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Relativity, Black Holes and Gravitons

Discussion in 'Science & Technology' started by FredLC, May 22, 2011.

  1. FredLC

    FredLC A Lawyer as You Can See! Retired Moderator

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    Hello, guys.

    Been a while since I've been here, specially to start a thread of my own.

    But recently I've been reading about modern physics, such as the theory of elementary particles, string theory, etc...

    One thing I didn't know before reading new books recently is that the forces of the universe are conveyed as particles, called messenger particles. A weird idea, but not weirder than extra dimensions, and other wild ideas of modern theories.

    But I'm having trouble converging that notion with the central idea of general relativity that gravity is caused by warps in the fabric of space; I mean, it's simple to conceive the idea that such warps can cause "slides" that matter will follow in space time, but how the heck a shape can be communicated as particles is something none of the books I read confronted.

    But at this point, I was taking this difficulty as a linguistic problem, as the inadequacy of rhetoric to explain what the warping of reality truly is. However, considering this difficulty, something came up that challenged all the understanding I was building, and again, that I didn't found confronted in the books I've read or the lectures I've watched on youtube:

    Here's the problem - the core idea of special relativity, what lead Einstein to his amazing achievements, was the concept that no matter, no energy, no information or influence, can travel faster than the speed of light - therefore, the speed of gravity also could not exceed this limit.

    If that is true, than how come the gravitons - the messenger particles for gravity - can transmit the monstrous force of a black hole? I mean, black holes are black because light-speed is not good enough as escape velocity; so, gravitons also shouldn't be able to reach escape velocity.

    It's easy to understand a black hole if you understand the concept of gravity as a deformation of the space-time, but as an effect of constant exchanging of messenger particles, it seems to me that gravity would neutralize itself, making it impossible for the particles to escape it's own shackles.

    It would be relatively easy to accommodate this if I thought that the particle escapes "only once" to cause the warping of space time, than later the already curved space would not need the trapped particles to exert influence. But this would create a gravitational influence that, once settled, is instantaneous across the space and not bound by the light-speed limit, flying in the face of the whole theory.

    I couldn't figure out how to reconcile these - and I doubt I'd be meeting many astrophysicists in my city for a chat, so, is there anyone here who is physics-prone who can enlighten the topic without getting overly mathematical?

    Regards :).
     
  2. Souron

    Souron The Dark Lord

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    Indeed there is no agreed upon reconciliation. Messenger particles are a facet of quantum mechanics and the standard model. Space curving is a facet of relativity. It is presumed that the theory the reconciles the two would include a messenger particle for gravity, but no proven reconciliation exists. You would have to read about a particular proposed quantum gravity theory in order to get answers to this question.
     
  3. FredLC

    FredLC A Lawyer as You Can See! Retired Moderator

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    Well, I've read Brian Green's The Elegant Universe. For the laymen such as me, granted, but he does embrace both gravity as a curvature (that notion being the reason for the incompatibility of relativity with the different concept of space in quantum mechanics) and gravitons as existing particles (in fact he explains the difference in strength between gravity and the other forces by assuming that loose ended graviton "strings" may disappear into higher dimensions).

    The problem I addressed, however, isn't even proposed, let alone explained, neither in the book or in the Nova documentary. Perhaps he underestimated the audience and thought we wouldn't figure it out...

    Anyway, so there is a conflict recognized in physics, than. Good to know it's not just me overthinking...

    Regards :).
     
  4. Kozmos

    Kozmos Jew Detective

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    I am reading right now Parallel Worlds by Kaku and he also mentions that gravitons could leak over into other dimension or simply hover on the surface of our 3-brane. It is a 2005 book but not much has changed I think.
     
