What's a graviton?

Naty1

A graviton is the quantization, that is the localization, of the gravitational field energy or gravitational wave, as the electron is of the electromagnetic field. Nobody knows exactly what any fundamental particle is. It's one view of gravity. General Relativity is another view.

Since everything popped out of a bang, it is believed all particles and fields were once unified, that is, combined in a high energy unstable environment, and via spontaneous symmetry breaking...the movement of the vacuum energy to a more stable and lower energy state where we now exist.... separate pieces emerged, those we now observe around us, particles, waves, energy, time, etc...all APPEAR now as separate entities.

A graviton has not yet been experimentally observed. General relativity does not speak to gravitons; GR is a continuous description of gravity.

Gravity, and hence gravitons, are not part of the 'Standard Model' of particle physics describes subatomic particles via electromagnetic, weak, and strong nuclear interactions. So the Standard Model falls short of being a complete theory of fundamental interactions because is missing gravity.

It has been discovered certain mathematical formalisms seem to match what we observe and have been useful in making predictions of what to look for experimentally.

It turns out that when Gauge fields in a theory are quantized, they describe carriers of the forces in the Standard Model. These quanta of the gauge fields are called gauge bosons, and the theories have been successful field theories explaining the dynamics of elementary particles. But,not so far, gravity.

Eric Verlinde thinks gravity is explained as an entropic force caused by changes in the information associated with the positions of material bodies. A relativistic generalization of the presented arguments directly leads to the Einstein equations.

On the Origin of Gravity
and the Laws of Newton
Erik Verlinde (69 pages)
http://arxiv.org/PS_cache/arxiv/pdf/...001.0785v1.pdf

Don't worry if much of this doesn't make a lot of sense: I could ask a hundred questions about what I just posted and pretty quickly would get to places where 'nobody knows'....

Leoragon

So what explanation of gravity should I follow? The distortion of space time or this graviton thingy. Or is it that the graviton is the particle that flows to each object that is gravity? Can these two be united? Because if you're just falling in space-time, what's the need of the graviton?

Naty1

You have to follow the theory that covers the regime you study: GR for large scale, like cosmological predictions; quantum theory, eventually maybe quantum gravity, for the very small. But right now neither GR nor QM cover black hole and big bang singularities.

Leoragon

So GR for large scales and graviton for small scales?

dextercioby

The only explanation of gravity to be followed is the one offered by the Theory of General Relativity. There's no final quantum theory of gravity as of yet, so use what we have for sure, just like one is invited to use the Standard Model of Particles and Interactions to explain the other 3 interactions.

Naty1

Leoragon:

I find answers like post #22 a bit too formulaic....but it's a valid perspective. Let me explain what I was trying to explain.

We are probably past the stage when we should have asked what you mean by 'gravity'. When I suggested quantum mechanics for 'the small', I was referring to things like degenerate matter:

http://en.wikipedia.org/wiki/Degeneracy_pressure

Some here might say "that's not gravity' and I'd have to agree....what is going on is not properly described by gravity...so we need something else....The gravitational physics of the large is inadequate at subatomic scales to explain observations we might expect by analogy with large scales.

When the core of a star more than about 1.5 solar masses collapses, as nuclear reactions run out of fuel, Chandrasekhar calculated the large scale effects using GR....
[This is a great story of science, by the way.] But the collapse of some such objects, smaller mass, may later be halted by degenerate electrons. By Pauli Exclusion principle....etc,etc...quantum effects may overwhelm gravitational effects.

Another example might be types of particle production: Horizons are described by GR [I'm not sure if they are also present in relativistic QM.], anyway, it seems that the expansion of geometry itself, especially during early inflation of the universe, can produce matter, as can acceleration, as in the Unruh Effect. But understanding what is going on at the micro scale here not fully explained by GR: it is likely quantum fluctuations in the vacuum become quanta [particles] at super horizon scales. Particle production via changing gravitational fields and expansion is believed a real phenomenon, but understanding it at the micro level seems to require some additional theory.

We can call that 'quantum gravity'.