Timecop throws relativistic physics out of the window, and produces a reasonably fast-paced action thriler. The story is set in the year 2004, where the ability to travel back in time is possible. In order to make sure this doesn't result in abuse leading to time lines being altered, a police system is set up. Jean-Claude Van Damme plays Max Walker, a Timecop, who is pitted against a senator who wishes to exploit time travel and become the most powerful person in the USA. Using the logic "same matter cannot occupy the same space" Walker finally prevails, but only after we get to see some good martial arts and shots of Van Damme's butt.
The action in the movie is pretty good. I personally don't care for Van Damme's acting, but I don't think that mattered much in this movie. The special effects and the concept are worth renting this one.