This query might involve definitions of theory in general, but here goes.
First, an assumption, asked as a question because it’s a good idea to start with a valid one:
I’ve been told that reconciling quantum theory (architecture) and general relativity necessitate gravitons, and LIGO developers and others can practically taste their Nobel prizes as they look for them. The vast majority of subatomic particles since the glory days of Gell-Mann and others have been “discovered” by theory and later discovered. Score one for the theory, at least that theory predicting them. After a while–and now–the architecture of the particle zoo is so clearly defined as a result of how the inhabitants behave that it is considered final, because (to continue the analogy) the whole edifice would collapse. Yes?
Are anti-gravitons part of the mix? What are their properties theoretically?
By wording alone, everybody’s heard of “antigravity”–which we smarties know is a violation of energy conservation, for starters. But local antigravity occurs every-time I spend energy lifting a book, and the universe, through the sun-to-food-to-metabolism gets its due in the larger picture.
Is then, “antigravity” a thing? And if so, does it–as a larger scale phenomenon–differ than other local creation of an antiparticle?
I hope at least some of these queries are not gibberish…
Quantum field theory usually has nothing to say about gravity; the masses of the particles invovled are so small and the interactions are so short (cf. the scale in astronomy or cosomology) that the contribution of gravity is almost always nil. Still, if you want to incorporate gravity into the quantum framework, fundamental forces operate by (skipping over technical details here) particle exchange, and we know enough about gravity to put some restrictions on that particle— the graviton— would be for gravity. That having been said, gravitons aren’t part of the Standard Model, and their existence or nonexistence wouldn’t change much about it.
Under most models of gravitons, they would be their own anti-particle. This has nothing to do with whether anti-gravity exists; the photon, for example, mediates the electromagnetic interaction but is also its own antiparticle.
Antigravity would not be caused by antigravitons, and I don’t see any reason why it would violate energy conservation any more than gravity or a replusive electromagnetic force would.
Detecting individual gravitons, in a manner similar to catching a single particle in a cloud chamber, is likely impossible - Can Gravitons be Detected. Don’t forget just how incredibly weak gravity is compared to the other forces in nature. A rinky dink fridge magnet can overcome 10[sup]24[/sup]kg of planet for example. What LIGO is looking for, and finding, are gravity waves - large scale changes in spacetime.
Theoretically a graviton would be its own antiparticle similar to how a photon is its own antiparticle.
Your “antigravity” is nothing more than a directed movement of EM particles and fields overcoming gravitational attraction. It is in no way antigravity.
If there is such a thing as gravitons, then a gravitational wave would be a beam of a great many gravitons, just like a light wave is a beam of many photons. But one can describe gravitational waves without recourse to particles, too, and the sorts of experiments that would make the particle nature clear are almost impossible to do with gravity (as in, they’re the sort of thing that a Type III civilization might do to impress other Type III civilizations).
And it’s really easy to have some other force counteracting the effect of gravity: As you say, you yourself do it all the time. What people usually mean when they say “antigravity” is some means of actually removing the gravitational force, or even reversing its direction. While there are ways this could be consistent with basic laws like conservation of energy, we have no evidence that it actually occurs, nor even any reason to believe that it should.
General relativity can be re-cast so that it is a classical theory of a self-interacting massless spin-2 field against some background spacetime (most of the time we would want this background to be Minkowski spacetime). When viewed this way, general relativity can be quantitized and the graviton is the related quantum. The basic properties of the graviton, for example that it is its own antiparticle, can also be easily deduced.
However many view that this particular way of obtaining a quantum field theory of gravity from general relativity as problematic due to its fairly ad hoc approach and that it leads to a non-renormalizable theory of not-so-much immediate practical use.
Still though it is expected that a ‘better’ theory of quantum gravity would contain artifacts like the graviton, at least as an approximation, and having the same basic properties as predicted by this approach.
General relativity can describe anti-gravity (that is gravity acting repulsively). For the most part such solutions are deemed unphysical, though arguably dark energy could be seen as having a form of anti-gravity.
Oh, and we certainly can’t just say “gravity is never quantized, and that’s that”. There are situations that can and would arise naturally where quantum gravitational effects must be relevant. We just can’t produce any of them in the laboratory, nor find anywhere already in the Universe where they’re occurring.