Did you know that you could

be older than your twin? Like, years older? According to Einstein’s

theory of special relativity, it’s possible, because time

can tick faster or slower, depending on how you’re moving. Wha? Yeah. We’ll get back to that. But first, we’re going to learn

all of special relativity. Don’t worry, there are

only two postulates. One is that the

laws of physics are the same for everyone’s

perspective, or frame of reference, while

in uniform motion. So that means that

on a plane cruising at 800 kilometers per

hour, an object you drop will fall straight down,

just as it would if you’re stationary on the runway. Same physics in

those two frames. Otherwise, plane rides

would get real weird. The crazy implication

of this postulate is that there’s

no experiment you could do to tell that

you’re moving, even at 800 kilometers per hour– even at

a million kilometers per hour– because you can only tell you’re

moving relative to something else, like the clouds

outside your window. The second postulate is that

the vacuum speed of light is the same for all observers–

300,000 kilometers per second. Let’s just pause

on that for a sec. Do you know how freaky this is? It means that if you’re flying

toward me in a spaceship going close to the speed of light

and you shine a laser at me, you’ll still measure

that light to be going at 300,000 kilometers

per second, and I’ll measure the light

to be going at 300,000 kilometers per second as well. So those are the

only two postulates of special relativity. The speed of light

is a constant, and the laws of

physics are the same in every inertial

reference frame, “inertial” meaning not moving,

or moving at constant velocity. Basically, you’re

not accelerating. And when you do accelerate, like

when you experience turbulence, or during takeoff when you’re

pushed back into your seat, you can tell you’re moving, and

special relativity no longer applies. So it’s from just

these two postulates that we derive an

entire physical theory and get crazy things like

length contraction and time dilation, and other weird

quirks of physics that are real. One such quirk is that time

can tick at different rates depending on how you’re moving. We call this time dilation. It’s weird, but it’s real. Why does it happen? Consider two frames. One is you stationary on Earth,

and one is your twin zooming by in a rocket. You have identical clocks. Let’s look at yours first. Each time light makes

round trip in your clock, you count by one. Your twin will measure the

same rate on her own clock. Now, things get weird

when you watch her clock. Because of her

sideways motion, you see that her light has to travel

a longer distance for one tick. And since the speed of light

is the same for all observers, her round trip ticks

must take more time. So time actually ticks

slower on her moving rocket according to you,

stationary on Earth. And this is a real phenomenon–

it’s not some weird mind trick. We don’t usually

notice this, though, because time dilation

is quite insignificant until you’re moving close

to the speed of light. So now, from your twin’s

perspective, you are moving. Therefore, your clock

must be running slower according to your twin. And because the

laws of physics are the same in both of these

frames, yours and hers, each frame is equally correct

in saying the other’s clock is running slower. This is where the

paradox starts. Imagine you and your

twin start off on Earth. You stay here, but

your twin zooms off in a spaceship at half

the speed of light, turns around, and comes back. The whole trip takes

30 years, but you see your twin’s clock tick slower. So due to time dilation

during the journey, she only aged 26 years,

four years less than you. Now, here’s the

crux of the problem. From your twin’s perspective,

she was stationary, and you on Earth moved

away and came back. You’re the one moving at

half the speed of light, so your twin should see

your clock going slower and should think you

are only 26 years older by the end of the trip. So yeah, that’s not possible. When your twin gets back, she’s

either younger or she’s older. She can be in a

superposition of both. This isn’t quantum. So how do we solve this paradox? Well, the answer

lies in the details. When your twin turns around,

she has to accelerate, which means she’s no longer

in an inertial reference frame while she accelerates, and so

special relativity no longer applies to her. It’s not as simple

as saying your twin sees you make round

trip, and you see your twin make a round trip. It’s not a symmetric

problem like that, because when your

twin accelerates, we can tell the difference

between the physics that might happen in those two frames. She will feel the acceleration

during the turn around, and you will not. So when she gets back, she will

agree with you that you are 30 and she is 26. One last question. What’s happening to the

