Complete Solution To The Twins Paradox
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- Опубліковано 25 сер 2016
- One of the most famous paradoxes of all of physics - who's older? Who's younger? and WHY? **** Thanks to The Great Courses Plus (free trial here: ow.ly/RCty302dIHU) for supporting MinutePhysics ****
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This video is about the famous “Twins paradox” of special relativity, how time can appear to be faster for two different observers at the same time, and which twin really is older (or younger) - the one who stays on earth or the one who flies in a rocket ship to the stars?
Music by Nathaniel Schroeder, / drschroeder
REFERENCES
Muon lifetime and time dilation/relativity: hyperphysics.phy-astr.gsu.edu/...
MinutePhysics video about Time Rotations & Einstein: • Einstein and The Speci...
Experimental test of time dilation using doppler shift of light: en.m.wikipedia.org/wiki/Ives-...
Lorentz Transformations: en.m.wikipedia.org/wiki/Loren...
Relativity of Simultaneity: en.wikipedia.org/wiki/Relativ...
Paper on twin paradox under constant acceleration: arxiv.org/pdf/physics/0604025...
Taking Cesium atomic clocks aboard airplanes: en.wikipedia.org/wiki/Hafele-...
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Created by Henry Reich - Наука та технологія
"You guessed it" you overestimate my intelligence
You were not alone
It's over my Twin brother Anakin, I have the high ground (and therefore less gravitational force)
@@melontusk7358 🤣
@@melontusk7358 Please twit about Bitcoin sir
@@melontusk7358 you are the CHOSEN ONE!
When I watch your videos, I nod my head and I'm like "Yeah, I totally understand that." I watch your videos to feel smart, but it just makes me feel really stupid.
He goes through everything so quick which doesn't help
Their videos are meant for people who already have a bit of base knowledge of certain things, not for people to find the base knowledge in the first place.
Isn't that a good thing? much better than pat yourself on a back for how smart you are. That's pointless and vanity.
***** completely agree
+Czeckie no it's for clarification of something you may have base knowledge of but don't fully understand.
The twins paradox has haunted me for most of my adult life. Thank you for finally explaining it to me, it is not a paradox at all. I can now die happy.
I thought this was hilarious.
Unfortunately, it still doesnt explain it!. The lorentz diagrams are drawn only from the pov of the guy on earth. Why? If it is done from the pov of the guy on the spaceship it will look exactly the opposite way. Paradox still remains.
@@narendrakrane Not true. If you try to do a single Lorentz transform on the rocket twin's worldline in order to squeeze IT into the stationary frame with the worldline just going straight up, it won't work! Because the pacing of rocket twin's time, no matter what single inertial frame you are in, changes during acceleration! So basically, YES it is true that if the rocket twin just were moving on one path (one constant velocity, one frame) then each would calculate the other's time as moving slowly and thus both would argue that the other was younger, the breaking of symmetry comes when you realize that at some point the rocket twin measures the frame to switch (acceleration). Now he is still calculating that the Earthbound twin is aging slower but from a different frame of reference, which changes how he has to consider the Earthbound twin's motion. He'll realize that HE, the rocket twin, is the one who accelerated when he gets back to Earth and sees that they all aged more than him.
@@ANGRYpooCHUCKER But then the difference of time that the twins see in there clocks when they reunite, should only be dependent on the amount of acceleration the flying twin experienced. cause it's a acceleration which is causing the breaking of symmetry. And that would also mean, that how long the twin travels with constant speed should not matter. Only how much it accelerated. Do we have a mathematical proof of the twin paradox. Basically math that is calculated from both the twins point of views?
@@narendrakrane That's not what that means at all. The acceleration only plays the role of making the rocket twin's journey take place in two separate reference frames. The actual velocity of the frames is still what determines the amount of time dilation. The thing that the acceleration does is change how time dilates for the other observer from the perspective of either one.
I like how the comments are pretty much an even blend of “This is a nice introduction to the concept, but here’s how I would expand on it” and “…You lost me at ‘setup’.”
there is a c square missing under the squareroot
how exactly do you mean it? what's the right formula??
He could just be using natural units and saying c is 1 , note how the c is also absent in the space time interval so he is just using c=1.
I'm still trying to figure out "time rotates"
Clockwise or antclockwise on the ... er..... clock ... :D
Its just natural unit c=1
Yeahhhh.... No. I don't get it
Yay someone one like me
I got nooooo idea
same!
Simple If the two atm of earth from water depth is equal to 80+psi generating the force to get off the planet would equal 20.5 seconds accounting for the weight of the rocket. If you keep traveling at the constant speed and you take out the gravitational pull by planets you can see that it will be 90.78*2.000 seconds behind. Then when coming back you can actually make up that time by speeding to 90.8dcp near a planet and it will launch you up creating a net force equal to 4/6 of the sun generating enough momentum to sling shot you back into earth atm at the precise moment you left.
+Paul Garcia obviously
+Paul Garcia that mightve made sense...if I understood it ;-;
"If you can't explain it simple enough, you don't understand it well." - Einstein
Frames of Galaxy Or you’re explaining it to someone who has a hard time understanding that their perception of the world isn’t always as it seems. Like how people didn’t (and still don’t) believe the earth is round.
@@12_Bitcat That's just crazy talk. It would roll off the back of the turtle.
Ma Boiii Galaxable TV, Minute science knows what he's talking about he just did a oversimplification so that people who already knows the basics of special relativity could understand it.
@@12_Bitcat yes we didn't believe in round earth before cavemen I mean the Greeks knew and probably some other cultures
@@12_Bitcat It's called Zetetic worldview, natural perception of a little kid. Like how parent's play peekaboo with toddlers. You either gradually grow out of it, or become a borderline psychopath and no amount of science or reason will convince you otherwise.
I think it's characteristic in many fields of life. Flerfers are just an extreme example of it, as their conman leaders exploit this trait of direct perception, while making this comfort group proud of what is essentially a fallacy of objectivity of human senses, ignoring both science and psychology processing these senses. (Deliberately left out the psychology from science as that is a debatable notion). Ironically, only psychological change can help them, not learning facts or science.
This is the cleverest, most concise, best reasoned, and least noisy Twins Paradox video I've found on UA-cam. Alas, it's also wrong. For example, if your spaceship is a muon swarm passing through our atmosphere, it shows continuous verifiable time dilation _without_ bothering to turn around. The gap in your figure works only because you added two _independently_ observable time dilations.
And this is probably the most accurate comment, unfortunally missed by many. So unsatiable is our hunger for easy explanations.
You lost me the second you said something about moving affecting time speed or something... basically lost me 10 seconds in.
Maybe I can help.
The speed of light (really the speed of causality, which not incidentally is also the speed of light in a perfect vacuum, but that is a different matter) is constant in every frame of reference. That is, not matter where you are or where you are going, the speed of light is always the same.
This would seem to cause a contradiction: If you move, for example you drive a car and turn on the head lights, then the light emitted from your car would move at exactly the same speed for you as it would for a passer-by - even though you are moving relative to them.
The solution to this is special relativity. Relativity means that the laws of nature are the same for everyone everywhere, and that includes the speed of light. Special relativity is special because it ignores acceleration and gravity, making it much simpler, but a special case for relativity, hence the name.
It works like this: Each of the two observers, you in the car, and the passer-by, see the other one as moving relative to them. And because the speed of light is the same for both, each sees the other one's time as passing slower. It's best to imagine that both have a clock, and both clocks tick at exactly the same rate. Then each one would see the other one's clock ticking slower. This way the light travels the same distance during the same time interval for both observers.
It may help to draw a diagram to better visualise it, but that's how it works.
And that leads to the twin paradox: If you and the passers-by compare clocks before and after your jaunt in your super-fast car, you'll notice a difference. But if each sees the other as moving slower, who is right? The answer to that is: Both are.
