minutephysics - 2016-08-26
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: http://ow.ly/RCty302dIHU) for supporting MinutePhysics ***** Thanks to everyone who supports MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon supporters here: http://www.minutephysics.com/supporters.html 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, http://www.soundcloud.com/drschroeder REFERENCES Muon lifetime and time dilation/relativity: http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html#c2 MinutePhysics video about Time Rotations & Einstein: https://www.youtube.com/watch?v=ajhFNcUTJI0 Experimental test of time dilation using doppler shift of light: https://en.m.wikipedia.org/wiki/Ives–Stilwell_experiment Lorentz Transformations: https://en.m.wikipedia.org/wiki/Lorentz_transformation Relativity of Simultaneity: https://en.wikipedia.org/wiki/Relativity_of_simultaneity Paper on twin paradox under constant acceleration: https://arxiv.org/pdf/physics/0604025v3.pdf Taking Cesium atomic clocks aboard airplanes: https://en.wikipedia.org/wiki/Hafele–Keating_experiment MinutePhysics is on Google+ - http://bit.ly/qzEwc6 And facebook - http://facebook.com/minutephysics And twitter - @minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich
You lost me the second you said something about moving affecting time speed or something... basically lost me 10 seconds in.
@Okebaram E https://en.wikipedia.org/wiki/Modern_searches_for_Lorentz_violation
You might want to take a look at this wikipedia article. It seems like scientists are well aware of the fact that it is important to have experimental evidence for a constant / isotrophic speed of light.
In addition, relativistic effects are already well documented in scientific literature as well. Time dilation has been well confirmed, as also explained at 2:23 in this video.
try thinking faster, as you approach the speed of light you gain a near perfect grasp of all knowledge. of course once you stop moving basically your a chimp again, but hey.
Well, 10 seconds in from your frame of reference.😂
Ibrahim Hassan If you are on a train moving at 50kph and you throw a ball with 10 kph, for a stationary observer the ball would be moving at 60 kph, while for you the ball would be moving with only 10 kph ( since you are moving at 50 kph because you are in the train ). However, if you turn a flash light on, you would expect it to move at 360 000 kph to you and 360 050 kph to the stationary observer but actually it moves at 360 000 kph for both
General rule of relativity my dood
"If you can't explain it simple enough, you don't understand it well." - Einstein
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.
@ANGRYpooCHUCKER I believe I understand the idea for what the Theory of Everything is, but I'm likely wrong. I basically understand that Quantum Mechanics and Relativity don't work together, and calculating answers that require both such as black hole (what, mass?) stuff gives nonsensical answers such as infinity. We just need to find where we are wrong in either of the theories or both, that simple explanation, which should just be at the root of the universe's existence. Again, I'm not saying there's any chance it's correct, I haven't done any math, but certain aspects of it could perhaps lead to the answer. I'll tell you once I read your reply.
@Al the Alligator You just explained the same thing that most people who are working on the problem are looking for.
We can use quantum mechanics and general relativity together just fine in most situations. But on very small or very energetic scales, such as at the singularity of a black hole, we need to be able to discretize or break up into pieces the metric of spacetime in a way similar to the way we do quantum fields. Otherwise, we do not have the right math to probe any further. We just end up with a bunch of non-renormalizable infinities, meaning we can't do anything to get rid of them in the math. There have been attempts to quantize spacetime this way, but thus far nobody is really satisfied with them and they are not complete pictures.
A theory which mathematically united spacetime with quantum fields, either by quantizing spacetime or some other idea, would as far as we know be a theory of everything: one single (albeit long and/or complicated) equation which describes all fundamental forces, particles and gravitational/spacetime phenomena.
Me too
@Alex Hsieh This video perfectly explains the problem and solution correctly in a concise way. The first alternative video you mention gives the description, but in a much more confused manner. The second video (Fermilab) is incomplete. It gives the same solution, but does not state WHY it is the travelling twin that needs to change perspective, and not the twin that is stationary. If you ignore the acceleration like Fermilab does, then the situation is completely symmetric, and therefore it does not explain the paradox.
par·a·dox
/ˈperəˌdäks/
Learn to pronounce
noun
a seemingly absurd or self-contradictory statement or proposition that when investigated or explained may prove to be well founded or true.
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.
So bad
So, imagine the following test concerning time dilation.
