The science behind 'Time Traveler's Wife'

This weekend brings two sci-fi movies: The allegorical alien flick "District 9" and the sci-fi-lite romance "The Time Traveler's Wife."

If you can only see one, our reviewer, Peter Rainer, clearly supports one over the other. "District 9" is "highly creative and amusing." Whereas "Time Traveler's" is without "logic, thrills, or romance."

The Washington Post also chides the latter movie for its "laughable plot."

But, Drexel University physics professor Dave Goldbery says that the movie is one of the very few that portrays time travel in a (mostly) scientifically accurate way.

"I'm so excited about the film adaptation of Audrey Niffenegger's The Time Traveler's Wife, which tells the story of Henry DeTamble, a man with a rare genetic disorder that causes him to skip around in time while his long-suffering wife, Clare, waits for him at home," the professor writes for Slate. "The premise is no more or less plausible than that of, say, Back to the Future, in which a tricked-out DeLorean must reach 88 mph to jump into the past. But The Time Traveler's Wife follows through on its premise in a realistic way."

How so? Goldberg lays out four scientific laws of time travel.

First, there is only one universe. No matter where or "when" you go, science won't let you split off into alternate, parallel realities. The movie (or at least the book) sticks to this single timeline idea.

Second, you can't go back in time beyond when you first invented your time machine. Einstein's theories say that "traveling through time would be much like traveling through a tunnel in space—in which case you'd need both an entrance and an exit," Goldberg writes. "As a time traveler, you can't visit an era unless there's already a time machine when you get there—an off-ramp."

I'll admit, this one doesn't make sense to me. Why are time machines on- and off-ramps and not the cars themselves – something that travels with you from place to place? Can a reader explain to me what the fine professor did not in the few-hundreds words that his editors allowed?

Third, "you can't kill your own grandfather." Everything that happened already happened. You can not create paradoxes. Whatever you can do in the past, you have already done – because it's the past.

Finally, don't like the third rule? Tough. "Free will" means little in time travel.

You should definitely check out his article on Slate for deeper looks into each of these rules and how the movie follows them.

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