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## Main Question or Discussion Point

When you derive the time dilation equation, and you see the light move straight down in one frame and in the other frame you see it move on a diagonal because the object is moving.

My question is in the moving frame when you use the horizontal distance to derive the distance that the light travels using Pythagorean theorem. It seems that the horizontal distance would be length contracted , or unless the ruler used to measure that distance is also length contracted. But isn't the length contraction formula derived using time dilation?

My question is in the moving frame when you use the horizontal distance to derive the distance that the light travels using Pythagorean theorem. It seems that the horizontal distance would be length contracted , or unless the ruler used to measure that distance is also length contracted. But isn't the length contraction formula derived using time dilation?