Gravitons or Warped Space-Time?

[shadowpuppet]

*Please read the thread before you vote in the poll!

Disclaimer: I am not advocating a fraudulent theory, I am presenting original evidence and logic (detailing the contradictions in quantized gravity) both of which are certainly open for debate.

Gravitation

In classical mechanics, the charge of the gravitational field is equivalent to the translational inertia, such that all objects experience the same acceleration regardless of their mass. This happily corresponds to the notion of non-accelerating motion (straight trajectories in space and time in agreement with the law of inertia) along geodesics (this even applies to massless particles such as photons) in curved space-time that defines the theory of general relativity. However, because general relativity explains the illusion of gravity as well as effects not covered by classical mechanics, such as Einstein rings and anomalous precessions among others, it has effectively replaced the latter as an authoritative construct. With the recent attempts to assimilate gravitation into the quantum mechanical formulation that is used to describe non-gravitational phenomena, gravitons - which represent coherent radiation from gravitational oscillators - are used to impart the force of attraction between masses.

Fields and Charge

However, if the carrier particles for gravity were considered to be energetic fluctuations of a simple classical gravitational field, the gravitons would be drawn closer to each other and to the mass of origin because of their own mass-energy equivalence and be selectively absorbed by the greatest masses, preventing gravity for very light objects. Additionally, every graviton would require additional gravitons to convey the influence of its own mass-energy, encouraging a divergent net of recursive bosonic emissions where interactions become sources and mass itself ceases to be conserved. Additionally, black holes (and other heavy objects) would be unable to transmit their own force of attraction because they would necessarily attract all of the gravitational bosons they have emitted.

Space and Time

This argument is a particularly strong refutation of the classical gravitational field as transmitted by bosons, so perhaps gravitons are the quantized curving factors of space-time. But space-time warping is a very local effect...rather than affecting each other directly by Newtonian 'action at a distance', masses warp space-time, which then acts on local masses without using intermediate masses: this way the transmission of gravitational potential is not inherently energized or massive and thus prone to an infinite regression of gravitational attractions among carrier particles. On the other hand, if gravitons are not energetic, then they can hardly account for the (yet-to-be-observed) potential radiated by pairs of orbiting neutron stars or colliding quasars. Also, space-time is not a field as it has no direction and no magnitude (it is rather the fields themselves, or the quantum mechanical Hamiltonians, that are defined with and are dependent on the linearly independent variables space and time); it is a spatio-temporal metric that does not exert forces and cannot be excited or transfer a de Broglie momentum because space-time information also does not collide or even interact with matter and matter-field resonances, thus the concept of motion along distorted geodesics seems highly unlikely to be replaced by bosonic momentum transfers made out of space and time. The Schwarzschild radius is derived from the dissipation of kinetic energy by gravitational potential independently of either de Broglie frequency, Lorentz factor, or any other terms that would imply momentum/energy interactions, because it is dependent on curved space-time not inertial scattering and thus is represented by the escape velocity without regard to the momentum because 'gravity' impulses never actually act on it. Gravitons, if they do exist, supposedly must be massless anyway owing to the infinite range of the gravitational interaction, and would rarely couple with matter, making them quite difficult to detect (this is due to the weakness of the force itself which might further implicate a rarity of emissions).

Possible Tests

A relatively easy test is one for linear dispersion for particles with different momentums during microlensing; this is useful for tests of starlight because the escape velocity is the same for all colors, and the effects of the interaction would be observable over large distances. If gravity were a force chromatic aberration would occur in gravitational lenses due to the momentum differences in photon color (over a standard interval of time, a field-induced impulse will exert a change in momentum that may cause the trajectory of a lower momentum photon to be affected in compton-like conservation differently than that of a higher momentum photon for equal unmassless photon rest masses acting as gravitational charge). If this does not occur then bent light must be traveling along straight lines in curved space-time. Another test would involve selective absorption on the event horizon of a black hole (or different event horizons for different frequencies of light). If gravity was acting on mass as a gravitational charge, the event horizon of a black hole would cause a gravitational redshift (of light) to beyond the 0 frequency and into the negative range at different radii for different photons, because the force would impart a constant impulse to the (equal) effective photon masses but the displacement into the negative range would occur more quickly for photons with an already low momentum. This should not occur if light is effectively massless and unaffected by bosonic momentum transfer, and so all frequencies would be affected equally at the same radius because they are traveling as null geodesics along distorted space-time intervals (this would also explain why light emitted by electromagnetic processes that are just inside the edge of a black hole don't have enough momentum to escape the black hole from the vicinity of the event horizon).

Conclusion

Since gravitons supposedly transmit the 'changes' in space-time caused by fluctuating matter, and because practically every other form of energy is quantized, when gravitons are released after conversion (or when massive particles are converted to pure energy) the transmitted energy that reflects the transition of a quantity of mass is also representing a discretely quantized transformation. But what of Bell's Inequalities? If a nuclear reaction releases an equal and quantized pulse of gravitational energy (and massless light), then this energetic resonance should be subject to the same principle of non-locality (by entanglement) that the other quantized energetic agents that originally contained it are, disputing the axioms that ultimately manifest in the space-time continuum (in fact discrete quantizations of space and time suggest that these metrics would be anything but continuous), right? What I find most interesting is that though the relative spans of space and time are independently dependent on one's relative velocity, this velocity is measured only with respect to space and time, the manipulation of which allow Einstein to preserve the speed of light in vacuo.

 

[Mentz114]

Shouldn't there be a 'Don't know' category ?

M

 

[Garth]

Or a 'Both' category?

 

[Haelfix]

It would help if the OP actually made the discussion underneath the poll accurate.

 

[shadowpuppet]

Shouldn't there be a 'Don't know' category ?

The poll is geared towards people who have opinions.

Or a 'Both' category?

That is a contradiction.

It would help if the OP actually made the discussion underneath the poll accurate.

What about it is inaccurate?

 

[RandallB]

Shadowpuppet The problem I see is not so much “inaccuracy” but the poll choices do not jive with two different questions being asked.
The poll choice is simple “I believe that gravitation can be quantized” Yes or NO

That does not address the given question “Do you believe in gravitons?”
Nor does it differentiate a choice between any “ideology”

Note that GR does not dispute that Mass or Energy can be quantized.
Therefore the amount of GR warping imposed by a quantized incremental increase of Mass or Energy would be a quantized increase in that warping. Thus it does not follow that adrhereing to GR requires saying NO to quantized gravitation as implied in your second choice.

Also, the poll implies a choice between ideologies with clearing stating them.
I would have guessed 1)Classical 2)QM/Non-Local/Standard Model 3) GR Warped Space
Already one to many for the options and I would have wanted to add 4)LR Local Realism; but that it does not fit within any of the other three is my opinion.

And the OP rather than help clear up any of that confusion only makes it worse by introduce a different interpretation of what the “ideology” choices addressing gravitons might be. What do you mean by ideology options ? Are they:
Gravitation
Fields and Charge
Space and Time

I consider myself very fixed in my opinions of how gravity and physics works and feel I understand opinions that differ with mine. But like Haelfix and others I am completely at a loss as to what anyones vote in this poll might really mean.

 

[JesseM]

With the recent attempts to assimilate gravitation into the quantum mechanical formulation that is used to describe non-gravitational phenomena, gravitons - which represent coherent radiation from gravitational oscillators - are used to impart the force of attraction between masses.