clocks during the period of acceleration? We still get time

dilation, but we have to use a

different set of rules from the general relativity. General relativity

states that clocks run slower in accelerated

reference frames. So while your twin is turning

around, her clock runs slower, and she sees the same thing. She sees your clock

running faster than hers, so you’re aging quicker. It’s during this

period of acceleration that you become the older twin. Now, this phenomenon of time

dilation in an accelerated reference frame is

related to time dilation in a gravitational field. General relativity

says that clocks run slower in

gravitational fields, as you may have seen occur

in the movie “Interstellar.” You can get time dilation

and other strange things occurring during

different forms of motion. Special relativity

and the twin paradox are just the tip of the iceberg. [MUSIC PLAYING]

What happens when the one in ship travels in circular path in inertial gram all the time

T ~1/(g) sqroot

Thats why t decreases when g increases time slow down nice video

Einstein time dilation theorie is wrong.

Two problems with this explanation: first, if the GR is the only cause of time dilation why you still say the twin in the spaceship agrees she aged only 26 as opposed to 30 on earth? The explanation should be on GR effect only not the SR. Second, the twin on Earth is in constant gravitational acceleration the Earth while the one on spaceship is mostly in gravity-free space and hence her clock should slow down too. see? Not good!

So how do we solve the twin paradox if the universe is spherical so no need to do a U-turn to come back?

Hi Dianna! I love your videos, but this time I think it seems that Don from Fermilab doesn't agree with you about acceleration. Check his video here https://youtu.be/GgvajuvSpF4

The special theory of relativity can't be correct because it results in paradoxes. Let's say there are two spaceships passing each other at a high rate of speed. At the moment the tail of one ship reaches the nose of the other ship, the nose has both passed and not passed the tail of the other ship. For example…

T——————–N

<—– N———-T

T———-N —–>

N——————–T

Depending upon which frame of reference you choose as being at rest the nose of one spaceship has either passed or not passed the tail of the other spaceship.

Please add the initial acceleration and the final deceleration, so the twins can reunite and be together, but at different age.

4:00 Nope. Acceleration is NOT what 'solves' the 'paradox.' Sorry, Physics Girl. That is succinctly demonstrated in a simple thought experiment presented by Dr. Lincoln — interested? View his video on the Fermilab channel.

But what if the twin had not tok the U turn and just kept moving there ? Will he then be older(at that moment) then his twin on earth(as they are relatively in inertial frame of refrence)?

Your a blonde. Dont tell us you really understand what your taking about. A brunette would. No more blonds. Please.

It's not about acceleration

It's about changing frames even if all of the frames are inertial ones

Yureka yureka finely my brain is under controled🤣

It is incorrect (or at the very least misleading) to say that we need general relativity to handle accelerating bodies. You only need general relativity to deal with gravitational fields, i.e. when the spacetime is curved. Special relativity is fully equipped to handle accelerations, as long as the spacetime is flat.

Thats ridiculous, time isn’t moving faster or slower, only the clock is; at which point it becomes an inaccurate tool of measurement. That’s like sticking your finger in a clock and spinning the hands really fast saying that time is literally moving faster. If two people play this video at the same time one moving at the speed of light the other not moving it at all then stop when it’s done they both will finish the video at the same time.

If a person moves the speed of light for 3 seconds and i start a timer stationary for 3 seconds both clocks will be the same at the end.

I wonder if time dilation is just an appearance, or if it's actually affecting someone. If a moving person has a clock and I'm watching them move, their clock "looks" slower to me since the light takes longer to get to me. But, if they all of a sudden stopped, and come back to me, wouldn't the clock "catch up" so to speak and it turns out that it all balanced out? From the moving persons point of view, they obviously didn't slow down or speed up, and from the stationary persons point of view, they are also in a normal state of time. I don't understand how the dilation isn't just a visual appearance. The clocks appear slower, but does the human body actually somehow slow down?

Whoever crawled out of the hole first, is the younger one, as she has crawled faster than the one behind. Weird, it is like saying your younger sister is older than you. Confused?