1. Two synchronized atomic clocks, one on earth, the other one in a vehicle going to the moon with astronauts. The astronauts report their clock status to earth.
2. Four measuring points, comparing the clocks:
A. Before the trip starts (showing the same time)
B. After the full acceleration, starting cruising
in space to the moon.
C. Before launching the brakes (before
decelerating) when coming close to the moon.
D. After landing on the moon.
I am 99,9% convinced that at point B there will be a significant time difference between the clocks. Between point B and C basically nothing happens (no time dilation). After point D, another significant time difference has occured.
In other words, I would eat my hat if time dilation is not always caused by a force (acceleration, deceleration, being close to massive matter) acting on matter, and never can happen when just cruising in "empty" space. Muons, yes, they live longer because of the deceleration caused by the friction in the earth atmosphere (which has the same time dilation effect as acceleration).
The spacetime concept works as a purely mathematical framework, but is like focusing on a shadow in a room with a physical moving object….
Time dilation is a physical phenomenon which involves a force field that slows down the particles of a system. When particles interactions take place with lower frequency, time is effectively slowed down. The mechanics of this is unknown. Time emerges from this effect, it is not "floating around" in space as a dimension.
Existence itself, and change in that which exists, are the only fundamental properties in the universe, everything else has emerged, emerges continuously, or has been defined into existence by humans.
Changes never began (a state of absolutely nothing isn’t even a state, which must exist with something “in it”) and are on their way towards infinity (but never reaching it).
One can not use Special relativity to solve this, Einstein himself didn't do or recommend that when dealing with the problem.
no such thing as understax or not or feel samx or stupix, cpu, think, do any nmw and any be perfx
i took the time to create a twin and i double check with him when he gets back. he can be annoying with the same old "hang on a minute" joke though.
Hey check out the special relativity series by minutephysics and then re-watch this video I'm sure you'll get it
im still having trouble with, "moving things experience time slower". how? why?
The closer you are to the speed of light, the closer you are to the speed of time. A moving object is closer to the speed of light (time) than an object that's not.
@AwesomepianoTURTLES its is time for a light or two bodies . one body on earth and another traveling in space for 10 years n come back how will time different for them .
The universe says so is the short answer.
Relativitätstheorie
it's all to do with bus timetables, it takes longer to go out and come home by bus than to stay at home, surely anyone can understand that.
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.
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).
Who gives scientific facts a thumbs-down? There's over 400 of them right now. What kind of mind watches a time dilatation video just to give it a negative rating?
@Adam Jensen "It's my thread." Look at you getting a power trip off of this youtube comment.
@Ivin3690 Nope just tired of the bullshit. Now I'm tired of this thread
The thumbs down is because the explanation is idiotic. The paradox occurs long before the turn around trip, and this joker is dismissing that observation as irrelevant completely. Plus, a turn around point would introduce acceleration into the discussion which has absolutely nothing to do with Special Relativity that is only supposed to be concerned with relative velocities. The only proper way to treat this problem is to ensure it only involves relative velocities, else you are not really dealing with the paradox inherent in Special Relativity.
Not everyone is in agreement with what thumbs up/down means. Some people may simply want to remove it from their suggested feed on their personal entertainment account. Others may simply not understand it or may even disagree with certain aspects of it, which is perfectly fine. Don't think too much about it...
Flat earthers and bots
i can tell you want thing. i dont understand
cuz its pseudoscience?
Whatcha mean by SR being pseudoscience? The fact that the results can be reproduced under many different conditions by multiple people says that SR holds true. Ancient astronauts, and astrology are considered pseudoscience.
@Rein Francks no it isn't
everyone want thing, but not everyone can have thing.
You dont understand because relativity theory is bullshit. Michelson and Morley have proven that earth is not moving. So they invented the special relativity theory to explain how something moves that is not moving. Thatswhy this theory makes no sense because it explanes something that is not true. Reserach Michelson and Morley Experiment.
+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?
We assume that we are measuring things in an inertial frame. In that inertial frame, the Earth twin is stationary and the rocket twin is moving. Boom. Done.
Now, the rocket twin can also claim to be the stationary one (as any observer in their own frame can), but the rocket twin's journey is NOT composed of a singular inertial frame. Remember, in our inertial frame, we see the rocket twin with two different velocities at two different parts of the journey. Therefore, the rocket twin is NOT in an inertial frame. Relativity doesn't apply the same way.