And you can't both be older than the other when you are both in the same car park at the same time, so what time is it? One of you is older than the other now, and which one and why is what this video tries to answer.
HTH
David Wührer Why is it a contradiction if you and a passerby see the light moving at the same speed, isn't that the point; that light moves at the same speed for everyone?
Red Panda
Yes. But in that example, both observers are moving relative to each other.
For you, light is moving relative to you, and for the passer-by it is moving relative to to them. But for both of you it is moving at the same velocity, even though you are not.
David Wührer Oh right, and the relativity is different because of the differences in speed you're traveling in?
Red Panda
No. Relativity means that both perceptions are equally valid. The paradox is that the perceptions contradict each other in Galilean relativity, where, if the light is travelling at the speed of light relative to you, it should be travelling at that speed plus your own relative to the passer-by, and vice versa. Just like you are standing still relative to your car, but in motion relative to the passer-by.
However, the speed of light is the same for both.
That's quite astonishing that in the time it takes you to very quickly decelerate and accelerate on your return journey, you can observe your twin back at home suddenly experiencing this large amount of time that you had missed due to your notion of time being on a very fast starship.
Imagine this being on a much longer scale where the time was 10 years rather than 10 seconds. Had you, as a space traveler, not watched this video, you would have come home 3.6 years later than you had expected! Thanks for minute physics for preparing the future space travelers to expect this phenomenon :P
(this of course taking into account only special relativity and not general relativity ;P)
+Cytrillex BagelsMan That's what makes this an interesting paradox. The apparent contradiction comes from analyzing both twins using special relativity and the resolution comes from realizing that since special relativity doesn't account for acceleration, you have to analyze all the parts without acceleration and then deduce that something weird and beyond the scope of special relativity must be happening during the acceleration to make it all match up. If you use general relativity, there's no paradox at all, since general relativity accounts for the weirdness that happens when the twin turns around.
+Sam Technically, special relativity can account for acceleration: just integrate over instantaneous reference frames. But yeah it's cool.
That sudden experience of reality due to the 'rotation of time' also accounts for the causal limit since wrt light (using convention) you'd be slower while in one direction and faster when you switch, and theoretically the experience of the lost time is evitable since the change is instantaneous. However, since the change does take some force, it cannot be practically instantaneous, thereby forcing the dude on the space rocket to experience what he lost and compensate for the 'lost time' proving Einstein's equation to be correct. It's rather incredible to see how this fits in so perfectly with the basic concepts of modern physics.
O-O EKKWHWNDKCUCKWBWBR ME NO UNDERSTANF
This is very good! On the surface, many paradoxes seem to defy logic, while really, all it requires is some different perspective to probe it and make sense of it. Paradoxes demands reform in the way we think and approach problems.
?How u don't see here the Idiocy? ARe u in a cave?
@@krzysztofciuba271 bro come out of ur mom's basement and fight me 🤜
""we use the fact that time rotates ..."
err,,,
that was the big givaway to this being either the presenter not knowing fuck all or ever clever on conning the viewers as per Brass Eye.
It's only really a paradox insofar as SR is all that's needed to solve it mathematically, but the mathematical setup in SR is apparently symmetric. All you need is the speed/time/distance traveled to and from the destination planet. IE Alice travels to the destination at 0.9c and it takes 1 year, then she travels back the same way. In this setup with just the information v=0.9c and t=1ly the problem can be solved. But if we look at the two individual situations, the twins travelling apart at 0.9c and approaching each other at 0.9c with just that information both can say the other's clock would be the one ticking slower; that's the key principle of SR. However just by knowing which twin took the trip, which one broke the symmetry we can say which twin would actually appear younger/older to the other.
Consider these variations of the Twin paradox.
Alice goes on vacation. She doesn't come back. Bob instead joins her. They are the same age.
Alice and Bob go in opposite directions at the same speed to different places equal distances away. They leave their 3rd friend Charlie. They return some time later. Alice and Bob are the same age as each other, but both are younger than Charlie.
All the way through I understood what he was saying, but then when it was done I didn't know what I'd understood...
i can tell you want thing. i dont understand
one*
what don't u understand
+Jeremy Playzxd ya I don't understand either
Yeah, you can enunciate these things in a minute but not explain them in a minute
the 8 seconds bit, how did he come up with this number?
Geez, im sure glad I did psychology at university!
David i want to be a psychologist too :D
lol, art was a breeze, no rules at all.not.one.single.equation. (other than tax avoidance of course).
I’m ten yet I got this
Thank you so much, I'm currently in my second year of A levels and time dilation was making zero sense as my mind would always find a paradox in my head. This makes so much sense now I think you may have saved me.
The graph you made was super helpful. I didn't know how to describe what I knew to be true but the graph you made was perfect.
But couldn't you say the ship is still and earth is moving away then accelerating then coming back? Why doesn't this work both ways?
The rocket-based perspective doesn't quite work. The easiest way to see this is to consider acceleration. On Earth the twin never feels anything if standing still, no forces. The rocket twin however must turn around and fire their boosters to head towards Earth. Doing so pushes them back against the rear of the rocket. If they wish to assume they're not accelerating, not moving, then they must assume a gravity field has 'turned on' and is exactly countering their booster rockets, while also pulling Earth (and the rest of the universe) towards them. But, gravity slows time, so during that acceleration\gravity burst their clock is unavoidably slowed.
+Gareth Dean this is a perfectly reasonable explaination.
No, because unlike velocity, you actually CAN feel acceleration. When you are in an accelerating vehicle, you feel the forces that are required to accelerate your body with the vehicle. It seems as if there is a force pulling you to the opposite side from the vehicle's acceleration. This you experience when your body lurches forward in a car as it comes to a stop.
+carultch Inertia.
Force (acceleration) takes you from one reference frame to another. When the rocket twin feels a force as he's turning around, he is changing to another reference frame. Both observers agree he feels a force because he can perform experiments during the turn around to detect it (dropping a ball for example). For this reason, even if you say the ship is still for the first leg of his journey, because of the force during the turn around, it cannot be also still for the second part. And if you set up the spacetime diagram this way, the result is the same that the earth twin is older.
I don't understand one thing. What if we choose person in spaceship as 'static' one and repeat all other steps. Wouldn't that lead us to conclusion that it was the other way around, 10s for spaceship, 8s for the Earth? Leaving us in the very same 'paradox' spot where we started.
The earth isn't accelerating
* deleted *
The spacecraft frame accelerates while changing direction. You cannot assume it static because your frame has to constitute both the person on earth and the spacecraft. And in any frame you choose, the earth is going at a constant velocity.
Acceleration is not relative like velocity is. The person in the spaceship experiences the acceleration when they turn around, the person on earth does not.
That's the difference right there. The important distinction isn't velocity, but changes in velocity.
I can't thank you enough I've been struggling with understanding this paradox for the past couple of days, and this is the only explanation that makes real sense. thank you!
This is such a good explanation! I've seen much longer videos that don't really get to the heart, of it even by the end.
Thank you so much my physics teacher had no explanation as to how both people can view each other as having a slower time AND for one to come back older. This has been a HUGE help :)
Huge help to what ?
He says " And since you are moving" ... then that explains it, only one is moving, only one has a time dllation. hence Einstein.
@@zakelwe the entire point of relativity is that velocity is relative
who actually understands his videos????
Henry
Engineers, theoretical physicists, particle and nuclear physicists, upright bass players
Me
+Tetrachromia upright bass players
I do.
+MinutePhysics 0:47 "since you're moving"
Wait a sec. How do we know who's moving and who's not?
Isn't that the original argument?
How can we know who's moving if there's no absolute motion?
Can someone please explain this to me?
Christopher Ramsey u are correct .
It doesn't matter who's moving. The only thing that matters is who's accelerating. The rocket man is experiencing a force that makes him go faster, so his clock ticks slower than one on Earth. That force is not relative: he experiences it as if it were a gravity field that affects him and not everything else.
