What if we moved within space rather than through it?
What'll really boggle your mind is, what if we already are? Speed is only relevant when measured relative to another point in space. Even now, you're sitting still relative to your desk in front of you, but you're actually travelling up to (depending on the distance from the equator) 465 meters/second relative to the center of the Earth - just from the Earth rotating on its axis. What if the entire universe is moving in some direction that we cannot measure, because we have no frame of reference to measure it towards? We would have to locate another universe outside of our own to make that measurement - and then, how would we know whether we're the ones moving, or they are? Maybe both are?
In the same manner, time is only relevant when relative to time measured in another speed. Assume we accelerated up towards c. In our near vicinity, nothing would have changed. From our perspective, time wouldn't slow - rather, time would appear to speed up for everything NOT in there with us. In what would have appeared as just the blink of an eye for us, the universe would have evolved, lived out its life, and died off.
In respect to the universe expanding faster than the speed of light, that's again measured relatively. Relative to us, there are galaxies that are moving away from us (and we from them) such that the speed of one galaxy measured relative to the other is greater than c. Imagine taking two guns and shooting them in 90 degree angles away. Lets say they leave the barrel at approximately 800 m/s and (for some reason) never lose any of their speed. In relation to us, each would maintain that velocity ad infinitum, but in relation to each other, their speeds would be closer to 1130 m/s (classic pythagoras). Now assume those bullets are photons. Suddenly you have a photon traveling faster than the speed of light relative to the other photon. This is usually what's meant by saying that the universe is expanding faster than the speed of light. It's all about relativity.
Nothing with any mass can travel faster than the speed of light, because the faster something moves, the more energy it accumulates. The more energy it accumulates the more mass it accumulates (E=mc^2, or m = E/c^2). The more mass something has, the harder it is to accelerate (compare rolling an empty can of beer vs rolling a full one - now multiply that with billions). At some point, you accumulate so much mass that it's literally impossible to move it faster. It just so happens that that point is c.
You bring up some very interesting ideas to ponder!
Even though we may not have some absolutely static frame of reference, we, thanks to relativity, can determine that nothing can move faster than the speed of light. Just think about it. Relativity guarantees that an observer can call their frame of reference inert and still make perfectly valid measurements. Even if observers in different frames of reference don't agree on some values, they will all come to the conclusion that the speed of light is a constant which cannot be exceeded.
Your analogy as to why the universe can expand faster than light is certainly unique, but flawed. Applying the Pythagorean theorem directly speeds wouldn't work; instead, you have to invoke some calculus. Work it out and you will find that the rate at which the distance of separation between the two photons is given by c*(x+y)*(x^2+y^2)^-1/2, where c is the speed of light, and x and y are the distances of the first and second photons from the origins, respectively. Note that x+y is always greater than sqrt(x^2+y^2), because the sum of the lengths of the legs of a triangle is always greater than the length of the hypotenuse. This indicates that the rate of change in the distance of separation between the two photons is actually increasing--the photons are accelerating away from each other! Now that we are dealing with accelerations, special relativity breaks down and we have to bring in Einstein's theory of general relativity. There will be effects in the space time between the two particles, but I don't know exactly what kinds.
However, the universe can expand faster than the speed of light. More specifically, space can. As far as I know, there is no speed limit on the rate at which space can expand.
Going back to the original question. If it were possible to move faster than the speed of light, one would not experience negative time. Time dilation involves the gamma function, (1-(v^2/c^2))^-1/2. As can be seen from this equation, if v surpasses c, then the radical becomes imaginary and one would be experiencing "imaginary" time, whatever that may be.
you dont hear a super sonic jet as it flys by, until its sonic boom catches up.
particles with no mass(?) going faster than the speed of light would be undetectable in our universe, i think.
