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What is the difference between the God Particle and the Graviton?

  1. Feb 25, 2009 #1
    What is the difference between the "God Particle" and the Graviton?

    I understand that they are looking for, and are hopefully close to finding the Higgs Boson, either with the Tevatron or with the LHC, whichever finds evidence for it first, and that the Higgs supposedly generates a field which gives to all other particles their appearance of mass, but how does the Higgs differ fundamentally from the supposed graviton particle, and why is there no race to find evidence for the later particle?

    As for your replies, I don't mind a few links being posted if you must, but I would really like to hear from your own words, and in plain simple language what the difference is. Please.
     
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  3. Feb 25, 2009 #2

    malawi_glenn

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    Re: What is the difference between the "God Particle" and the Graviton?

    The higgs particle gives particle mass, gravitons makes particle interact via their "mass charge".
     
  4. Feb 25, 2009 #3
    Re: What is the difference between the "God Particle" and the Graviton?

    For another difference, the Higgs is supposed to be a scalar, whereas the graviton would have spin-2. Also, please don't call the Higgs "the Lederman's particle" or whatever else. Call the Englert or the Brout boson if you like.
     
  5. Feb 25, 2009 #4

    blechman

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    Re: What is the difference between the "God Particle" and the Graviton?

    HA! You must be a Beligan! I'd call it the "Kibble-Guralnik-Hagen Particle" (Hagen was my QM professor!). :biggrin:

    For those that don't know the joke: 3 papers came out within a month or two from each other (in the SAME issue of the same journal, no less!) independently proposing the "Higgs" particle. They are:

    Brout, Englert: Phys.Rev.Lett.13:321-322,1964.
    Higgs: Phys.Rev.Lett.13:508-509,1964.
    Guralnik, Hagen, Kibble: Phys.Rev.Lett.13:585-587,1964.

    I guess Higgs must've had the best publicist! :wink:
     
  6. Feb 25, 2009 #5
    Re: What is the difference between the "God Particle" and the Graviton?

    What is the difference between "mass" and "mass charge" and is the graviton a more speculative type of particle than the Higgs?
     
  7. Feb 25, 2009 #6

    malawi_glenn

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    Re: What is the difference between the "God Particle" and the Graviton?

    mass charge = mass
     
  8. Feb 25, 2009 #7
    Re: What is the difference between the "God Particle" and the Graviton?

    I take it that scalar means that the Higgs is spin zero?

    Let's see, so the Higgs field gives particles their mass, and the supposed graviton causes all particles with mass to interact with each other gravitationally. So the graviton generates a gravitational field? Can it be said then that one field generates another? How is it that massless particles are also influenced by gravity if they are not influenced by the Higgs field?
    Is the graviton a totally speculative type of particle, or is there indirect standard model evidence for it's possible existence?
     
  9. Feb 25, 2009 #8

    blechman

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    Re: What is the difference between the "God Particle" and the Graviton?

    The Higgs boson and the graviton are fundamentally different beasts. Do not confuse them with each other.

    The Higgs boson is a spin zero, massive particle that, through its couplings to matter and the electroweak gauge bosons (W,Z), creates "inertial mass", that thing that describes a particle's rest energy. Gravity, on the other hand, does not "create" mass, but it couples to everything that has ENERGY; mass energy being one example, but massless things (like the photon) can couple to gravity as well, but not to the Higgs.

    Gravitons couple to all things with energy, inlcuding electrons, photons, Higgs bosons, and other gravitons! This is a form of the "Principle of Equivalence". The Higgs boson, on the other hand, only couples to certain particles in very specific ways.

    As far as "speculation" of the graviton.... that's a tricky question. To the extent that we see gravity, we see gravitons! Naive calculations that describe graviton interactions at room temperature (or even in the largest particle physics accelerators) give us things like Newton's Laws, and the corrections to Newton's Laws proposed by General Relativity. In that sense, there's nothing "speculative" about gravitons. But as the energy gets cranked up (and I mean REALLY cranked up!) is where our understanding of gravitons falls apart. So I guess the answer is: "Gravitons exist, but we don't know what they do as the energy gets very high!" That's where things like string theory, and many other proposals, come into play.