Yes, i'm also missing the point of the video :/
That's right of you to think that way. It should be related to acceleration if not speed.
Christopher Ramsey yeah that one has been buging me also..its all true like he says when u watch only on one diagram. But what if you take this diagram from rockets perspective, then the earths diagram would be that one that is skewed and on earth should be passing time slower?
I liked this video a lot. I have seen many UA-cam videos on Twin Paradox. I am shocked to see those videos because, when you go through those videos, you will find that the people who have made those videos, do not understand even basics of Physics. You will be further shocked to know that some of them are tutors in Physics coaching centers. On the other hand, your explanation is so good, especially the diagram of the time lines where you explain what happens during the period the spaceship turns.
Incredible! I've been looking for a good explanation of the twin paradox when changing velocity instantly for a while, and all the videos I found confused me a little bit more. This one here is really awesome.
Because it just gives a completely different explanation where the effect is solely due to acceleration. I am not if this explanation is right or all the others. Just because we understand it better doesn’t make it right!
I actually have no clue which explanation is the right one but the explanation with instantly changing velocity is more common among the scientific community. Could both explanations be right?
The children in here trying to prove that time does not change need to stop. You dont understand why you're wrong and it pisses me off. Do yourself a favor and stop trying to prove einstein wrong with your pre diploma knowledge and save yourself some credibility. Go study.
They don't need to stop, they just need to do a much better job and tell scientific journals rather than UA-cam comments. They'd be fucking legends if they could actually prove it.
these 'children' arn't wrong, and time doesnt change. YOU ARE the one that is wrong because suddenly someone has a different opinion than you and so its 'fingers in your ear time and singing the national anthem' unless your kapernack, as he wont stand for that.
+kenns9
??? I'm so confused right now. Are you really claiming that Einstein was wrong this whole time and that the things we've tested and OBSERVED are somehow false? That wouldn't be that bad if you actually provided evidence, you know the thing science is literally based off. Seriously it takes alot of ignorance to say what you just said.
And by the way from my relative perspective (see what I did there) you're the one plugging your ears. Our ears are fine we just can't believe what we're hearing.
+kenns9 it is not a matter of opinion. it is scientific fact. stop being so pretentious. you have no idea what you are talking about
+Nxrv It's fact? I accept the theory of general relativity, but I thought it was just that - the most widely accepted and plausible theory we have. Is it actually a proven fact?
I’ve been so confused about this but this short video just helped me understand it thank you very much!
THANK YOU... finally I understood this, that's what I've been looking for, 3:33 minutes and it's already clear
How does "perceived" time has any effect on the aging process?
so imagine for a sec this thing called a frame of reference. basically, what he said about the train. anyways, time is not a constant, it is a dimension, just like width, height, and length. (3d movies are actually 4d because they include time!) since everybody seems to be moving at the same speed through time, we assume it is time moving forward. however, what is more likely is that it is us moving through time at the exact same pace as everyone on earth. due to this, someone going really fast or moving near high gravity can change speeds and move forward faster than everyone else, and suddenly this isn't such a headache anymore.
It doesn't have any effect on the aging process. Lets say you're going to live until you're 80 years old. Then you'll live until you're 80 years old as perceived from your own frame. If 1 second in your frame is 10 seconds on Earth (because you're in a higher gravitational field or moving close to the speed of light), then you'll live until you're 800 years old from Earth prespective, but in your own frame you'll still live until you're 80 years.
Time feels like it's moving at a different pace depending on what your doing for example time flies when your having fun as simple as I can put it .
yeah, but isn't this still just only how you "experience" or "feel" it or do you in fact age slower during that time.
MeetMeViceVersa You experience and feel time the same way no matter what. You don't "age" slower in a biological sense. What you experience as say 8 years, both in a biological aging sense and in a physical sense, can be what someone else experience as 10 years both in their biological aging sense and in a physical sense.
Yes, in principle you can time travel into the future. If you're in a frame where 1 second is 10 seconds in Earths frame and stay there for 10 years, then you'll have aged 10 years, but everyone on Earth will have aged 100 years.
Thank God for this video! I was getting really worked up over this issue and thought this would imply multiple timelines, one where the first twin is older and another where the second twin is older.
He actually didn't explain anything. The reason it is a paradox is that either one of them can see the other one is travelling but he himself is not. Once we know who is stationary which exactly we can't tell and which exactly why it is a paradox, which he somehow magically decides the one on earth is, it is not a paradox anymore.
@@519stream3No, the key point is that one of them *accelerates*. One of them has to come back for there to be a paradox, and it’s precisely this “coming back” that causes one to be older or younger
@@michaelibrahim9275 I don't think acceleration matters, lorentz factor changes as the speed changes. It tells us dilation occurs because of the speed. The traveling one's time will be slower for the fact that traveler has a speed but the stationary one does not. To determine which one is actually traveling the reference has to be a thing that is not one of them or absolute. Even the acceleration has to be absolute since both of them see the other accelerates. The fact that the twins age differently proves the existence of that reference.
@@519stream3 Acceleration is not based on reference frame, and you don’t need an absolute reference frame to determine who is accelerating. Imagine we are holding glasses of water that are filled to the brim. You are initially running away from me, but then abruptly turn around and come back. You will have spilled some water due to the acceleration, while my glass would be perfectly fine. Unlike velocity, acceleration is *not* based on the observer. Acceleration has tangible, measurable effects that all parties must agree on. If you are spinning in a wheel, there is a reason everyone else doesn’t go flying away from you. You are the one accelerating and they are not. (Look up Mach’s principle for a better understanding). The crux of this is at 1:10, when one party abruptly changes direction (in reality, this is not possible and instead it would be a gradual change, but the same principles still apply)
@@michaelibrahim9275 that is what I call an absolute acceleration. It is an acceleration caused by a force but not a one measured by an observer. For instance the moving twin could see the stationary one accelerating.... Regardless still acceleration is not the cause of dilation but it does indicate who is moving in this case since an absolute acceleration causes movement if the other is stationary relative to an absolute stationary reference. The key is who is moving or who is stationary but not how he moves. in case both of them travel with all kinds of different speeds and accelerations and finally meet again, who is younger? The answer should be the one travels shorter in distance in space spends or experiences or feels more time. Same reason the one who is stationary moves the least in distance but moves more in time. In this case the distance would be absolute since both of them travel exactly the same distance relative to each other. In another word the distances should be measured with a reference point independent from neither of the travelers.
The first satisfying answer I find for this paradox !! Thanks
I didn't understand this paradox earlier in your special Relativity series. This is of course better
What if the universe is closed, like surface of the earth? If two twins travel in opposite direction at constant velocity, but eventually meet up again, will one be younger than the other?
👍 you don't seriously expect answer to that. It's a good question though, similar to what I just asked.
Not if they are both moving at the same speed.
@@DaysDX they are moving opposite direction hence each one sees the other one moving doing the same lap and each others clock tick slower relatively to the other one. The fact that they spun at the same speed relatively to some 3rd observer who stays put at the point of origin doesn't matter, what matters is that they both see the other one moving relatively to them.
Haven't I watched this before?
Wait never mind
NIIIIIIIICE
+icewarm2 so did Vsauce 3
Mandela Effect
no
I'm currently reading A Brief History of Time and I wanted to see the mathematic to understand the Twin Paradox Stephen Hawking was speaking of in Chapter 2. Thanks for explaining so clearly!
Sooo useful and interesting, and easy to understand. Thanks man!
Ok, but what about a closed universe (say, a positively curved one)? You could return to your starting point without having to accelerate at all.
General Relativity has not been taken into account here - this is Special Relativity, where spacetime is flat.