Well, yes, to a point. More precisely, if you had a particle moving faster than the speed of light, then from the point of view of another observer (depending on his speed relative to you) the particle would travel back in time, also faster than light. You'd also have another observer according to whom the particle's speed is infinite and it would take no time at all to travel from point A to point B. Such a particle - tachyon - would have an imaginary rest mass and would be impossible to slow down to the speed of light or below. (And yes, if you had a way to produce and detect tachyons, it would have been possible to violate causality.)
There's a deeper meaning to this. Take events A and B separated - from your point of view - by a particular distance and interval of time. If the distance between them is smaller than the interval, i.e. it is possible for light or a massive particle to travel between the two events, then it is possible for one event to have caused the other; all observers will agree on the order of the two events (but from the point of view of some observer the distance is zero). Conversely, if the distance is greater than the interval (scaled by the speed of light), then two observers travelling at a particular velocity relative to each other may not agree in what order the two event occurred; it is not possible for the two events to influence each other, because neither a massive particle nor light could travel from point A and reach point B in time (or vice versa). This is the separation of space-time intervals into time-like, space-like, and light-like intervals.
So much to digest.. Will need to watch again..
This is the best channel ever how did I not know about this until now.
wow Gabe spoke faster but you are equally awesome man!!👌👍👍
If atomic clocks are the most accurate clocks we can make, how can we know that they drift by a billionth of a second in a day? As in, we'd have nothing more accurate to compare it to and know that it drifted
So I'm re-watching this video for the hell of it a year later, came up with an answer and then noticed I made the comment. I'm thinking the drift figure is what you get when you compare the results of multiple atomic clocks, it's never been seen to drift off more than that. If I'm right, I'm disappointed no-one answered my question, but given that I'm the original asker of this question, I suck even more so bleh
Old comment but that's a great question that I too would like the answer :)
@@delespai5592 I guess if you have 100 clocks & your superaccurate caesium clock is the only 1 out by a millionth of a second & all 99 other clocks are in sync, you'd probably think oh the caesium 1 got hit by a cosmic ray or a g wave rather than doubt the 99?
Photons, immortal timeless particles traveling at the speed of light, that is until evil you kills them by seeing them. 😮
Oh no, i am a serial killer
IKR. When I look at stars I imagine those particles crossing millions of years of emptiness just to suddenly bump in my retina. I guess that's an analogy for death. I'm gonna take my antidepressants, excuse me.
@@WillMauer Everything you see is just a hallucination inside your mind created by your brains. It's not like there's projectors or anything, so it's kinda cool.
They die every time they interact with ANYTHING, only to sometimes birth a new photon clone with a different vector.
One of my favorite episodes. Cleared up my fundamental doubts about light speed and time.
This is easily one of the best channels on UA-cam.
Nooo! The video ended! Now I have to wait another week for the next part D:
How can the clocks of both observers slow down relative to each other? When we put atomic clocks in orbit, those clocks slow down relative to us. Doesn't that mean that our clock speeds up relative to them?
+Virtuously .Selfish It works like that for the same reason that a rod will look shorter if you incline it by 45 degrees. Lorentz transformations are hyperbolic rotations and work similarily. You should think of the system as the time directions for the two observers being rotated relative to each other, and neither one is "special".
+BosonCollider he wants to know how the end result is different.
in the clocks case one of them kinda is "special" because they won't match up.
***** But neither of them is "special". Both look like they slow down to the other. There is no absolute time in relativity like you have in Newtonian physics. Velocity is relative, the only thing that is absolute is acceleration(i.e. in the accelerated clock case, everyone will agree that the accelerated clock slows down).
+BosonCollider now your answering a different question. or rather the correct one. in +Virtuously .Selfish original question atomic clocks would NOT see each others clock be slower because one of them is "accelerating" (experiencing more gravity)
the ground clocks would see the space clocks time travel faster
your first reply was related to the constant speed case, not this one.
+Virtuously .Selfish It does mean that.
Imagine that we both have a clock each, both perfectly synced.
Then imagine that I get into a space ship and accelerate away from you on the ground, you look into the window of my spaceship and see my clocks are moving slower, I look at you and see your clock is slower too.