Measurable gravitons would probably only be present when gravitational oscillators produce gravitational waves, in the case of the "force of attraction between masses" one might use "virtual gravitons" in one's calculations, just like virtual photons are used to explain attraction/repulsion between charged particles in quantum electrodynamics, but this could be seen as just a sort of bookkeeping device, with no actual measured force-carrying particles present. The last section of this online FAQ on virtual particles has a helpful discussion:

I hear physicists saying that the "quantum of the gravitational force" is something called a graviton. Doesn't general relativity say that gravity isn't a force at all?

You don't have to accept that gravity is a "force" in order to believe that gravitons might exist. According to QM, anything that behaves like a harmonic oscillator has discrete energy levels, as I said in part 1. General relativity allows gravitational waves, ripples in the geometry of spacetime which travel at the speed of light. Under a certain definition of gravitational energy (a tricky subject), the wave can be said to carry energy. If QM is ever successfully applied to GR, it seems sensible to expect that these oscillations will also possesses discrete "gravitational energies," corresponding to different numbers of gravitons.

Quantum gravity is not yet a complete, established theory, so gravitons are still speculative. It is also unlikely that individual gravitons will be detected any time in the near future.

Furthermore, it is not at all clear that it will be useful to think of gravitational "forces," such as the one that sticks you to the Earth's surface, as mediated by virtual gravitons. The notion of virtual particles mediating static forces comes from perturbation theory, and if there is one thing we know about quantum gravity, it's that the usual way of doing perturbation theory doesn't work.

Quantum field theory is plagued with infinities, which show up in diagrams in which virtual particles go in closed loops. Normally these infinities can be gotten rid of by "renormalization," in which infinite "counterterms" cancel the infinite parts of the diagrams, leaving finite results for experimentally observable quantities. Renormalization works for QED and the other field theories used to describe particle interactions, but it fails when applied to gravity. Graviton loops generate an infinite family of counterterms. The theory ends up with an infinite number of free parameters, and it's no theory at all. Other approaches to quantum gravity are needed, and they might not describe static fields with virtual gravitons.

However, if the carrier particles for gravity were considered to be energetic fluctuations of a simple classical gravitational field, the gravitons would be drawn closer to each other and to the mass of origin because of their own mass-energy equivalence and be selectively absorbed by the greatest masses, preventing gravity for very light objects. Additionally, every graviton would require additional gravitons to convey the influence of its own mass-energy, encouraging a divergent net of recursive bosonic emissions where interactions become sources and mass itself ceases to be conserved.

Gravitons would be self-interacting which is part of what makes coming up with a quantum theory of gravitation difficult (although my understanding is that string theory has shown that you can actually derive general relativity from a quantum theory of stringy gravitons), but with no quantitative analysis whatsoever, you have no basis for your claim that the self-interaction would have the effect of "preventing gravity for very light objects" or violate conservation of mass/energy.

Additionally, black holes (and other heavy objects) would be unable to transmit their own force of attraction because they would necessarily attract all of the gravitational bosons they have emitted.

Because the force-carrying particles in quantum field theories are only "virtual" rather than real and measurable, it's not wise to generalize one's intuitions about how real particles behave to these virtual particles. See How does the gravity get out of the black hole? from the Usenet Physics FAQ, which says:

Often this question is phrased in terms of gravitons, the hypothetical quanta of spacetime distortion. If things like gravity correspond to the exchange of "particles" like gravitons, how can they get out of the event horizon to do their job?

Gravitons don't exist in general relativity, because GR is not a quantum theory. They might be part of a theory of quantum gravity when it is completely developed, but even then it might not be best to describe gravitational attraction as produced by virtual gravitons. See the physics FAQ on virtual particles for a discussion of this.

Nevertheless, the question in this form is still worth asking, because black holes can have static electric fields, and we know that these may be described in terms of virtual photons. So how do the virtual photons get out of the event horizon? Well, for one thing, they can come from the charged matter prior to collapse, just like classical effects. In addition, however, virtual particles aren't confined to the interiors of light cones: they can go faster than light! Consequently the event horizon, which is really just a surface that moves at the speed of light, presents no barrier.

I couldn't use these virtual photons after falling into the hole to communicate with you outside the hole; nor could I escape from the hole by somehow turning myself into virtual particles. The reason is that virtual particles don't carry any information outside the light cone. See the physics FAQ on virtual particles for details.

Space and Time

This argument is a particularly strong refutation of the classical gravitational field as transmitted by bosons, so perhaps gravitons are the quantized curving factors of space-time. But space-time warping is a very local effect...rather than affecting each other directly by Newtonian 'action at a distance', masses warp space-time, which then acts on local masses without using intermediate masses

There is no "action at a distance" in quantum field theories like quantum electrodynamics either, at least not of a measurable kind; a measurement of the behavior of a particle at one point in spacetime won't tell you anything about events outside the past light cone of that point.

this way the transmission of gravitational potential is not inherently energized or massive and thus prone to an infinite regression of gravitational attractions among carrier particles.

Again, this argument about the "infinite regression" somehow leading to predictions which disagree with general relativity is worthless without any quantitative analysis. As I said, I believe in string theory it is possible to reproduce the predictions of general relativity using a theory of self-interacting stringy gravitons; somehow or another, the math works out.

Also, space-time is not a field as it has no direction and no magnitude

In physics "field" does not exclusively mean a vector field; GR deals with tensor fields in spacetime, and the fundamental equations of GR are known as the "Einstein field equations".

it is a spatio-temporal metric that does not exert forces and cannot be excited or transfer a de Broglie momentum because space-time information also does not collide or even interact with matter and matter-field resonances

This sounds like pure technobabble, and given the handwaveyness of your other comments I doubt you have any well-defined technical definition of what it would mean for "space-time information" to "collide or even interact" with matter of "matter-field resonances".

Possible Tests

A relatively easy test is one for linear dispersion for particles with different momentums during microlensing; this is useful for tests of starlight because the escape velocity is the same for all colors, and the effects of the interaction would be observable over large distances. If gravity were a force chromatic aberration would occur in gravitational lenses due to the momentum differences in photon color

Would it? Can you show detailed quantitative calculations that indicate the magnitude of this effect, or point to some other published paper which makes such a calculation?

Another test would involve selective absorption on the event horizon of a black hole (or different event horizons for different frequencies of light). If gravity was acting on mass as a gravitational charge, the event horizon of a black hole would cause a gravitational redshift (of light) to beyond the 0 frequency and into the negative range at different radii for different photons

Again, calculations?

Since gravitons supposedly transmit the 'changes' in space-time caused by fluctuating matter, and because practically every other form of energy is quantized, when gravitons are released after conversion (or when massive particles are converted to pure energy) the transmitted energy that reflects the transition of a quantity of mass is also representing a discretely quantized transformation. But what of Bell's Inequalities? If a nuclear reaction releases an equal and quantized pulse of gravitational energy (and massless light), then this energetic resonance should be subject to the same principle of non-locality (by entanglement) that the other quantized energetic agents that originally contained it are, disputing the axioms that ultimately manifest in the space-time continuum (in fact discrete quantizations of space and time suggest that these metrics would be anything but continuous), right?

The violation of Bell inequalities simply shows that a certain class of hidden-variables theories going by the name "local realism" can be ruled out. It doesn't show that you can ever have a measurably nonlocal effect--in fact it's provably true that you can't according to the accepted rules of quantum field theory, since as I said no information that you obtain via a measurement of a quantum system at one point in spacetime can ever tell you anything about events outside the past light cone of that point.

What I find most interesting is that though the relative spans of space and time are independently dependent on one's relative velocity, this velocity is measured only with respect to space and time, the manipulation of which allow Einstein to preserve the speed of light in vacuo.

What does "measured only with respect to space and time" even mean? In relativity each inertial observer measures the speed of light relative to physical rulers and clocks at rest relative to themselves, spacetime is not an entity with its own rest frame so it's meaningless to talk about measuring the speed of any object relative to spacetime.