    Hope that helps!
     
  10. Feb 26, 2009 #9
    Re: What is the difference between the "God Particle" and the Graviton?

    Thanks blechman.
     
  11. Feb 27, 2009 #10
    Re: What is the difference between the "God Particle" and the Graviton?

    Every force in nature has exchange particles - gluons for Strong nuclear, W+, W- and Z0 for Weak Nuclear, photons for Electromagnetic and therefore Gravity must have an exchange particle.

    Gravitons is the postulated exchange particle for gravity.

    As a result of investigating certain Weak interactions, Higgs came up with a mechanism (the Higgs mechanism) that involved a particle which became known as the Higgs boson.

    Hence the Higgs boson and graviton are essentially different. (N.B. graviton is Spin 2 while Higgs is Spin 0)

    Initially the Higgs mechanism was able to explain why W+,W- and Z0 are massive while the photon is massless. That same mechanism was applied to quarks and leptons and it was found that the Higgs particle coupled with fermions in proportion to their mass.

    To me that has an essential difference then the often common statement that the Higgs boson causes mass which is not perfectly accurate.


    Back to your original question Dusty Matter,

    The Higgs mechanism has not been applied to the graviton because other than its postulated existence and obvious participation in gravitational interactions, very little is known about the graviton and its interactions
     
  12. Feb 27, 2009 #11
    Re: What is the difference between the "God Particle" and the Graviton?

    Thanks Deathless,
    Why is it that the only thing that is stated for sure about the graviton, is that it is a spin 2 particle?
    If it interacts with the Higgs boson, then I assume it is also speculated to have mass, so, if so, how massive is it speculated to be? Are we expected to be able to find it with the current upgraded particle accelerators, or is it still out of range?
    I understand that all of the known forces have a particle messenger that carries that force, and that all save gravity can be reconciled into a quantum state, but if gravity cannot be fit into both a relativistic and a quantum state then is it possible that gravity has no particle messenger, but is only a warping of the space/time field that surrounds everything? Is it possible that gravity requires no particle?
     
  13. Feb 27, 2009 #12

    blechman

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    Re: What is the difference between the "God Particle" and the Graviton?

    The graviton is described by a massless, rank-2 symmetric tensor (the metric), which behaves as a spin-2 field under rotations. That's why the graviton must have "spin-2".

    First of all, just b/c Higgs interacts with the graviton doesn't mean it has mass. Remember the graviton interacts with anything with ENERGY (think of the photon).

    That being said, the Higgs is expected to have mass. The estimates are rather broad, but without getting into technicalities, we expect it to be around 114 GeV/c^2. Although in some models, it could be as light as 85 GeV/c^2. It CANNOT be much heavier than about 250 GeV/c^2, however, since that would screw up the precision measurements that we have nailed down over the last 20 years of data taking. The lower bound comes from direct searches.

    If the Higgs exists and behaves as we expect it to behave, and has the mass that we expect it to have (see last paragraph), then the LHC will see it. There is also a change for the Tevatron at Fermilab to see it, but that's much harder since the Tevatron experiments will have a harder time dealing with the backgrounds.


    Again, we do not really understand how quantum gravity works! But ASSUMING that quantum gravity works SOMETHING like the way any other quantum system works, we would expect the gravitational field to be QUANTIZED (hence the name "quantum gravity"!). Your suggestion is tantamount to the statement, "There is NO quantum theory of gravity!" But who knows?

    It should be said that even in descriptions like string theory, there IS a graviton; that is what is meant by the statement "String theory contains quantum gravity."
     
