h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hey, this one reads good!
Have you considered announcing it to the peer review? If not, you /should/, or else...



... I'm going to do that on your behalf

Have I got this right?

Anne sets off into space on 1st January 2020, her 20th birthday. Her twin brother Bert is in mission control.

On 1st January 2050, his 50th birthday, Bert is there again to see Anne's craft return. She has been on a long trip at an average speed of 0.9 times the speed of light.

When they meet, what will Anne say about the duration of her journey, and therefore her age?

I think you can state the equation in the following terms:

Tearth = Tspace / sqrt(1 - (sqr(0.9c) / sqr(c))

where Tearth and Tspace are the perceived durations of the trip on earth and in space, sqrt is "square root of", sqr is "square of" and c is the speed of light. So we go on with the particular case...

30 years = Tspace / sqrt(1 - sqr(0.9) / sqr(1))
= Tspace / sqrt(1 - 0.81 / 1)
= Tspace / sqrt(1 - 0.81)
= Tspace / sqrt(0.19)
= Tspace / 0.436
30 * 0.436 = Tspace
Tspace = 13.01 years

So Anne would feel that she was just past her 33rd birthday. As I said, have I got it right? I suspect that it is over simplified even if it's "correct", because of that little word "average" to cover acceleration and deceleration, but is it a reasonable starting point?

Relativity tends to be discussed in impossible terms. There are people travelling at enormously different speeds, and therefore a very, very long distance apart. And yet they can see each others' clocks...

I want to know whether people think there would be a serious effect on ageing if you went off into the universe at a sufficiently high speed and then came back, or whether everything would come back together as speeds are equalised.

Which would mean that the effects of relativity could not be demonstrated in real life...