 

[shadowpuppet]

Shadowpuppet Note that GR does not dispute that Mass or Energy can be quantized. Therefore the amount of GR warping imposed by a quantized incremental increase of Mass or Energy would be a quantized increase in that warping. Thus it does not follow that adrhereing to GR requires saying NO to quantized gravitation as implied in your second choice.

I did address your concern:

Since gravitons supposedly transmit the 'changes' in space-time caused by fluctuating matter, and because practically every other form of energy is quantized, when gravitons are released after conversion (or when massive particles are converted to pure energy) the transmitted energy that reflects the transition of a quantity of mass is also representing a discretely quantized transformation.

What I am disputing is bosonic momentum transfer in gravitational interactions, which is incompatible with General Relativity. In General Relativity space-time is also not discretely quantized and is not even continuously variable over very small distances (according to Einstein's local equivalence principle; this is the domain of the graviton, unless there is a massive but microscopic black hole, the physics of which I could hardly imagine). The mutual exclusivity of the poll is mainly dependent on this discrepancy, but if you still do not agree with either of the first two choices, then you are free to select the third (I am also not familiar with LR Local Realism; Classical Mechanics fails to account for a lot of gravitational effects, and I consider it to be obsolete for this reason among many others). The headings of my own synopsis describe the introduction (or subject content), the failures of quantifying Classical Mechanics, and the failures of quantifying General Relativity, respectively; they are not meant to accommodate alternate perspectives nor discourage the freedoms of the poll (as I said in the disclaimer, I am biased in favor of option two, and I will vote accordingly if that makes this more comprehensible). Naturally, if you are fixed in your opinions then you will not account for anomalous information, and if you encourage incompatible opinions then you can hardly support your own with authoritative exclusivity. Personally, I am just curious to see if these issues can or have been addressed at all in a unified physics, and my own incentive is derived from the unresolved aspects of a series of comprehensive debates with sincere advocates of quantum gravity.

 

[Fredrik]

Just a few thoughts...

"We believe in gravitons": To me this would mean that we believe that a quantum field theory of gravity makes some sense even though it isn't renormalizable (which considerably limits its predictive power).

"We believe gravity can be quantized": I would interpret this as meaning "We believe that a theory of gravity can be formulated in the framework of quantum mechanics".

"We don't believe gravity can be quantized": This is just the negation of the previous statement, so it certainly doesn't mean "I adhere to GR". It could also mean that we don't believe QM is sufficient. (Also, adhering to GR would be really dumb. GR includes a mathematical representation of matter, and matter can't be described by classical mechanics, so there's no way GR can be the final theory of gravitation).

I think I believe in gravitons. I think gravity can probably be quantized, but I wouldn't be shocked if it can't (i.e if QM needs to be replaced too). I certainly don't adhere to GR.

 

[DemTings]

I don't know. I believe in Gravity obviously, but to give an explination on what Gravity actually is, that I can't comment on. Do I believe that Gravity exists on the quantum scale? Yes. Do I believe it's a Gravaton? I don't know. Sometimes I picture gravity as actually being the fabric of space it's self and not an actual entity on it's own. But time will tell, I just hope I live long enough...

 

[yuiop]

Some of the newer quantum gravity theories like CDT do not require carrier particles like gravitons, so Garth is right that there are not enough options in the poll. I would like to vote " I believe gravity can be quantisized but not necessarily require gravitons".

 

[Haelfix]

Spuppet, most of the discussion in the original post is erroneous. There are so many errors and misunderstandings its hard to even begin to dissect it.

The quantum field theory of gravitation is completely mathematically isomorphic to general relativity at tree level! There is no sense in which any of the bizarre distinctions you seem to draw are correct in the slightest.

The answer to the poll question is 'both' classically.

 

[shadowpuppet]

Measurable gravitons would probably only be present when gravitational oscillators produce gravitational waves, in the case of the "force of attraction between masses" one might use "virtual gravitons" in one's calculations, just like virtual photons are used to explain attraction/repulsion between charged particles in quantum electrodynamics, but this could be seen as just a sort of bookkeeping device, with no actual measured force-carrying particles present. The last section of this online FAQ on virtual particles has a helpful discussion:

Gravitons would be self-interacting which is part of what makes coming up with a quantum theory of gravitation difficult (although my understanding is that string theory has shown that you can actually derive general relativity from a quantum theory of stringy gravitons), but with no quantitative analysis whatsoever, you have no basis for your claim that the self-interaction would have the effect of "preventing gravity for very light
objects" or violate conservation of mass/energy.

Because the force-carrying particles in quantum field theories are only "virtual" rather than real and measurable, it's not wise to generalize one's intuitions about how real particles behave to these virtual particles. See How does the gravity get out of the black hole? from the Usenet Physics FAQ, which says:

If no actual force transmitters are present, then presently no actual force is being transmitted. Virtual particles are real, but they only exist for a temporal duration that is dictated by their energy and the Heisenberg Uncertainty relation. It is clear that energy is not being transmitted, because gravitons do not travel through space and time, they are space and time, and as such have no energy to transmit and are thus not prone to mass-energy equivalence and bosonic carrier-interactions. Do you agree that gravitational potential (even when it is radiated) is considered an illusion in the context of space-time geometry? To say that I have no claim for asserting mass-energy equivalence for energetic resonances when this has been demonstrated and the existence of non-interacting (or even interacting) energy-transmitting gravitons has not is scarcely an empirical argument. Also your assertion that virtual particles transmit the non-oscillating component of acceleration is negated in both FAQs you tried to use as proof (both FAQs never answered a single relevant question and other than admitting that quantized gravity is inherently inconsistent, they never made a single definite point concerning the transmission of gravitation and made the entire topic seem much more ambiguous and elusive than it really is).

in the case of the "force of attraction between masses" one might use "virtual gravitons" in one's calculations

Furthermore, it is not at all clear that it will be useful to think of gravitational "forces," such as the one that sticks you to the Earth's surface, as mediated by virtual gravitons.

Gravitons don't exist in general relativity, because GR is not a quantum theory. They might be part of a theory of quantum gravity when it is completely developed, but even then it might not be best to describe gravitational attraction as produced by virtual gravitons.

You may want to rethink your virtual particle theory.

There is no "action at a distance" in quantum field theories like quantum electrodynamics either, at least not of a measurable kind; a measurement of the behavior of a particle at one point in spacetime won't tell you anything about events outside the past light cone of that point. Again, this argument about the "infinite regression" somehow leading to predictions which disagree with general relativity is worthless without any quantitative analysis. As I said, I believe in string theory it is possible to reproduce the predictions of general relativity using a theory of self-interacting stringy gravitons; somehow or another, the math works out. In physics "field" does not exclusively mean a vector field; GR deals with tensor fields in spacetime, and the fundamental equations of GR are known as the "Einstein field equations".

Though I did mention this in the context of Newtonian Mechanics, action-at-a-distance may occur between two entangled states (thank you for bringing this up), but that General Relativity does not use intermediate particles to transmit gravitation is still true (which was my point, so I fail to see yours). In String Theory the exact opposite is also probable...there is nothing specific in String Theory that makes empirical reality seem necessarily favored over its rational alternatives more than it seems using a random collection of noises spoken in the English Language. Also, if you are going to defend your theories with math, I prefer equations to sentences. Tensor fields (like the set of Stress-Energy-Momentum Tensors) are mathematical structures used to describe the spatially varying characteristics of real objects while preserving the invariance of these physical quantities across many different frames of reference; they are not real fields and they do not provide a physical mechanism for bosonic emissions.

