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Time and Gravity

  1. Mar 12, 2008 #1
    To quote from ‘Time, Gravity and Quantum Mechanics, by W. G. Unruh’;
    “A more accurate way of summarizing the lessons of General Relativity is that gravity does not cause time to run differently in different places (e.g., faster far from the earth than near it). Gravity is the unequable flow of time from place to place. It is not
    that there are two separate phenomena, namely gravity and time and that the one, gravity, affects the other. Rather the theory states that the phenomena we usually ascribe to gravity are actually caused by time’s flowing unequably from place to place.”

    It seems that perhaps gravity and time should be equated (though I personally think that they are aspects of the same phenomena seen from 'different angles' so to speak), surely this will lead to an evaporation of many of the issues that arise when trying to unify QED and GR

    Any thoughts on this line of thinking would be appreciated as I am trying to put together a paper using this perspective
    Last edited: Mar 12, 2008
  2. jcsd
  3. Mar 22, 2008 #2
    time subset of gravity

    Well,what is gravity 1st of all?G.R says it is the distortion of spacetime,hence the distortion of the entity "spacetime"causes time to slow down,but neither is time equivalent to gravity.but to its family(spacetime) plus its property which is the curvature of this family.
  4. Mar 22, 2008 #3

    Ken G

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    Yes, I think Unruh could be paraphrased as saying "gravity does not cause time to flow differently, it is the way time flows". But that is inherent in the theory of GR, and the problem with unification with QM persists despite that insight. As I understand it, the barrier to unification is the fact that time is only a parameter of quantum mechanics that is carried through the predictions into our classical sense of time, but in GR it is a real attribute of an event. Apparently the situation would be more satisfactory if gravity acted on the wavefunction rather than on the parametrization of the wavefunction, because we don't know how to propagate the tensor information through the Shrodinger equation-- though I do not understand the details.
    Last edited: Mar 22, 2008
  5. Mar 24, 2008 #4
    Gravity & QM

    lets return to the current theoritical physicists realm(string theory),according quantum mechanics we all know that space is not an empty vacuum but the soup of the so called virtual particles which are popping in &out of existence.hence string theory portrays particles as nothing else but tiny vibrations of a string which is about a planks length long you all know this.thus string theory would then define vacuum as the soup of the so called virtual vibrations &anti-vibrations which are availing themselves into existence &then dissapears again now & then continously....now the questions are,what triggered this phenomenon &what is the nature of the energy involved?
  6. Mar 24, 2008 #5
    That question is unanswerable since you're asking us to speculate on hypothesis (String theory) Saying if string theory exists, without having any model of strings but a mathematical one. It means the only thing you can do is write out some more maths to explain it, and even then it's merely pure maths and proof given x by induction.

    So in short how can we answer that question?

    Why is there a soup of virtual particles? Well since they violate causality that's a little difficult to speculate on also? But let me try, the ether exists, hehe. :wink:
  7. Mar 24, 2008 #6
    Im totally not convinced by your ans.if you are one of those individuas who believes not in string theory what then do you believe in?string theory is a deep MATHEMATICAL consequence of GR & QM.the fact that it is currently impossible for us to carry out experiments pertaining the predictions made by string theory it doesnt mean the theory is not correct.I am sure that one day we will be proud to say we are now capable of carrying out the experiments,if not us then the generation to come will.
  8. Mar 24, 2008 #7
    No I don't believe in hypothesis, apparently God exists, but I'm agnostic about that too. It's quite true I don't believe without evidence, theories now that's a different matter. String theory is a consequence of pure mathematics and that alone atm. Unless you have some scientific evidence for it being true, it therefore follows all you are doing is speculating on speculation, no? It's no different from trying to explain how you can travel through a black hole and not be destroyed, what black hole? Although at least that has inferred evidence.

    Thus your question is unanswerable, it would be philosophising on philosophy to try and do so.
  9. Mar 24, 2008 #8


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    Wow, this thread's gotten way too philosophical! Note that science has nothing to do with beliefs; science is either right or wrong, regardless of a person's own opinions.

    This comment doesn't make any sense. You are comparing string theory to something that is basically science fiction-- travelling "through a black hole without being destroyed" contradicts the current theory of gravity.
  10. Mar 24, 2008 #9
    Show me one single piece of evidence for string theory, now show me one single piece of evidence for God. Now the FSM. Science involves the scientific method, string theory does not, thus science, thus philosophy, pure maths does not a theory make.

    It is wise when there is no evidence either way in science to be at least somewhat agnostic, otherwise it's just belief, and faith and hope, and that will cloud your judgement. Is String theory a theory: no. Is it a hypothesis: yes. But then so are the existence of tachyons.
    Last edited: Mar 24, 2008
  11. Mar 24, 2008 #10


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    I don't recall saying that string theory has been tested, or that it is in fact strictly "science," thus I'm not too sure what you're replying to.

    You were comparing string theory to science fiction-- this is incredibly misleading, at best.
  12. Mar 24, 2008 #11
    Thus the misunderstanding? Michio Kaku said that, if he was talking about the plot of Star Trek then he kept that quiet.

    Are you trying to tell me that we have more evidence for string theory thus any speculation on it is more valid? Because I'm not too sure what your point is atm? :confused:
  13. Mar 24, 2008 #12
    I have fairly severe misgivings about string theory myself. However, this response was more than reasonable.

    Schrodinger's Dog, I don't get your star trek/God/FSM analogy either.

    How does a concession that string theory is not tested nor strictly "science" translate to you implying that cristo implied there is "more evidence"? Are you implying that science is not allowed to speculate outside the standard model without the evidence? That to me means you want theories to make new testable predictions before they are developed.

    There is much you can criticize string theory and associated claims for but cristo clearly didn't cross that line. You did.
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