Thanks for the corrections, my area is mostly classical GR, not Standard Model physics. And a good point on the Unruh effect. As for quantizing GR, note the “useful” disclaimer. I am deeply suspicious of any technique that treats GR as an effective field theory on some background spacetime, as it throws away the whole reason why GR is unlike any other field theory. Weinberg is especially prone to to doing that, so, while I respect anything he does in HEP, I don’t put much stock into his GR-related efforts. If anything, I expect the progress to come from the entropic gravity crowd, with nothing to quantize.
When I worked in physics I did perturbative QCD stuff in graduate school and then effective theories for medium energy scattering, and finally axiomatic quantum field theories as a postdoc before I left physics for a field with actual employment opportunities (statistics/big data stuff).
But why shouldn’t GR be treated as just another field theory? It certainly has the structure of a field theory. Feynman and then Weinberg managed to show that GR is THE self-consistent, massless spin-2 field theory- so to that extent it IS just another field theory.
Treating GR as an effective theory works. I doubt that the theory is asymptotically safe, but for an effective theory, who cares? Why should we treat the matter part of the action any differently than we treat the spacetime piece of the action?
But why shouldn’t GR be treated as just another field theory? It certainly has the structure of a field theory.
That’s a separate discussion, but let me just note that the action would have to be summed not just over all paths (in which spacetime?), but also over all possible (and maybe impossible) topologies, as well.
Thanks for the corrections, my area is mostly classical GR, not Standard Model physics. And a good point on the Unruh effect. As for quantizing GR, note the “useful” disclaimer. I am deeply suspicious of any technique that treats GR as an effective field theory on some background spacetime, as it throws away the whole reason why GR is unlike any other field theory. Weinberg is especially prone to to doing that, so, while I respect anything he does in HEP, I don’t put much stock into his GR-related efforts. If anything, I expect the progress to come from the entropic gravity crowd, with nothing to quantize.
When I worked in physics I did perturbative QCD stuff in graduate school and then effective theories for medium energy scattering, and finally axiomatic quantum field theories as a postdoc before I left physics for a field with actual employment opportunities (statistics/big data stuff).
But why shouldn’t GR be treated as just another field theory? It certainly has the structure of a field theory. Feynman and then Weinberg managed to show that GR is THE self-consistent, massless spin-2 field theory- so to that extent it IS just another field theory.
Treating GR as an effective theory works. I doubt that the theory is asymptotically safe, but for an effective theory, who cares? Why should we treat the matter part of the action any differently than we treat the spacetime piece of the action?
That’s a separate discussion, but let me just note that the action would have to be summed not just over all paths (in which spacetime?), but also over all possible (and maybe impossible) topologies, as well.