The researchers would adjust the position of the second detector to find the spot where the stream changes from a fuzzy diffraction pattern to a more defined, wavy interference pattern. If they're successful with the first experiment, they would try a more elaborate demonstration: One stream would be sent directly through the screen to a detector - while the other would be split by the slits, then take a detour through two 6-mile (10-kilometer) lengths of optical cable before reaching a second detector. Let's allow both of these possibilities to have a little bit of play.'" Without giving away the plot, Greene said that the writers of the "Deja Vu" movie "took a very creative approach. You'd just be an alien visitor from a different reality, living out a scenario that's called the "many-worlds interpretation." But it wouldn't be the same universe you came from. You could go back and shoot your father, creating a universe where you were never born. Causality can be changed, sending the universe down different forks in the road.Nature would conspire against changing causality, something Cambridge physicist Stephen Hawking has called the "chronology protection conjecture": For example, if you tried to shoot your father before you were born, somehow the gun would fail to go off.If you assume that such reversals are possible, Greene said physics would allow for two possibilities: What we're talking about here is reversing time's flow, and perhaps influencing the stream of causality to follow another course: one in which, say, Hitler died in childhood, or 9/11 never happened, or Britney Spears stayed happily married. For example, astronauts returning from a space station mission might find that their watches were a few nanoseconds behind earthly timepieces, thanks to relativity.īut most time-travel plots involve more than just slowing down or speeding up the forward pace of time. Over the past 100 years or so, physicists have come to understand that time travel is all relative: In a sense, we're all traveling through time, and depending on your reference frame, some would seem to be doing it more quickly than others. "It opens the door to doing all kinds of really bizarre things," he said. "It was a kick to be in the room with Jerry Bruckheimer and Tony Scott and the writers, talking about special relativity and general relativity and wormholes," he told .Ĭramer, meanwhile, has done research into ultra-relavistic heavy-ion physics at CERN and Brookhaven National Laboratory - but he's also written two science-fiction novels and pens a regular column for Analog magazine called "The Alternate View." If his experiments show that retro-causality is a reality - that one event can determine the outcome of another event taking place 50 microseconds earlier - it could lend support to the ultimate alternate view of quantum physics. He and his colleagues plan to try just such an experiment next year.Ĭramer acknowledged that the concept of retro-causality doesn't seem to make sense, "but I don't understand why not."īoth Greene and Cramer know the science as well as the fiction side of the time-travel issue: Greene is the author of "The Elegant Universe," a best-selling book on string theory - but he also played a cameo role in "Frequency," a time-travel movie released in 2000, and served as a scientific consultant for "Deja Vu." Theoretically, at least, it might be possible for the future to influence the past, said John Cramer, a physicist at the University of Washington. Over the next few years, some experiments hold out a chance of finally being able to show whether or not time can move backward as well as forward. "But many of us, including me, are impressed that nobody's been able to prove that." "Many physicists have a gut feeling that time travel to the past is not possible," said Columbia University theoretical physicist Brian Greene. ![]() Despite years of debate, scientists still haven't completely ruled out the possibility of going back in time.
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