In compact spaces, there is an absolute frame of reference, and both twins will agree on what that frame is, and thus will agree on which twin is younger, avoiding the paradox. Here's a paper on it: arxiv.org/abs/gr-qc/0101014
This has been confusing me as well. In a compact universe there is only one inertial frame, therefore special relativity can not be aplied. Could we, from the fact that we can apply special relativity, conclude that we do not live in a compact universe?
No, because special relativity would still hold locally, as long as you or your observations don't cross the "boundary" of the universe, where you'd turn up at the other side. As far as we know the universe is at least 85 billion light years across, so to find any deviation we'd have to look really, really, REALLY far :)
+Kasper Meerts +Strichcoder
If there is no special inertial reference frame and all of them are indeed equivalent, then space must be unbounded, because if space were bounded then one could find a special point, fixed with respect to the boundaries, from which to measure distances and therefore velocities in an absolute sense. But we know that this is not the case, therefore, space must be unbounded.
Great video, Henry! Thanks for bringing this to the lay person. This particular topic is very tricky (acceleration causes the change in age) and has never been addressed in such an easily accessible way. Again, bravo!
Amazing!! Super clear!! Never found anything better!! Thanks a lot
Finally, I finally understand the twin paradox. So many of the articles and videos I watched just skipped over the acceleration (one article even said the acceleration is NOT the reason for the difference and gave no reason as to the asymmetry!). Fantastic video. It really frustrates me when other sources confuse and mislead on an already difficult topic.
Well... acceleration isn't the proximate cause of the difference in aging. It happens to be necessary in this scenario. But, to make an analogy, imagine you are riding a bike and you fall down and break your arm. If someone asks you how you broke your arm, the most direct reason would be that you impacted the ground at a bad angle which snapped the bone. But, you would probably tell them you fell off your bike. Falling off the bike wasn't the direct cause of the break, but it was the thing that led to hitting the ground in such a way as to cause the break. Same with the acceleration. The direct cause is the fact that the traveling twin is not stationary in a single inertial reference frame between his departure and return, while the Earth twin is. This happens because the traveling twin accelerates, but there are ways to construct scenarios that involve different amounts of time passage without using acceleration.
@@Arkalius80 Can you give an example? It seems to me that in order to not be stationary in a single inertial reference frame the speed would have to change, which requires acceleration?
@@alexking1129 Imagine two rocket ships with clocks on them moving at relativistic speeds in opposite directions, so that they cross near each other at some point. Rocket A leaves Earth and B is heading toward it. When they cross, rocket A transmits its time to rocket B, and rocket B's clock is set to this time, and starts counting from there
When rocket B arrives at earth, the elapsed time that its clock shows will be less than the time elapsed on Earth since rocket A left.
@@Arkalius80 Actually I think I get it, acceleration isn't needed for time dilation but it IS required to explain the twin paradox. Makes sense
@silverrahul ohh, I see, so acceleration is not required but like arkalius said the inertial reference frame is switched when the time starts being tracked from rocket B
Love your videos. Can you do a video on Bose-Einstein condensates?
I can't understate how amazing this explanation is. Thank you.
Before anybody gets impressed so easily, look very closely if anybody is solving the real Twin Paradox and not their own version. Anybody can solve the obvious watered down version ( and even this watered down version is absolutely false if people really knew) so to make sure the cult of Einstein is bought and sold. Solve this:
""How each twin would use the Lorentz factors to figure out the other's age before they meet whenever the meeting just might happen to demonstrae the true context of relativity in this correct form of Twin Paradox, two inertial frames, you in one vessel and your twin in another vessel in the middle of The Great Nothing?"
One tells the other will meet in a month. They just take off to nowhere away from each other. That is the whole point. All they know is that the other will be younger since it is what see in each other's clock.
@@alchemy1 thing is... the traveler's frame isn't really inertial, if it gets decelerated and accelerated back, now, is it? :-)
@@polygontower a good clue would be if you see the other planets and stars accelerating at the same rate as the twin... then it's likely us not them. ;-)
You did a great job explaining us I wish my physics teacher explained it easier like this LOL I have seen the notation that you were talking about before though during class so I already had a good understanding of what you’re referring to thanks for the video by the way
Thank you for hitting the nail squarely on the head with such a clear concise explanation!!!! I have been puzzled by this paradox for decades and have read untold many explanations which talk all around the problem without really quite coming to grips with it. Yours is far and away the best explanation I have ever seen. Congratulations on a great job!
you lost me at twins
Julius Tranquilli he lost me at 0:00
it's a pradox because genetic mutations will arise when the egg is growing so they rn't genetically identical
try this: give one twin an orange, if they like oranges they will appear to move closer to you.
Interesting how this came out when Vsauce 3's time dilation video came out and someone in the comments recommended the previous video of the twin's paradox to explain some of the questions in the comments.
Thankgod you made a video about this. My damn phsyic teacher asked his student to re-explain the twin paradox after he explained it for like 10 minutes. And even worse we just learned about relativity that day as well for like half an hour.
Without this video i wont be able to do it
that's a tall order. I'm an expert, and it took a lot more than 10 minutes to understand it.
Thank you for your great science videos, sir.
im still having trouble with, "moving things experience time slower". how? why?
It's kind of misleading to say you experience time slower. It's not like your life goes into slow motion or something. Its just that as objects move relative to each other, they will each observe time passing more slowly for the other object from their own perspectives.
It is touching on the concept of the relativity of simultaneity. Two events separated by some non-zero distance that appear to happen at the same time for one observer will appear to happen at different times for another observer moving relative to the first one. At the relative velocities humans are used to, these effects are imperceptibly tiny, but they become noticeable when you start to move at velocities approaching notable fractions of the speed of light.
Arkalius80 I don't think anyone said you experience time slower. You experience (observe) other's clocks moving slower.
HarshColby The original poster said it, and even put the phrase in quotes. Whether he was quoting something someone actually said or not isn't really important. I was addressing the precise statement over which he expressed confusion.
Ahh... A good time to copy & paste what is my most 'humble' opinion, my best post yet:
Okay, so first thing first = time is not constant.
Second thing = speed of light IS constant.
If Bobby here
:)
and I start running towards the right (I would be travelling as fast as I can run = 1 m/s [I'm a long distance runner so don't judge!]) -->
Then the relative speed of the photons to me would be
c - as fast as I can run
= 299,792,458 m/s - 1m/s
= 299,792,457 m/s
But since the speed of light is constant, then the universe (Let's say the universe is conscious) gets all mad and goes: 'Stop breaking the rules!' So what the universe do? It slows down time for me until I'm travelling at 0 m/s.
c - 0 m/s
= 299,792,458 m/s - 0m/s
= 299,792,458 m/s
Universe: Thank goodness! Crisis averted!
Sorry, if you do not get my humour.
A second will still feel like a second, except it will be longer than a second for someone who isn't moving.
It's derived from the fact that light moves at a constant rate, so space and time have to be stretched and squished to make sure light ALWAYS moves at the same rate no matter what.
I find the paradox easier to understand if you look at length dilation instead.
The twin on Earth sees the rocket shrink in the direction of movement, but that makes no difference to the trip time.
The twin on the ship sees the Earth shrink, but also the distance to the turning point shrinks, because Earth and the turning point are both in the same frame of reference. So he gets there faster from his perspective because the distance shrank.
Relating it back to what the clocks show during the journey is more mind-bending. This video _feels_ correct, better than the last 'length dilation' explanation that I read which had the clocks running faster on the return journey.
But I've yet to see an explanation that doesn't amount to needing to do a whole lot more reading.
ua-cam.com/video/5ODGnbkobNg/v-deo.html
This is the best explanation I have seen . Well explained sir, you got it just right!