Btw…..that girl is a damn beauty…..did she come from Mars??? Where do they reside…😍😍

also if u sit next to a black hole your time will run much slower that your earth twin as well.

If we are considering the two twins, one moving and the other stationery on earth. The one on earth can be considered moving or seem to move from the spaceship. Two possible ways arise, the one on earth would seem to be aging slower than the one on the spaceship.. or the one on spaceship would seem to age slower w.r.t the one on earth.

nice video but acceleration is the wrong answer – it has to do with reference frames which don't rely on acceleration. the travelling twin sees two reference frames while the homebound twin sees only 1. when you pass it through the Lorentz transforms it makes sense. You should update this video as it is clearly giving wrong info.

Well actually they’re probably both the same age if they were conceived at the same time ! 🤗

Einstein was a lunatic with no relatives ! 🤔😂😂😂

This explanation is what I keep getting and IMHO, this is complete BS (no offence intended but I am getting tired of this faulty argument repeated over and over again).

1) "If I am accelerating, I can tell I am moving.. and the relativity no longer applies.. bla bla .. " My question is: "Accelerating" wrt what? If all the motion is only a relative thing and depends on the observer, then my acceleration or lack of it should also be wrt some observer. which means I should be acceleting at different rates and in different directions wrt different observers and then which one observer's measured acceleration will I feel?

2) If the twin paradox depended upon acceleration then the length of the trip where the speed of the travelling twin was constant should not affect how many years she is younger than the twin on earth. Only the deceleration and acceleration of the travelling twin should affect how many years of difference that will be created. Because, when the travelling twin was moving at a constant speed (0.5c) wrt the other twin, they both saw each other's clocks ticking slower by exactly same amount. Why should 30 years of travel with constant speed matter?

Can someone genuinely answer these two questions?

None. There is a missunderstanding on this twin paradox. People will understand this in future.

The 9 paradoxes of physics by Jim Khalili brought me here

FACT, Planet X is 5 light years away.

FACT, you chart a course there traveling at half the speed of light.

FACT, Traveling at half the speed of light you figure it’ll take you 10 years to get to Planet X and 10 years to get back to Earth traveling at the same speed.

FACT,Simple!

Opinion, You get back to earth and you have aged less than someone on earth, per Time Dilation?

QUESTION, So, how fast DID you go? If you aged less than someone on earth, you were NOT gone for ten years. You did NOT travel at half the speed of light and go a distance of 10 light years.

If time dilation exist you can NEVER calculate how long a course will take to travel while traveling at any given speed (unrealistically high speeds)

this explanation makes no sense to me. let's simply the experiment. the rocket is already moving at its cruising speed when it passes the earth observer. we stop the experiment before the rocket decelerates the first time. Now we will still have an age difference but it cannot have been by caused by changing speeds. so ….?

Too bad one of the postulates is wrong!

If one shines a laser beam ahead of a spacecraft moving forward at 0.6 x the velocity of the light, the velocity of the front of the beam will only progress at 0.6 x the velocity of light relative to the surrounding cosmos because that is a natural limit for the motion of photons. But, if there is some way of measuring the beam relative to the spacecraft as it leaves the laser, it will only be moving forward at 0.4 times the velocity of light. It will, however, experience a large doppler shift in its frequence toward a higher frequency due to the motion of the spacecraft. Also, a spacecraft approaching the front of the lengthening laser beam at 0.6 x the velocity of light will note that the incoming beam is moving at 1.6 times the normal velocity of the light's photons due to the motion of the second spacecraft. I think this will eventually be demonstrated when we finally can achieve high velocities for light sources and can directly measure the velocity of laser beams extending from them in different directions.

To "explain" time dilation they like to use that "clock" made by a two mirrors reflecting a burst of light back and forth between them. Then they tell you that the clock slows down as the motion of the spacecraft carrying if increases toward light velocity. Actually, the forward motion of the spacecraft has no effect on the time it would take a real burst of light to travel between the mirrors. There is no change in the rate of time aboard a spacecraft approahing light velocity. However, the

motionof matter, right down to the subatomic level, does slow down, but this effect can be explained as due to the changes in the velocity of light photons due to the motion of the spacecraft.Well your explanation is actually wrong

The cells in the twins body are still running at the same rate…so yeah…none of this matters. "Time" is not changing pace.

