Gravitons or Warped Space-Time?

[yuiop]

...
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.

Does that not present a problem for the existence of gravitons? If gravitons are a source of gravity themselves then they could only do that by emitting gravitons themselves because in that model gravity is transmitted by gravitons. The gravitons emitted by the gravitons would themselves be a source of gravity and have to emit more gravitons to communicate their presence and the process continues ad infinitum resulting in infinite gravity everywhere. The alternative is to suggest that mass communicates it presence to the field by emitting gravitons but gravitons can communicate their presence to the field by means that do not require gravitons.

 

[shadowpuppet]

The FAQ at http://arnold-neumaier.at/physics-faq.txt was very ambiguous; though I agree that virtual particles can exist for a very short time and because of that the their influence on reality is small, however if they are real enough to facilitate adjustments in Feynman Diagrams then they must have a physical correlation that is more than just an 'artifact of theory' as the author describes it. He mentions that energy conservation is violated even though that is already explained by Heisenberg Uncertainty. The discussion of the influence of virtual particles on particle discussion made no sense and avoided describing how and why virtual particles actually affect measurements, and it was very underhanded in its equation of virtual momenta with integral terms (and though the author tries to make the application of virtual particles in calculations seem limited, specialized, and obsolete, he keeps coming up with more examples of the usefulness of these concepts apparently in order to devalue them), which is why I distrust the rest of the FAQ. He tries to envision a more perfect non-perturbative quantum field theory that does not contain virtual particles, but of course this doesn't exist, the virtual particles do...

 

[shadowpuppet]

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.

Please don't oppose my position if you do not have a definite position yourself. There is no space-time in which space-time can travel. There is only space-time in which matter can travel. If you don't like words, I can draw a picture showing how even though you can move a ruler through space, you can't move space through space, nor can you move time through time though you can daydream that you can as time passes (but not through time).

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).

Let me draw you a mental picture. If one graviton has mass, then it must impart gravity.
Because gravitons also transmit gravity, the graviton must emit another graviton to do so. Sorry that it's not infinite like I verbally said it would be.

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.

What then is a positive argument? And what is handwavey? Is that gravitons are transmitted?

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:

You must have very bad eyesight because I put both negations directly under that statement so that you wouldn't miss them. Perhaps visual impairment is the reason that you think space can travel through space? I don't know where you got the new quote (One of the first steps in the development of quantum mechanics...), but the quotes I used were from your original post.

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".

Yes you did claim that, it was the first sentence you posted on this thread so go look it up. It's not my problem that you think 'real' accelerations are mediated by 'imaginary' particles, but even that was negated. The FAQs claimed both this and that quantum gravity is inconsistent and I am posting the quote below SO THAT YOU DON'T MISS IT THIS TIME!

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.

If you still don't know where the quote is, then you missed it.

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).

Many Worlds is an interpretation of quantum mechanics that has about as much predictive power as String Theory. How do you explain the Alain Aspect experiments?

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.

You can't prove that until a Quantum Gravity proves to be more accurate than General Relativity. The other three forces are irrelevant to the measure of gravity.

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.

Yes...there are no problems at all in the Many Worlds of String Theory...and please don't bring up topics that are irrelevant to your point.

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.

On the contrary...your understanding of theoretical physics and interpretation of experimental results is obviously unique to you, and judging by the inconsistent and irrelevant arguments you have envisioned, spanning from Many Worlds to String Theory, I am not surprised that you rely on others to carry the burden of calculation and experiment.

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.

General Relativity predicts that gravity is not imparted by gravitons, real or virtual. The Riemann Curvature Tensor does not impulsively deflect matter as would a physical vector field, it describes the curvature of the track on which matter moves unaffected by anything though the track itself is affected. How many times do I have to say this? Stop watching my 'wavy hands', ignore your dislike of verbal expression, and listen to what I'm saying!

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.

Yes, you finally seem to understand what I am talking about! Yay! But QED does rely on collisions, they are known as 'scattering', and there are many different types of scattering: Brillouin scattering, Thomson scattering, Raman scattering, Rayleigh scattering, Compton scattering, Mie scattering...

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).

String Theory is hardly 'Mainstream Physics', and neither is Quantum Gravity. General Relativity, which is what I am defending, is in the title of this forum.

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.

That's not true. Maxwell's Electrodynamics, like Newton's Mechanics, allow action-at-a-distance; this is why charges repel or attract at-a-distance.

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.

I am going to bed.

:zzz:

 

[shoehorn]

That's not true. Maxwell's Electrodynamics, like Newton's Mechanics, allow action-at-a-distance; this is why charges repel or attract at-a-distance.

Oh dear...