This sounds like pure technobabble, and given the handwaveyness of your other comments I doubt you have any well-defined technical definition of what it would mean for "space-time information" to "collide or even interact" with matter of "matter-field resonances".

If you don't understand what the words 'collision' or 'matter' means, then you will certainly have trouble defending a theory of gravitons.

Would it? Can you show detailed quantitative calculations that indicate the magnitude of this effect, or point to some other published paper which makes such a calculation? Again, calculations?

You are certainly very thirsty for calculation for someone who offers none of his own; I might do this for someone who already understands what I am talking about but if you do not understand the concepts themselves I doubt that you will follow the math.

The violation of Bell inequalities simply shows that a certain class of hidden-variables theories going by the name "local realism" can be ruled out. It doesn't show that you can ever have a measurably nonlocal effect--in fact it's provably true that you can't according to the accepted rules of quantum field theory, since as I said no information that you obtain via a measurement of a quantum system at one point in spacetime can ever tell you anything about events outside the past light cone of that point.

If you cannot describe the entire state of a local system locally, then information does exist which must be transferred to the system. General Relativity is fully described by local quantities and does not allow for non-local interactions and this is not true of quantum mechanics, which is what I said, so what is your point?

What does "measured only with respect to space and time" even mean? In relativity each inertial observer measures the speed of light relative to physical rulers and clocks at rest relative to themselves, spacetime is not an entity with its own rest frame so it's meaningless to talk about measuring the speed of any object relative to spacetime.

Why are you attacking me? I said that it was interesting, and I mean because the speed of light is not affected by the laws of physics thought thae varibales out of which it is constructed and measured are. In case you never took Calculus I, velocity is the first derivative of length with respect to time. Are you scared to address the real issues or is it just your dislike for me that blinds you from which assertions I am actually making?

 

[shadowpuppet]

Also, adhering to GR would be really dumb. GR includes a mathematical representation of matter, and matter can't be described by classical mechanics, so there's no way GR can be the final theory of gravitation.

Here I mean with regard to the theory of gravitation, not the theory of everything.

I don't know. I believe in Gravity obviously, but to give an explination on what Gravity actually is, that I can't comment on. Do I believe that Gravity exists on the quantum scale? Yes. Do I believe it's a Gravaton? I don't know. Sometimes I picture gravity as actually being the fabric of space it's self and not an actual entity on it's own. But time will tell, I just hope I live long enough...

I concur. Gravity is one manifestation of the orientation of the fabric of space.

Some of the newer quantum gravity theories like CDT do not require carrier particles like gravitons, so Garth is right that there are not enough options in the poll. I would like to vote " I believe gravity can be quantisized but not necessarily require gravitons".

I apologize for the inconvenience, but I am not familiar with even a single quantum theory that does not rely on discrete carrier particles. Would you care to elaborate?

Spuppet, most of the discussion in the original post is erroneous. There are so many errors and misunderstandings its hard to even begin to dissect it.

The quantum field theory of gravitation is completely mathematically isomorphic to general relativity at tree level! There is no sense in which any of the bizarre distinctions you seem to draw are correct in the slightest.

The answer to the poll question is 'both' classically.

I refuse to accept your argument unless you defend even a single assertion that you make...since you haven't dissected it I will assume that you have not understood it...

 

[DaveC426913]

I am confident that both theories will usable to describe the same physics. It's kind of like asking if you believe photons are particles or waves.

So, IMO, the answer to the poll is the one that is not listed: both.

 

[yuiop]

...
I apologize for the inconvenience, but I am not familiar with even a single quantum theory that does not rely on discrete carrier particles. Would you care to elaborate?

...

I was referring to to the Causal Dynamical Triangulations theory which is being discussed in the Cosmology forum. A introductory paper is here http://arxiv.org/PS_cache/gr-qc/pdf/0607/0607013v1.pdf and a nice introductory article from Scientific American is here http://www.scribd.com/doc/3366486/SelfOrganizing-Quantum-Universe-SCIAM-June-08

I only posted the links because you asked and because they were already given in the Cosmology forum.

 

[shadowpuppet]

I am confident that both theories will usable to describe the same physics. It's kind of like asking if you believe photons are particles or waves.

So, IMO, the answer to the poll is the one that is not listed: both.

I would be hesitant to accept that, especially until gravitons are actually discovered...at one point people were certain that the luminiferous æther existed and could describe the same physics as the other models, but this is not so...

I was referring to to the Causal Dynamical Triangulations theory which is being discussed in the Cosmology forum. A introductory paper is here http://arxiv.org/PS_cache/gr-qc/pdf/0607/0607013v1.pdf and a nice introductory article from Scientific American is here http://www.scribd.com/doc/3366486/SelfOrganizing-Quantum-Universe-SCIAM-June-08

I only posted the links because you asked and because they were already given in the Cosmology forum.

Thanks, I'll look into it.

 

[Haelfix]

I recommend picking up the following textbook:

https://www.amazon.com/dp/0471925675/?tag=pfamazon01-20

It goes through the math of general relativity from the point of view of a spin2 particle, and shows why they are completely equivalent. I don't recommend the book to a beginner, but I do when it comes to discussions like this (where there is excessive fog)

 

[JesseM]

If no actual force transmitters are present, then presently no actual force is being transmitted. Virtual particles are real, but they only exist for a temporal duration that is dictated by their energy and the Heisenberg Uncertainty relation.

Please define what you mean by "real" and "actual". If you look at section 3 of http://arnold-neumaier.at/physics-faq.txt, the author makes the argument that according to at least one reasonable definition of "real", virtual particles should not be considered physically real, but are simply terms in a certain mathematical calculation similar to the individual terms in a Taylor series. In particular, in section 3c he writes:

--------------------------------------
S3c. How real are 'virtual particles'?
--------------------------------------

Virtual particles are used in perturbation theory with
Feynman diagrams. (See the FAQ entry ''Why Feynman diagrams''
for an explanation of their meaning. They do _not_ describe
processes in space and time, but certain multiple integrals...)

Feynman diagrams change their nature depending on the way
one does perturbation theory and what is resummed.

In their treatise on QED, Landau and Lifgarbagez discuss virtual particles
in Section 79. They start at the outset with the remark that things
depend on which kind of perturbation theory is used, and contrast
'virtual' explicitly with 'real'. Virtual particles are called that
in contrast to 'real particles' which are observable and hence real.
Unlike the latter, virtual particles occurring in computations _must_
have disappeared from the formulas by the time the calculations lead
to something that can be compared with experiment.

Whence their 'reality' if there is any is like the reality of
characters in a dream. For example, just as we can fly in a dream,
virtual particles can be faster than light (since they may have
imaginary mass)...

The following is a more detailed discussion of the question how
meaningful it is to ascribe some sort of reality to virtual particles.


All language is only an approximation to reality, which simply is.
But to do science we need to classify the aspects of reality
that appear to have more permanence, and consider them as real.
Nevertheless, all concepts, including 'real' have a fuzziness
about them, unless they are phrased in terms of rigorous mathematical
models (in which case they don't apply to reality itself but only to
a model of reality).

In the informal way I use the notion, 'real' in theoretical physics
means a concept or object that
- is independent of the computational scheme used to
extract information from a theory,
- has a reasonably well-defined and consistent formal basis
- does not give rise to misleading intuition.
This does not give a clear definition of real, of course.
But it makes for example charge distributions, inputs and outputs of
(theoretical models of) scattering experiments, and quarks something
real, while making bare particles and virtual particles artifacts of
perturbation theory.

Quarks must be considered real because one cannot dispense with them
in any coherent explanation of high energy physics.