Thank you so much. No one had ever been able to explain to me how the reciprocity of the relative motions still allows for one of the twins to be older, and you have done it beautifully.
and didnt solve yet. every of that arguments is applicable in opposite direction. Even You can find physicians who are telling using Minkowski, that "each of two observers is seing the other be younger". They just use a thum rule "moving clocks are slower" and silent they are defining the Ertch inertaila frameto be prefered one, contradicting to that relativity principle of Mr.Einstein. Ignoiring own theory.
@@kondrahtiz7370 Yeah wtf
Great video. I must admit, I've never seen this as a paradox. However after watching your video I can see how someone could see it as a paradox.
You've taught me something. Thank you.
Put simply for those who still don't get it:
The Earth twin can confidently claim that they remained in one inertial frame the whole time--it is "straight" (as in straight up the time axis). But if you look at the spacetime diagram from the Earth twin's perspective, the rocket twin's journey is made in two DIFFERENT inertial frames. One for the trip out, one for the trip back. If any object's worldline is not straight in some reference frame, then it CAN'T be made straight in ANY reference frame because the journey objectively does not lie in ONE inertial frame. Thus, if you tried to Lorentz transform into the rocket twin's frame to make it straight, you would see that you can only make straight one leg of the journey OR the other. You can't do one Lorentz transform to fit the entire rocket journey into one straight worldline, even if you "start" with it (which will not make sense mathematically and thus you can't do it graphically), so there is no frame where the rocket twin is stationary for the whole trip. Thus, the perceived symmetry is broken. The rocket twin must be the one who accelerates and in doing so, the time axis rotation/stretch factor flips in such a way as to make the rocket twin younger than the Earth twin by the time he gets back.
I understood the first sentence
To those who don't get it, I will tell you a complicated summary for your complicated brain to understand this complicated paradox.
Interesting explanation, but I don't think you really understand what "simply" means. The video was simpler.
Thank you, I finally got it!
ANGRYpooCHUCKER what if the acceleration never happens? What if the rocket never comes back? Who will be considered younger then?
The question I asked my Physics teacher 8-9 years ago finally got answered!
Thank you for the great work, but you're really fast,making the concepts complicated to grasp
Very well explained. I struggled last year to fully resolve the twin paradox in my physics course too but fortunately I met a great professor who basically just said what you said, except with more maths XD
I recently herd about a branch of mathematics called the Chaos Theory and am reading Chaos by James Gleick and it's hard to understand... Could you make it simple please?
Just thinking Random Hahaha Chaos theory simply? good luck with that!
A common oversimplification (ie wrong but it helps) that works ok is: 1we can't make exact measurements, as that would require infinite precision (which even if atoms and quantum uncertainty didn't complicate things would be impossible anyway). 2 many systems are dependent on initial conditions (like the starting temperature of a reaction, or the starting position and speed of a ball). 3 even more complicated systems have 'feedback loops': if it moves to a position, then what that position is will affect where it moves next.
So very quickly error builds up, and the range of possible outcomes (based on your initial measurements) becomes so wide that predictions become inaccurate
Only video needed. Well done. Best part, I'm gonna steal the math.
this is still hard to understand but so much Simpler the the ted Ed one. Thank you.
yeah but like why do moving things experience slower time?
Something about light must be measured moving at the same speed no matter your frame of reference.
E.g.: Firing a photon while standing still and while on a moving car, both will be measured the same.
For light to travel the same speed even when you are moving, time must slow down, or you will measure the speed of light as less than the speed of light.
DONT ASK ME IM NOT A PHYSICIST IM 14
Since time is like a fourth dimension, moving through space means you have to turn away from the time "direction" ever so slightly. Kinda like if you slowly veer off from a path, you're not going in the path's direction as quickly anymore.
+The Ender Golem pretty damn smart to know this if your only 14 😂😂
they don't experience time slower it's just relative to each perspective.
example, if we both have a watch set to the same time ie 3 pm then I leave earth travelling at the speed of light with my watch on. my watch still moves normally while moving at the speed of light to my perspective. say the journey takes for me 10 minutes, your watch would only say 7 minutes for example. this is due to the fact time is related to how fast you're going relative to your perspective. if I, while travelling at the speed of light look back at you on earth, you would like you are moving slower in time like in slow motion.
You can easily prove that light travels a longer distance within a moving object. Search it up. The model I learnt in my module is a vertical light beam in a train moving horizontally.
"change in velocity"
But what if I do an orbit and remain at a constant velocity for the whole trip?
Then you will not be coming back.
oh and btw, you cannot be in an orbit at constant velocity. Velocity is a vector (speed and direction). Changing the direction changes the velocity, so you can't say that the velocity is constant in an orbit.
But if I reach apoapsis and do not apply any change in velocity how would the "time shift" happen if no deltaV is expended?
You can't stay at constant velocity during an orbit because you are constantly changing direction.
I think the best explanation is to use zentripetal force its formular is F=m×a and this force is always "there" when you turn around e.g. in with the car and due to the fact that then the force is not 0 and the mass is constant you also have to have an accelaration
+falschgedenkt ok the formular is F=m×v^2/r but its easier to see if you use a instead of v^2/r
The solution in one sentence: only one of the twins changed inertial frames from their own POV.
THANK YOU, I'VE BEEN CONFUSED BY THIS PARADOX FOR AT LEAST 3 YEARS UNTIL NOW
I don't understand why this logic doesn't apply equally to the Earth. In the rocket's frame of reference, the Earth was doing the acceleration. Isn't it irrelevant that the rocket had to fire engines? Suppose that acceleration was provided by a different means, such as gravity. In that case I imagine we would need general relativity, but do we *not* need GR when the acceleration is provided by chemical rockets? That would be weird.
It's not the acceleration. It's the frame jumping that occurs as the ship turns around. On the way out, it's in one reference frame, but on the way back it's in a different one. (Note the change in angle of the orange lines, which indicates his reference frame.) You can do the same conversion drawing with the blue lines, but both ways of looking at it will result in the traveling twin being younger.
sheldon is that you?
Note that SR is strictly the theory of two inertial frames. As soon as one person accelerates in any way, it goes into GR territory.
Velocity is relative, but acceleration is absolute. An observer on the rocket will either notice that the ship is accelerating back towards the earth, or (if he adopts an accelerating frame for that moment) say that the earth is falling towards the rocket due to fictitious forces applied to both the earth and the observer. By either calculation, we indeed conclude that there is a difference between the rocket firing engines and heading back towards the earth and the earth "firing engines" and heading towards the rocket.
The only reason you can feel that force is because it acts non-uniformly on your body. You can imagine a force which acts uniformly (such as a gravitational field -- which, of course, requires that we use general relativity to analyze the issue).
I was wondering the same thing, but James and bengski explained it perfectly, thank you!
That... does not seem like a paradox for me.
Most paradoxes are solved, making them not paradoxes anymore.
The first thing written in this video "not exactly a paradox"
Then don't call it a paradox
+Leonidas Pereira en.m.wikipedia.org/wiki/Twin_paradox
That's the paradox.
After 2h, of reading and watching videos. I got it! 😩 Finally!!!
Thank you so much, everyone else just leaves out the acceleration.
Now do the "Bell's spaceship paradox", because people keep getting contraction wrong just as well.
Indeed. If you don't understand how "Bell's spaceship paradox" actually works then you don't really understand the solution to the Twin Paradox.
I'm still not getting one important thing, in the rocket's perspective, isn't erath's speed bring rotated. Everything about this experiment seems relative, how can the result possibly not be?
I'm actually asking and would appreciate a relevant answer
The thing is, while velocity is relative, acceleration is not. If you're sitting in a moving car and close your eyes, you can't tell if the car is moving or stopped, but you can definitely feel when the driver floors the gas or slams the breaks. The person on Earth is not accelerating, but the person in the rocket is.
but then it's not speed or movement, only acceleration (witch you can substitute with gravity)… man, so many time dilation videos got it so wrong
Mt_Xing no one says that the rocket has to accelarate what if it was just passing by with constant velocity and do a big circle to come back..it doesnt have to be accelarating in straight line rhen decelarating just to turn and then back
@@ajvanslevik8592 A circle, big or not, requires acceleration.
the explanation utilises general relativity, but the irrelevance of the measurement frames is a feature of special relativity. You can't use one theory to solve the problems with another. Special relativity on its own produces the paradox, therefore some feature of SR is wrong.
