Internal (gauge) symmetries and spacetime symmetries

[TrickyDicky]

I do not want to identify specific loopholes for a given framework (quantum field theory on spacetime, operators, S-matrix, ...) but I want to question the framework itself!

Hey, didn't know you were so radical.

Formulating theories for emergent or discrete spacetime like (colored) spin networks may render the concept for "S-matrix on spacetime" meaningless. The question then is whether you can still use this S-matrix approach which is restrcited to a certain regime to derive a no-go theorem for the whole theory. I doubt that this will work and therefore I expect that many of these no-go theorems will cease to exist when identifying a fundamental theory of quantum gravity. Besides the Coleman-Mandula theorem the Weinberg–Witten theorem is another candidate to fail.

I share this view about no-go theorems.

 

[tom.stoer]

Hey, didn't know you were so radical.

depends on the enemy ...

 

[PhilDSP]

I doubt that this will work and therefore I expect that many of these no-go theorems will cease to exist when identifying a fundamental theory of quantum gravity.

Now I have a question bearing some level of radicalness :)

Is there an empirical reason to be led to believe that gravity is (or should be) quantized? Or is it principally a consistency in frameworks that one assumes should be accommodated?

 

[TrickyDicky]

Now I have a question bearing some level of radicalness :)

Is there an empirical reason to be led to believe that gravity is (or should be) quantized? Or is it principally a consistency in frameworks that one assumes should be accommodated?

I remember having read somewhere a physicist that claimed that gravity was already "quantized" in GR. I will try to find the reference because I can't remember what kind of arguments he used or what he meant.

 

[tom.stoer]

Is there an empirical reason to be led to believe that gravity is (or should be) quantized? Or is it principally a consistency in frameworks that one assumes should be accommodated?

There is no direct experimental evidence for quantum gravity, so I would say that the indications are mostly due to theoretical and consistency reasons; but there are a lot ...