@wolf480pl I was just reading about Lorentz contraction as a solution to the Michelson–Morley null result, and I'm back to not understanding it.
Here's my logic, lets imagine the arms are 10 units long and the half-silvered mirror is at x,y of 0,0.
At rest: Light on the X axis bounces from 0,0 to 10,0, to 0,0, doing a total of 20 units of motion. Light on the Y axis bounces from 0,0 to 0,10 to 0,0, also doing 20 units of motion.
At speed (X travel of 2 units per light-bounce-time), light on the X axis bounces from 0,0 to 11,0 to 2,0, doing a total of 20 units of motion. Light on the Y axis bounces from 0,0 to 1,10 to 2,0 doing 20.1 units (if I'm not mistaken, the hypotenuse is 10.05 so the sum is 20.1).
You had me convinced earlier that because the X beam starts at 0,0 and ends at 2,0, it has to have taken extra time to move those 2 units, but considering the mirrors instantaneously moving from points 0->1->2, the numbers seem to indicate that the opposite is true.
But now the problem is that there's no amount of X contraction that can fix this, when the X travel is 20 and the Y travel is 20.1.