[monster_group]

Author's description of twin paradox is incorrect. In fact, the paradox is not described at all. The paradox is that since motion is relative then from both twin's perspective the other twin goes on a journey and ages slowly. So why it is that on returning, only the traveling twin has aged slowly? The answer is that both twins indeed see each other age slowly but for the traveling twin to come back they have to slow down to zero and reverse direction. At that moment the frame is no longer inertial. While turning around, the traveling twin will see the stationary twin age very quickly (enough to catch up with their earth age), so when they meet there's no paradox. For each of them the other has aged as per their observations.

[nyrikki]

The twin paradox holds in a Pacman universe where there is no change in direction.

The main issue with the twin paradox is that it demonstrates where our euclidian intuition fails us.

There are several interpretations on how to resolve it, but they are all just flawed lenses, intended to help you along a curriculum until you understand the math, and also understand the limitations of intuition.

The 'turn around' explanation is part of that and unfortunately often sold as the ultimate resolution.

[floxy]

>The twin paradox holds in a Pacman universe where there is no change in direction.

That is awesome, I've always wondered about special relativity in a flat torus world. Do you have a recommendation for reading more about this?

[Osmium]

Can you expand on this? I was only ever taught the "turn around" explanation.

[nyrikki]

All I can offer without going into the weeds is that it is not the shape of the paths, but mearly the relative length of two paths though spacetime that matters.

Proper time and proper acceleration is possibly a pathway in flat spacetime?

Learning that the order, timing, and sometimes causality of events is also relative tends to be a barrier, thus some of these didactic half truths are useful.

The "Einstein train paradox" is the classic intro to the relativity of simultaneity if you aren't familiar.

In the SR case, proper acceleration is possibly the better option.

[nayuki]

This is an extremely detailed explanation of the twin paradox that covers things from multiple angles, even situations that involve no acceleration: https://www.youtube.com/watch?v=vv5d5KHKDVE

[pkoird]

Are you suggesting that two people in a shared inertial space when venture into other intertial frames but ultimately end up in a same frame later will agree on how much time has passed in between?

Because I lowekey believe this to be true but don't have means to prove it.

[euroderf]

Thank you for this explanation. So it is time spent in a non-inertial frame - decelerating and reversing direction.

[mpclarkson]

This has been updated

[sigmoid10]

The whole site seems very much like it is AI generated. In particular the css is very close to what I've seen ChatGPT generate when I used it to create similar things.