Mass, Gravity,and the Higgs Boson

[bison]

Will pose this in the form of a question. If, as we're often told, it is the Higgs boson that confers mass upon matter, and gravity is merely the warping of space by mass, what exactly do we need with the graviton, the postulated boson that conveys the force of gravity? Won't the mass conferred by the Higgs be sufficient, by itself to produce gravity? There is no apparent quantum exchange of energy between one particle of matter and another in gravity, as we see in the other three forces of Nature. Objects are simply attracted to one another, in proportion to their masses, or so it seems. . .

[sepulchrave]

Will pose this in the form of a question. If, as we're often told, it is the Higgs boson that confers mass upon matter, and gravity is merely the warping of space by mass, what exactly do we need with the graviton, the postulated boson that conveys the force of gravity? Won't the mass conferred by the Higgs be sufficient, by itself to produce gravity? There is no apparent quantum exchange of energy between one particle of matter and another in gravity, as we see in the other three forces of Nature. Objects are simply attracted to one another, in proportion to their masses, or so it seems. . .

There still is need for a graviton. The Higgs field is sufficient to supply inertial mass to particles (as a consequence of ``renormalization'').

Presumably, gravitational mass is equivalent to inertial mass, but we still need a gravitational field for an interaction to occur.

In general relativity the gravitational field is equivalent to space-time warping, but gravity is still the cause of space-time warping.

In any event, we still need another field, whether one calls it ``gravity'' or ``space-time'' is, in a sense, irrelevant. The question is, does this field have quantized excitations?

IF this field can be treated with perturbation theory (like all the other fields from fundamental forces), then static gravitational forces can be treated as superpositions of quantized excitations - in other words, ``virtual gravitons''.

There is some evidence to suggest that gravity cannot be treated with perturbation theory, so ``virtual gravitons'' may be a meaningless expression. (``Virtual particle-antiparticle pairs'' and ``virtual photons'' are clearly not meaningless, while they cannot be detected directly they do alter a quantum vacuum in predictable and measurable ways, such as the Casimir effect and vacuum polarization).

Secondly, IF gravity is capable of producing gravitational waves, then (I think) a graviton is needed to avoid the same type of ``ultraviolet catastrophe'' that occurs with electromagnetic fields.

So as far as I know, unless gravitational waves do not exist (which would be odd) and gravity is a non-perturbative field, a graviton is necessary.

[MedicTJ]

What if there are more than 4 forces of nature?

[sepulchrave]

What if there are more than 4 forces of nature?

There is no reason why there couldn't be more than 4 forces... but the extra ones are doing a good job of hiding.

[bison]

Thanks, Sepulchrave, for a helpful, clear response. As you note, perturbation theory may not apply to gravity. The evidence, so far, seems to suggest that it does not. There is the expectation that gravitational waves exist, of course, but even indirect evidence of this is minimal. The evidence from the Hulse-Taylor binary pulsar is somewhat equivocal for orbital decay via the radiation of gravitational waves.

It appears that our best current gravitational wave detectors are near the threshold of detecting what we consider a signal of reasonable strength, given the circumstances. This may explain the failure to find direct evidence of gravitational waves.

What struck me about the situation, is that an explanation of gravity within a completed grand unification theory would be simpler than having to evoke a graviton. It seems that if Relativity and Quantum Theory are to be unified, there may be a point, moving into the macroscopic scale of things, where a boson may not be required for a field to exist.

[sepulchrave]

What struck me about the situation, is that an explanation of gravity within a completed grand unification theory would be simpler than having to evoke a graviton. It seems that if Relativity and Quantum Theory are to be unified, there may be a point, moving into the macroscopic scale of things, where a boson may not be required for a field to exist.

I agree, the graviton may not exist.

I tend to believe it does exist - but may not be ``fundamental''.

There are lots of quantized excitations that exist as a consequence of fundamental fields and physical configurations: phonons, magnons, spinons, etc. in crystals are good examples of these.

For a given configuration of matter with gravity I think there should be some sort of graviton, even if gravity isn't a fundamentally quantized field on its own.

But this is just my opinion, and I think your reasoning is sound as well.