Dark Matter/Energy

Dave,

I mentioned this theory previously on this thread. This is currently a serious theory being followed by - oh I forget her name. Personally along with Gravitons I think it's bunkum. There is a lot about string theory which is beautiful and elegant, but this is not one of them.
There seems to be some "serious" work going on with respect to this theory, I recently watched a documentary where this theory seemed to get pride of place in the recent development category. If gravitons don't exist then this theory goes down the pan, and I'm not a fan of gravitons.

Do you mean on a previous thread, I dont see it above?
Anyway, what is it about gravitons that you dont like? or to put it better why dont you think they exist.

Do you mean on a previous thread, I dont see it above?
Anyway, what is it about gravitons that you dont like? or to put it better why dont you think they exist.

Sorry your right, I'm getting my threads tangled. Here is the thread I meant. www.irishastronomy.org/boards/viewtopic.php?t=4050
Sorry about that both themes seem to be converging.

Ok why don't I believe gravitons exist?
For electrical energy we have the corresponding particle the electron.
For light we have the photon.
And for gravity we have the graviton (or do we?).
GR says nothing about the need for a graviton and no-one is looking for it apart from some string theorists who need it to unify a theory of everything to include gravity.
Also gravity per se is not truly a force (in the sense that electrical force is)see the thread mentioned above for the arguments.

Also if you think of in these terms - Matter curves spacetime to create what we call gravity, it's not a force it's simply curved spacetime. Why does matter then also need to create another particle just because spacetime has been curved? It just doesn't add up.
Ask what are the predictions for a graviton - does it have mass? a charge? a spin? Do a search on google and you'll come up with some very indeterministic predictions - "The graviton is the exchange particle for the gravity force. Although it has not been directly observed, a number of its properties can be implied from the nature of the force. Since gravity is an inverse square force of apparently infinite range, it can be implied that the rest mass of the graviton is zero." - and also it has no charge is long range and apparently can travel much faster than the speed of light (all this is very convenient 'cause there is then no way to ever detect the'particle'). -Bunkum
The main reason there is no particle is that Gravity is not a force in the true sense.

I would 100% agree with you except that we have an example of a dual property "particle" already.
Light behaves as a wave and a particle, I do realise that light is an electromagnetic phenomena, and that gravity is not.
I do tend to agree with your above points, just dont be completely surprised if someone somehow manages to prove that the graviton has a mass, does spin and all that, nature has a quirky way of throwing many spanners in the works. Surely we dont have enough info yet to come to a definitive conclusion, or do we??
For instance, many years ago who would have thought a black hole could evaporate.

Ok why don't I believe gravitons exist?
For electrical energy we have the corresponding particle the electron.
For light we have the photon.
And for gravity we have the graviton (or do we?).
GR says nothing about the need for a graviton and no-one is looking for it apart from some string theorists who need it to unify a theory of everything to include gravity.
Also gravity per se is not truly a force (in the sense that electrical force is)see the thread mentioned above for the arguments.

The graviton is pretty much the hope of String Theory and has quite a lot of History behind it.

For the past century there have been two major schools of theoretical physics, "relativists" and "particle physicists".
The first is based on General Relativity and the later based on Quantum Field Theory.

In 1970 when Particle Physics managed to explain the three non-gravitational forces, Particle Physicists attempted to tackle gravity.

They presumed the same treatment would work that they used on the other forces:
Get the classical field, turn it into a giant Quantum Field Theoretic Integral and solve this integral using Feynman Diagrams.

For gravity this did not work and could not work, however most Particle Physicists trained in the 70s and 80s (which include today's String Theorists) were not educated that well in General Relativity.

The problem was that Quantum Fields live in flat spacetime, but in General Relativity, gravity isn't another field in flat spacetime, it is the curvature of spacetime, so we can't quantise it.
(At least we can't make a Quantum Field Theory out of it)

For a graviton to exist gravity would have to not be the warping of spacetime, but just another field in flat spacetime that looks like the warping of spacetime at the classical level.

The String Theory community grew out the belief that Quantum Field Theory is right and gravity is just another force in flat spacetime.
The Loop Quantum Gravity community grew out of the belief that gravity isn't a force in spacetime, so we need a different way to do things.

(There is also a third school of thought which thinks we aren't ready to make turn Gravity quantum just yet)

The Loop Quantum Gravity community grew out of the belief that gravity isn't a force in spacetime, so we need a different way to do things.

Personally I think the Loop Quatum Gravity theory is more to my taste, though still not entirely, it's still got some "hairys" I don't like, but I do think it's a more accurate model.

Getting back to GR. It still baffles me how many physicists have still not grasped it's significance/importance - they still try to marry classical and GR physics - which seems an impossibility. Again, I say that that once a student reaches third level that all notions of newtonian physics (apart from obviously the working ones) be thrown out, and that the midset of GR be instilled. Else, we will continue to have ridiculous theories on gravity leaking thro' dimensions, when gravity iteself is only an observabale result of spacetime curvature. What physicists should be concentrating on is why matter causes spacetime to curve. ( I have some ideas on the subject, but until I have I have it fully worked out in my own spacetime I won't elaborate, and I certainly won't be showing the math).