# Ageing and Space Travel

#### sidders007

Hiya all, I was listening to Prof Brian Cox and he told the story that....
If i asked an astronaut to fly in a rocket away from earth for 5 years then turn around and come back to earth, ten years will have passed for said astronaut but on earth 29 years will have gone by.
I do know that time slows the further away from earth you get from a clocks point of view, but.....
If this is so what effect on the human body would the astronaut be? Would his body only have aged 10 years or 29 ?

At no point did he mention any speeds
Hope that makes some sense

#### Helio

Time isn’t fixed when relative motions are compared. At speeds near the speed of light, a space traveler will not notice any change in the rate of her ship’s clock. But, upon return, the ship’s clock rate compared to the Earth’s clocks will reveal it has run slower. Distance from Earth has no effect on rates, only relative speed.

The traveler will see life progress as normal, so too for those on Earth, of course.

This fact is necessary for GPS accuracy since GPS satellites travel briskly, requiring use of the time dilation equations.

#### FromBelow

I do know that time slows the further away from earth you get from a clocks point of view, but.....

Would his body only have aged 10 years or 29 ?

It's because of the speed, not the distance.

Things with mass cannot reach or exceed the speed of light. You can keep on accellerating as long as you want, but weird things happen as you get closer and closer to the speed of light; instead of accelerating faster through space you experience time more slowly relative to slower objects. The astronaut would experience 10 years of time, everything would feel normal onboard the ship, but back on Earth we'd watch them travel for 29 years.

This is an imaginary scenario from Carl Sagan's Cosmos, with light speed set to only 40km/hr:

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#### SyfoDias

This reminds me of Intersteller

#### utemim

aging & limited amount of food and oxigene on earth arepositively related

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