Virtual particles must not be considered real since they arise only in
a particular approach to high energy physics - perturbation theory
before renormalization - that does not even survive the modifications
needed to remove the infinities. Moreover, the virtual particle content
of a real state depends so much on the details of the computational
scheme (canonical or light front quantization, standard or
renormalization group enhances perturbation theory, etc.) that
calling virtual particles real would produce a very weird picture of
reality.

Whenever we observe a system we make a number of idealizations
that serve to identify the objects in reality with the
mathematical concepts we are using to describe them. Then we calculate
something, and at the end we retranslate it into reality. If our initial
initialization was good enough and our theory is good enough, the final
result will match reality well. Because of this idealization,
'real' real particles (moving in the universe) are slightly different
from 'mathematical' real particles (figuring in equations).


Modern quantum electrodynamics and other field theories are based on
the theory developed for modeling scattering events.
Scattering events take a very short time compared to the
lifetime of the objects involved before and after the event. Therefore,
we represent a prepared beam of particles hitting a target as a single
particle hitting another single particle, and whenever this in fact
happens, we observe end products, e.g. in a wire chamber.
Strictly speaking (i.e., in a fuller model of reality), we'd have to
use a multiparticle (statistical mechanics) setting, but this is never
done since it does not give better information and the added
complications are formidable.

As long as we prepare the particles long (compared to the scattering
time) before they scatter and observe them long enough afterwards,
they behave essentially as in and out states, respectively.
(They are not quite free, because of the electromagnetic self-field
they generate, this gives rise to the infrared problem in quantum
electrodynamics and can be corrected by using coherent states.)
The preparation and detection of the particles is outside this model,
since it would produce only minute corrections to the scattering event.
But to treat it would require to increase the system to include source
and detector, which makes the problem completely different.

Therefore at the level appropriate to a scattering event, the 'real'
real particles are modeled by 'mathematical' in/out states, which
therefore are also called 'real'. On the other hand, 'mathematical'
virtual particles have nothing to do with observations, hence have no
counterpart in reality; therefore they are called 'virtual'.

The figurative virtual objects in QFT are there only because of the
well-known limitations of the foundations of QFT. In a nonperturbative
setting they wouldn't occur at all. This can be seen by comparing with
QM. One could also do nonrelativistic QM with virtual objects but
no one does so (except sometimes in motivations for QFT),
because it does not add value to a well-understood theory.

Virtual particles are an artifact of perturbation theory that
give an intuitive (but if taken too far, misleading) interpretation
for Feynman diagrams. More precisely, a virtual photon, say,
is an internal photon line in one of the Feynman diagrams. But there
is nothing real associated with it. Detectable photons are always
real, 'dressed' photons.

Virtual particles, and the Feynman diagrams they appear in,
are just a visual tool of keeping track of the different terms
in a formal expansion of scattering amplitudes into multi-dimensional
integrals involving multiple propaators - the momenta of the virtual
particles represent the integration variables.
They have no meaning at all outside these integrals.
They get out of mathematical existence once one changes the
formula for computing a scattering amplitude.

Therefore virtual particles are essentially analogous to virtual
integers k obtained by computing
log(1-x) = sum_k x^k/k
by expansion into a Taylor series. Since we can compute the
logarithm in many other ways, it is ridiculous to attach to
k any intrinsic meaning. But ...

... in QFT, we have no good ways to compute scattering amplitudes
without at least some form of expansion (unless we only use the
lowest order of some approximation method), which makes
virtual particles look a little more real. But the analogy
to the Taylor series shows that it's best not to look at them
that way. (For a very informal view of quantum electrodynamics in
terms of clouds of virtual particles see
http://groups.google.com/groups?selm=3EBBE37C.4D771C4B@univie.ac.at
and the later mails in this thread.)

A sign of the irreality of virtual particles is the fact that
when one does partial resummations of diagrams (which is essential for
renormalization), many of the virtual particles disappear.
A fully nonperturbative theory would sum everything, and no virtual
particles would be present anymore. Thus virtual particles are
entirely a consequence of looking at QFT in a perturbative way
rather than nonperturbatively.

In the standard covariant Feynman approach, energy (cp_0) and
momentum (\p; the backslash indicates 'boldface') is conserved,
and virtual particles are typically off-shell (i.e., they
do not satisfy the equation p^2 = p_0^2 - \p^2 = m^2 for physical
particles). To see this, try to model a vertex in which an electron
(mass m_e) absorbs a photon (mass 0). One cannot keep the incoming
electron and photon and the outgoing photon on-shell (satisfying
p^2 = m^2) without violating the energy-momentum balance.

However, many physicists work in light front quantization.
There one keeps all particles on-shell, and instead has energy and
momentum nonconservation (removed formally by adding an additional
'spurion').
The effect of this is that the virtual particle structure of the
theory is changed completely: For example, the physical vacuum and
the bare vacuum now agree, while in the standard approach,
the vacuum looks like a highly complicated
medium made up from infinitely many bare particles...
But bare particles must still be dressed to become physical,
though less heavily than in the traditional Feynman approach.

Another group of physicists calculate consequences of the standard
model using quantization on a lattice.
Here virtual particles are completely absent.

Clearly concepts such as virtual particles that depend so much
on the method of quantization cannot be regarded as being real.

Of course, physicists would not talk of virtual particles if the concept
had no relevance at all. One can argue with virtual particles to get an
intuitive idea of 'dressing', and to gain in this way some
understanding of phenomena such as the Casmir effect, Rabi
oscillations, the Lamb shift, anomalous magnetic moments, etc.
From a nonperturbative point of view, these effects all show up as
a consequence of renormalized, effective interactions between
physical (dressed, on-shell) particles.


See also earlier discussions on s.p.r. such as
http://www.lns.cornell.edu/spr/2003-06/msg0051674.html
also
http://www.lns.cornell.edu/spr/1999-02/msg0014762.html
and followups; maybe
http://www.lns.cornell.edu/spr/2003-05/msg0051023.html
is also of interest.

[For a longwinded alternative view of virtual particles
that I do _not_ share but rather find misleading, see
http://www.desy.de/user/projects/Physics/Quantum/virtual_particles.html]

It is clear that energy is not being transmitted, because gravitons do not travel through space and time, they are space and time

This is another handwavey argument based on english-language definitions rather than any technical considerations. In attempts to find quantum theories of gravity involving gravitons, I believe the gravitons are treated as moving in some sort of background spacetime, though I could be missing some subtleties here.

To say that I have no claim for asserting mass-energy equivalence for energetic resonances when this has been demonstrated

What are you even talking about? When did I say there is no "mass-energy equivalence for energetic resonances"? Is "energetic resonance" a technical term used in quantum field theory for interactions mediated by virtual force-carrying particles (if so, please provide a reference), or are you just inventing your own technobabble again? I did say that gravitons would be self-interacting (i.e. they themselves would be a source of gravity), if that's what you're trying to get at here. But claims that this would "prevent gravity for very light objects" or "encourage a divergent net of recursive bosonic emissions where interactions become sources and mass itself ceases to be conserved" are nothing but pure fantasy unless you have some actual calculations to back them up (or can refer to some peer-reviewed literature which makes such claims).

and the existence of non-interacting (or even interacting) energy-transmitting gravitons has not is scarcely an empirical argument.

But I'm not trying to make a positive argument for the existence of gravitons, I'm just pointing out that your arguments against them are uninformed and handwavey.