 

[JesseM]

The FAQ at http://arnold-neumaier.at/physics-faq.txt was very ambiguous; though I agree that virtual particles can exist for a very short time and because of that the their influence on reality is small, however if they are real enough to facilitate adjustments in Feynman Diagrams then they must have a physical correlation that is more than just an 'artifact of theory' as the author describes it.

Consider the path integral approach to ordinary nonrelativistic QM (i.e. not quantum field theory). One can get predictions by doing a sum over an infinite number of possible paths, much like the sum over Feynman diagrams showing virtual particle interactions (I believe Feynman's work on the path integral approach was a major influence on his development of the Feynman diagram technique in quantum field theory); do you think this means all the paths are "real"? If so, what about the fact that one can get identical predictions without the need to sum over paths at all, just by using the Schroedinger equation to calculate the evolution of the wavefunction? If not, what do you think is fundamentally different about summing over Feynam diagrams to get predictions about actual measured results?

Please don't oppose my position if you do not have a definite position yourself. There is no space-time in which space-time can travel.

Who said gravitons were supposed to be space-time, rather than just another type of particle moving through spacetime? But on the subject, in classical general relativity without gravitons, we can talk about gravitational waves traveling through spacetime, and yet they themselves are just localized ripples in the curvature of spacetime.

Let me draw you a mental picture. If one graviton has mass, then it must impart gravity.

Gravitons are not theorized to have rest mass, but they would have energy, so they would impart their own gravity as you say.

Because gravitons transmit gravity, the graviton must emit another graviton.
Because that graviton also has mass and imparts gravity, it must emit another graviton.
Because that graviton also has mass and imparts gravity, it must emit another graviton.

...

Because that graviton also has mass and imparts gravity, it must emit another graviton.

Sorry that it's not infinite like I verbally said it would be.

Are you unaware that in accepted quantum field theories like quantum electrodynamics, the calculations already involve an infinite sum of Feynman diagrams, each with distinct sets of virtual particles? But a series with an infinite number of terms can nevertheless produce a finite answer, as we all learned in calculus. I don't understand the technical details, but from what I've read renormalization is apparently the technique that allows you to get finite answers from the infinite sum of Feynman diagrams in quantum field theory. Quantum gravity does have problems with renormalization, but replacing the notion of gravitons as point particles with the notion of gravitons as strings is apparently one way to solve this.

What then is a positive argument? And what is handwavey? Is that gravitons are transmitted?

A positive argument would be that there are convincing reasons to believe that the gravitational force is mediated by gravitons. "Handwavy" is a term often used by physicists and other scientists to describe arguments that aren't at all rigorous and leave out important steps, see here for example. My argument is just that you haven't presented any convincing, non-handwavy reasons to believe there is something impossible about the idea that the gravitational force is mediated by gravitons.

It's "negated"? Where, exactly?

You must have very bad eyesight because I put both negations directly under that statement so that you wouldn't miss them.

Please spare me the childish taunting, of course I read those statements, but neither is a "negation" of the statement that "that virtual particles transmit the non-oscillating component of acceleration" in quantum field theories. The two statements you quoted only said that it is unclear whether a theory of quantum gravity would be a quantum field theory at all (though they certainly did not deny it was possible), but even if it turns out that gravity cannot be described by a quantum field theories, the fact remains that in any quantum field theory (like quantum electrodynamics), virtual particles are responsible for forces that are not associated with the waves produced by oscillating charges. I never said that this would definitely be true in a theory of quantum gravity, because I never said a theory of quantum gravity would necessarily be a typical quantum field theory.

Perhaps visual impairment is the reason that you think that space can travel through space?

No one said that gravitons are "space", whatever that is supposed to mean.

I don't know where you got the new quote (One of the first steps in the development of quantum mechanics...)

From the very first paragraph of the same FAQ on virtual particles that your first quote came from.

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".

Yes you did claim that, it was the first sentence you posted on this thread so go look it up.

In the first sentence I was only talking speculatively about how a theory of quantum gravity involving gravitons might look, not saying anything definite. Read it again:

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

It's not my problem that you think 'real' accelerations are mediated by 'imaginary' particles

Are you using "imaginary" to mean virtual? Again, in a quantum field theory like quantum electrodynamics, it's definitely true that if no electromagnetic waves are present (and electromagnetic waves are only created when charges accelerate), then there will be no non-virtual photons, but virtual photons can still create forces between charges.

but even that was negated.

No, it wasn't. Again, the quotes you posted only said it was questionable whether quantum gravity would be a standard quantum field theory, but nowhere do they negate what I am saying about how standard quantum field theories such as quantum electrodynamics work. Again, the first section of the virtual particle FAQ echoed what I am saying about real vs. virtual photons in quantum electrodynamics:

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. Here is a picture (a "Feynman diagram") of the exchange of one virtual photon.

