Why Gravitons?

[Daecon]

Is the existence of the graviton particle really neccessary?

 

If gravity is merely a side-effect of mass in the space/time universe, why is it regarded as a 'force' such as electromagnetic, weak and strong?

 

I don't believe it requires a specific entity to transmit this force, as gravitational influence is just an inherent property of the universe, caused by the pressure of matter in space/time.

 

Oh wait... darn it. *ahem* If pressure causes friction, gravitons could be what are generated by that 'friction'.

 

I was all convinced, then I had to go and re-confuse myself by writing it down using pressure as an analogy.

[5614]

Have you heard of quantum mechanic's wave-particle duality?

 

It works something like every particle moves in a wave shape and every wave has a particle carryer.

 

Light has photons, sound has the air (or whatever medium it's travelling through), heat has the phonon (not photon), gravity has to have something....

[Daecon]

But gravity isn't really a wave though, is it...?

[5614]

hmmm, ignore my last post!!!

 

Moving on very swiftly...

 

Basically QM has worked very well in almost every area of physics with the quantization of several things, mainly light and photons. It was assumed that the same method would work for gravity. A lot of people were expecting a quantum gravity theory quite soon, but it is proving hard to detect this theoretical graviton, mainly because it is soo weak.

 

Every force has an exchange particle: Light has photons, strong force has gluons, weak force has W and Z bosons, it seems only natural that gravity would have an exchange particle (a force carrier).

[Flareon]

But gravity isn't really a wave though, is it...?

 

It can be. You probably have heard of gravitational waves or ripples in spacetime. Like when a boat sailing through water will leave ripples in its wake, massive moving bodies like stars and blackholes will produce gravitational waves. General Theory of Relativity postulates their existance, but because the waves decrease with distance, they have been too small for us to detect for now.

[BlackHole]

1) The other three forces (strong, weak, and electromagnetic) are carried by bosons. Particle physicists naturally expect that whatever the successes of GR, gravitation should be carried by a gauge boson too.

 

2) GR cannot be a final theory because it has singularities. This is disingenuous; QED the most accurate of relativistic quantum field theories has singularity problems too. Look up "Landau pole".

 

3) There are technical reasons that prevent the coupling of quantum theories such as the standard model to GR. Many workers believe that a quantum theory of gravity would remedy this, and provide a single theory covering all four forces.

 

There is no self-consistent theory of quantum gravity (and i highly doubt there'll be one in my lifetime). Quantum gravity should also explain how gravitons interact with the gravitation caused by a photon.

[5614]

Gravitons: For gravitons to always attract (gravity never repels), work over any distance and come in unlimited numbers they must be an even-spin (spin 2 in this case) boson with a rest mass of zero.

[Daecon]

It can be. You probably have heard of gravitational waves or ripples in spacetime. Like when a boat sailing through water will leave ripples in its wake, massive moving bodies like stars and blackholes will produce gravitational waves. General Theory of Relativity postulates their existance, but because the waves decrease with distance, they have been too small for us to detect for now.

 

I figure Gravity was just an effect of 4D space in 3 dimensions, and not actually 'transmitted' by anything.

 

Or am I taking the 'ball on a trampoline' 2D-3D analogy too far?

[5614]

Or am I taking the 'ball on a trampoline' 2D-3D analogy too far?

Basically..... yes!

[ydoaPs]

Gravitons: For gravitons to always attract [i'](gravity never repels)[/i]

that isn't true. what about negative energy?

[5614]

You can't have negative gravity...

 

Here's the debate in my head:

 

If there was negative gravity I would have heard of it because I just would have! It will have been detected (it would effect universe expansion) and people would know about it, I'd have read it somewhere. If it was there and no one had detected, well, how could it? It would effect universal expansion, people would detect it or at least wonder wtf is going on and I'd have read about that.

 

I suppose like the mathematically proved but never physical proved 'white hole' it might exist, but I'm sure there isn't negative gravity.

[ydoaPs]

read "The Fabric of the Cosmos" it's in there. i'd bet four billion yen on it.

[Daecon]

I'm sure I read about an experiment that produced an energy reading of less than zero, something to do with particle/antiparticle pairings where one of the two was removed, leaving an absence of energy where there wasn't before...

 

Or perhaps it was negative mass. Or something. It was a while ago and I don't remember the exact details very clearly.

[5614]

hmm, if we went with GR then negative gravity would require negative mass and the closest we've got to that is negative pressure in the casimir effect.

 

Most physicists agree that even antimatter has a positive mass.

 

¥4Bn really isn't much!

 

I need more convincing!

[ydoaPs]

i know, that is why i said it. it looks like a lot to people that don't know, but it really isn't much.

 

if i have time, i'll try to find it in TFOTC.

[5614]

i know, that is why i said it. it looks like a lot to people that don't know, but it really isn't much.

HUH?

 

What do you know?

Lot of people don't know what?

What isn't really much?

 

[ydoaPs]

¥4Bn really isn't much!

 

sorry, probably should have put that in there. thought you could get it by the context.

[BlackHole]

What is the difference between spin 1 and spin 2?

 

I think gravity can be repulsive. Gravity doesn't depend just on mass and distance, but it also depends on density and pressure.

[5614]

What is the difference between spin 1 and spin 2?

http://www.scienceforums.net/forums/showthread.php?t=9475

[Daecon]

Density is just an aspect of mass, although I don't think pressure would have any effect - after all, pressure against what?

[Rekkr]

So what exactly is gravity? If Transdecimal was taking the analogy too literally, then is it right to assume gravity is an all-permeating aether as Descartes suggested? For example, imagine a pond. That pond is the universe and the water molecules are gravitons. Is this correct? Someone please explain.

[BlackHole]

If the pressure is negative, then gravity becomes repulsive, and that's basically what contributed to the early expansion of our universe according to inflation cosmoslogy. In fact the early universe behaved almost like a liquid and much less like a plasma.

[CPL.Luke]

yeah read some of the stuff done by one Allen Guth specifically relating to his work on false vaccuums.

 

Fasle vacuums are supposed regions of negative pressure and thus negative gravity. supposedly these are what created the universe

[Kygron]

If you read a 'net article about a spinning, (charged?) black hole, they say that near, but not at, the singularity, gravity becomes repulsive.

[BlackHole]

How physically plausible is the idea of a non-zero cosmological constant?