The paradox starts by making an initial assumption: the Earth twin is in an inertial frame which is stationary relative to the rocket twin. In other words, we are first viewing the situation from the perspective of the Earth twin, who we assume is in an inertial frame.
Therefore, we have already resolved the paradox. If you are in an inertial frame for the whole journey, and you see the rocket twin change velocities, you know that the rocket twin is NOT in an inertial frame. Thus, the symmetries of relativity do no apply in the same way. The rocket twin will objectively be younger.
@Ervin Arnold your answer doesnt make sense either. The one on the rocket can also claim that the universe itself is accelerating towards him (e.g. approaching him faster) while himself remains still in the rocket.
@Corey Bray acceleration is relative. Acceleration is literally the first derivative of speed, in other words any change in your speed IS acceleration. The earth twin can claim the rocket accelerates (his speed changes), but the rocket twin may AS WELL the universe itself around him changed its speed.
Christopher Ramsey don't mean to be rude or anything but y'all are a bunch of nerds
Not that there's anything wrong with that
All the way through I understood what he was saying, but then when it was done I didn't know what I'd understood...
"You guessed it" you overestimate my intelligence
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’.”
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.
@ANGRYpooCHUCKER I don't remember if I made another reply here which is no longer available, or if my cellphone didn't send it, or... I replied in a different video but yeah, after watching again FemiLab's video I understood there was no need for considering acceleration as the reason of the time gap, jumping from one of the rocket twin's frame of reference to the other was enough and it was a matter of the transformation of the frame of reference (thus acceleration can be put aside). This is better explained in FermiLab's video.
Yeah but what if rocket dude just keeps on going? What then?
Who says that he has to come back! No frame switch = no time dilation or what...see the problem?
@Yves Nyfeler Ph.D. If rocket dude keeps on going, then each twin will see the other as aging slower. No problem there, that's just relativity. Then, when you ask "who is actually older" during that version of the journey, the question only makes sense when you specify a frame.
@John Mactavish It actually depends. For each of them, they see the other person younger than them. You can see minute physics twin paradox primer
So, the GPS sattelites need to have their clocks constantly adjusted (or the ones on the ground, tracking them).
But if they came back to earth, would they suddenly be off again by the amount of time we've adjusted for them all along? 🤔 And it would all somehow catch up in the moment of return?
The thing I dont get is why you claim that "when things move faster, their time is slower" like how does that work
So, speed is relative, but acceleration isn't?
Yes - only during the time of acceleration/deceleration it is possible to tell, which frame is changing it's velocity. Also only while accelerating, we can experience the physical effects of lenght contraction - if strong enough, g-force can make you flat, like a pancake. It makes me wonder, if time dilation is not caused by the acceleration only - and not by the velocity differential, as it is being said. How can we connect time flow with the velocity of a frame, if velocity is RELATIVE and NOT A DEFINITIVE value? If I would be right, it would mean, that time starts to flow at different rate, only during the time of acceleration - as only at this time, the symmetry of relativity gets broken and a measurable g-force is experienced only inside the accelerating frame ...
Relativity is of inertial frames of reference either one of the observers is in constant motion or is stationary. not accelerating
@Alex DeLong I agree with you. IMO the concept of relativity is interpreted improperly. I think the real explanation is that space is not nothing. Let's just call it some medium through which light travels at the speed of 300k kms/sec (let's call it C). Now if the speed of light in the space when you are not moving wrt the space (the medium) is C but when you are moving wrt this medium (the space), speed of light wrt the space is same (C) but because all the processes in your frame of reference are dependent on the transfer of electric and magnetic fields which happens at this specific speed C, all the processes in your frame of reference will slow down proportionately. This way your time actually slows down. This way we can explan the twin paradox without any paradox. i.e. because person B is travelling wrt the space, the medium through which the speed of light is fixed and all the processes that happen depend on the speed of light, all those processes in the frame of reference of person B slow down. The same is not true with person A who is stationary wrt the space and hence all the processes (and thus his time) are happening at the highest speed and hence person A ages faster while person B ages slower.
