# Twin Paradox and Time Travel (Special Relativity)

## Homework Statement

Identical twins Speedo and Goslo join amigration from the Earth to Planet X. It is 20.0 light years away in a reference frame in which both planets are at rest. The twins, of the same age, depart at the same time on different spacecrafts. Speedo's craft travels steadily at .950c, and Goslo's travvels at .750c. Calculate the age difference between the twein after Goslo's spacecraft lands on Planet X. Which twin is older?

## Homework Equations

(1-v^2/c^2)^1/2 x time of travel

## The Attempt at a Solution

Speedo travels for 21 years.

## The Attempt at a Solution

Speedo travels for 21 years.

That's in the frame of reference in which the planets are at rest. How long does it take on Speedo's clock?

I'm really unsure on how to figure that out.

What concepts that could be relevant here have you encountered so far in special relativity?

Just the above equation and length contraction

It's really time dilation that you would use together with your result of "21 years", but length contraction will work, too, in a slightly indirect way.