# Twin Paradox and Time Travel (Special Relativity)

1. Oct 26, 2008

### scurry18

1. The problem statement, all variables and given/known data
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?

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

3. The attempt at a solution
Speedo travels for 21 years.

2. Oct 26, 2008

### borgwal

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

3. Oct 26, 2008

### scurry18

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

4. Oct 26, 2008

### borgwal

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

5. Oct 26, 2008

### scurry18

Just the above equation and length contraction

6. Oct 26, 2008

### borgwal

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.