Discussion in 'Physics & Math' started by Wolv1, Aug 25, 2008.
Big bang violated causality.
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Please don't listen to Reiku, he doesn't really know what he's talking about.
And I'm not sure that CTC's violate causality. The way I understand it is that the CTC will closes on itself in space and time. That means if you travel along one, you'll be returned to exactly the place and time you left. This doesn't seem to violate causality to me.
what could be used to disprove closed timelike curves?
Well, one would have to find some principle in the full quantum theory of gravity which prohibited them---some symmetry or something. I am not an expert in this field, so I don't know precisely why people think they will be disproved in a full theory of QG. They ARE a feature of the classical theory, this much is certain.
I do know what i am talking about Ben.
One of the reasons why the famous Fred Hoyle, (an astrophysicist, and a better physicist than what me or Ben will probably turn out to be), was that big bang was a cause, without any prior effect.
Ben, what do you get off, trying to say i don't know what i am talking about? I don't say these things for no reason.
i know ctc's exist in kerr's metric,but would it be possible for us to use it?
You mean, could we use CTC's to move through time? Possibly. If we can even endure a trip, including that they need to exist also.
o so we we dont know if they even exist?
So you don't actually read the replies...
post NUMBER TWO for crying out loud:
ive also heard and read that quantum mechanics don't go with ctc's?
Deliberately trolling now?
Also answered in this thread.
oli,do you think ctc's exist?
So now your "research" includes personal opinion?
What I "think" has no bearing on science...
Ben answered correctly, as he usually does.
They have not been observed.
Anything else is speculation, so if I said I think they do then it's unsupported speculation.
no it was just out of curiosity,reiku dosent know what he is talking about?
Was that a question, or stating something? You know, about me?
I wrote this a long time back now. For someone who doesn't know what they are talking about, it's more than half of what people round here can say on the subject in an essay. I went on to talk about retrocausality, but it spoke about subjects Ben would not agree with.
''Closed Timelike Curves
In physics, when we consider a particle and its past, present and future path throughout the universe, we call its definite path a ‘’worldline.’’ A particle will always try to move in straight lines throughout spacetime, but because space and time are curved into each other, most of the time, they follow curved paths through space.
This is what we mean by a warped space, or distorted spacetime. We find that these distortions are in fact just gravity, or curved spacetime. And gravity is the presence of matter itself. Even light cannot escape the wrath of gravity at very strong levels, but usually, a tiny photon traveling in empty space will almost definitely travel in straight lines.
But there really isn’t just one straight line, or worldline for any particle. We find that according to Feynman’s Sum Over Histories, a particle actually has every possible path to its disposal – these path’s are of both times past and times to come.
We find that these paths have themselves a statistical element about them and will variably shape how a particle will end up in any state given upon measurement. Take a photon traveling from the past: It will take every known possible path, even those improbable paths through a black hole (but as you can imagine, the statistics for this are so vanishingly small, we can nearly neglect them, but Hawking shows that it is possible for allowing a particle to travel at superluminal speeds using the uncertainty principle), and upon arrival at Earth, we can measure the photon, and all the paths its could have taken, according to the wave function, suddenly collapses into a single probability!
For Feynman’s Sum Over History to apply to physics, one must use imaginary time, rather than the concept of real time. Imaginary time is the same thing as real space, whereas real time is the same thing as imaginary space. The two concepts are pivotal to understanding how we contemplate different ways to look at our universe at large, and even at small scales.
Granted, the concepts themselves are purely mathematical, but they play an enormous part in relativity and quantum mechanics. You need to first gather up all the possible path a particle can take, bundle them together so-to-say, and then we need to measure those statistics against real time, and the result is the real conditions of the particles history; but even those results have a slight statistical aura about them.
In the case of the universe at large and gravity, Feynman would need to have analyzed all possible histories of a curved spacetime, and this at large affects everything that has a worldline in this universe. There would indeed be a finite number of possible outcomes, but one would need to chose which outcome best fits this universe today.
Hawking reminds us, that if this is indeed the case, the class of curved spacetime that determines the universe today (including those spaces and times which are blown into unimaginable proportions, or singularities), the probabilities of such spaces cannot be determined by the theory. However, he says it is possible if we calculate them in some arbitrary way. Dr. Hawking is very cryptic this way, but what he means is that science cannot predict any history for the universe if there is a singular past. So any attempt to learn how a universe with a singularity would result, is really a disaster for science.
Now, since this study is about time and space at large, let’s consider CTC’s or ‘’Closed-Timelike-Curves.’’ This is a worldline describing a physical system which is ‘’closed’’. This means something physical in fact returns to original starting point. We call such movements ‘’sinusoidal’’.
The idea of CTC’s was in fact developed by Willem Jacob van Stockum in 1937 and later by the infamous Kurt Godel in 1949. There is indeed a lot of controversy over their existence, but if they do exist, it could revolutionize relativity including our ability to create machines capable of a global causal violation; in other words, a path that twists in space and moves through time.
Worldlines and of course Feynman’s Sum Over Histories is best described in terms of ‘’light cones’’, which is really a more specified term that is timelike in nature. It will probably be more recognized than the last two concepts. Light cones describe every possible future of a physical object in spacetime, given a current measurement during the present time. This can seem a bit strange, because not only does one deflate all possibilities of the past events to a single value upon measurement (the collapse of the wave function), but one can now calculate all possible path’s in the future in real time.
Because particles don’t have a specific arrow of directionality following cause and effect, one can have in special conditions, a particle which experiences a timespace and spacetime that is so heavily curved, it can return to the place it began – in other words, things at very small levels are able to move back through time… From effect to the cause instead of cause to the effect. These are simply basic rotations through space and through time, which are conveniently called, ‘’closed-timelike-curves’’, so just think of a loop that twists in space and moves through time back into its original starting point.
Frank J. Tipler, Prof. of mathematics and physics at Tulane University in New Orleans, developed an ingenious idea involving such closed-timelike-curves. I have read his article… it’s a good read. He explains that classical relativity does in fact predict pathological behavior. The exact nature of the pathology, or, CTC’s, are however very debatable, since the predictive nature of relativity has itself many outcomes.
His design is quite old now, but it is still a probability in physics creation of time machines today. His design is to create a huge rapidly rotating cylinder (possibly in space – I assume), and the spacetime around the cylinder will be warped to such an extent, that even time itself becomes sinusoidally warped so that instead of flowing in the correct direction… that is forwards, it in fact varies in an oscillating manner. Of course, one might think that such a spacetime would rip a spacetime traveler apart, but we aren’t talking about black holes here. If one entered this machine carefully, one could avoid being turned into spaghetti and experience a dilated time frame. Perhaps this is the time machine of the future?''
how could the big bang violate causality? also are ctc's only a solution? i also read that while GR might allow ctc's,that quantum mechanics might not allow them, is this true?
Relativity, and their solutions, can apply to any stretch of physics. This is what makes relativity universal, and invariant, so if CTC's are real, it even applies to the quantum world as well.
Big Bang kind of violates causality, in the sense that cause and effect breaks down at this point. All of a sudden, space and time appeared at big bang, but there is no prior cause that can explain why it all came about. This is why in some light, it does seem to violate causality.
but woudlnt it be impossible to use a ctc in kerr's metric becuase we would be destroyed by the intense black hole?
There are many theories surrounding a black hole. Since both black holes and CTC's are purely hypothetical it's very hard to surmise actual working absolute theories on these subjects, without a bit of experimental proof. A lot of mathematical work has gone into both theories, and both theories are accepted in mainstream.
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