Problem is, that physics is an experimental science.

Relativity is confirmed by an incredible number of experiments.

Taking (at random) a relatively recent one:

NASA Announces Results of Epic Space-Time Experiment

May 4, 2011: Einstein was right again. There is a space-time vortex
around Earth, and its shape precisely matches the predictions of
Einstein's theory of gravity.

Researchers confirmed these points at a press conference today at NASA
headquarters where they announced the long-awaited results of Gravity
Probe B (GP-B).

"The space-time around Earth appears to be distorted just as general
relativity predicts," says Stanford University physicist Francis
Everitt, principal investigator of the Gravity Probe B mission.

see

http://science.nasa.gov/science-news...011/04may_epic

What do you have to say to that mister?