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Will the discovery of the graviton lead to the redundancy of general relativity even though it has been so well established. If not, will it mean that gravity will have two separate theories that ultimately give the same answer.

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    $\begingroup$ Nobody expects there to be a discovery of gravitons anytime soon, and potentially ever. It's not even clear to me that it's a necessary or even borderline useful concept for gravity. $\endgroup$ – CuriousOne Jun 24 '16 at 23:21
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    $\begingroup$ Actually, even though there are good answers here, I think the ultimate answer to your last sentence is a resounding "yes", although the question does become a bit philosophical. This is because, as far as I understand it (I don't understand particle physics very well), a graviton, as a force mediator, would be diametrically opposed to one of the fundamental notions of GR, which is that gravity is not a force but spacetime geometry. If the two theories were indistinguishable in what they foretold other than that graviton particles were observed, then we would have to say ..... $\endgroup$ – WetSavannaAnimal Jun 25 '16 at 6:04
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    $\begingroup$ ..... that the GR were more of a way of simulating, through geometric analogy, the effect of the graviton field. After all, GR was derived from very broad physical principles, it doesn't tell us anything about how or why spacetime takes on the properties GR deals with. It says nothing about the "internal machinery"that makes this happen. But these are more philosophical points if you are a pure physicist thinking about experimental results and calculating them correctly. $\endgroup$ – WetSavannaAnimal Jun 25 '16 at 6:04
  • $\begingroup$ I disagree, electromagnetism can also be seen as geometry of some space. Just, for some reason, the target space of gravity is the spacetime itself while other forces target other spaces $\endgroup$ – Andrii Magalich Jun 25 '16 at 9:44
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    $\begingroup$ @wetsavannaanimal aka Rod Vance. Realize that geometry can still be valid at (so called, i.e. Above Planck length) low energy and large sizes without being a simulation. While at Planck sizes it needs the graviton and quantum gravity to be correctly described. It's like an effective theory. One approach is that geometry may be an emergent property of quantum gravity. That does not at all make a geometrical theory of gravity at so-called low energy a simulation. Just like electric current is not a simulation. Thing about quantum gravity is that it does not seem possible to have it be a std QFT $\endgroup$ – Bob Bee Jun 25 '16 at 18:48
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Does the discovery of a photon and development of quantum electrodynamics make Maxwellian electrodynamics redundant? Not a bit.

Each physical theory has its domain of applicability. Electrodynamics successfully describes the macro phenomena of electricity and magnetism which are very much obscured when you look at them from the point of view of QED. Honestly, it is not so simple to derive even Coulomb's law.

One might say that QED encompasses everything Maxwell equations do, but in most cases the Maxwell equations will be more practical. On the other hand, QED is designed to solve problems that Maxwell equations can't solve.

The similar thing will most probably happen with the graviton. General Relativity is an amazing theory that is tested on the scales from our daily life to cosmological ones. We haven't seen any deviations from it yet, but we expect it to fail at some point — at small distances and high energies.

But development of a more fundamental theory won't make GR obsolete. For the same reason you still use Newton's equations.

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    $\begingroup$ QED is distinctly different than what quantum gravity may be. Saying it is the same, in the sense of the question, is the same as saying that we can quantize gravity using the same techniques, eg canonical quantization or Feynman's and others least action path. We can NOT, it has NOT be able to be quantized that way or any other way we know. It is a no renormalizable theory that way. Answering about gravitatons by answering about photons, unfortunately, is a mistake that has been known since about the 60's or before. $\endgroup$ – Bob Bee Jun 26 '16 at 1:55
  • $\begingroup$ You do no understand the point of the answer. Replace QED with GR and classical electrodynamics with Newton's equations — it still works. I do not say how you should quantize gravity, I explain the domain of applicability of scientific theory. $\endgroup$ – Andrii Magalich Jun 26 '16 at 10:50
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    $\begingroup$ You should not say what I understand. You assume too much. You can try clarifying your point. I take your comment as a clarification. Replacing those two as you did does not work. too many differences. Unless you (or anyone) face (notice I did not say understand) the differences, what you state is somewhat simplistic. People can get something out of top level similarities, but will think they know more than they do if one also does not explain or at least state the differences. $\endgroup$ – Bob Bee Jun 26 '16 at 20:10
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If the graviton is detected and its cross section and other properties and interactions are measured well find out something about quantum gravity and maybe even how to unify gravity and the other forces. As @CuriousOne says we are pretty far from discovering it, nobody is looking for it, and we don't have any way of even coming within 10 orders of magnitude of having the energy to probe the sector where it might be possible to see it.

Without a good quantum gravity theory we are also a little blind in any search we might do, know little about what to look for. We know it should be spin 2, no mass, interacts with all matter sort of the same way, and almost nothing else.

General Relativity has been proven. If at much higher energies something diverges fro GR, it does not make any difference, GR is known that it does not apply to those energies (and such small sizes, generally thought to be the Planck energy and length)

Nothing to worry about except that quantum gravity nobody yet knows what it is.

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In a quantum world, all oscillations are quantized (if they are truly periodic, not just approximately periodic). For example, oscillations of a solid are quantized and the quanta are called phonons. That doesn't mean that the model of the solid as a lattice of (quantum) atoms is wrong, or even that it's an approximation with a limited domain of validity. On the contrary, it is exactly right, and it predicts the existence of the phonons.

Fundamental (as far as we know) particles like electrons are oscillations of the fundamental field of the Standard Model. They are quantized for the same reason as any other oscillation, and we call the quanta particles, but it is the fields that are fundamental, not the particles.

Gravitational waves are oscillations of spacetime, and should be quantized for the same reason. The rules of quantum mechanics don't (and can't) distinguish between different kinds of oscillation. All that matters is whether the system returns to the same state at different times. If we manage to show experimentally that gravitational waves are quantized, that doesn't mean that there's anything wrong with the geometric picture of gravity.

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