The FAQs claimed both this and that quantum gravity is inconsistent and I am posting the quote below SO THAT YOU DON'T MISS IT THIS TIME!

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.

Hmm, this quote actually backs up what I said about standard quantum field theories when it refers to "The notion of virtual particles mediating static forces", and it does not say that this standard quantum field theory picture is definitely wrong when it comes to quantum gravity, only that "it is not at all clear" whether this picture will work. They also that "the usual way of doing perturbation theory doesn't work", and here I think they are referring to what I mentioned above about renormalization, which is part of perturbation theory (see the third paragraph of wikipedia's renormalization article), failing to give finite answers when gravitons are treated as point particles. But as I said, my understanding is that you can get finite answers again if gravitons are treated as 1-dimensional strings instead. This is not to say that string theory is definitely correct, but that it provides at least one possible way out of the problem that quote is referring to at the end.

Many Worlds is an interpretation of quantum mechanics that has about as much predictive power as String Theory. How do you explain the Alain Aspect experiments?

All interpretations of QM make the same predictions about every possible experiment, including the Aspect experiment, that's why they're called "interpretations" rather than actual theories. If you'd like a simple picture of how a MWI-like picture can explain violations of Bell's inequality without the need to violate locality, see my post #11 on this thread; basically the idea is that each experimenter splits into multiple copies when they make their measurement, and the universe doesn't have to decide which copy of experimenter #1 gets matched up with which copy of experimenter #2 until there's been time for a signal moving at the speed of light to go between them.

But just as I am not trying to argue for any definite conclusions about gravitons or quantum gravity, so I am not trying to argue that there is any reason to believe the MWI is correct. My point is just that your definitive statements on these subjects are unjustifiable since there exist possible ways in which they could be wrong that are perfectly consistent with everything we do know.

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.

Yes...there are no problems at all in the Many Worlds of String Theory...and please don't bring up topics that are irrelevant to your point.

They are relevant to showing that definitive claims like "there is no possible way a theory of quantum gravity involving gravitons could match the predictions of general relativity" (a paraphrase of what I think you have been arguing on this thread, correct me if I'm misunderstanding) or "action-at-a-distance may occur between two entangled states" (a direct quote). Again, although there is no strong reason to believe either string theory or the many-worlds interpretation are true, each one represents a "proof of principle" that either of the statements above could be wrong without it contradicting things we already know.

On the contrary...your understanding of theoretical physics and interpretation of experimental results is obviously unique to you

Really? Point to a specific statement about physics which you think is "unique to me" and I will try to refer you to an example of a professional physicist stating the same thing.

General Relativity predicts that gravity is not imparted by gravitons, real or virtual.

And classical electromagnetism predicts that the electromagnetic force is not imparted by photons, real or virtual. Quantum electrodynamics says something different, and it reproduces all the successful predictions of the classical theory.

 

[JesseM]

(continued from previous post)

The Riemann Curvature Tensor does not impulsively deflect matter as would a physical vector field, it describes the curvature of the track on which matter moves unaffected by anything though the track itself is affected. How many times do I have to say this? Stop watching my 'wavy hands', ignore your dislike of verbal expression, and listen to what I'm saying!

I like verbal expression just fine when people adhere to standard technical definitions, and don't try to make physical arguments based on words which have no accepted rigorous definition, like saying that force fields "impulsively deflect" matter whereas tensor fields describe how matter "moves unaffected by anything though the track itself is affected". Perhaps you just mean that in GR matter moves on geodesics, while in classical electromagnetism charged particles don't? If that's what you meant, I agree, but it would have been nice if you'd used the standard terminology; and anyway, how would this support your statement that tensor fields are "not real fields and they do not provide a physical mechanism for bosonic emissions"? The classical electromagnetic field also does not say anything about "bosonic emissions", yet it can be generalized to a quantum field which does; do you have any actual reasons why you are confident the same couldn't be true of the tensor fields in GR, other than the ill-defined notion that tensor fields are not "real" while electromagnetic fields are?

By the way, note that instead of seeing tensor fields as causing curvature of spacetime, one is perfectly free to take an alternate picture where the field just pushes and pulls objects in flat spacetime, with particles being deflected away from geodesic paths in this flat spacetime by the gravitational field, and both pictures lead to identical predictions so they are really just like different "interpretations" of GR. This is discussed at some length in Kip Thorne's book Black Holes and Time Warps, starting on p. 397. To quote from part of this chapter:

Is spacetime really curved? Isn't it conceivable that spacetime is actually flat, but the clocks and rulers with which we measure it, and which we regard as perfect in the sense of Box 11.1, are actually rubbery? Might not even the most perfect of clocks slow down or speed up, and the most perfect of rulers shrink or expand, as we move them from point to point and change their orientations? Wouldn't such distortions of our clocks and rulers make a truly flat spacetime appear to be curved?

