Novikov Self-Consistency Principle: Why You (Most Likely) Cannot Use A Time Machine To Change The Past

If we have a time machine, is it possible to go back into the past and change it?

That's a question many people have thought about. It turns out that if there's no parallel universes, the Novikov self-consistency principle should hold and that there is no way to change the past. What has happened cannot be undone. Whatever actions from the future are already accounted for in what has happened.

So, the movie The Terminator agrees with this principle: The terminator going back in time created a consistent loop that would create John Connor who would then get into a situation where a terminator must be sent back in time, and in the process would create John Connor, and so on. However the Terminator 2, 3, and 4 movies deal with changing the past/history, so they are less realistic according to this principle.

Novikov gave a short speech about this idea also.

Some Info About Time Travel

At least two of the big movies coming out in 2009 involve time-travel, so it's a good time to review what we know and don't know about the possibility of the real time-travel to the past. Two informative and easy to understand links are Time Travel and Modern Physics and Rules for Time Travelers.

By the way, we are all traveling through time in the forward direction, so the only unknown time travel is time traveling to the past.

I think the movies Time Crimes (Los cronocrímenes) and Primer are probably closest to the real time travel if it is indeed possible.