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June 19, 2005
Yes, you can time travel into the past--but no touchie!
The following New Scientist piece explains new theoretical research into the paradoxes that we all thought should kick in if one was careless enough to travel back in time and kill off an elderly ancestor. Not that you would, of course.
Turns out that yes, you can go back (once you solve certain large-scale non-trivial problems, of course), but the nature of quantum whatsits pretty much prevents anything paradoxical from happening--ie, anything that might create, er, problems for you existing later, and such.
Since I'm currently writing a time-travel story, this is good news. Said story, btw, is currently up to 13,100 words. I'd be doing better, now that I'm banging out around 1000 words a day, if I hadn't had to chop 2000 words this past week.
In headache news: I've been seeing a musculo-skeletal physiotherapist every Monday morning. She's got me sitting differently, doing things with my arms differently, and trying to figure out what's going on with the upper-most vertebra of my spine, the right-hand side of which seems problematic. I'm wondering if it could be something as simple as that I'm right-handed, and thus do a lot of mousing. I'll ask. Upshot: I'm getting fewer, and less-intense, headaches lately, and they are turning up much later in the evening than hitherto. Not always, but often enough to draw comment.
Anyway, read on for intriguing time-travel-related goodness.
No paradox for time travellers
* 10:00 18 June 2005
* NewScientist.com news service
* Mark Buchanan
THE laws of physics seem to permit time travel, and with it, paradoxical situations such as the possibility that people could go back in time to prevent their own birth. But it turns out that such paradoxes may be ruled out by the weirdness inherent in laws of quantum physics.
Some solutions to the equations of Einstein's general theory of relativity lead to situations in which space-time curves back on itself, theoretically allowing travellers to loop back in time and meet younger versions of themselves. Because such time travel sets up paradoxes, many researchers suspect that some physical constraints must make time travel impossible. Now, physicists Daniel Greenberger of the City University of New York and Karl Svozil of the Vienna University of Technology in Austria have shown that the most basic features of quantum theory may ensure that time travellers could never alter the past, even if they are able to go back in time.
The constraint arises from a quantum object's ability to behave like a wave. Quantum objects split their existence into multiple component waves, each following a distinct path through space-time. Ultimately, an object is usually most likely to end up in places where its component waves recombine, or "interfere", constructively, with the peaks and troughs of the waves lined up, say. The object is unlikely to be in places where the components interfere destructively, and cancel each other out.
Quantum theory allows time travel because nothing prevents the waves from going back in time. When Greenberger and Svozil analysed what happens when these component waves flow into the past, they found that the paradoxes implied by Einstein's equations never arise. Waves that travel back in time interfere destructively, thus preventing anything from happening differently from that which has already taken place (www.arxiv.org/quant-ph/0506027). "If you travel into the past quantum mechanically, you would only see those alternatives consistent with the world you left behind you," says Greenberger. “The most basic features of quantum theory may ensure that time travellers could never alter the past”
"This is a very nice idea," says physicist Avshalom Elitzur of the Weizmann Institute in Rehovot, Israel, who also suggests that further work in the area could help to clarify the nature of time itself. "Time is a very mysterious thing."
Posted by adrian at June 19, 2005 06:29 PM
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