2 ms·

> underlying medium that allows forces to be propagated General Relativity is a local theory concerned with the mechanisms that generate the metric, the geodes

> underlying medium that allows forces to be propagated General Relativity is a local theory concerned with the mechanisms that generate the metric, the geodesics implied by the metric, and the coupling of objects to those geodesics. The relevant forces are those which accelerate objects into non-geodesic motion (or boost them from one geodesic to another). Those are local[1] as well: electromagnetism and the nuclear interactions. There's nothing like a luminiferous aether or underlying medium in the Standard Model, even if you look funnily at the gauge bosons -- they obey Lorentz covariance. I made a couple of sibling comments to yours, one of which deals directly with your comment's parent's idea of a gravitational aether. - -- [1] RM Wald, _Quantum Field Theory on Curved Spacetime and Black Hole Thermodynamics_ (University of Chicago Press, 1994). Cf. the top of page 6 of Hollands & Wald 2014, https://arxiv.org/abs/1401.2026 https://arxiv.org/abs/1401.2026

NotAnEconomist 8y ago
Isn't every "field" in QFT basically an aether?
- raattgift 8y ago
  Please tell me what you mean by aether, as rigorously as you can, and then I can give you an answer to the question which seems to be bedevilling you. Meanwhile I can guess at what you're asking: The Standard Model (a QFT) has interacting quantum fields obeying purely local dynamics. The behaviour "here-and-now" depends on the field-values "here". It does not depend on field-values "now" but far from "here". Moreover, the Standard Model is Lorentz-invariant, meaning its laws hold in any inertial frame of reference, thus the scare quotes in the previous sentence. The luminiferous aether that Michelson & Morley were looking to measure was motivated by finding a single special (and universal, or at least covering the whole solar system) inertial frame of reference in which Maxwell's equations hold exactly. No such frame exists; there is a huge democracy of inertial frames in which relativistic electrodynamics is exact in the classical limit. ( https://en.wikipedia.org/wiki/Preferred_frame https://en.wikipedia.org/wiki/Preferred_frame )

NotAnEconomist 8y ago

Isn't every "field" in QFT basically an aether?

raattgift 8y ago
Please tell me what you mean by aether, as rigorously as you can, and then I can give you an answer to the question which seems to be bedevilling you. Meanwhile I can guess at what you're asking: The Standard Model (a QFT) has interacting quantum fields obeying purely local dynamics. The behaviour "here-and-now" depends on the field-values "here". It does not depend on field-values "now" but far from "here". Moreover, the Standard Model is Lorentz-invariant, meaning its laws hold in any inertial frame of reference, thus the scare quotes in the previous sentence. The luminiferous aether that Michelson & Morley were looking to measure was motivated by finding a single special (and universal, or at least covering the whole solar system) inertial frame of reference in which Maxwell's equations hold exactly. No such frame exists; there is a huge democracy of inertial frames in which relativistic electrodynamics is exact in the classical limit. ( https://en.wikipedia.org/wiki/Preferred_frame https://en.wikipedia.org/wiki/Preferred_frame )