Also your assertion that virtual particles transmit the non-oscillating component of acceleration is negated in both FAQs you tried to use as proof

It's "negated"? Where, exactly? The FAQs are not completely explicit about the fact that real photons are only associated with electromagnetic waves (which only come about due to oscillating charges) while virtual photons are associated with the transmission of the electromagnetic force even in the absence of waves, but this is correct nevertheless, and the virtual particle FAQ does at least strongly imply it in the opening section:

One of the first steps in the development of quantum mechanics was Max Planck's idea that a harmonic oscillator (classically, anything that wiggles like a mass bobbing on the end of an ideal spring) cannot have just any energy. Its possible energies come in a discrete set of equally spaced levels.

An electromagnetic field wiggles in the same way when it possesses waves. Applying quantum mechanics to this oscillator reveals that it must also have discrete, evenly spaced energy levels. These energy levels are what we usually identify as different numbers of photons. The higher the energy level of a vibrational mode, the more photons there are. In this way, an electromagnetic wave acts as if it were made of particles. The electromagnetic field is a quantum field.

Electromagnetic fields can do things other than vibration. For instance, the electric field produces an attractive or repulsive force between charged objects, which varies as the inverse square of distance. The force can change the momenta of the objects.

Can this be understood in terms of photons as well? It turns out that, in a sense, it can. We can say that the particles exchange "virtual photons" which carry the transferred momentum.

(both FAQs never answered a single relevant question and other than admitting that quantized gravity is inherently inconsistent, they never made a single definite point concerning the transmission of gravitation and made the entire topic seem much more ambiguous and elusive than it really is).

Where do they say it's "inherently inconsistent"? The sections you quote only say that it is uncertain whether a theory of quantum gravity would include the idea of forces mediated by virtual gravitons or not (although they also point out it's pretty likely that quantum gravity would say the energy levels of gravitational waves are quantized, which suggests that the theory must at least include real gravitons of some kind). I have never claimed that a quantum gravity theory will say the force of gravity is mediated by gravitons--I'm just saying that your arguments which purport to prove there is something inherently impossible about the idea are, again, uniformed and so handwavey as to be "not even wrong".

 

[JesseM]

(continued from previous post)

Though I did mention this in the context of Newtonian Mechanics, action-at-a-distance may occur between two entangled states (thank you for bringing this up)

No, there is absolutely no measurable action-at-a-distance in quantum theory. There are correlations which are incompatible with local realism, but these correlations can never be used to transmit information FTL, and whether one imagines there is some "hidden" nonlocality to explain them depends on your interpretation of QM (the many-worlds interpretation popular among quantum physicists purports to explain these correlations without giving up locality, by getting rid of the 'realism' assumption that each measurement has a unique outcome--see my post #8 on this thread for some references).

but that General Relativity does not use intermediate particles to transmit gravitation is still true (which was my point, so I fail to see yours).

Of course it's true, just as it's true that classical electromagnetism does not use intermediate particles to transmit the electromagnetic force. But since general relativity is manifestly incompatible with quantum physics, it is generally not believed to be the final theory of gravity, and it's thought that its predictions will become significantly wrong at the Planck scale; to find the correct predictions we'll need a theory of quantum gravity, which may or may not include the idea of virtual gravitons mediating the gravitational force.

In String Theory the exact opposite is also probable...there is nothing specific in String Theory that makes empirical reality seem necessarily favored over its rational alternatives more than it seems using a random collection of noises spoken in the English Language.

Whether string theory turns out to be on the right track or not (and quite a lot of physicists think there's a good chance of that) is irrelevant to my point, which is just that one can construct theories in which the gravitational force is mediated by gravitons, which still manage to reproduce the same predictions as general relativity and don't create the sort of problems that you imagine in your handwavey arguments.

Also, if you are going to defend your theories with math, I prefer equations to sentences.

They aren't my theories, since I am not trying to make any original arguments, just summarize results found by professional physicists who have done the math. If you want references to the literature where the mathematical derivation of general relativity from string theory can be found, I'm sure someone could direct you to them. In contrast, your own arguments about the impossibility of gravitons seem to be original to you rather than just a summary of conclusions stated by professional physicists, so the burden is on you to show that you have some actual rigorous basis for them.

Tensor fields (like the set of Stress-Energy-Momentum Tensors) are mathematical structures used to describe the spatially varying characteristics of real objects while preserving the invariance of these physical quantities across many different frames of reference; they are not real fields and they do not provide a physical mechanism for bosonic emissions.

Tensor fields describe real physical quantities like spacetime curvature at each point in a given coordinate system, so it's unclear why you think they are less "real" than fields describing quantities like electromagnetic force vectors at each point. Again, it would help if you would define the word "real", and then explain rigorously how showing the tensor field of GR is not "real" in whatever sense you choose proves the conclusion that it would be impossible to reproduce GR's predictions using a quantum field in a theory of quantum gravity.

If you don't understand what the words 'collision' or 'matter' means, then you will certainly have trouble defending a theory of gravitons.

I wasn't asking what "collision" or "matter" mean in the normal well-understood contexts, I was asking what it would mean for matter to collide with "space-time information", which sounds like gibberish to me. Maybe you were just looking for a technobabblish way of saying that in general relativity, gravity is spacetime curvature which determines how matter moves on geodesics, which is totally different from the quantum picture of forces involving interactions (not really 'collisions' in the classical sense) between real particles and virtual force-carrying particles; I agree they are totally different, but this doesn't rule out the possibility that two such dissimilar theories could lead to the same predictions. It is also true that classical electromagnetism is quite different from quantum electrodynamics, since classical EM involves a continuous field assigning a force vector to every point in space, not particle-particle interactions or "collisions". Nevertheless quantum electrodynamics reproduces classical EM's predictions in the limit, just as it is hoped that a quantum theory of gravity (possibly involving virtual gravitons) would reproduce GR's predictions in the large-scale limit.

You are certainly very thirsty for calculation for someone who offers none of his own

Because, once again, I am not making original arguments but summarizing the views of mainstream physicists. Since you are making original arguments, you should provide calculations proving the impossibility of reproducing GR's predictions in a quantum field theory involving gravitons (such as string theory), which is certainly not a widely-accepted conclusion among physicists. And in any case, if you've read the IMPORTANT! Read before posting thread you'll know that this isn't the correct forum to offer original results which contradict mainstream ideas (for that you should head over to the Independent Research forum).

If you cannot describe the entire state of a local system locally, then information does exist which must be transferred to the system. General Relativity is fully described by local quantities and does not allow for non-local interactions and this is not true of quantum mechanics, which is what I said, so what is your point?

Again, although QM rules out local realism, whether this rules out all forms of locality is a matter of interpretation. What's more, if this is meant as a definitive argument against finding a quantum theory which reproduces the predictions of GR, then the same argument could also be used to say that no quantum theory could reproduce the predictions of classical electromagnetism, which is just as local as GR is; and yet we already know it can, because we have the theory of quantum electrodynamics.

Why are you attacking me? I said that it was interesting, and I mean because the speed of light is not affected by the laws of physics thought thae varibales out of which it is constructed and measured are. In case you never took Calculus I, velocity is the first derivative of length with respect to time.

Yes, and in relativity length only has meaning when measured relative to some particular physical ruler, and time only has meaning when measured relative to some particular physical clock. I thought you were saying that we could measure the velocity of light "relative to spacetime" rather than relative to the rulers and clocks of specific inertial observers, which would be wrong; if I misunderstood you here, I apologize.

 

[yuiop]

I recommend picking up the following textbook:

https://www.amazon.com/dp/0471925675/?tag=pfamazon01-20

It goes through the math of general relativity from the point of view of a spin2 particle, and shows why they are completely equivalent. I don't recommend the book to a beginner, but I do when it comes to discussions like this (where there is excessive fog)

So in less than 50 words does the book suggest gravity can be explained by gravitons or not?

