Quantum Gravity.

Son Goku

What are people's opinions of this search for a quantum theory of the gravitation field?

What do you think of current routes being taken.

nesf

I honestly don't know enough about it. I'd be interested if you had links to any good papers/articles on it though

Son Goku

Very wide field.
Wikipedia would be the best starting place, just search quantum gravity.
I can't really recommend any papers because all of our current ideas could be wrong.

I'll wait to see what others say before I continue, but my basic opinion of a quantum theory of the gravitation field is that it isn't the correct approach.

I'll elaborate depending on how the thread continues.

planck2

why do you think that a quantum theory of gravitation is not the correct approach, if it wasn't then (at least the way I'm reading it) one would have to conclude that qm is incorrect, because they are quantising with all known methods that work for ordinary fields. There maybe some other way to quantise which does exactly what the others do, but quantises gravity. I think there has to be such quantisation of gravity, simply because of unity.

Son Goku

Sorry to not go into it right know, but my full reason is about ten pages long.
Once I can summarise it correctly I'll put it up.

Basically I'm more an advocate of Quantum Field theory in curved backgrounds, than quantum gravity.

In other words I believe Quantum field theory should be generalised out of purely Minkowskian space into curved space, rather than the field equation been seen as the result of a spin-2 field in Minkowski space.

To anybody who isn't familiar with the terminology, I believe Quantum Field Theory should have General Relativity as it's background, rather than General Relativity being quantised as another quantum field.
(I realise this might mean a non-linear quantum theory)

There is more to it than this, but I can't summarise at the moment.

planck2

Quantum Field theory in curved spacetime just describes how fields of a quantum nature behave in regions of strong gravity, and in the limit as R goes to zero ( => flat spacetime, i.e. Minkowskian) we should get ordinary qft.

I think one must be able to quantise the geometry otherwise being able to quantise all the rest and not gravity wouldn't make sense because then you'd have no symmetry, remember symmetry plays an impotant role in physics, from Faraday's laws of induction to Einstein's formulation of Special relativity.

Son Goku

Quantum Field theory in curved spacetime just describes how fields of a quantum nature behave in regions of strong gravity, and in the limit as R goes to zero ( => flat spacetime, i.e. Minkowskian) we should get ordinary qft.

I should make it clear that I'm not proposing Quantum Field theory in curved backgrounds in place of Quantitised Gravity.
I should have said I'm more of an advocate of trying to formulate Quantum Field theory in curved backgrounds than Quantum Gravity. I believe it is of more descriptive and predictive use. Although I could be wrong.

However the reason I disagree with Quantum Gravity is as follows:

The general opinion on the unification of Quantum Field Theory and General Relativity is that the Einstienian Field Equation must be converted to a quantum field theory.
I think (and I am in no way proposing I thought this up, because I didn't, I just agree with this idea) it is quantum mechanics that is to be modified in the union rather than GR.

Take the singularities of the Big Bang and black holes.
The Big Bang is a rather special singularity, entropically speaking.
Where as the singularity of a black hole is rather generic.
This is a rather gross time asymmetry and this time-asymmetry is against the implications of a standard quantum field theory.

I will expand if necessary.

P.S. I am in no way implying that I am right. This is the next physical theory we're talking about, so I definitely can't be sure of myself.
I merely presenting what I think might be wrong with the current road of thought.

nesf

Son Goku wrote:

P.S. I am in no way implying that I am right. This is the next physical theory we're talking about, so I definitely can't be sure of myself.
I merely presenting what I think might be wrong with the current road of thought.

I'd debate it with you, but I just don't have the understanding of the topics involved to properly analyse what you've suggested. My specialities/interests are in other areas.

But your points seem well reasoned and thought out (as usual). Although as I said, I'm not sure if my opinion counts for much in this issue.