We both think that we're the normal one and you're the slow one.
Then I stop, turn around, accelerate down, slow down and land. Your clock will be ahead of mine.
Why? Because I was the one who accelerated. And it was when I was accelerating back to you that I saw you speed up instead of slowing down.
Dude, I know exactly what you guys are talking about. One time, my watch stopped working and I had to fix it all by myself.
I am addicted to these episodes!
Hi PBS Space Time!
First of all, congratulations for your UA-cam video series,
you're doing a great job of explaining science and getting more people involved in it.
In the series of videos about time ("When time breaks down", "The origin of matter and time"), you spoke about a very interesting idea about passing of time depending on the internal structure and evolution of particles and atoms, and ultimately on motion.
I got particularly curious about the idea, and I was looking for some more precise reference about it (I am a physics PhD, so it would be wonderful if you could point me to some paper or book).
Thank you very much in advance, for the references and for your awesome job!
If one could ride on a photon, or strap a gopro camera to it, or something similar, and take a ride from let's say the Sun to the Earth, how long would that journey take you if you timed it? About 8 minutes for an earthbound observer, but what about the guy on the photon? Would it take no time, i. e. an instantaneous journey, or would it be an eternal journey? I think it would be instantaneous, right? A journey to the edge of the observable universe would be instantaneous on a photon. Right?
+Joe Brown First you'd need to make a GoPro out of light. Veritasium talked about this. The conclusion was, yes, instantaneous.
+Joe Brown If you could build a massless clock and strap it to a photon, you could send it across the universe before the first tick. You could send it infinitely far without it ever ticking.
That guy moves his hands more often than an Italian :D
Great vid though!
This episode blows my mind every time I watch it after I get high
Velocity and gravity are not the only things that dilate time. Well packed bowl or bong can almost freeze the time too :D
This Guy is so brilliant and he really knows physics and can explain it in the best possible way to me as a layman.
Best explanation of time, and lorentz transformation-time dilation,, matter and mass that I've ever seen/heard. So many physicists and physics educators have attempted to explain the relationship between velocity and time yet do a bad job of it. in not explaining the question everyone wants answered, WHY? Why does it do that? Well done. It does raise a point, and that is the approach of Heisenberg, author of the Heisenberg uncertainty principle in quantum mechanics. He took a non reductionist approach to reality, unlike the trying to find smaller and smaller fundamental building blocks of the universe. The block universe concept is not based on reductionist fundamental particles and/or forces/fields. Reality's secret may not rest in the smallest, but in the largest structures.
Question: You mentioned that a photon experiences no time.
Let's say i'm a photon, and time is standing still for me. I get emitted from a star lightyears away and got absorbed in some lucky observers eyeball. This happens then instantaneously ? So in a photons reference frame, speed doesn't seem to make sense anymore (speed=distance/time and time=0)
+MrHighvolt yep, for the photon its all at the same time
+MrHighvolt Yes. Remember that speed also causes length contraction. To the photon the eyeball isn't light years away, it's infinitely close. No matter what speed it traveled at it'd arrive instantly, from its perspective anyway. The fact that time, distance and speed break down when you travel at light speed inspired the title of this episode.
+Feynstein100 Photons *don't* evolve, from their point of view anyway. Everything they do and experience happens all at once for them. It's only us, massive systems who see it evolve.
In a way we're just limited to seeing part of it at a time. Right now I cannot see the sun, but it is still there, the evolving nature of night and day is just me being limited in when I can interact with the sun.
+Gareth Dean So when the distance is infinitely close, the universe looks like a singularity ?
I rewatched the video a couple of times and I still find it confusing since in the video at 4:24 he says that from an observer standing still, the moving clock seems to slow down. However, from the reference frame of the moving clock, time is experienced as normal, and it's everything else that slows down (time dilation).
I get that, but it also means that in that saying, a photon DOES experience time as normal, doesn't it ?