 

[Haelfix]

"you should provide calculations proving the impossibility of reproducing GR's predictions in a quantum field theory involving gravitons "

Alternatively the OP could just pick up a textbook on field theory and see the derivation himself. Its a simple proof.

When you write down the lagrangian for a spin 2 particle, the field equations of general relativity uniquely fall out. You can find this in pretty much any textbook on the subject. Zee in his 'QFT in a nutshell' does it in one page.

 

[Haelfix]

So in less than 50 words does the book suggest gravity can be explained by gravitons or not?

The whole book does GR pretty much entirely with fields. If you want the 50 word minimum, see the A Zee book. Maybe you can find a pdf somewhere on the internet.

 

[yuiop]

Can I reprase that to

"In less than 2 words, does the book suggest gravity can be explained by gravitons or not"?

Yes or no?

 

[shadowpuppet]

I have not yet read the paper, but this is in response to the article:

This article does not propose a quantum theory of space-time (it even rejected Wheeler's notion of Quantum Foam), it tries to simulate relativistic space-time over very short intervals using discretely quantized elements (despite the fact that curvature is negligible in this regime due to the weakness of the gravitational force for particle masses and especially because of the local equivalence principle, which states that space-time is relatively flat over very short intervals, and relatively flat does not mean actually flat for one unit but curved over two in a way that necessitates infinitesimal modeling elements). Four-simplices were described as more of a modeling tool than something that the authors were confident was the discrete unit of curvature or space-time...

'The tiny building blocks themselves have no direct physical meaning. If one could examine real space-time with an ultrapowerful microscope, one would not see small triangles. They are merely approximations.

It is not hard to otherwise imagine gravitons as phonons of this tetrahedral mosaic propagating in four dimensions, perhaps stretching along them to maintain spatio-temporal continuity, but because space-time is not composed of matter it would still be hard to correlate a coupling of gravitons with matter to a physical phenomenon. Additionally, because discrete particles are exactly that (discrete), I find it hard to imagine that a continuous space-time presently requires infinitesimal elements for independent manipulation (though emergent properties of such fundamental constituents may prove beneficial in the future)...however the mechanism for a continuity of superimposed 'fabricons' is conspicuously lacking: though the wavefunction for each shape may be continuous in space and time (whatever that means because we are talking about the wavefunction of space and time), the maxima of each may promote a disjointed space-time that is not connected where the locally dominant orientation becomes improbable and a very different one takes its place (like the Red Queen in Through the Looking Glass: you might chase her all day for many miles and not catch her, and then turn away and be right beside her - even the fiber-space cross-sections of the fiber-bundle formulation of General Relativity exhibit continuity along the fiber, and each world-line affected by it has a very non-probabilistic progression; disjunct histories were not covered by the article, but the 'causal' dynamics of triangles implies a total discontinuity among separate four-simplices for separate observers, such that the absolute continuity of space and time is compromised); this may also occur temporally - time may split open when another superposition is suddenly favored...because uncertain observables and their wavefunctions are usually defined in space and time (which are considered continuous and independent of each other to allow a continuous probability distribution to be described) and not composed of them, it is hard to imagine discrete units of space-time described in this manner. If the annihilation of mass caused a sudden retraction of space-time, in General Relativity you might expect to be translated a reasonable distance (due to the delay of the response of space-time to matter as might occur in the Lense-Thirring effect), however if the most probable shape of space-time under the new stresses did not accommodate your current situation and was suddenly realized without intermediate steps (by quantum 'jumps'), you might find yourself on the other side of the universe, or not in it at all; this will occur for mappings that are not isomorphic, or structure-preserving, a case that is certainly worth considering if the quanta of space-time are allowed to self-assemble as suggested by the article. Haelfix suggested that the transition of General Relativity to Quantum Gravity is isomorphic, but this one (self-claimed to be the only successful one) is obviously not (see my introduction).

Spuppet, most of the discussion in the original post is erroneous. There are so many errors and misunderstandings its hard to even begin to dissect it.

The quantum field theory of gravitation is completely mathematically isomorphic to general relativity at tree level! There is no sense in which any of the bizarre distinctions you seem to draw are correct in the slightest.

The answer to the poll question is 'both' classically.

This discontinuity might be tested locally if certain parts of you weren't torn to shreds by the sudden expansion and reorientation of space, or slowed down in time and refused to allow blood to flow. If the definite shape of space-time is only a probable entity, then it is indifferent to the spatio-temporal distribution of mass (unless it occurs in stable 'orbits', but this would not imply continuity) and it could hardly be conducive to expressing gravitation (because the operations of General Relativity are definitely applicable only in the local regime, non-probabilistic internal space-time stresses must be used to transmit curvature to adjacent points far away from the mass of influence in a very deliberate manner because only non-random space-time configurations are capable of transmitting curvature to adjacent points when no mass is present), and if it fluctuates in response to the probabilistic creation of mass, then there is no need to quantize it. However, to suggest the opposite, namely that quantum particles are tossed about more randomly than classical objects because of brownian motion among space-time constituents (as the author suggests) is preposterous; though a dynamic interaction between space-time curvature and random particle behavior is possible (but negligible because of the weakness of gravity, unless the volume of individual space-time quanta is on the scale of the volume of discrete matter quanta, in which case this model is hardly likely in itself to represent anything factual though it might explain the lack of internal structure in leptons), a reliable concept of space-time is required to facilitate a large scale accommodation of gravity (as they said, you cannot ignore causality and hope that it will manifest on its own). I also cannot accept an empirical study of spectral processes (by itself) as a rational basis for the dimensionality of space-time. Additionally, I have trouble accepting the author's notion of causality...no mention of locality is ever made, though things must be locally applied to cause something in the context of General Relativity. The model as presented also fails to account for Gravitational Time Dilation in General Relativity and Time Reversal Symmetry in Quantum Mechanics (symmetry in the fundamental forces is the prime rational expectation that favors the quantization of gravity). Perhaps time is a 'coherent' manifestation of the alignment of time arrows (what they propose is the only thing that separates this Quantum Gravity from its predecessors, and what suspiciously reminds me of the fiber bundle model of General Relativity described with infinitesimal space-time elements), such that disordered crumpling decreases the 'net' progression of time (unfortunately the 'causality' premise prohibits time-like curves or tipping light-cones in curved space-times against the predictions of General Relativity) in a way that might explain many quantum phenomena, such as energy-time complementarity or the inverse quantum zeno effect. However, overall I felt that this article did not address the main concerns involved in the assimilation of gravitation into a holistic quantum formulation of the universe.

 

[shadowpuppet]

What's funny about this whole thing is that if gravitons do exist and can be generated and measured, then the temporal duration of an infinitesimal unit of time can be determined using the Nyquist frequency (though inducing the aliasing of gravitons would be a bit of a challenge) and the spatial density of space-time elements can be determined using the plasma wavelength (attenuation might be conceivable if the constraints of graviton transmission velocity, minimum time duration exhibited in space-time, maximum energy of oscillation, and Heisenberg Uncertainty allow it, perhaps using pair productions that create and annihilate each other at a constant frequency)...

 

[yuiop]

If the annihilation of mass caused a sudden retraction of space-time, in General Relativity you might expect to be translated a reasonable distance (due to the delay of the response of space-time to matter as might occur in the Lense-Thirring effect), however if the most probable shape of space-time under the new stresses did not accommodate your current situation and was suddenly realized without intermediate steps (by quantum 'jumps'), you might find yourself on the other side of the universe, or not in it at all;

It is, of course, not possible to suddenly annihilate mass. Even in the event of matter being annihilated by by anti matter the resulting photons have energy and a gravitational field and there will be a finite time for the photons to disperse

(unfortunately the 'causality' premise prohibits time-like curves or tipping light-cones in curved space-times against the predictions of General Relativity)...