There is a big flaw in the concept of velocity and time dilation. By assuming, that the moving twin will experience less time, than his stationary brother, we break the main rule of relativity - the one, which tells, that if the velocity of a moving frame is constant, it can be treated as a stationary one and there is no way of telling, if it is moving, or not. If the time of travel for the moving twin would be shorter, than expected, then he would be able to learn about his own motion - and according to SR, this shouldn't be possible...
Only one of the twins changes inertial reference frames (by accelerating). Remember that (proper) acceleration isn't relative.
I know it - and this is why I think, that difference in the rate of time flow will appear only during the time of acceleration. Difference between constant velocities can't be responsible for time dilation, no matter, how fast objects will move, as velocity is a relative and not a definitive value...
Relative velocity is the cause of time dilation in special relativity. A scenario that involves a constant speed looping trajectory is more complex to solve than a simple straight out and back trajectory, but the result will be the same (numerically probably different, but the traveling twin will be younger upon his return).
One of Einstein's assumptions in SR is that you cannot tell the difference between the two frames (the other that the speed of light is constant). If you create an asymmetry (for example by accelerating one twin) your explanation is outside the scenario which Einstein carefully (and critically) provides and therefore is no longer a demonstration of SR. Unfortunately the twin paradox breaks SR. Generally you can apply the Lorentz contraction (which Einstein did) in an ad hoc fashion to supply the answer you crave, which perhaps accounts for some of the inertia (:-)) in the physics community to address the issue. Whether time dilation is an ontological ('real'), or measurement effect, there is an effect (time dilation has been measured). It is also crucial to the question of the ether, which motivated Einstein in the first place. New theory needed!
Oh my god ,thanks, I've been staring at my text book like literally .two hours and now I'm finally starting to get the idea what .it's all about ,THANKS
It becomes much easier to understand when you work with a common reference Frame. Either virtual Ether which is common to both. Or the Lightspeedframe which is common to both. Or the Rotation Center between both (similar to Center of gravity).
If I hide which one is the earth and which one is the space ship, and tell you that a separation between them grows quickly, then shrinks, can you tell me which one is younger, and which one is older? Answer that!
I feel like sometimes physicists just answer our questions like if they don't have intellectual merit and just sort of never listen because "we gots your answer, just accept it". I totally don't see anyone answering the fundamental thing that is paradoxical about it. Just a bunch of dancing around untill the paradox falls between the floorboards. I hope this question better communicates the problem I see, and I believe others see.
The one that changes direction can measure (and actually) feels the acceleration when turning. The other stays whole time in one inertial frame.
There is one sometimes confusing factor in how the experiment is usually framed out (like here) - namely that the 'inertial' twin is placed on Earth. Now Earth is of course not an inertial frame in a pure sense - so in a more pure form the 'stay home' twins home floats in free space.
@@EneriGiilaan There is no need to "feel" the acceleration, it can be measured in free fall too.
But the acceleration is made for a portion of the trip, and only during that time time dilate.
@Chike
The framework here is Special Relativity - thus 'floating free' equals to 'inertial frame' which equals to 'no acceleration'.
The time dilation and length contraction result from the Lorentz transformation - transforming coordinates (time and place) of events (at a certain time at a certain place) from one *inertial* frame to another (and vice versa). No acceleration is to be found in the equations. The transformation is symmetric and thus both twins observe the other one's time to go slower. The 'paradox' raises from the result: when they finally meet again their clocks are out of sync. The one that has changed direction (requires acceleration) has aged less. The changing of direction breaks the symmetry and dissolves the paradox.
Please note. One can consider a situation with triplets. One stays. Second travels a certain distance and turns back with a short period of constant acceleration. Third travels twice the distance and then turns back using the *same* amount and duration of acceleration. The time dilation of the third one will be twice the one of the second one.
Very well said, Daniel! But then here comes Eneri with more of the same variants of nonsense that cannot truly answer the question.
@Okebaram E
Perhaps you can be more explicit and tell where my explanation was wrong?
One big problem with these videos trying to explain the physics theories to the common audience is that in order to be palatable they try to avoid the mathematics as much as possible. In the long run this might give the impression that the theories themselves are indeed based on rhetoric and 'verbal' logic and perhaps some pretty diagrams. That is not the case - the rigorous logic provided by mathematics is essential in understanding and discussing of these issues.
That is also the case here. In order to really get a grip of the SR and understand what is happening you need to understand the mathematics behind the theory. The model of SR is strictly mathematical - basically linear algebra in a 4D space with a bit more 'interesting' metrics than the one we are taught in the High School for the 3D Euclidean space. Because of its pure mathematical character we can be sure that the model is internally consistent - there are no real paradoxes. For example the 'twin paradox' solves naturally in all frames we care to consider - and all observers agree what each others clocks show at certain events (like when the twins met at the end).
I think every physicist when student (at least everyone I know - me included) have tried to find a hole in the SR. The real understanding comes only after you have yourself gripped pen and paper and played with different scenarios using the tools provided by the theory and mathematics in general .
That said - the mathematical consistency of a theory does not prove that it is the *right* theory. A physical model can never been *proven* right - on the other hand a single repeatable experiment/observation is enough to *prove* it wrong.
Everything in your video is correct, but it is not the full story. The person accelerating in the spaceship will think that there is a gravitational field throughout the entire universe exactly balancing out the thrust from his rockets causing him to remain standing still, and causing the Earth to accelerate towards him. It is the gravitational time dilation from this perceived gravitational field which is what causes him to think that time on Earth is passing more quickly during the time that his space ship is turning around.
Yes, this is the most important bit of information to solve the twin paradox. Unfortunately, it is omitted in this video and most other videos about this topic. Experiencing acceleration (i.e. experienxing a Newtonian, non-fictitious force, i.e. being for some time in non-inertial conditions) is the only difference between motion of B (spaceship) relative to A (Earth) and motion of A relative to B. It is the only reason why the spacetime diagram describing motion of A relative to B is not legitimate in this context. Otherwise, it would be perfectly identical to the diagram shown here by minutephysics (which describes motion of B relative to A). With that diagram, I would be able to prove, using exactly the same argument used by minutephysics, that at the end of the round-trip, the astronaut (B) will be 2 seconds OLDER than his twin on Earth (A). In short, it would be possible for me and minutephysics to reach opposite conclusions using identical arguments applied to two equivalent thought experiments.
It's not the acceleration that causes the difference, it's the fact that the "moving" twin experiences time in 2 different reference frames while the "stationary" one only experiences time in a single frame. The acceleration is not the relevant part, it's just how he goes from one frame to the other.
@@Paolo_De_Leva yes and this is what I’m trying to understand. The perception of time is both different but the simple fact that once a person exits the womb that’s when their time on earth starts. We understand that we can perceive time in two different ways but what I wanted to know is if the “twin” in space spent more time on her journey, would she actually physically appear older when she arrived back on earth. No one seems to answer that question. Which leads me to believe that the time difference between both trips through time are just an observation from two different perspectives. Time is a earthly measurement and can be distorted outside of our domain. Meaning yes TIME has speed up due to the way we perceive it physical and cosmetic properties of aging will not have been touched because each perspective of time was just simply viewed from a different point of view.
@@b-tothejay.2257 You haven't got this example: it's just that. Not a paradox. Perception is just the same as clock, it is not time, it just counts the vibrations of time for humans to understand, thus this example shows how time itself slows down (besides the space shortening to the 'still' reference point);
It's distortion of spacetime itself close to the speed of light. Utterly counterintuitive, same as how two beams of light, travelling at the speed of light in opposite directions do not exceed the speed of light relative to one another. There are enough of irrefutable evidence, to assert this as certain. Nothing to do with biology or perception of the mind or body.
