I disagree. Experimental agreement is not grounds for establishing a theory. There needs to be a reason, based on some principle, that can explain why these things are true.Originally posted by HallsofIvy
Same reason that would be given for questions on any physics point:
"That's what the experimental evidence says". Arguments about "reasonableness" cannot stand in the face of experimental evidence. (And the experimental evidence in favor of relativity is overwhelming.)
For example, if I am in a space ship traveling the speed of light relativity says that I can not walk from one end of the ship to the other. What is the reasoning being this? If all you can say is that there is experimental evidence then your understanding is not complete.
It is extremely strange that although SR has been arround for almost 100 years no one has conclusively answered this question. In fact, it seems that there is very little contemplation given to this question which lies at the foundation of modern physics.