I was wondering if someone could help me see where I am messing this up: Lets say we have our train with a relative velocity of .5c, Also suppose it is .816ls tall, and that there is a mirror mounted on the floor, another mirror directly above it, and a third mirror about .577m to the rear and attached to the ceiling. To the observer on the train: Two photons are sent out, Photon A hits the mirror directly above the bottom mirror in .816 seconds, Photon B hits the .577m behind mirror in 1 second. To the observer on the platform: Two photons are sent out, Photon B hits the mirror .5(the distances measured on the train should be contracted yes?) behind in .816seconds, and then Photon A hits the mirror that was directly above in .958s, The normal explanation for photon A is timedilation occured and time went slower to make up for the difference, Photon B however, indicated time must have sped up. Comparison: Photon A Photon B Train .816 1 Platform .958 .816 what gives?