??Correct? You are fooled like already P; Langevin in AD 1911 and also A.E. in 1905 in being surprised by a "particular consequence".I see u don't know even that he rejected his own arguments in AD 1918 paper (GR/acceleration involved!) and he died in....darkness though he "smelled" sth wrong in it (R.Schlegel's report on the conversation with him)
That really clears it up for me
Very nicely done
what if the twin on the rocket held up a clock and the twin on earth watched it through a telescope, how would the clock appear to move for them?
The rocket twin's clock would look just like expected, it would be ticking more slowly than the clock on Earth.
it would tick slower, but since light travels at a finite speed, you would also see it as it was some time ago (in fact, we always see the past when opening our eyes).
@@korilas4387 Tick slower as in a few seconds behind or at a slower rate?
@@EcPRyZeReal , slower rate.
Lets consider this:
According to rocket man's prespective, he did not changed his reference frame at all, instead earth's man is changing its frame, ..
i.e, rocket did not travelled with respect to earth and came back to earth, instead, earth travelled with respect to rocket and returned to rocket.
So CONCLUSION:
After the trip,
An observer from earth would say that rocket clock was slower, and from observer from rocket would say that earth clock was slower, so the same paradox arises
They both travelled not one.
Yes, but only one of the twins accelerates: the one on the rocket. The rocket's reference frame is not inertial and is therefore not a valid frame from which to apply special relativity. Because the rocket accelerates, the situation is not symmetric, and because special relativity cannot handle acceleration, you must resort to general relativity to resolve the problem. The "paradox" only arises when you fail to apply general relativity and treat the non-inertial reference frame of the rocket as inertial.
ExtravagantPanda
I understand your point,
But here is a point:
How can we say that rocket is the one which accelerates(we can only say this if the observer is from the earth),
From the observer of the rocket, the earth accelerated not its rocket(rocket is stationary from rocket's observer prespective)
So from earth's prespective rocket accelerated, and from rocket's prespective earth accelerated.
If two see it more clearly, imagine two similar particles in an empty space rather than a rocket and the earth.
Acceleration is "absolute:" you don't need to specify what something is accelerating relative to, it is enough to say that "this object is accelerating." We must say that the rocket accelerated, in all reference frames, while the Earth was stationary (of course the Earth is also under acceleration in its orbit around the Sun, the whole solar system's movement through the galaxy, etc., but the rocket is also undergoing those same accelerations so we can ignore that). The reference frame of the rocket is non-inertial. Any time you do physics from a non-inertial frame, you must make modifications to the physical laws to counteract the acceleration of the reference frames. In classical mechanics problems, for instance, you must introduce "fictitious forces" (or equivalently fictitious accelerations) to offset the acceleration of the reference frame from which you are performing measurements. The Earth only appears to accelerate away from the rocket in the rocket's reference frame, but this isn't a real acceleration, only a fictitious one due to the fact the rocket itself is accelerating.
ExtravagantPanda
So your whole point is that both the frames are completely distinguishable, one under acceleration, and one not, here rocket is under acceleration, that is why relativity applies in only one way not both ways, okay, i get that.
But now the question arises how we can know that which frame is accelerating to which frame
For instace consider this experiment:
Imagine 2 particles in an empty space, now somehow the distance between them increasing with varying velocities(i.e 2 particles are going apart with some acceleration),
Now how we can decide which particle is accelerating to which ??
And now how we can relate this experiment with relativity?
Acceleration must be accompanied by a force (Newton's law), so any experiment to determine whether an object is being acted on by some force will do. For example, if you are inside a car (suppose it has no windows) and you don't know whether it is accelerating, you can suspend a mass on string from the roof; if the string deflects at some angle, the car is accelerating. If it just hangs straight down, it is not accelerating. It's the same principle that causes your body to lurch to one side when you take a particularly sharp turn in a car. Now if instead of large objects like cars you want to determine which of two particles are accelerating, you might have to do something more elaborate. It's easy if the particle's happen to be charged though: the accelerating one will radiate energy.
Thank you for helping me understand the answer to the twins paradox😅
This actually makes so much more sense now :DD
The second equation for the Lorentz transformation missed 1/c^2 for the second term in the bracket.
He is using natural units where c=1 and so the equation is correct. Natural units are useful to simply equations and demonstrate properties and relationships as they get rid of annoying constants. Not great for accurate calculations.
V will be in terms of C... So they dont have to bother about c^2
@@garethhanby If physicists instead of setting c = 1 set it to one of the square roots of -1 (say, for example, i), would as many equations be simplified as made more complex, among the equations typically used in physics?
@@b43xoit en.wikipedia.org/wiki/Wick_rotation
@@mbrusyda9437 So, the rotation is useful sometimes, but not always?
So if the reverse acceleration never happened and one of the twins just kept travelling out, they'd both keep thinking that time is going slower for the other one? How does that work?
It's nice to see that there are people that actually think.
And then imagine if they communicated with communication signals sent at light speed. Imagine A says "Hello" when he sees that it is 12 noon at where B is, and his own time is 1pm, but since from B's point of view time is slower where A is, when B says "Hi" in response at 12 noonish, it is 11am where A is. So A would hear the "Hi" at 11 am in response to the "Hello" that he is going to say in one hour at 12 noon but hasn't said yet.
@@okebaram A says Hi where, B hear it where and where is B when it rely A?
Where A see B when the time of it's clock is 1pm and B clock is 12 pm is not where A is.
It is not A who see B clock ticking slow it's his co-observer with a synchronized clock at a distance.
Depending on their speed B may receive it's Hi much later.
If we talking light signals it goes like this ibb.co/0J2HXbR
Notice thaa middle observer who is at equal relative velocity to both of them events occur at the same time simultaneously.
@@nadavdanieli according to the theory, which I am pointing out is flawed, the speed of light is constant regardless of where any person is and what speed they are moving at. This means that A would in fact receive his reply "Hi" without any delay due to his motion or time dilation. What I have described is really a version of something known as the Tachyonic antitelephone paradox
@@okebaram Which theory is flawed?
This was an awesome one
This one has made the most sense so far.
Luckily I don't have to learn all of these since I am not taking pure physics.
Plot twist: I am taking pure mathematics.
oh no. I'm taking my first pure math class and I think this will be my last.
how the fuck did a rocket take 10 seconds to leave earth and return?
Minato Namikaze theoretical science. Aka just saying if you had a starship that could travel at such a rate.
Minato, what the fuck are u doing here, go and defend the village from obito
is this liner?? meaning does the speed of which you move and the time you are moving directly corolate with the time differential between you and the people on earth? or is there more of a curve so to speak... and at what speed would you need to trevel for a year to pass in only a couple days??
I love Paradoxes, such an interesting concept.
*NEXT WEEK ON LIFE NOGGIN* The entire solution to the paradox of the twins
One thing, how do you determine which object is changing in acceleration if the objects movement is relative. Because if you assume the universe moves instead of the ship(if we can make that assumption) then the rotation would be happening over the person on Earth and they'd lose the time the person would have lost in the rocket. Is that interpretation correct?
(I want to clear up for people, you don't feel acceleration as much as you might think. It's mostly Jerk that you feel, your body is constantly accelerating and it's adapted to feel that as normal, the sometimes sickening feeling you get is when you change your acceleration as your body isn't really well suited for changing gravitational environments and that's what the additional acceleration makes it feel like. So while you do feel acceleration, you feel it in the same way you feel how heavy your arm is, higher acceleration just feels like a heavier arm, Jerk feels like your arm is getting slammed down.)
I was wondering about that, I don't know.
