I once saw a movie on cable that I do not know the name of, not sure how old it was.

The movie is about people who travel into what is known as a "system" which is essentially like time travel because the system they created was created to be in the past. Later in the movie the main character realizes his own world is a system. The people in the system and in the "real world" look the same but in a different time period. Any idea what movie this is and the name?