Timeline for How are gravitons compatible with general relativity?
Current License: CC BY-SA 4.0
11 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 25, 2021 at 3:32 | comment | added | Deschele Schilder | "a superposition of many graviton states would look like the macroscopic metric tensor." indeed."look like". It's not the same though. | |
| Apr 24, 2021 at 3:19 | comment | added | Vegard | @stix: I think we are veering too far off into digressions, but suffice to say that I don't think nobody knows exactly how it would work. There's no complete theory for this, like Jerry has detailed. But see this question and its answers for some musings on massless particles and gravity - it also includes some statements about the emission of gravitons by photons. | |
| Apr 23, 2021 at 22:03 | comment | added | Zo the Relativist | @stix: yes, everyone agrees that the background independence problem and nonlinearity of general relativity really is the core problem of quantizing the theory. "Can this be made to work" is a different question than "what is this?". No one has made any quantum theory of gravity work. Maybe the picture is something like the string theory picture, where you just have a fixed background spacetime, and then the dynamics happens on worldsheets and branes. No one knows what the final picture will be until someone has a final picture. | |
| Apr 23, 2021 at 21:22 | comment | added | stix | @EricTowers But we also know Kaluza-Klein theory is wrong, or at the very least, incomplete. Shrug | |
| Apr 23, 2021 at 20:44 | comment | added | Eric Towers | @stix : "But, to our knowledge, E&M doesn't affect spacetime, and gravity by definition does." I see that you are unfamiliar with Kaluza-Klein theory which expresses electromagnetism as curvature of a 5-manifold. And others have already expressed that energy in E&M fields bends spacetime in the Standard Model. | |
| Apr 23, 2021 at 17:55 | comment | added | stix | @JerrySchirmer But spacetime being a the same as a quantum field is itself problematic in that you have quantum fields defined in terms of a flat spacetime. In essence, your QM fields are built on top of your spacetime field. | |
| Apr 23, 2021 at 17:53 | comment | added | stix | @Vegard That answer begs the question of why a graviton can affect spacetime much more strongly than a photon, when both are considered to be massless under the standard model and its extensions. Also, if we're saying gravitons carry gravity, then it seems we're also making the claim that the reason a photon can exhibit gravitational effects is because it somehow emits a graviton. Now you have a force carrier emitting a force carrier. How's that supposed to work exactly? | |
| Apr 23, 2021 at 2:54 | comment | added | Vegard | @stix: In GR, also massless particles affect spacetime due to the mass-energy equivalence. Meaning there's in principle no difference, as far as spacetime being affected or not goes, between a collection of photons (which is the EM mediator) and a collection of protons and electrons. So it's as you say not the case that the EM field can make a clock tick slower directly, but excitations in the EM field can bend spacetime just like normal particles can - and the result will indeed be that the clock ticks slower, because bent spacetime is bent spacetime regardless of how & why it was bent. | |
| Apr 22, 2021 at 21:44 | comment | added | Zo the Relativist | @stix: in the "graviton" picture of the world, "spacetime" is a field that is expressible as a "background" and a "dynamical" part. The metric tensor if the analogue of the E and B field (really, it's the analogue of $A_{a}$) And I'm not saying that we can do this, if it was definitively possible, there would be an accepted quantum gravitational theory right now. I'm saying that this is what people are trying to do when they write down theories with gravitons in them. | |
| Apr 22, 2021 at 20:28 | comment | added | stix | But, to our knowledge, E&M doesn't affect spacetime, and gravity by definition does. Do we have any scientific examples showing how an EM field can make a clock tick slower? It seems a bit of a stretch to say that just because we were successful in casting EM in a particle view, that we can automatically cast gravity in the same way. In fact, casting EM in the quantum framework in some ways makes it less compatible with GR, which only aggravates the problem raised by OP. | |
| Apr 21, 2021 at 19:44 | history | answered | Zo the Relativist | CC BY-SA 4.0 |