I think my brain just rebooted
+Gareth Dean Poor photon :(
0 DISLIKES SO FAR. DONT FUCK THIS UP GUYS
*edit*
1500 to 5 ain't bad
it wasn't me but too late!
+cams kick ass throwaway 3 Dislikes now... that´s youtube for ya´ll! ;)
-dislikes-
Who the fuck dislikes this?
+Code Slinger Ever see a video like this and then youtube suggest you might also want to see something about Planet X or the spiritual universe? People who get sent here from those videos dislike it.
Can you trap light within an enclosed mirror forever? If you opened up the door would it all escape?
Jared Theurer No because the mirror would absorb the energy of the photons
There's a big loophole in the time dilation concept. At least as it comes to me. Time should run fastest if I sit statically on a borring algebra lecture. But it's other way round. It's ticking fastest when I'm running back and forth from table to the blackboard on a calculus classes. It's very well tested.
But seriously, this is the best show on youtube. I know 300k of subscriptions and views is not much compared to mainstream shit. But what you're doing is really outstanding. Giving inspiration to people to seek and keep on overcoming hard times with algebra and calculus for the bigger goal - the beauty of science ^^. You're doing great job. It's even more awesome that you're not begging for subscriptions which would be totally reasonable based on the amount of work put into preparing of each episode. I'd be happy to donate some $$ every now and then, given the promise it would be distributed among the people preparing the show (not the money people behind the scenes, if there're any ;)). I'm pretty sure there're others like me, feeling gratitude for great stuff you're making.
Thanks!
The ends of these videos are always such a tease!
All this depends on a perceiver. Conscious attention creates the false perception of the passing of time. Creating any device to measure time is just us bolstering that false perception.
1 question here that has been on my mind for quite some time! HELP
If space and time are linked (spacetime) and 'space' is thought to be expanding, shouldn't its linked property (time) also expand at a directly proportionate rate? wouldn't the implications of this be quite large? (just to name one, s=d/t. the speed of light is just a distance light travels over a certain period of time... if space expands say by a factor 10 (extreme, i know), time would also have to expand by a factor of 10 to maintain the same overall magnitude of speed: ~3.0x10^8m/s (increase in time would serve to increase the denominator in proportion to the numerator). and furthermore, if we didn't take into account this expansion of time and failed to adjust our own measurement of the second proportionately, we would most definitely perceive light's speed to be increasing. now clearly, its not increasing... so therefore im led to believe that the properties of spacetime, although 'linked', are separable.
bump
+James Corbett Let's imagine light travelling from A to B. Let's say it takes 10 years for it to travel that distance. So now it's been a million years since that data was true. The distance now between A and B is now greater. Light would still travel the same distance, at the same velocity, but it wouldn't reach B this time, only where it used to be. So it would than have to travel a larger distance thus taking longer.
So no. It doesn't have to be considered. Since it's the space *between* matter expanding and not matter itself.
+s1lverbullet1234 ok i understand this supposedly... however i believe the expansion of the universe is a 'homogenous' expansion, meaning the expansion of space between ur two ears is the same as the expansion of space between galaxies. but the reason we dont see the effects is due to the strong and weak nuclear force, which is far stronger than the strength of the expansion of space. but i think that if the expansion continues to accelerate, there will someday come a time when the force is so great everything will literally rip apart...
+s1lverbullet1234 also think about this for a second. when space is warped by gravity, so is time. essentially, when the fabric of 3d spacetime is manipulated, u get time dilation effects as well as gravitational effects... so wouldnt u then be led to believe that ANY warping of spacetime would affect its time property associated with it?
James Corbett you're *completely* right, actually there's some really cool vids on this topic. Space eventually going poof. Kinda interesting but depressing. :/
Could someone explain me how they tested that the speed of light is constant? I never really understood why we cant say that time is constant and the speed of light is dependent on the speed of the movement
I get that it works because of satellites and stuff, but I would like to understand how they tested it.