I paused the video multiple times to think over few things to understand and I'm still lagging.

In SRT, two clocks appear equally slow due to the same delay of light at C across the same distance to measure them. Just reciprocity. SRT uses parsimony to ignore the absolute rate of time for all light delays at C. In GRT, acceleration changes a clock's rate, but its absolute rate of time is ignored again. This error enables absolute time (and space) to be dependent on matter, not visa versa, for a universe expanding into literally nothing. Inane, or insane. M.C. Escher must turn in his grave.

So two rockets pass each other at .866c, in the emptiness of space. Each ship transmits a radio signal which pulses 100 times a second. Each can receive the others signal. Doppler shift is compensated for. Who sees 100 pulses per second, who sees 50 pulses per second, who is twice as old as whom? No changes in inertia, to muddy the water. Each "sees" the other as moving while they are stationary. If you say it has anything to do with who accelerated when, then you are saying "space" has a preferred frame of reference. That there is your paradox.

This is the best version. I finally get [email protected]

Special still applies when you have an accelerator just in a way you apparently can’t comprehend

The whole trip took 30 years in whose perspective ?

I'm no physicists but let's say your twin passes you in a ship going 50% the speed of light. The twins stamp the time recorded at the moment of intersection. Rocket twin continues still at 50% to alpha cen and upon passing stamps the elapsed time. Earth twin can calculate based on 50% light speed at about 8 years. Then rocket twin can return at a unrecorded speed. Upon return what will the recorded elapsed time be for rocket twin and earth twin during the one way constant non-accelerated and non-decelerated portion between the time stamped event? Earth twin will record 4 years and rocket twin will record less than 4 years. Doesn't that rule out acceleration as the determining factor? There has to be a different explanation.

okk I get it that ..I can't get it 😵

Please take this video down because it is not correct.

Those who are serious about physics should watch these two videos instead:

https://www.youtube.com/watch?v=UInlBJ4UnoQ

https://www.youtube.com/watch?v=GgvajuvSpF4

thank u so much for such a good explaination

What if both the twins decide to leave in opposite directions and then return back?

This hasn't been proved. What if you use digital clock, instead of analogue. In that video, the time on fast moving observer is not depend upon light from stationary source. The way in which clock run should be the same, unless you have some external effects such as a defective clock that measures slowly

The very definition of a second is an event like a tick and that should be the same for everyone. Let us say I have two digital clock showing the same time. I move one clock alone, even then the time on both the clocks will be the same because the mechanism which displays the time output is internal to the clock such as it's battery, circuits etc and its operation is not affected by movement of the clock, because of good quality digital clock

Very good video,, but according Dr. Don Lincoln (Fermilab) this is not the real explanation. See his video: Twin paradox: the real explanation. In any case, thank you very much for your excellent channel. I enjoyed very much your videos.

A case of length contraction is discussed in respect of μ-meson surging towards Earth after its origin in upper atmosphere. It is argued that the space between Meson & Earth appears shrunken from the perspective of meson. This is perplexing. Is it the (hypothetical) measuring system in μ-meson is elongated ? This argument is some what like Geocentric Model of Universe where whole of the universe was considered revolving around Earth( It appears so to us on earth ).

Let us imagine a ‘Fizeu Experiment’ (Fig: 1) conducted in a hypothetical lab on μ-Meson generated in the upper atmosphere & moving towards earth. The Meson is moving towards Earth at .998c OR (299.4 mtrs/ micro-second w.r. to earth) Consider an Electro-Magnetic Pulse Genrator & Receiver (G-R) inside a lab on Meson sending pulse in the direction of motion. Let there be a Reflector ( R ) at 300 mtrs in Meson Scale ( 18.9642 mtrs on Absolute Scale or Earth’s Scale for all practical purposes)

e = v/c = 299.4/300 = 0.998

γ = 1 / √ (1-v2/c2) = 15.8193.