Similarly, if we take the example of our solar system, who is revolving around whom? We intuitively know that all the planets are revolving around the sun and that is infact true. Heavier objects accelerate less in space that the lighter ones. If everything were relative, then and there's no fixed reference then why would smaller bodies revolve around heavier ones. The medium theory fits perfectly here IMO.
Also, we have now detected waves of warping of space itself when two black holes collide. Waving is a property of a medium. I dont know why people are not bringing back the concept of aether? Cause I think that is the most sensible explanation.
What michaleson and morley missed in their experiment that, if you take a sound wave or any other wave in a moving medium, you can measure the difference of speed of the waves wrt you. but what if every process in your frame of reference, depended on that relative speed between you and the wave? If the relative speed of the wave wrt you also slows down all the processes in you and your reference frame then you would not be able to measure the relative speed of the wave wrt you. Which is what happens with the light. Because everything depends on this conversion of electric field into magnetic and back at speed C in space, if you are moving wrt space, you would still measure the speed of light C. I know I am writting very poorly here as I am just writting my mind here without properly preparing a write-up but hope someone is understanding what I mean.
IMO, space is the aether that we once denied.
Mt_Xing wrong, no such hting as wx poorlyx or understand or not, cepux etc, say, think any no matter what and any s ok
Kind of.
We assume at the start of the Twins Paradox that the Earth twin is sitting in their own inertial frame for the duration of the journey. In other words, if you are an external observer watching the entire thing, and YOU are in an inertial frame, and you see the Earth twin as stationary the whole time, then you know the Earth twin is also in an inertial frame.
Thus, because the rocket twin changes velocities as measured in your frame, you know that the rocket twin is NOT in an inertial frame, so the usual symmetries of relativity still apply.
However, relative acceleration is still a thing. If we had not specified the Earth twin to be in an inertial frame the whole time, then without more information it would be impossible to tell which twin is accelerating and which isn't, or if both twins are accelerating but at different rates.
Luckily I don't have to learn all of these since I am not taking pure physics.
Plot twist: I am taking pure mathematics.
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.
"Moving things experience time more slowly" "Moving things experience time more slowly" "Moving things experience time more slowly"....the more you say it the more you believe it, its not an assumption its the law.
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
@Gareth H 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?
I can't understand what he's saying..he's talking too fast
Apps 2000 But wouldn’t changing the video speed affect time somehow?
Thumbs up if you didn't understand and never will.
The faster you go relative to the speed of light, the more someone looking at you will think you're traveling in slow motion.
you're really good at explaining these things. thanks for uploading!
NEXT WEEK ON LIFE NOGGIN The entire solution to the paradox of the twins
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.
1:26 THIS IS THE POWER OF KING CRIMSON
I thought this was obvious? Maybe if we go fast enough we can go to the future :0
We are falling through time into the future.
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
Then why does time only dilates for the person in the spaceship?
@Dr Deuteron I am aware, I was referring to the velocity of the individual on a spaceship, not of light.
@Asher Flanagan then I don't understand "it is dependent upon an individual's speed relative to the speed of light in a vacuum." since that is the same for all inertial observers.
@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.
@Asher Flanagan we're talking special relativity, why bring in the the CMB and the not special relativity FLRW metric to confuse things? In that metric, any 2 distinct positions that are at rest w.r.t to the CMB (or Hubble flow, take your pick) will be moving relative to each other. In SR there is simply no such thing a single observer moving.
@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.
OH MY GOODNESS! THANK YOU!
OMG... I clicked this video by mistake 😂..
The first satisfying answer I find for this paradox !! Thanks
3:01 is hast to be delta x divided by v not multiplied
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.
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?
Quite possibly, though this will also apply if the sun wasn't there. We could imagine it to take place in deep intergalactic space.
We could also accelerate a rocket into a reverse orbit with Earth so that it orbits the sun without accelerating, treating itself as still and the sun and Earth as moving. If we start the experiment when the rocket is already in orbit it will feel no acceleration from the start to when Earth 'comes back'.
@Gareth Dean it is not gravitational time dilation. The turn around takes zero seconds in both coordinate systems, moreover: it is *reversible*, just by turning around again. Not only is it not time dilation, it is not even the passage of time. It's entirely a coordinate effect.
@Dr Deuteron Interesting. I've certainly heard a solid enough explanation using acceleration as a turnaround. How does the co-ordinate effect work? Can you link to a more through explanation?