  14. Feb 27, 2009 #13

    blechman

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    Re: What is the difference between the "God Particle" and the Graviton?

    It should also be mentioned, by the way, that a massless, spin-2 field (assuming some rather weak assumptions such as Lorentz invariance and the existence of an S-matrix) IS gravity! There is a famous and powerful theorem, called the "Coleman-Mandula Theorem" that says this (techincally it says something a little different, but my statement is a corollary of this theorem).

    So when you ask, "why spin-2?" that's another important point. Notice that this is quite different from ordinary QFT, where massless spin-0 and spin-1/2 theories can be varied, and massless spin-1 theories are always Yang-Mills theories, but they could be based on any gauge group. For spin-2, there is only ONE theory, and that is gravity!

    Gravity is unique. Neat, huh?
     
  15. Feb 27, 2009 #14
    Re: What is the difference between the "God Particle" and the Graviton?

    Thank you for trying to explain it to me blechman. Most of this over my head but I'm trying to understand. Please bear with me. Let me see if I've got this.

    A spin 2 field basically means the same thing as gravitational field, so a graviton is said to be a spin 2 particle.

    Now the Higgs particle interacts only with particles having mass, so it doesn't interact with say photons. The graviton interacts with all particles including the Higgs. It is possible however that the graviton may be massless however because the Higgs does not interact with the graviton?

    I am not saying that their is no quantum theory of gravity. I am saying is only what I've heard: that quantum gravity and relativistic gravity cannot be reconciled into one coherent theorem mathematically. What I am asking, is that, is it possible that one of the theories is wrong? Could quantized gravity be wrong? We know that relativistic gravity is right. Might there be no such thing as a graviton? There is no proof that gravity is quantized is there?
     
  16. Feb 27, 2009 #15

    blechman

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    Re: What is the difference between the "God Particle" and the Graviton?

    sorry, maybe i'm talking too fast. feel free to slow me down at any time! :wink:

    I might have opened a Pandora's Box with that last post. If it confused you, then forget about it. The point to remember is that when we say "spin" we are talking about how a field behaves under rotations. The graviton, being described as a perturbation to the metric, behaves as a "massless spin-2" excitation. This is not difficult to show, just apply the usual "Theory of Angular Momentum" to a symmetric tensor field. It's a graduate QM problem.

    The stuff I said before was just that there turns out to be only ONE "massless spin-2" theory that is consistent with things like Lorentz invariance and the existence of an S matrix. But that's just an amusing side note.

    the graviton must be massless since gravity obeys a [itex]\frac{1}{r^2}[/itex] force law. If the graviton had a mass, then this would not happen. Also, graviton masses cause damage to the Principle of Equivalence, a big no-no. Of course, as always, there are ways around this, but sticking to the MINIMAL theory, gravitons are massless, and spin-2.

    The Higgs interacts with the graviton (since the graviton interacts with the higgs, and "interact" is a symmetric relation!), however, the Higgs does not give mass to the graviton. I'm not sure of a words-only way of justifying this, but to the extent that I can appeal to authority, I can tell you that it just doesn't. If you don't believe me (and I hope you don't!) you should study this and convince yourself, but perhaps you should finish your QFT course first!

    I certainly wasn't accusing you of anything! :wink: It is certainly true that if you take the "naive" theory of quantum gravity (think E&M: quantize the classical fields and see what happens), then you find that the theory does not make sense. It is not renormalizable, and it breaks down at high energies. Not only that, but there is a funny thing going on with gravity, since in order to define a quantum theory you have to define a TIME, and since TIME is now a dynamical field in your gravity theory (part of that evolving spacetime manifold) then how do you define "equal time commutation relations" that you need to define a quantum field theory?! You see, something deep down is flawed with the picture.

    That being said, once again, as long as you restrict yourself to weak fields and low energies, you can do okay. But of course, such "weak fields" are WEAK - [itex]10^{-39}[/itex] the strength of QED, so while you might be able to calculate something, you'd never be able to see it in an experiment!

