Say I get on a Sci-Fi speed Rocket Ship and leave Earth at .999999% the Speed of Light to me I travel for 21 minutes reach Mars then U-Turn back to Earth for another 21 minutes at 0.999999% the Speed of Light again. Back on Earth if I compared my watch to someone else’s would my watch be slightly ahead or slightly behind?
Like if I’m the one traveling I’d expect their watch to be slightly ahead of mine because slightly less time has passed. But at the same time from my frame of view. Earth and my bussy with the watch just shot away from me for 21 minutes and then returned and came back 21 minutes later so my watch should be ahead of theirs since they were the one traveling.
In: Physics
The answers given so far are good but not really ELI5.
So I’ll give it a shot with a boomerang analogy.
When you throw a boomerang, it is accelerating away from you. Yet if you placed a camera on the boomerang, that camera would suggest you are accelerating away from it.
That is the twin paradox.
However, that is really just an optical illusion. In reality, only one object is actually accelerating – the boomerang – while you are stationary.
Time dilation occurs to the person/object being accelerated, not the one which is stationary.
So if we threw the boomerang at 99% the speed of light, what you see and what the camera sees would still be the same as throwing it at any speed. But in terms of actual time dilation, it would occur to the boomerang, not the observer.
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