Acceleration, unlike motion, isn't relative. A person can't possibly know whether it's moving "absolutely" only relative to something. The same isn't true for acceleration. A person that is accelerating (or decelerating) knows it, without needing a "reference frame", acceleration is analogous to gravity. The twin inside the spaceship would suddenly feel an increase in g-forces as the ship's velocity changed and the ship started travelling earthbound
You can absolutely detect acceleration or gravity, as you can absolutely detect spin. You can't absolutely detect your velocity. If you imagine the twins initially blindfolded in two cars, one of which is parked and the other drives away then back to the same parking spot, they will know which is which because one felt the acceleration.
Rafa Carvalheira Thank you, that's what I wasn't sure of with relativity. I was under the assumption that if motion was relative acceleration was also relative, but this makes more sense if acceleration isn't.
Unfortunately you are wrong. Acceleration is also relative. It is easy to understand because velocity is relative, and acceleration is nothing more than the derivative of relative velocity.
Space shuttles rotating around earth do have acceleration, but astronauts inside won't be able to tell whether it is accelerating.
Another example, consider an indefinitely free falling elevator, which is of course accelerating, but people inside won't be able to tell whether there is acceleration (suppose they can't see outside of elevator).
In all above examples, the people inside will feel like in outer space without any gravity. They literally can't tell the difference, but yes, they do have acceleration if you pick something out of the shuttle or elevator as reference frame.
Or, think about two accelerating rockets in parallel. If each rocket picks something on earth as reference frame, both rockets have acceleration; but if each rocket picks the other rocket as reference frame, they would both have zero acceleration. So, do you still insist acceleration is absolute?
First of all, there is no acceleration in Special Relativity, so we need to resituate the problem so it fits entirely inside Special Relativity. Twin A is in a ship heading back to earth where twin B is waiting for his brother to return. The relative velocity these two frames are moving with respect to each other is some value 0 < v < c, like v = .8c. At time t = 0, an explosion occurs at the midpoint between both twins, and the light reaches each observer at the same time one second later, causing both clocks to start counting from the same moment in time. Since each twin is armed with a telescope in hand, they will each see the clock in their own frame run normally, but the clock in the other twin’s frame will be observed to slow down by the amount dictated by gamma(v) as compared with the passage of time they observe in their own frame. Both twins will insist that the other twin’s time is slowing down relative to their own, the law of algebraic Trichotomy has been violated, and the paradox remains.
Special relativity handles acceleration just fine. It's gravity it doesn't handle.
Those hyperbolic curves always sneak in somewhere to save the day!
Then why does time only dilates for the person in the spaceship?
Actually it occurs for everyone, all the time. The only thing that changes is how severely time dilates. For this kind of time dilation (there are actually two) it is dependent upon an individual's speed relative to the speed of light in a vacuum. The closer you get to that speed, the more time dilates. Thus, as the person in the spaceship is moving closer to the speed of light than the person on earth, time dilates more for them.
All person in the earth moving relative to the spaceship. So earth shouldve experience time dilation too.
Sorry this theory just bring more paradox, adding black matter, black energy, black anything just to justify this theory because of its inconsistency. Stop handicapping this theory with another black this and that, then start accepting that this inconsistent theory is wong.
@Dr Deuteron I am aware, I was referring to the velocity of the individual on a spaceship, not of light.
@Dr Deuteron Relative to the CMB, an individual floating in space, not on a planet, can be "at rest" relative to the speed of light. Put more simply, said individual isn't moving. In this circumstance, far from any massive bodies and with a velocity of zero, the individual is experiencing the minimum possible time dilation. Now, suppose this stationary individual gets on a spaceship and hits the accelerator. Now the spaceship, and by extension the individual, is accelerating, and thus their velocity, relative to the CMB, is increasing. If this continues, the individual's velocity will continue to increase until, assuming an ideal spaceship, it reaches 99.99% the speed of light. Once that happens, the individual within the ship is experiencing the maximum possible time dilation for a entity made of matter in our universe.
@Dr Deuteron I'm sorry, by all means, take over here. Please educate Allison Blown in advanced topology and special relativity in the span of a single comment. I'm sure that will be an enlightening experience for everyone involved.
Who else thought they understood but felt stupid when it ended
My real brain: yeah it does take 8 seconds for the other guy.
My dumb side of brain: No the rocket took 2 seconds to start
Question: If a ball is rotating, two points at different distances from the center experience time dilation due to their difference in acceleration toward the center (if I understand correctly). Does relativity only rely on the two reference frames for the two points? If so, what is the difference in acceleration judged against, since (I think) the two reference frames don't change their observations of each other? Is it a backdrop of immutable space-time or something similar? (Mathematician, not a Physicist)
I feel like this explanation was a bit weaker then your usually ones. This whole rotating time thing is a little under explained (I have seen the video). That being said this is a super hard topic to explain even if your given like thirty minutes, I don't know how you could have explained it better in such a short time. I just think there is going to be a lot of confused people in the comments.
As he mentions, look up the 'Lorentz transformations' if you want to understand what he means by rotating time.
*****
Oh thank you, I already know just giving some feedback.
this is actually the kind of stuff i think of in math class when the teacher is explaining stuff i learned 3 years ago
One of the weirder things I've ever done was tell a physicist (or maybe they weren't, we were talking about physics) that something in orbit is undergoing constant acceleration.
So, what I don't understand is if you locked the point of view to the rocket, the Earth is the thing accelerating to turn around, so it still seems paradoxical to me.
Here's an example: say the rocket launches from earth and burns fuel to stay in the same fixed position relative to the sun, but the Earth flies around and a year later catches up to the rocket, which observer was moving faster?
Here you're adding complications that don't fit within the thought experiment. The Earth orbiting the sun involves gravity, which doesn't exist in special relativity. Special relativity is so named because it deals with the special case of flat spacetime (ie, no gravity). You need general relativity to deal with curved spacetime (gravity).
To answer your question, while it does appear to the twin on the rocket that Earth is accelerating away, the fact is the twin can measure his own acceleration without looking at Earth, because he is experiencing a force from the rocket engines. Earth doesn't experience a force like this and wouldn't measure any acceleration if not looking at the ship. Acceleration isn't relative the way speed is, you can measure it without referencing anything external to your frame of reference.
Nice one! Thanks. One of the best youtube replies I've ever gotten :)
Hi, reading your answer over and over still only confirms to me that the explanation lies only in the general relativity, not in the special relativity, the symmetry of the paradox is broken by the acceleration. But the graph does not cover that!!! The graph is drawn for an observer attached to the non-accelerating twin. If you draw the graph for an observer attached to the accelerating twin, you get exactly the same drawing (well, ok, mirrored right-to-left). Only now it is non-inertial frame of reference (which is, as you described, the solution to the paradox, this is THE sought asymmetry breaking the seeming symmetry from which the paradox arose). But this you don't see in the graph!!! Or are graphs for non-inertial observers forbidden and that's it? What you explained in words is NOT present in the graph, the graph only analyses "growing and shrinking distance" and can pinpoint that something important happens when the rate-of-position-change changes but the graph does not make an absolute difference between the two twins, which of them should be made responsible for this change. The difference is made by our initial choice whose frame of reference to use. Let's better think of two twins initially floating next to each eather in the space, no Earth, so that we have no pre-bias in the mind regarding which frame of reference is the "correct one". Then, how can this method give the correct answer??? On the other hand, I don't think I am smarter than the minutephysics guy (awesome channel), so if you can see where I go wrong, I'd appreciate your comments.
On a Minkowski spacetime graph, the worldline for something is only straight when it is inertial. Thus there is no Miknowski diagram that would represent the space twin's full journey as a single straight line.
Thank you. I've been thinking about the proof in the meantime and I slowly start to realize that my understanding of the acceleration itself was rather superficial. Thank you for sharing another piece of the mosaic.