... Einstein's relativity . Einstein's theory of general relativity changed how physicists understood the universe in an instant. ... Special relativity says the laws of nature are the same in all frames of reference moving at a constant velocity. ... If your friend s car is moving at a steady speed, the laws of special relativity apply, but if the car is accelerating, we have to apply general relativity. ... Only registered members of Astronomy.com are allowed to comment on this article. ...