Shrinkage Factor, S = 1 / γ = 0.06321

i.e., 1 E-mtr = 15.8193 M-mtr,

1 E- μsec = 1/ 15.8193 M-μsec ( where E stands for measurement on Earths scale

= 0 .06321 M-μsec & M stands for measurements on Meson scale.)

Dist GR to R = 300 M-mtr = 18.9642 E-mtr.

Speed of E-M pulse w.r.t G-R is 0.6 mtrs on earth’s scale.

Therefore to traverse 18.964 E-mtr time reqd = 18.9642 / 0.6 = 31.607 E.μsec = 1.998 M. μsec

Reverse journey time for Photon = 18.9642 / (300+299.4) = 0.03164 E. μsec = 0.002 M. μsec.

Total Journey time = 31.607+ 0.03164 = 31.63864 E. μsec = 1.998 + .002 = 2 M.μsec.

Bidirectional Speed of Light w.r.t Meson = 600 / 2 = 300 mtr / μsec.

Forward Speed of Light w.r.t Meson = 300 / 1.998 = 150.15 M-mtr / M. μsec.

Return Speed of Light w.r.t Meson = 300 / .002 = 150000 M-mtr / M. μsec.

Speed of Meson as measured on Earth with earth’s scale & clock ( which is at negligible speed ) = 299.4 mtrs / μsec

Speed of Light w.r.t Meson’s scale & clock = 300 * 15.8193 * 15.8193 = 75075.075 mtrs/ mi-sec —- (1)

Distance to Earth in Meson’s measuring scale = 9500 * 15.8193 = 150283 mtrs —- (2)

Dividing (2) by (1) we get about 2.0018 mi-sec

Fig 2. is a case of similar experiment in Transverse Direction. Here also the observer on Meson finds speed of light @ 300 mtr / μsec.

Therefore from the above result it is evident that the Meson generated at upper atmosphere finds earth at about 150000 mtrs in its scale & it surges towards Earth at about 75000 mtrs/mi-sec in its measuring scale & clock to reach earth in 2 mi-sec on its clock.

I hope this should answer 'Twin Paradox' case. If Time Dilation is Relativistic, the unidirectional traveling of Meson should have had identical effect on Meson from upper atmosphere as well as Meson generated in the lab. But the Meson falling with almost speed of light is encountered by Ether causing increase in Mass & consequent slowing down of vibrations which will enhance its life. This Ether-al Resistance is just like Air Resistance for Speeding Macro Objects, Omni-directional.

I have worked-out a Mathematical Model explaining reason for Negative Result of Michelson-Morley Experiment.

Seetharam. V

[email protected]

OK. What if you DO make the problem SYMMETRIC ? What if you put the twins in identical spaceships and they accelerate away from each other to 0.5 C and travel for a while at 0.5 C and then they both turn around simultaneously (decelerate and accelerate) back up to say 0.5 C towards each other. When they meet again will they now this time be both the same age ?

The aging thing doesnt make sense to me… Can anyone help?

Do tell me one thing, if there is difference in time then is there any difference in physical bodies according to age??

what about their physical appearance?

I don't think you have the twin paradox solved … what if one twin is on a train moving close to the speed of light and the tracks encircle the Earth, while the other twin is on the platform. According to you the twin on the train is accelerating and so he would be the younger … BUT… the twin on the train feels stationary while the platform goes round and round, ie accelerating. Just who will be gray when they reunite?

What if the observer is moving towards the light ?

I still cant get it right. All starts with the speed of light… But the objects moving in space are not all light. The clocks you are talking about might be even mechanical. Then how you will explain time delineation ?

See the real explication here!!!

www.youtube.com/watch?v=noaGNuQCW8A

I have a question

If there are two identical people and one is in spaceship moving near the speed of light.

And the other on earth.

And they both have a 100 meter race and start at exact same time.

Will they both finish the race at the same moment ?

Maybe, acceleration is not the answer… look at this Fermilab video…https://www.youtube.com/watch?v=GgvajuvSpF4

My question is this.

