Most time-travel stories have plots “that violate strict physical laws,” but the time skipping in the upcoming film adaptation of the Time Traveler’s Wife would likely work—if we could travel in time at all, writes physicist Dave Goldberg. That’s because it follows four key rules:
- There’s only one universe. Many films move between parallel universes (think Back to the Future), as theorized in quantum mechanics. But “there’s no evidence parallel universes exist,” and Einstein’s work suggests otherwise. Henry and Clare stick to one timeline.
- It’s impossible to travel to a time before your time machine existed. Time travel would be “like traveling through a tunnel in space—in which case you'd need both an entrance and an exit.” In an era before your machine, there’s no “off-ramp.” Henry is his own time machine, so that covers his life—and the book makes no jaunts to, say, 1776.
- Travelers can’t kill their parents. The Terminator learned this the hard way: You can't travel back to kill your father—if you did, you wouldn't have been born. Because of No. 2, Henry can't travel back any further than birth, so he's safe.
- Free will is very limited. “If you've already seen what your destiny is, then the future is already written,” Goldberg writes. Henry and Clare "enforce the (predetermined) future by giving each other instructions and hints about how things are supposed to happen."