# Q & A: special relativity

Q:
could you please explain the twin paradox theory? the relationship between time and velocity in space, between two identical object.
- glen (age 17)
A:
In Special Relativity, it turns out that any observer sees the clocks on objects moving with respect to him as running slow. Of course they look back at him and see him as moving and thus see his clock as running slow, since the laws of physics are the same in any reference frame which moves at a constant velocity. This sounds paradoxical.

The twin paradox goes as such:
When one twin gets in a rocket and blasts off from earth. he speeds off and comes back and since he has been traveling at a high rate of speed, he should be young. however, from the rocket twin's reference frame, it looks like the earth twin flew off into space with the earth and then came back. both view points are 100% correct. so which one is older?

the answer to this come from einstein's theory of general relativity. it turns out that the situations are not completely similar. the rocket twin must turn around to come back. when he does so he will feel an acceleration which lets us know that he is the one that is moving. The Special Relativity laws don't include this effect, and thus don't actually tell us what things look like from the point of view of the one accelerating.

James

(published on 10/22/2007)