The Twins Paradox Hands-On Explanation | Special Relativity Ch. 8

This video is chapter 8 in my series on special relativity, and it presents a hands-on explanation of the resolution to the Twins Paradox using the mechanical minkowski diagram, aka mechanical Lorentz transformation, aka spacetime globe. Of course, the Twins paradox can be resolved with an understanding of spacetime intervals, relative inertial frames of reference, etc, but this is a nice hands-on version where you actually measure the proper times on a real, physical spacetime diagram with a ruler.

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[micahphilson]

I just keep getting more and more impressed with this device every video!

It seems so simple, yet all these things I've tried learning in the past make so much more sense when you can physically see them graphed out and can manipulate it, seeing the dilations and contractions physically and in real time!

[firefly]

I love to instantaneously change my velocity by .6c! It's so easy!

[void]

Still waiting for this spacetime globe to made available, wither in reality or as a program.

[new-knowledge]

The idea of a "squeeze stretch of Space-Time" confuses the living daylights out of some folk. If you have several objects moving at different velocities, each has its own perception of the depth of space, and the rate of the passage of time. But this does not mean that there are multiple space-time environments all existing at the same time, that each are of a different measure and are each dedicated to specific observers in their specific frames of reference. In truth, there is only one space-time environment, but the observation of it changes depending on ones direction of travel across it.

[feynstein]

Dr. Brian Greene's resolution of this was quite amazing. I can't seem to find the video anywhere on YouTube. I watched it on World Science University. As for what the twins actually see, as long as one twin is moving away, both twins see time passing slowly for the other. But as soon as as the second twin turns around, the stationary twin seems to age extremely quickly and eventually becomes older. It's a amazing video.

[Arkalius]

The twins paradox is what is known as a veridical paradox. It is something that, as typically represented, does not seem to make logical sense, and appears impossible or contradictory, but upon further examination is actually true and consistent.

This is contrasted with a falsidical paradox, which is where a superficially convincing case is made for something that seems absurd or contradictory, but where the conclusion is actually incorrect when you examine the situation in greater detail. An example of such a paradox are some of the clever and tricky "proofs" that 1 = 0 that you can find around the internet.

There is also the antinomy, which is what some may call a true paradox. It is a statement that fails to admit of being either true or false due to some logical flaw or failure in its construction. A statement like "This sentence is false" is a trivial example.

[NessHX]

The simplest explanation of the twin's paradox is that on the spacetime diagram straight line is actually the longest possible path you can take to go from point A to point B. Since it's special relativity, "path" actually translates to amount of time that passed for the moving body, standing still (not changing one's reference frame) guarantees the biggest amount of time passed between two events.

[mon]

Just rewatched the entire series in a row

Not recommended my brain has little coolant left

[diwakarisonyoutube]

I'm the first to comment.
Others are false.
Time is relative.

[Mike__B]

Great video, I think the largest issue with confusion of the "paradox" is exemplified by your first drawing with each saying "2s for me is 1s for you" and as the time dilation effect doesn't quite work like that in a linear fashion, so it goes deeper than "that person is moving with respect to me" as your observation of another person does not dictate how fast time moves for them as shown with your (8 chapters in, this is the 8th time I'll say this) absolutely FANTASTIC visual tool in the spacetime globe.

[turbomopie]

That was really awesome to see the Lorentz transformation visually

[nihilistmia]

This is like the 3rd time I've watch this series, its absolutely brilliant, thank you so much for this

[tetraedri_]

Just popped into my mind: how does this work if our universe is toroidal, like in the Asteroids arcade game? To make the experiment as symmetrical as possible, suppose you leave the Earth with constant velocity, get around the universe and once you pass the Earth again, your twin jumps into your space ship. Who is now older? Both of you change the inertial frame once, and by reversing time your twin first left your frame, so the experiment is fully symmetrical in this sense.

[michelemasotti]

For everyone wondering where the paradox is and what the solution is, I highly recommend to check his older video on the topic cause this one really doesn't get to the point. The paradox is about the symmetry, because for the traveling twin he is the stationary guy. The solution is indeed in the acceleration necessary to change velocity, since special relativity only applies when the reference system is inertial

[sakumar]

Absolutely fantastic series! Bravo. In less than an hour it gave me an intuitive understanding of special relativity that I didn't have after reading a couple of popular science books on the topic.

[SlipperyTeeth]

"And they accelerate in between"
NO. You just ruined them. Now they have to understand the 3 person analog to understand that acceleration is irrelevant.

[tejing]

I prefer to think of it as geometry. We all know that in normal geometry, if a, b, c are vertices of a triangle, then ab + bc >= ac. However in this (admittedly odd at first glance) geometry where the Pythagorean theorem has a minus in it, if a, b, c are vertices of a triangle (and ab, bc, ac are forward-directed and timelike), then ab + bc <= ac. This has the advantage of leaving out what reference frames you're talking about altogether, much as normal geometry leaves out the choice of coordinate system.

[FoliageTerrascapes]

That felt like the quickest 4 seconds in my life.

[Bodyknock]

Good video but I wish Henry hadn't used the word "acceleration". There are a lot of people in the comments incorrectly saying that the reason the spaceship twin experiences less time is due to "acceleration" which isn't the case. The reason is due to the spaceship experiencing two reference frames on the journey versus the Earth experiencing one reference frame. The sum of the proper times in the spaceship's two frame is less than the proper time of the Earth's single frame. There's no acceleration or gravity or general relativity or anything like that involved here, it's all about two frames combined experiencing less time internally than one frame that watches the ship travel through them.

[berni]

Now I understand the idea of this paradox, it's still hard for me, but sure, you helped me to understand the basis of the problem. Thank you, as always :D