    You say, "We know that relativistic gravity is right." Is that really so? I mean, REALLY? We think it's right. But keep in mind that QM has passed EVERY test known to us, so are you really justified in just throwing it out? In fact, QM has been justified to MUCH higher precision than GR! Why are you so anxious to accept a less-tested theory over a more-tested one?

    I don't know, maybe. I guess you have to decide for yourself. The simple calculations that make sense, like single tree-level graviton exchange, give you things like the Newton potential, so it seems that you might be on the right track. But really, no one knows what goes on at the quantum level right next to a black hole singularity. And probably, we never will...

    Deep questions. Who knows what the answers are...
     
  17. Feb 27, 2009 #16
    Re: What is the difference between the "God Particle" and the Graviton?

    Thank you very much blechman. Let me think about this for awhile.
     
  18. Mar 2, 2009 #17
    Re: What is the difference between the "God Particle" and the Graviton?

    Okay, Thank you again for trying to teach me this stuff.
    To say that interactions are symmetric makes sense. (Action-reaction, tit for tat) and I can see that the graviton must have no mass for it to work or else it would interact with itself. (Gravity would create more mass which would generate more gravity, which would create … and on and on.) So if the Higgs interacts with the graviton, then the graviton must interact with the Higgs. The higgs gives mass to the particles that it interacts with, but Not to the graviton. Why? There are different possibilities? The interaction is canceled somehow. The Higgs and the graviton don't interact? There is no graviton? Or a possibility I have not considered.

    I agree with QM, when it comes to all of the known forces and particles. (save gravity) I would never attempt to throw it out as a working model. I understand that it is a great success in the understanding of particle physics. And Relativity too is also a great success. It displays itself everyday in particle accelerators when particles are brought up to such high speeds. From a cosmological point of view it stands up as well. When I start asking about whether it is really so, when it comes to the graviton particle, I am not questioning QM or Relativity. I think that they are both outstanding pillars in the understanding of physics. I am questioning the ideas and theories for the graviton itself. I am questioning the graviton particle.

    I do see gravity from a more relativistic point of view. Most of the books I have read have dealt with physics from a historical point of view, or from the understanding that a layman can grasp. Let’s face it. The older physicists are just easier to understand because their discoveries are more basic. Relativity came before the Standard Model and Quantum Mechanics, and it describes gravity quite well. No one has ever seen the graviton. And I also have a point of view from a cosmological angle that questions the graviton particle. You’ve probably already seen this though.

    Black Holes. The event horizon of a BH will not let even light escape. The gravitation at that point overcomes the speed of light, so that not even particles cannot escape from below this realm. If gravity can be explained QM style (a sub light particle) then how is it that gravity can still reach up from below the event horizon of a BH? If particles cannot escape from below the event horizon, then gravity too, should be cut off.

    Now from a Relativistic point of view, this conundrum is not an issue. Gravity is strictly a warping of the space/time fabric, and we really have no way at this time of determining just how warped this fabric can become. No particle is required. The fabric can simply be warped to such an extent that light and everything else cannot escape and yet gravity still reigns as king.

    Now I certainly don’t have the education that blechman and most of you have, but from what I understand, even you have admitted that there is a problem reconciling QM and Relativistic gravitational theory.

    I originally only wanted to know the difference between the Higgs and the Graviton, especially when I learned that there may be evidence and reason for a Higgs particle. I had thought that they were one and the same, but just a separate theory as to how they worked. Thank you for explaining to me that they are completely separate entities. If now, you can correct my thinking regarding the graviton particle, please do. I am not arguing and trying to present my ideas as gospel. I am only trying to explain why I’m reasoning the way I am. If you have knowledge that can help me to see things more clearly in regards to the graviton and why I should accept a particle theory for it, then please do.
     