@Gareth Dean "now" depends on your motion, and turning around makes now on Earth jump to the future:
https://en.wikipedia.org/wiki/Rietdijk–Putnam_argument
when spaceman turns around, Earth twin is instantly older, even though no one can see it happen. It's t_earth = t_space +/- distance * speed/c**2, with +/- speed being the turn around.
@Gareth Dean for me, the twin paradox is resolved by the Andromeda paradox, and that paradox is just baffling: there is no meaning to time ordering outside the light cone. For any future event outside the cone (say Andromeda blowing up in 2 million years), there are frames on earth where it has already happened.
Moreover: right now, at the Andromeda Galaxy, it is the year 4519 on Earth, and if an alien there took off at 0.2c in the opposite direction, it would be 481 BC.
We just watched one of your videos in my university lecture, so glad you're making these videos!
All of this for 10 seconds 😂 😂
Sometimes you talk so fast I need to re-watch the whole thing a couple of times to fully get it
This actually makes so much more sense now :DD
i recently learned this in physics so i understand :)
Too complicated and hard to visualize, i get lost 10 seconds into the video. can you be more like vsauce or something
This is the main idea of general theory of relativity. right?
Well he really didn't discuss any principles that are part of general relativity. The paradox can be resolved using such principles, but he didn't go that route here, probably for simplicity's sake.
Kim: This is the main idea of general theory of relativity. right?
No! The Twin Paradox is ultimately a problem for Special Relativity. The problem gets kicked into General Relativity when folks toss in the acceleration step in the turn around trip which really does nothing to resolve the paradox in Special Relativity where it is most dangerous to Relativity.
The theory of General Relativity has its main ideas rooted in a theory of relativistic gravity. In General Relativity GR, Einstein wanted to show that gravity was not as Newton explained it, an attractive force between two massive objects, but rather, in GR, gravity is described rather as a warping of the fabric of space/time around a massive object creating a gravity well that other objects fall into. Of course, this would make gravity a fictional force, and since no real force of gravity is involved, it calls into question why something in space that is at rest along a geodesic of this gravity well would magically decide to start falling further and further into the well in question. Without a force to give such a body at rest a motivation to move in one direction or another, the object at rest should simply remain at rest. All the warping of space/time would appear to accomplish is to change the direction of objects already in motion which move along the curvature in space time. But, to give a physical explanation for why something at rest along a geodesic of a gravity well magically starts accelerating with a given direction deeper into the gravity well, and not in some other direction, is kind of nebulous in GR. It is not like there is any imposed orientation of up or down in space. So, without a motivating force to impose direction on objects at rest along a geodesic, are we supposed to believe that there is some magic space/time grease or something that makes space/time slippery perhaps? Well, there is no evidence of that either. And if there were, without a motivating force, which direction would the object at rest slip and slide in and why would it choose that direction becomes the persisting question for me that makes me tend to think that General Relativity has serious problems too.
I can imagine this channel being “Vsauce 4”
Wow, thanks man, I actually had this question some days ago. I was thinking what does the guy in spaceship see, if they continuously look at each other's clock.
The guy in the spaceship would look at the clock on earth and be like: Wait wha... Is it just me or is that clock moving faster then usual?
It's amazing, although it's hard to imagine the dark zone exist.
(It's easy to understand while following your tutorial, but hard to reproduce it in my own)
still Thanks a lot <3
Finally a good explanation of this on youtube, all others have flaws! thanks!
I've always struggled with this paradox and this video and the primer finally made me understand what was going on!
THANK YOU... finally I understood this, that's what I've been looking for, 3:33 minutes and it's already clear
Great! Best explanation I've seen :)
Adam Cushnahan - 2016-08-28
Yeahhhh.... No. I don't get it
douchebag patrol - 2018-11-30
lol ur a stupid cunt...like me :D
Lilou ou - 2019-01-04
ahah awesome!
Wizard Koer - 2019-07-30
The distance that needs to be traveled is defined by Twin A (Earth twin). Since Twin B (travelling twin) is wizzing past Twin A, the distance that needs to be traveled is shorter for Twin B than Twin A hence Twin B spends less time than Twin A.
DANG JOS - 2019-12-21
@Paul Garcia Pretty sure you're just making stuff up that sounds smart
maalls maalls - 2020-02-25
I wonder how minute physics feels about having this as top comment.