  5. Abaddon

    Abaddon Deity

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    I have nothing to add to the discussion, but I am excited Fred is back here! :D
     
  6. Gigaz

    Gigaz civoholic

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    Thats rather tricky.
    First of all, every force can be considered as a continuous in space and time. On the other hand, it is thought to be transmitted by virtual particles, which are waves. But one can transform every funktion from the real space into the frequency space via the fourier transformation, as long as one has infinite many wavelengths to work with. And the theory in fact states that the number of virtual particles in an interacting system is infinite. :p
     
  7. dutchfire

    dutchfire Moderator Moderator

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    Good question! The matter you discuss is rather advanced physics and partly (especially gravitons) speculative. What is important to understand is that the two "modern" theories, quantum mechanics/quantum field theory and General Relativity, deal with totally different regimes. QM deals with small things, GR with heavy things. There currently is no good theory for things that are both heavy and small. A lot of work is being done in this area. There is a wide consensus that the Standard Model of elementary particles, which is the current best proven theory about small things, has some holes in it that need to be explained better (to name a few: CP-violation, the matter-antimatter balance, why neutrinos have mass, the Higgsmechanism giving mass to the other particles). General Relativity also has issues, for example the cosmological constant and "Dark Energy". There are several attempts trying to fix these issues and combine the two, such as string theory, but none of them is really appealing so far.
     
  8. uppi

    uppi Deity

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    Gravitons are the result of the (so far) unsuccessful attempt to apply Quantum Field Theory to gravity. So it is not surprising that they seem to be inconsistent with General Relativity, because in the end QFT itself is inconsistent with GR.

    Or in other words: When your only tool is QFT, you tend to see all forces as gauge bosons.
     
  9. peter grimes

    peter grimes ... Moderator

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    To a man with a hammer, everything looks like a nail ;)

    I just finished reading a book that deals with some of this tangentially: Decoding the Universe by Charles Seife. It deals with Information Theory, and how Information, Entropy, and such are all related.

    He doesn't talk about Quantum Gravity, but he does deal with black holes as information processing objects. And I've read other things that look at gravity as related to information gradients.

    I still don't understand anything at all about this idea of information :lol:
     
  10. Kozmos

    Kozmos Jew Detective

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    Information makes sense when you put it into a quantum perspective and various entanglements.
     
  11. FredLC

    FredLC A Lawyer as You Can See! Retired Moderator

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    Hehe; looks like CFC haven't forgotten me yet.

    Thanks.

    Regards :).
     
  12. FredLC

    FredLC A Lawyer as You Can See! Retired Moderator

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    That's why I only pictured the problem when I started reading about string theory. Indeed, this particular issue wouldn't exist in each theory individually considered.

    I heard of all those problems; however, regarding the cosmological constant, wasn't it abandoned by Einstein after Hubble proved the universe was indeed expanding?

    I actually remember reading an article in which the author suggested that perhaps the constant should be revived and used to explain "dark energy", that may very well be just a symptom of a defect in gravity equations instead of an entirely different influence.

    Regards :).
     
  13. ParadigmShifter

    ParadigmShifter Random Nonsense Generator

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    We thought you had been attacked and kidnapped by rolls of tape wielding fascists!

    I'd never thought about the black hole/graviton thing before... interesting.

    EDIT: Cosmological constant is back last I heard, it explains dark matter/energy.
     
  14. Millman

    Millman Mark the Magnificent

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    I saw the article about Hawking condemning heaven. Unless you hear it from his own mouth the current constant argument stands. Physical proof proving otherwise. You can most likely see your monitor and read this. You can feel your hands stroke the keys. Maybe your kids walked into your room.

    We can see all those events but when you're invisible and/or science hasn't defined you it's physcoligically that much harder to believe. There is another thread though. ;)
     
  15. dutchfire

    dutchfire Moderator Moderator

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    The cosmological constant is one of the "explanations" for dark energy, another one of those vaguely understood things in physics. As far as I can see, it's currently the main explanation of dark energy.
     
  16. Souron

    Souron The Dark Lord

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    For a book that deal with the subject directly, try Three Roads to Quantum Gravity, by Lee Smolen. I can't say that the book does a clear job of explaining how the models it talks about resolve these problems, but it tries to, and it does does explain the contention between relativity and QFT two theories.
     