Speed of light =distance÷time=constant c.Then,as distance increases,time should also increase.that means time should get faster for the moving spaceship?

3:51

Michael: Or can she?

Okay they are different ages, but physically they are the same age, they didn't just speed up there death that's bs

You are absolutely amazing!! The way you explained was so much more simpler than all the other YouTubers. Thank you so much for that amazing video, Physics Girl!

This is wrong. It has nothing to do with acceleration.

If time dilation was real then there would have to be an algorithm represented as computer code to sync computers with satellites. Otherwise how does Voyager 2 compensate for y2k glitch? Likewise the iss would be out of sync with firmware updates. It's a garbage theory because there is no theorem that exist for time dilation represented as computer code.

Please tell what will happen if we do video call while remaining inertial

Still no prove to time dilation. Just someone said, GPS, Satellite, but never prove time dilation really exist. A kid can also said Goosebump is the prove of ghost exist. Justlike you said GPS is the proof of time dilation.

So… turning around introduces massive "gravity" thus slowing your time down?

Nice, but i still cant make sense out of TD. The speed of light appears instant to us but not in the far distant universe. Viewers observers might be different but it dont change time.

How you make video by which app

Twin 1 : On Earth

Twin 2: Went to space and came back to Earth, became 4 years younger

Twin 1 : Her turn. Went to space and came back to Earth, became 4 years younger

Both twins are now in equilibrium.

this guy knows more than we do about this: https://www.facebook.com/Secretlytacklingonlinepredators/videos/2321766401427931/?t=279

this is so weird

if there is a third twin standing on another planet which is stationary to earth and the twin on the spaceship travels from the earth to that planet, will she be younger or older than that twin as she arrives?

Imagine about jumping inside a fast moving bus near the driver without its roof and jump as high as you can…. does it affect your position like you'll able to move a bit backward or still remain on the spot where you jump?

|“““““““““`

< < < | <– 😎 ]

●● ●●

-cool bus tho (exclude the roof)

Anyone can learn this stuff, but no one else can explain and teach it as well as Physics Girl. Even the other youtubers can't do it as well as she did in this short video.

This guy from fermilab says physics girl's explanation is wrong. https://www.youtube.com/watch?v=GgvajuvSpF4&t=1s

I love the way you presented the information in this video, which was very clear and understandable. However acceleration is the incorrect answer to the problem, the key lies with the frames of reference of each observer, as derived from the Lorentz transforms. The actual explanation is way too long to put in a comment, but in short when you divide by gamma (which is always 1 or more) you get a shorter time for the traveling twin.

I will direct you to take a look a the videos made by Fermilab on the Twin paradox (one with math and the other without it) where Dr. Lincoln really explains the solution to this problem and why it has nothing to do with acceleration.

Keep up the good work, I really enjoy your videos.

I still don't understand why this is a paradox 🙁 If you were actually able to perform this experiment. Woulnd't the result be that the twin who made the trip to space and back show that this twin is actually younger? I mean based on the science we know? Where does the paradox come in? Is it the fact that relativity says that the space twin should be able to observe the earth twin's clock as the one moving slower?? I wish i could buy an expert physicist and have them answer questions at my discretion. Oh and also, I juuuuust watched a video by fermilab where he says acceleration has nothing to do with it…. CONFUSED!

Except prof. Don Lincoln from fermilab made a video explaining why acceleration is not the issue

Hi Physics Girl. Great video. I wonder what you think of the idea that the past still exists when vast areas of space are taken into account. Is it really true that everyone who lived in the past still exists as Brian Greene among others seem to be saying?

What you say about time and light are all wrong…

Speed alone does not affect the passage of time. If I am travelling at a constant speed the only way to quantify that is to compare myself to an object that appears to be stationary.

What I am actually measuring is the relative velocity between myself and the "stationary" object. That is the foundation of Relativity. The more G's you pull, the more time dilation occurs.

Within my inertial frame I can only detect acceleration and deceleration. In a vacuum the only thing that can affect time is gravity. Since acceleration/deceleration mimics gravity within my

inertial frame, I experience time dilation.

