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1. Sep 20, 2016

### kevinki

Definitions:
Astronaut is A
Person on Earth is B

A travels to a star far away at near light speed,
A would see B's time dilate.
B would also see A's time dilate

What would happen if A returns to B at a very slow speed?
Then both frames of reference would see each others' time dilated.
A thinks 20 years passed, but only 10 years passed for B,
ans B thinks 20 years passed, but only 10 years passed for A.

2. Sep 20, 2016

### Ibix

As always, the travelling twin would experience a shorter time. You are, I think, failing to account for the relativity of simultaneity, which means that the traveller's definition of "now on Earth" changes at the turn over. That doesn't happen for the stay-at-home, and that leads to both twins having consistent expectations of the other's journey duration.

3. Sep 20, 2016

### phinds

The Twin Paradox, at its core, does not have anything to do with high speeds, it's just that the outcome is more dramatic when high speeds are involved. Airline pilot's ages routinely differ from what their age would be had they never flown, it's just that the difference is in milliseconds (if that much) rather than more noticeable amounts.

4. Sep 20, 2016

### Staff: Mentor

5. Sep 22, 2016

### Stephanus

Okay...

A travels to a star far away at near light speed,
A would see B's time dilate.
B would also see A's time dilate

Yes-s-s, but you must account for doppler effect. Actually what A (and B) actually see for each other opposite will be much slower. It's because of Doppler effect.

What would happen if A returns to B at a very slow speed?
Then both frames of reference would see each others' time dilated.

Yes. But don't forget doppler effect. Actually both will see (no matter the velocity is) the other clock runs faster. But after adjusting to doppler effect the other clock actually runs slower wrt the observer.

A thinks 20 years passed, but only 10 years passed for B,
ans B thinks 20 years passed, but only 10 years passed for A.

Come on...
$\gamma = \frac{1}{\sqrt(1-v^2)}$
$2 = \frac{1}{1-v^2}$ $v = 0.866$
In my hometown 0.866c is not in the very slow category.

But the essense is.., slow or not. Both will see the other clock dilated.

Yeah, that's why flight seems shorter with a beautiful stewardess,

6. Sep 23, 2016