+Gunar Kroeger Check the michelson morley experiment :)
+Gunar Kroeger This was first observed by looking at a binary star system aka two stars rotating around the same point. It was seen that the wavelength of the light coming from both stars was the same despite one of the stars heading away from Earth and one star heading towards Earth. If the wavelength/speed of light depended on the velocity of the emitter there would have been interference effects from the light as it was observed on Earth. However, there was none, so the speed of light is independent of the velocity of the emitter and is therefore constant.
PineappleQuesadillas
That's wrong, actually, since the frequency of light does depend on the velocity of the source due to the Doppler effect.
***** I suppose I worded that poorly, but remove wavelength from that and it's all logically sound. There would be weird effects happening if one path of light was travelling faster than the other, and this was not observed in the experiment. The binary star system "experiment" was very real, and I believe it predated the Michelson-Morley experiment and the discovery of stellar aberration.
I'll have to watch this a few more times to fully absorb it, but it's still the best explanation of time dilation and the relationship between matter and time that I've seen.
I'm loving this series of videos.
I think I'm getting smarter! My brain only blue screened once!
I has a question: Does time even exist, or is it all just motion?
That's what I've been trying to tell people, but they don't take it seriously. Time is just a system of measuring motion. Events always occur in the present.
They occur at the space-time points they're at, Steve. Because of this, you NEVER see an event as occuring in YOUR present; there's always the travel time to you of the light, involved, so that your senses always report to you on events slightly past. (Or greatly, if you look up at the stars at night.)
This is why, in even special relativity, let alone general, "simultaneously" is meaningless; closest you can get is "space-time interval of zero"... because the t axis slopes at different angles when two inertial frames are moving relative to each other, so it's not particularly useful to say whether two events are "really at the same time". "The present", as in "everything happening when my t = 0", is different slices of spacetime in differently-moving frames of references. There's no unique consistent "the present" covering everywhere.
Time's a variable just like space; it acts differently cuz it has a minus sign attached. Our perception of time is quite possibly completely erroneous; the universe CAN be described in a way where no motion or change ever exists, just particular sets of connections between various space-time events, which happen to always follow the "laws of motion" when interpreted in x,y,z,t terms.
--Dave, sorry dude
Time is a human illusion. It does not exist at all. Its just events occuring at a faster vs slower rate due to the reasons described in many of these videos..
Just imagine. If humans were immortal would the concept of time ever be invented ?
Both, but most commonly time is symmetrical with space (and by extension motion since motion is derived from space)
p.s. it doesn't mean time is space and time is motion. They are models.
Question. I'm in a rocket in space flying past my friend who is also in space. If there's NO such thing as absolute motion or absolute rest, then why don't we both experience the same degree of time dilation? Ie to me it appears as though he's in motion, but to him it appears as though I'm the one in motion. If we both observe that we are in motion relative to each other, who experiences the time dilation? Shouldn't it cancel out, because we each observe the others photon beam clock to be moving?
P.S best channel on UA-cam, thanks for all the vids
+Manveer Singh The time dilation in case of objects at constant speed is just apparent effect - you observe each other as being time-dilated. However, time dilation caused by acceleration is absolute - because only one of you experiences the acceleration. If I remember correctly, PBSspace time made a video about this some time ago...
i really love your vids, they delve deeper into physics than most on youtube.
Could you please make a video about entropy and thermodynamics in the same thorough manner? Would be awesome to learn something new about these subjects.
These videos give me an afterglow, they change the way I look at everything.
"Con-feynman-t" or confinement?
Sample analogy from physics documentaries I used to watch back in the day: "Imagine that this cup of yoghurt is the entire universe..." Geez...
If as you approach the speed of light time starts to move slower at at the speed of light it freezes, if you could go faster than the speed of light you would go back in time?
If you went faster than c, you would SEE that time goes backwards but I don't think you would actually go back in time.