  17. Terrapin

    Terrapin Prince

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    I am not sure that it addresses the How can gravitons get out of a black hole question, but I highly recommend Leonard Susskind's "Black Hole Wars" for learning more about quantum physics, general relativity, string theory and the holographic principle. Susskind is the only physicist I have read who can actually write well. Also, for almost daily updates on new findings, I recommend Lubos Motl's blog, The Reference Frame.
     
  18. FredLC

    FredLC A Lawyer as You Can See! Retired Moderator

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    Such gruesome and sticky fate...

    And it still bugs me!

    Really? I liked Brian Green's book a lot. The other physicist I read, Marcelo Gleiser, probably isn't as renown, though he is pretty good. He does not write as elegantly as Green, though, and probably his books gets disproportional editorial attention in Brazil, 'cause he is Brazilian....

    What surprises me in your statement is that I've seen several lectures on the internet from most of the people mentioned here. Susskind didn't strike me as particularly eloquent, even though he has a good domain of rethoric, as expected from someone with his brains.

    Ok, this thread took an unexpected turn to the cosmological constant. Here is what I have read on the topic, please feel free to correct me if I misrepresent something:

    After Einstein's general relativity was confirmed, it became obvious that the universe could not be stable, because matter attract matter, hence everything had to be gathering together due to this intrinsic attraction.

    With no good reason, just because his "political" cosmology was that the universe had to be infinite, Einstein postulated, rather than concluded, a force that opposed Gravity equally - which he called "cosmological constant".

    It never really explained anything, nor related to any phenomenae, it just served Einstein in the one instance where he failed to make the bold prediction that his theory was demanding - a finite universe with an expiration date. The theory of the "cosmic egg" from George Lamatre, that eventually became known as Big Bang, came exactly from studying Einstein equations without the prejudice of having to have an endless eternal universe.

    But it was a blow for the cosmological constant, that didn't derive from the theory, nor corresponded to the observations.

    When Edwin Hubble found out the universe was actually expanding, it surprised everybody, but could still be easily explained by simply suggesting that the momentum of the explosion could still be stronger than the attraction.

    But when modern techniques brought about a second surprise - that the expansion was actually accelerating rather than slowing down - that raised some hairs, because there was no way to accommodate it within Gravity's einsteinian description.

    The unknown force that is powering this acceleration is called "dark energy", and that name is just a filler for the fact that we don't know what the heck it is. Some suggest it may be a 5th force of nature; some, think it's a symptom that we got gravity wrong again, others think it's regular energy from unknown sources - we just don't know.

    Ok, than - my problem with suggesting the "cosmological constant" as an explanation for dark energy (and dutchfire, I acknowledge you put explanation between quotation marks as well) is that it seems to me that a language filler is being used to explain another language filler, and the term is being thrown around just because Einstein suggested a marginally similar function when he postulated it (though originally it should keep the universe still, rather than make it grow).

    Regards :).
     
  19. peter grimes

    peter grimes ... Moderator

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    Fred, are you aware of the wonderful blog Starts With A Bang authored by Ethan Seigel? He has several posts dealing with dark matter, and a couple on dark energy.

    He has a particular point of view, I'm sure other experts in the field may disagree with him. But I find his explanations very accessible.

    Plus he uses lots of pictures :)
     
  20. dutchfire

    dutchfire Moderator Moderator

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    Two things: The cosmological constant was added for political/philosophical reasons by Einstein. However, it is theoretically possible to add the term to the field equations, which is quite special. The various properties the field equations need to have, gravely limit the possiblities for terms in the field equations. As such, it might be better to talk about models with cosmological constant 0 than about models without cosmological constant.

    Second, the cosmological constant is not just a language filler. It can be interpreted as the energy-density of vacuum. So it basically tells us how much energy a tiny bit of "nothing" possesses. Of course, the question then is, why does a piece of "nothing" have a certain amount of energy associated with it. A microscopic (quantum) explanation explaining correctly the energy density of the vacuum measured in astronomy would surely result in a Nobel prize.
     

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