Stress Will do that to you:-/

Thank you very much mam I subscribe d ur channel

This explanation is INCORRECT!!! See FermiLab

youtube.com/watch?v=GgvajuvSpF4&list=PLCfRa7MXBEsoJuAM8s6D8oKDPyBepBosS&index=20&t=0s

These are liars, twins are always in same age no matter where they go

Information in this video is hardly accurate or informative. Our clock, our measure of time, and our calendar are all relative to the earths rotation and and orbit around the sun. This is very basic knowledge. Two individuals born on earth at the exact same second will always be the exact same age until one ceases to exist. I don't care if individual one travels through space for 50 years and comes back to earth and reunites with individual two or not, because once they reunite they will have been alive for the exact same amount of time. Prove me wrong. There is no other function of time than the one we have created.

Nice work 👌 I learned the special relativity theory

My brain just melted…

Then you say that interstellar theory was wrong…you say that father should get old not his daughter….

Is time travell really possible.

I watched a lots of video on YouTube but I think all of those are fake.

Are you Scientists plz tell me.

I reviewed this video and many others on the topic of Time Dilation. See it here: https://youtu.be/xySlWYlKu7w

This is from 4 years ago, I think she knows that the explanation is actually wrong now (I do love physics girl!) but it would be nice if she went back and corrected it in her front-post so people don't come away confused.

Basically, it is not the acceleration that resolves the paradox. The acceleration itself has almost no effect on the time dilation for the purposes of this experiment. In fact, you could even make them equivalent as the twin on earth is also in a 1g acceleration field (due to gravity). And you can also run a slightly different experiment that completely removes acceleration from the entire problem simply by having one observer get up to speed first and then pass Earth at the starting gate, passing by another observer going the opposite direction (also already up to speed) at the target star. The clock's timestamp is passed between observers as they pass each other.

In anycase, what resolves the paradox is that (ignoring things like the Earth's rotation and the Earth going around the sun, etc, which don't really contribute anything much)… So what resolves the paradox is that reference frames for the two twins take different paths. The reference frame for the twin on Earth effectively doesn't change, but the reference frame for the twin in the rocket ship does because the rocket has to turn around and go the other way (or the message has to be passed to another observer going the other way… who will be in a different reference frame). And again, the acceleration involved, if any, is not a major contributor to the difference in time. It is the fact that the reference frames for the paths are not symmetric that resolves the paradox. The symmetry of the two twin's motion is 'broken' at the turn-around.

And yes, this actually does mean that while the twins are separated, both can in a completely valid way say that the other is moving slower in time. The range of the possible difference in time is not infinite… it can be calculated, and it will collapse back down as the twins coordinates merge (i.e. they meet up again), but until that happens neither twin can make make any sort of absolute exact calculation as to relative aging.

This becomes apparent if you use a space-time diagram to map both twins. No matter what third-party reference frame you choose, one twin's space-time path will have a kink in it and the other's will not.

This is MUCH weirder than people think. Just the very fact that constant motion affects time, forget about acceleration… just motion alone has a time dilation effect.

-Matt

Everything she said went over my head

i dont remember science class being this interesting. nerds are so cool

As i understood (tell me if i'm wrong ) the speed of light is invariable in VACUUM.

Here ,one of the twins is on Earth ,so light is crossing atmosphere then goes in her eyes: light speed will vary,so the theory of relativity can't be used here.

Each observer will have a different value of the speed of light in your example.

Nonsense. The Lorentz Transformations have nothing to do with acceleration. Learn about it, learn to construct world lines and simultaneity lines, then make a new video and take this one down.

This is really weird

Try running to the front of a train versus the rear of the train, one postulate fails. It also fails because who is moving fast is arbitrary, so either twin could age slower. Therefore the theory is falsified. A lot of word babbling in this video attempting to confuse the issue.

I used to have a really really loud stereo in my car. when I would pass my friends they would say the music sped up until I pass them and then it slowed down. Would that be something like you are describing.

She used SI. Yeah