Posted on 06/20/2005 9:35:37 AM PDT by LibWhacker
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 (http://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.
"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."
Cool.
"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."
I want to have a word with me about some mistakes Ive made.
Lunchtime, doubly so.
What a shame. Michael J. Fox did all that worrying for nothing. Bring back the flux converter.
Well...there go my weekend plans.
sigh.
All these time travel theories - both in acedemia and in entertainment - fail to deal with the biggest issue of all: Time travel isn't just about time, it's about space as well.
Simply put, even if you go back only a short amount of time, the place you left from (today) is millions and millions of miles away due to
1) the earths's orbit around the sun
2) Our solar system's position in our galaxy
3) our galaxy's position in the ever expanding universe.
So if you're in cleveland today and try to jump back to cleveland in 1984, guess what: Cleveland 1984 hasn't arrived here yet.
Let's see, they are saying time travel is possible if you go back in time, but if you can only travel backwards how do you come back to the present or are you stuck in the past?
Alternatively, Cleveland is in the same place it has always been -- it's the rest of the universe that has moved around it.
I have an excellent book which deals quite well with the subject. It's called "Something Under the Table is Drooling."
Calvin goes back in time to get an earlier version of himself to do the homework he procrastinated on, only to find out that the earlier version of himself is content in the belief that the work is the responsibility of his future self, whom they conspire to beat up, until they realize that they will eventually experience any suffering they inflict on the future Calvin.
Fortunately, Hobbes recognizes the silliness of these exploits, and the three Hobbeses wrote the paper, which he entitled, "How Hobbes Saved the Day, No Thanks to That Dundering Chowder-head Calvin."
Or were you thinking something a little drier, maybe?
No time today...I'll read this yesterday.
Oh, I also forgot the other of the two biggest roadblocks to time travel that are never mentioned: The first law of thermodynamics
You take billy bob from 2005 to 1984. The departure could be consistant with the first law if there was some billybob size release of energy. However in 1984, billy bob would have to suddenly appear, introducing a new amount of matter into a universe of 1984,where the first law tells us matter/energy can neither be created nor destroyed.
So they only possible way for billy bob to get back to 1984 would be to have a corresponding machine on the other side that turns energy into matter. So after you deal with this issue, you have to go back to the space/time issue.
>> Alternatively, Cleveland is in the same place it has always been -- it's the rest of the universe that has moved around it. <<
Can't be... My girlfriend isn't in Cleveland. So there's a basic conflict between your theory and hers.
I can see myself running into that problem. I am quite happy with the man I am today and I might be more of an interference with today self than a help to past self.
Great. So much for me & Clark Gable hooking up. I'm bummed now. ;-)
Forward, backward, doesn't matter much to us here and now; we're nowhere close to being able to do either, in practice.
So you're saying we shouldn't even study the subject? Interesting. Thanks for your input.
read for later ping
But what if you knew someone in the past was experimenting on a tachyon detection field, until something very big and very secret happened to him?
(Tachyons are a theoretical construct, conceived to reconcile Newtonian Physics with Einsteinian Physics. According to Tachyon theory, for every photon launched forward in time, an equal and opposite photon is launched backwards in time. This anti-photon is called a tachyon. But we simply are unaware of their existence because they have no effect on matter moving forward through time.)
You could send him instructions of how to build your machine, in the hopes that it is his reception of your instructions which explain what happened to him. Thus, you can prove the existence of God by demonstrating a logic bubble which is the cause of itself.
Or, you could aid return trip star-travel by anticipating your desire to return to a given time before you left. (For instance, if I wanted to send travellers to a star 500 light years away, I could immediately begin constructing a time machine to permit their descendents to return shortly after they left.)
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