Question

Well, let's think about the relativity theory. The length becomes shorter when an object is moving at high speed. But the ruler will also be shorter. So how do we know that it's become shorter, anyway?

Answer 1

I don't really understand Einstein. (although it's really Fitzgerald not Einstein...)

Answer 2

you can compare the length of the ruler which is not moving in your frame of reference with the ruler that is moving in your frame of reference, but you cannot check exactly that the one which is moving is shorter. You can only say that it seems to be shorter.

Answer 3

So there has to be an observer "outside" the object. And no observer(or tools) "inside" can be useful. (?)

Answer 4

then you look at the observer "outside" and you see the same effect. You can say than that the observer "outside" is moving with the speed that you have

Answer 5

And another curiosity that I have had is... when the two observers meet again, they(or one of them) would have to accelarate. Then to find out what would happen then, should you use the general relativity theory? Or.. well, what happens then?

Answer 6

When two observers are in non-inertial reference frame (one move relative to the other with acceleration and vice versa) with huge speeds than you have to use general theory of relativity. If it's inertial frame of referance you use special theory of relativity.

Answer 7

How should you use the general one in such case?

Answer 8

What's the result of it?

Answer 9

if the object is uniformly accelerated use the Rindler coordinates

Answer 10

what's Rindler?