I look forward to the day a new quantum gravity model is generally accepted and it is realized that some of the so called predictions of GR, such as closed time like curves and singularities of infinite density are merely artifacts that arise from incorrect physical interpretations of what the maths of GR is telling us.

 

[Haelfix]

"In less than 2 words, does the book suggest gravity can be explained by gravitons or not"?

Well the book has more than two words =) but yes it does, at least classically and semiclassically.

 

[shadowpuppet]

It is, of course, not possible to suddenly annihilate mass. Even in the event of matter being annihilated by by anti matter the resulting photons have energy and a gravitational field and there will be a finite time for the photons to disperse

I look forward to the day a new quantum gravity model is generally accepted and it is realized that some of the so called predictions of GR, such as closed time like curves and singularities of infinite density are merely artifacts that arise from incorrect physical interpretations of what the maths of GR is telling us.

That is debatable...in General Relativity photons are considered to be massless disturbances of the electromagnetic field following null geodesics in curved space-times. It is also General Relativity that has made accurate predictions and not Quantum Gravity. If a photon did have a nonzero rest mass, its relativistic energy would have to be infinite just to satisfy Special Relativity alone. But if annihilation is not sufficient for this purpose, then consider spontaneously forming virtual particles (the kind allowed by Heisenberg Uncertainty not the kind used by JesseM to impart gravitation). Wouldn't these work?

 

[JesseM]

That is debatable...in General Relativity photons are considered to be massless disturbances of the electromagnetic field following null geodesics in curved space-times.

Photons of course have zero rest mass, but they do carry energy, and in general relativity all forms of energy contribute to the curvature of spacetime, not just energy in the form of rest mass...so, the idea that an annihilation of mass would cause "a sudden retraction of space-time" doesn't seem to make sense, since energy is always locally conserved in particle interactions, even ones where mass is annihilated.

But if annihilation is not sufficient for this purpose, then consider spontaneously forming virtual particles (the kind allowed by Heisenberg Uncertainty not the kind used by JesseM to impart gravitation). Wouldn't these work?

In quantum field theory there aren't two different kinds of virtual particles, the virtual photons and gluons that are "allowed by Heisenberg Uncertainty" are the same ones that transmit the electromagnetic or strong force (again, whether or not a theory of quantum gravity will end up involving virtual gravitons is uncertain). I believe the question of how virtual particles influence spacetime curvature is one of the reasons physicists think general relativity is incomplete, because although it's known how to do quantum field theory on a fixed curved spacetime, it's not known how to take into account the possibility that virtual particles will themselves influence the spacetime curvature (and in quantum field theory you have to sum over an infinite number of possible virtual particle diagrams, each of which might involve its own distinct spacetime curvature). See this page for a brief discussion of this.

 

[shadowpuppet]

"In less than 2 words, does the book suggest gravity can be explained by gravitons or not"?

Well the book has more than two words =) but yes it does, at least classically and semiclassically.

First of all, this is a book about General Relativity, not Quantum Gravity. Second of all I own this book, and it states the exact opposite, so I am afraid that my discussion is not inaccurate as you suggest.

Please refer to:

Part 3: Applications of General Relativity =>
Chapter 10: Gravitational Radiation =>
Section 8: Quantum Theory of Gravitation =>
Page 285

At present there does not exist any complete and self-consistent quantum theory of gravitation, and it would be out of place in this book to describe in detail the attempts that have been made to construct such a theory. However, it will be possible and it may be useful to give the reader some taste of what a quantum theory of gravitation would be like.
To start at the simplest level, we would interpret a gravitational plane wave, with wave vector $k_\mu$ and helicity :1: 2, as consisting of gravitons: quanta with energy-momentum vector pJL = lik JL and spin component in the direction of motion :1: 2n. (Here n = 1.054 x 10- 27 erg sec). Since kJLkJL = 0, the graviton is a particle of zero mass, like the photon and neutrino. According to Eq. (2.8.4), the energy-momentum tensor of an assembly of gravitons, all of which have four- momenta pJL = nk JL , is...

It would seem that the author agrees that photons are massless particles.

 

[lucien86]

Dear what a complex argument. This seems a simple question to me - the question is do gravitons exist ? the answer is no.

The graviton is supposed to be some electromagnetic particle of quantum flux that imbues massed objects with mass - so the graviton must be emitted and absorbed it must travel through space and must be the most common object in the universe.
The (first) problem for the graviton comes because the atom is not very heavy, so the graviton must have a truly tiny quantum value. This tells us its frequency must also be low (very low)- therefore its wave must be big (huge). However it can act on a single atom so it must have a very tiny wave and a very high frequency, oh dear. Let's make its frequency zero - but now its no longer an electromagnetic wave at all. Worst of all though, if the graviton is an electromagnetic wave then why can't we shield it? Basically the graviton doesn't exist, it can't exist. You can't unite the four forces because gravity is just to different - in fact as far as I know there is no evidence that gravity even obeys quantum rules at all. At a simple logical level the graviton just looks wrong.

So I'm afraid that Relativity wins the argument.

But to me making gravity a result of curved space time is itself (slightly) wrong - Relativity can stand just as well without it. My difference is that . . . I know not to give personal theories here.

 

[JesseM]

The graviton is supposed to be some electromagnetic particle of quantum flux

No, it is not supposed to be electromagnetic. There are four fundamental forces in nature--electromagnetic, gravitational, and the strong and weak nuclear forces--and each except for gravity is known to have its own separate force-carrying particles (electromagnetic = photons, strong = gluons, and weak = W and Z particles...see here for details), so the graviton would just be another type of force-carrying particle, separate from the others.

The (first) problem for the graviton comes because the atom is not very heavy, so the graviton must have a truly tiny quantum value.

Tiny quantum value of what? Energy? Of course just as different photons can have different energies and frequencies, the same would be true of gravitons.

 

[Haelfix]

Shadowpuppet, good I am glad you own the book, it will make things easier.

General relativity is the tree level diagram of the quantum theory. Quantum gravity is the summation to all orders of the path integral. No one knows what the latter is b/c it is divergent, but the former is well understood.

The book deals with that classical theory, since that is what GR is and as you can read it is completely described by the dynamics of the spin2 gauge boson 'the graviton'. No different than classical electromagnetism is described by the dynamics of a spin 1 gauge boson 'the photon'.

 

[yuiop]

It's "negated"? Where, exactly? The FAQs are not completely explicit about the fact that real photons are only associated with electromagnetic waves (which only come about due to oscillating charges) while virtual photons are associated with the transmission of the electromagnetic force even in the absence of waves, but this is correct nevertheless, and the virtual particle FAQ does at least strongly imply it in the opening section."

Hi, your comment prompts an interesting thought.
If electromagnetic force is transmitted by virtual photons and if the source of the charge in black hole is inside the event horizon, then the virtual photons would become real photons if they passed out through the event horizon. I got that impression from an early description of Hawking radiation that stated that a virtual particle created just outside the event horizon becomes a real particle when it passes to the inside of the event horizon so presumably the converse is true. Would it possible that all real particles that pass into a black hole become virtual? Normally, virtual particles have very short lifetimes but possibly their lifetimes are extended by extreme time dilation inside a black hole? If that is the case would it be possible that virtual charged particles inside a black hole transmit electromagntic force in the form of real photons that become virtual photons as they pass out the event horizon and become the virtual force carriers of the black hole?