Yes.

Figure 11.1 gives a concrete example: the measurement of circumference and radii around a nonspinning black hole.

...

If space is actually flat around the black hole, but our perfect rulers are rubbery and thereby fool us into thinking space is curved, then the true geometry of space must be as shown on the right of Figure 11.1, and the true distance between the horizon and the circle must be 16 kilometers, as demanded by the flat-geometry laws of Euclid. [the diagram shows the circumference of the horizon as 100 km, and the circumference of the circle 16 km away from the horizon as 200 km] However, general relativity insists that our perfect rulers not measure this true distance. Take a ruler and lay it down circumferentially around the hole just outside the horizon ... When oriented circumferentially like this, it does measure correctly the true distance. Cut the ruler off at 37 kilometers length, as shown. It now encompasses 37 percent of the true distance around the hole. The turn the ruler so it is oriented radially ... As it is turned, general relativity requires that it shrink. When pointed radially, its true length must have shrunk to 16 kilometers, so it will reach precisely from the horizon to the outer circle. However, the scale on its shrunken surface must claim that its length is still 37 kilometers, and therefore the distance between the horizon and the circle is 37 kilometers. People like Einstein who are unaware of the ruler's rubbery nature, and thus believe its inaccurate measurement, conclude that space is curved. However, people like you and me, who understand the rubberiness, know that the ruler has shrunk and that space is really flat.

What could possibly make the ruler shrink, when its orientation changes? Gravity, of course. In the flat space of the right half of Figure 11.1 there resides a gravitational field that controls the sizes of fundamental particles, atomic nuclei, atoms, molecules, everything, and forces them to shrink when laid out radially. The amount of shrinkage is great near a black hole, and smaller farther away, because the shrinkage-controlling gravitational field is generated by the hole, and its influence declines with distance.

The shrinkage-controlling gravitational field has other effects. When a photon or any other particle flies past the hole, this field pulls on it and deflects its trajectory. The trajectory is bent around the hole; it is curved, as measured in the hole's true, flat spacetime geometry. However, people like Einstein, who take seriously the measurements of their rubbery rulers and clocks, regard the photon as moving along a straight line through curved spacetime.

What is the real, genuine truth? Is spacetime really flat, as the above paragraphs suggest, or is it really curved? To a physicist like me this is an uninteresting question because it has no physical consequences. Both viewpoints, curved spacetime and flat, give precisely the same predictions for any measurements performed with perfect rulers and clocks, and also (it turns out) the same predictions for any measurements performed with any kind of physical apparatus whatsoever. For example, both viewpoints agree that the radial distance between the horizon and the circle in Figure 11.1, as measured by a perfect ruler, is 37 kilometers. They disagree as to whether that measured distance is the "real" distance, but such a disagreement is a matter of philosophy, not physics. Since the two viewpoints agree on the results of all experiments, they are physically equivalent. Which viewpoint tells the "real truth" is irrelevant for experiments; it is a matter for philosophers to debate, not physicists. Moreover, physicists can and do use the two viewpoints interchangeably when trying to deduce the predictions of general relativity.

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.

Yes, you finally seem to understand what I am talking about! Yay! But QED does rely on collisions, they are known as 'scattering'

This is why it is better to use standard terminology like "scattering" and "geodesics" rather than inventing your own idiosyncratic terminology like "collisions" with "space-time information".

String Theory is hardly 'Mainstream Physics', and neither is Quantum Gravity. General Relativity, which is what I am defending, is in the title of this forum.

It is mainstream in the sense that few physicists think there is anything about it which is obviously incompatible with experimentally-tested results, and thus few physicists would accept the impossibility claim that there is no plausible way that general relativity's successful predictions could ever be replicated by a quantum gravity theory involving gravitons.

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.

That's not true. Maxwell's Electrodynamics, like Newton's Mechanics, allow action-at-a-distance; this is why charges repel or attract at-a-distance.

I suppose it depends on precisely how you define action-at-a-distance, but there is certainly no violation of locality in Maxwell's electrodynamics, any more than there is in GR, which was my only point above. A charge's motion is determined only by the local force vectors at its location, and the force vector at any given point in space and time is only influenced by events in the past light cone of that point. If I am an inertial observer and there's a charge resting at constant distance from me, I'll feel a constant electromagnetic force from that charge; then if someone accelerates that charge to move it closer or farther from me, I will not feel any instantaneous change in the electromagnetic force at my location, I won't know what happened until there has been time for a wave in the electromagnetic field, which was created by the acceleration of the charge, to propogate at the speed of light and alter the electromagnetic force vector at my own location. Do you disagree?