    Last edited: Mar 2, 2009
  19. Mar 2, 2009 #18

    blechman

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    Re: What is the difference between the "God Particle" and the Graviton?

    OK, there is a wrong statement in this paragraph. Gravitons DO interact with each other, and this is not a contradiction (it has nothing to do with the fact that it has no mass). Let me say it again: gravity couples to ENERGY, not mass! Massless particles feel gravity (think of the bending of light).

    You're statement about how the backreaction of gravity to itself is precisely the point of why gravity is a "nonrenormalizable theory" - that is (one of the reasons) why we do not understand how to quantize it.

    To answer the question of the paragraph I have to appeal to some authority. The graviton cannot do what the Higgs does because it would (1) violate Lorentz invariance, something nature does not seem to do, and (2) violate the Equivalence principle, again something nature doesn't seem to do. (1) has to do with the fact that the graviton has spin, and (2) has to do with the fact that letting the graviton give mass means that it gets mass, and a massive graviton does not obey the equivalence principle (see your favorite advanced QFT textbook that discusses gravity). These are experimental constraints, and cannot be waylaid.


    The issue of particle accelerators refers to SPECIAL relativity, not the general theory. There is no problem of SR and QM - this is nothing less than QFT itself. The problem is GR. That might have just been a semantic thing, but I wanted to be sure we were on the same page.

    As to the rest of this paragraph: I can only say what I said before. We do not know what "quantum relativity" is, and therefore we cannot talk about what a "graviton" is. HOWEVER, to the extent that we can APPROXIMATE "quantum relativity" in a low-energy limit in terms of things like gravitons, we do pretty well. The **REAL** test is the gravity-wave experiments. If they see gravity waves, then we'll know that the "graviton approximation" makes sense. Unfortunately, since Gravity waves are so difficult to see, if they don't see them, that won't rule out the theory.

    As a "professional" I don't agree with this paragraph completely. Historical approaches often lead to the wrong ideas, since people can spend 100 years doing it wrong! But let's not get sidetracked.

    Besides: relativity and QM were discovered at roughly the same time. :wink:

    What is your cosmological anti-graviton argument? If we see gravity waves, then that's that. There are gravitons!


    it is!!

    Gravitons are emitted FROM THE SURFACE of the event horizon (remember: gravitons are massless, and therefore move at the speed of light). THAT's what we see. There is NO information (gravitational or otherwise) that can escape from INSIDE the black hole. This is not a contradiction of the existence of gravitons.

    Black holes ARE a serious... no, I take that back... VERY!!!!! serious problem for quantum gravity, but not for the reasons that you mention. It has to do with "conservation of information" but that will take us too far afield from the the thread. If you want to talk more about that, just ask.


    Good, you are right that they have absolutely nothing to do with each other! If you gain nothing else from my and other's contributions to this thread, let it be that! :wink: I tried to answer your questions and correct any flaws in your arguments above. Feel free to ask me anything else, or ask me to get into detail on any of the above points, or if I did a bad job explaining something, then I apologize and I'll try again.
     
  20. Mar 3, 2009 #19
    Re: What is the difference between the "God Particle" and the Graviton?

    The Higgs *boson* couples with a particle having a mass. It does not give other particles mass or create mass.
    Indeed when the Higgs mechanism was first used it explained why photons have no mass and the W and Z particles do.

    The Higgs *field* is responsible for creating mass and is a property (theoretically) of space time - exactly how, I don't know.:wink: The Higgs boson itself, is theorized to have mass through the presence of this field as do other massive particles.

    So a hypothetical direct interaction of the Higgs boson and the graviton is impossible since the Higgs couples *only* with particles with mass.

    Sorry, not having a go at you but that is indeed a 'bad job' (in places only) as you tend to cloud the issue occassionally :smile:
     
  21. Mar 3, 2009 #20
    Re: What is the difference between the "God Particle" and the Graviton?

    Do Higgs bosons have energy ?
     
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