Neil deGrasse Tyson may have had issues with the science in 'Gravity', but he's holding off on any objections to the time travel in 'X-Men: Days of Future Past'.
The 'Cosmos' host and astrophysicist was asked if he thought it would be possible for Wolverine to travel back to 1973, as he does in the film, to prevent a war between humans and mutants.
In a series of tweets in October, Tyson gamely picked apart scientific errors in 'Gravity', wondering for example why Sandra Bullock's hair didn't float in zero gravity. But he took it easy on Wolverine.
“We don't know enough about time travel to assert what the rules of time travel are,” Tyson said.
“Normally when you set up the rules and regulations of some branch of science, it's because you've done the experiments to see how nature behaves when you poke it, prod it, put it in a petri dish. So as far as we know, we have no time travel experience other than being prisoners of the present, forever transitioning from the past into the future.”
The time travel scene from 'The Terminator'
“So that being said,” he added, “there are some leading thinkers among us, Stephen Hawking counted in this, who have hypothesized a time-travel rule. They want to put it in to avoid paradox: You cannot travel back in time and interact with the world that created you that enabled you to travel back in time. In other words, ‘The Terminator’ scenario would not be possible because it would create an unresolvable paradox.”
'The Terminator' scenario, of course, is one in which someone from the future sets in motion the events of the past.
In the original film, the futuristic John Connor sends Kyle Reese back in time to protect his mother before he is born. Reese ends up fathering John Connor. Time is a loop.
Tyson said of Hawking and other believers in the anti-paradox rule: “They're just making this up because they don't know how to resolve the paradox, not because they've done the experiment.”
Wolverine (Hugh Jackman) goes back in time and meets a young Professor X (James McAvoy) and Hank McCoy (Nicholas Hoult)
We've seen 'Days of Future Past', and wouldn't dream of spoiling what happens, other than to say it has an interesting take on the question of whether people from the future can change the past. Tyson had not seen the film when he spoke. But he does have a favorite sub-genre of time-travel stories.
“I've seen some science fiction stories that suggest that some of the greatest thinkers we've had, who were way ahead of their time, were actually time travelers. People like Newton or Einstein or Da Vinci. People who are thinking as no one had thought before, and got plunked in a time, but they already saw what would come and they'd just write it out. And it freaks everybody out around them and they transform the future. There's no evidence to support it other than that they're way ahead of their time.”
So, to summarize: Tyson can say for sure that Bullock's hair was wrong, but can't say for sure that Wolverine couldn't journey into the past. There's simply been no testing to prove it could or couldn't happen.
“And that's what makes it especially fertile material,” Tyson said.