You probably read Timeline, the book by Michael Crichton in which a group of historians travels back in time. As the movie adaptation is about to be released, Scientific American discussed with theoretical physicist Michio Kaku, whose ideas inspired Crichton, and asked him if time travel was plausible.
Before reading this interview, here are some references to the movie. Below is a production photo from the official site of the movie (Copyright 2003 Paramount Pictures and Mutual Film Company).
And for your viewing pleasure, you also can watch in different resolutions a teaser or a trailer of the movie which opens in a theater near you on November 26 -- at least in the U.S..
Now, let's go back to Haku, who says that it's possible now to speak publicly about time travel without putting a career at risk, a thing unbelievable ten years ago.
Originally, the burden of proof was on physicists to prove that time travel was possible. Now the burden of proof is on physicists to prove there must be a law forbidding time travel.
He goes back to the past to tell us when scientists started to think about time travel in a rigorous way, from Einstein to logician Kurt Gödel or mathematician Roy Kerr.
Here are selected excerpts.
SA: The idea in Timeline is that you can "fax" particles into the past. What is the kernel of truth there?
MK: In the last ten years, there has been enormous progress in something called quantum teleportation. This is not science fiction anymore. Now, to be real, we're not talking about sending Captain Kirk across space and time. But we are talking about sending individual photons across space. In a few decades, maybe we will teleport the first virus, if the virus consists of a few thousand molecules. But at the present time, that's the limit of what we can do. And we can only teleport things in space, not time. But the concept of faxing matter is not totally out of the question. And that was also raised in my book. So, there is a little bit of truth there.
SA: How practical would it be to build one of these time machines?
MK: In fact the energies we are talking about are the energies of stars. It would take a civilization far more advanced than ours, unbelievably advanced, to begin to manipulate negative energy to create gateways to the past. But if you could obtain large quantities of negative energy -- and that's a big "if" -- then you could create a time machine that apparently obeys Einstein's equation, and perhaps the laws of quantum theory. You need string theory to ultimately control all the divergences [i.e., to make sure a hail of gravitons doesn't fry you when you open or close the time machine]. Some cynics say quantum effects may still make the machine blow up. But at this point the burden of proof has shifted: people who are skeptical of time travel have to prove it's impossible. And so far they have failed.
Kaku also speaks in detail about the paradoxes implied by time travel. and he discusses string theory or the influence of science fiction on physics. Scientific American also asked him what was his favorite time travel movie.
MK: Oh, that's a hard one. There is a problem being a physicist, and that is when you see these movies, you say, "Well, that's not right." And it really ruins it. But I like the Back to the Future series. Here was a movie where you actually saw the scientist building and doing things; he was an essential character in the entire series. Doc Brown was this crazy man, but at least they showed him. He was there. He was making the series work.
So is time travel possible? I'm still not sure, even if it would be fantastic to visit our past or our future.
Source: JR Minkel, for Scientific American, November 24, 2003
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