- #1

Hak

- 709

- 56

That said, in reading the Feynman I came across an ideal experiment that is not entirely clear to me. The context is the usual two spacecraft moving at relatively constant speed. With the reasoning I give below Feynman tries to explain why the lengths along the axes perpendicular to the direction of motion are the same in the two frames of reference:

What is not clear to me is the dynamics of the "reunion" between the two: to reunite at least one of the two must have changed frame of reference, so how can I know that in the new frame of reference its lengths along the ##y##-axis will be the same as before it changed frame of reference?How do we know that the perpendicular lengths do not change? Men can agree to make marks on each of the rods along the ##y##-axis [the relative velocity is along the ##x##-axis], when they pass each other. By symmetry the two marks must be found at the same ##y## and ##y'## coordinates, because otherwise, when they come together to compare the results, one mark will be above or below the other, and so we might know who was actually in motion [contradicting the principle of relativity]

The problem is that I cannot do any kind of math since Maxwell's transformations have as an assumption that ##y=y'##.

I hope I have been clear. Let me know, thank you very much for any clarification.