Our astronauts when they go orbiting around the earth, they actually come back slightly younger than a twin that they would have on the planet Earth who was stationary. 

This is called the twin paradox.  So in some sense astronauts are time travelers; however, your own body in some sense is also a time machine because time does not beat at the same rate inside your body which is now a measurable affect. 

It was an effect predicted by Einstein, but only recently have our atomic clocks become so accurate we can now nail that calculation to the wall. 

In Their Own Words is recorded in Big Think's studio.

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