Timeline for Is there any interpretation where GR and QM can be compatible?
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 8, 2023 at 8:02 | vote | accept | Sazzad Hissain Khan | ||
| Oct 18, 2022 at 21:29 | comment | added | Andrew | Just a note that detecting gravitons might be more than a practically difficult problem: publications.ias.edu/sites/default/files/poincare2012.pdf Not to say that the effective field theory of gravity doesn't work (I think it probably does), but it's an interesting thing to think about. | |
| Oct 18, 2022 at 20:07 | comment | added | Avantgarde | @TimRias Quantum mechanics is a fact, and has been observed in every interaction except gravity. It is natural to expect that gravity also has a quantum description. Detecting individual gravitons is practically difficult problem, but we have already observed large, coherent collections of them in the form of gravitational waves. Hawking radiation is a problem that comes much later. Perturbative GR (not quantum gravity) is a perfectly consistent effective (quantum) field theory at low energies. E.g. Quantum corrections to the Newtonian potential have been calculated, but are too small to detec | |
| Oct 18, 2022 at 18:58 | comment | added | TimRias | @Avantgarde At this point it is not "a fact" that gravity is quantized. I would be surprised if it isn't, but it is certainly not a fact. Any predictions based on perturbative quantum gravity, at this point are conjecture, not predictions of GR. E.g. if there is no graviton Hawking radiation this would not falsify GR. | |
| Oct 18, 2022 at 18:49 | comment | added | Avantgarde | @TimRias You can call things by different names. It does not change the fact that quantum mechanics is a fact of our universe. GR is no different. It is a classical theory as usually studied, but it can be used to give concrete predictions (yet to be observed) at the quantum level. Electromagnetism is a phenomenon, not a theory, and so it doesn't get a new name when you quantize it. GR and quantum mechanics are perfectly consistent at low energies. The real problem is the high energy behavior of gravitational interaction. | |
| Oct 18, 2022 at 18:26 | comment | added | TimRias | @Avantgarde once you quantize electromagnetism it gets a new name: quantum electrodynamics (QED). A priori, it is not clear that general relativity needs to be quantized, e.g. maybe the RHS of the Einstein equation is given by the expectation value of the energy momentum tensor. (If you try to make this self-consistent you still end up with trouble). | |
| Oct 18, 2022 at 16:38 | comment | added | Andrew | @Avantgarde No, sorry, I meant -- the point you are making that electromagnetism is electromagnetism even if you quantize it, is also my point of view. That's why I said I am ok with using "GR" to refer to a quantum theory in my comment. I was just trying to explain where Tim is probably coming from. | |
| Oct 18, 2022 at 16:33 | comment | added | Avantgarde | What does it become, then? | |
| Oct 18, 2022 at 16:31 | comment | added | Andrew | @Avantgarde That would be my point of view :) | |
| Oct 18, 2022 at 16:30 | comment | added | Avantgarde | Is electromagnetism no longer electromagnetism if you start quantizing it? | |
| Oct 18, 2022 at 16:29 | comment | added | Andrew | @Avantgarde One point of view is that GR is the mathematical framework where gravity is defined as curvature in spacetime and the metric is related to the stress-energy tensor via Einstein's equations. Then GR is a classical theory, and if you quantize the metric then by definition you are no longer talking about GR. I tend to take a different point of view that all physics is really quantum mechanical (as far as we know), and I use "GR" as shorthand for the Einstein-Hilbert action even if treated quantum mechanically. IMO so long as everyone is clear what they mean, it doesn't matter much. | |
| Oct 18, 2022 at 16:23 | comment | added | Avantgarde | @TimRias What does that mean? | |
| Oct 17, 2022 at 14:33 | comment | added | TimRias | The moment you start quantizing GR, it is no longer GR. | |
| Oct 17, 2022 at 14:09 | history | edited | Andrew | CC BY-SA 4.0 |
added 271 characters in body
|
| Oct 17, 2022 at 13:55 | history | answered | Andrew | CC BY-SA 4.0 |