If you could jump over the speed of light, you'd SEE the rest frame as moving backwards in time ... because your trajectory FTL goes OUTSIDE its own light cone, so the further you went from point B, the further back in the past light emitted from stationary B would have had to have been emitted to get to your location. (Remember that in a spacetime diagram, light always travels at 45 degrees to the x and t axes.)
If you suddenly reversed direction, now you'd be moving TOWARDS stationary B faster than light, so you'd be catching up with its light-cones on your side, and you'd see B living its point life FASTER than normal until you got back to it, at which point you'd've caught up to t=0 and passed it enough for t to be 2 * (distance you went) / (your speed) and the light from your furthest point away couldn't reach B until 2 * (distance you went) / c .
--Dave, and you COULD go back in time and arrive back at B before you left it, but doing so involves stopping, then changing your velocity correctly at your furthest point, to move your location in Elsewhere relative to B =below= the t=0 axis - and in the process getting B to appear to be living more slowly enough, THEN heading back towards B at your same FTL speed from that frame
best explanation yet , I will have to delve into pbs back catalogue more often !
Dang, those mass questions about the thought experiments were good!
I particularly liked the question about compression of a spring being related to momentum. That’s sharp!
how do I download a minecraft texture pack
You gotta move it to the mods folder in roaming my guy
I like how when the clock was moving, the tick got lower due to doppler shifting.
Thank goodness he's wearing a t-shirt, otherwise this stuff would confuse and frighten me.
This is my new favorite Space Time video!
the best channel ive ever subscribed to
How can I determine whether the speed that I'm traveling with is close to the speed of light or not?
I think I'm standing still on the chair, but if you add up the speed that the Earth is spinning me around its axis and around the Sun and speed of the solar system within the galaxy, I'm moving quite fast.
So how can I determine what fraction of speed of light (v/c) I'm traveling with?
One half of the cosmic background radiation should be slightly cooler on average than the other. You could use this to estimate your "absolute" direction and velocity relative to the universe as a whole.
The question to answer your question, maereanm, is "... relative to what?". You're never "just moving" - any time you say you're moving, it's always in relation to something else.
("But I can FEEL when I start to move!" Because you are at that time moving relative to the fluid in your semicircular canals, in your ears, and to some extent relative to the fluids in your body, which don't catch up quite immediately when some outside force presses part of your skin to make you change velocity.)
--Dave, as Chris notes, "relative to the CMB" is the usual answer, but you still need that answer to make the original question make sense at all
@@daviddelaney2407 Relative to light you are always travelling at the speed of light. What is your point?
So, you covered a very nice, intuitive explanation of the physical source of time dilation caused from motion and acceleration. I was hoping you could explain the same thing for length contraction. I've never understood why we must have length contraction when time dilation seems to have us covered.
Length contraction keeps the speed of light constant relative to all observers.
this one is the best and clearly explained
I love these videos. It's like having a Maester from Game of Thrones teach you about stuff.
I have no idea what you're talking about half the time but I still love these videos :)
Best UA-cam channel ever
These videos are great. Time Dilation has always fascinated me.
Youse should make a app! I love this channel!
I've been watching a lot of the videos on this channel for a few weeks now. I'd say I understand very very little of it most of the time, but in find it fascinating nonetheless so I keep going. As I keep looping around through different topics I understand a little more. This is the first time I've actually kind of sort of understood time dilation in the theory of general relativity and this is the first that I'm kind of sort of wrapping my mind around e=mc2. In short, great videos, not easy(for me at least)... but great.
Here's a great youtube series on special relativity: ua-cam.com/play/PLoaVOjvkzQtyjhV55wZcdicAz5KexgKvm.html
A difficult subject presented very well. Bravo!
This is the best visualization of special relativity I've ever seen. Brilliant.
Wow, never heard this described so well. Very well explained.
I LOVE this series.
These videos are simply amazing. Wow.
When I first learned about energy being the source of most mass this was my first question. Thank you for answering!