6 ms·

> In 1887, the Michelson–Morley experiment gave the first experimental disproof of the "aether". In what way is LIGO not a bigger, and successful, version of t

> In 1887, the Michelson–Morley experiment gave the first experimental disproof of the "aether". In what way is LIGO not a bigger, and successful, version of the Michelson-Morley experiment? I'm honestly asking, because from my limited understanding, it seems to be. From Wiki: > This result is generally considered to be the first strong evidence against the then-prevalent aether theory, and initiated a line of research that eventually led to special relativity, which rules out a stationary aether. It seems that LIGO merely confirmed properties of an existent aether, not that we no longer believe in one: > Aether theories (also known as ether theories) in physics propose the existence of a medium, the aether (also spelled ether, from the Greek word (αἰθήρ), meaning "upper air" or "pure, fresh air"[1]), a space-filling substance or field, thought to be necessary as a transmission medium for the propagation of electromagnetic or gravitational forces. Naively, spacetime and quantum fields are both forms of aether theories.

whatshisface 8y ago
There might be some philosophical or creative writing overlap in the way the two are described, but the actual things that the theories are saying are completely different, lacking even a conceptual similarity.
bsder 8y ago
If LIGO confirmed "aether", then the measurements in the perpendicular arms would vary depending upon time (orientation of Earth in rotation, orientation of Earth around Sun, etc.). As far as I know, they very much do NOT vary--to an absolutely amazing precision. As far as I can tell, if the "aether" existed and we could detect it, we basically would have no hope of detecting gravitational waves. > Naively, spacetime and quantum fields are both forms of aether theories. Not ... really. The existence of "aether" implies a preferential frame of reference. And every experiment we have done to attempt to establish such has failed.
- NotAnEconomist 8y ago
  But the arms are predicted to vary in those cases by the same theory that LIGO is confirming: our rotation causes frame dragging, and there's some weird Sun-Earth orbital relativistic effects as well, right? I know the Sun-Jupiter orbit produces a large portion of the estimated 5,000 watts of gravitational emissions given off by our solar system. My mental model of this is that it perturbs the aether ("spacetime") through which it travels, radiating waves which carry energy out of the system. Is there a different one? It's just the power output in those waves is incredibly, incredibly low -- LIGO can only hear much larger events, such as large astral bodies colliding. So I'm not sure I understand -- there seems to be at least a gravitational aether.
  - axilmar 8y ago
    By aether, do you mean an underlying medium that allows forces to be propagated? I guess that using that definition, there is an 'aether'. The difference with the rejected concept of aether is that this "aether" is deformable by gravity, whereas the rejected one is not.
    - raattgift 8y ago
      > 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
tntn 8y ago
Interesting article by Wilczek on the subject of aether: http://ctpweb.lns.mit.edu/physics_today/phystoday/Ether.pdf http://ctpweb.lns.mit.edu/physics_today/phystoday/Ether.pdf Einstein also gave a talk in the late 20s (?) in which he discussed how spacetime in GR could be considered a kind of aether, though stripped of most of its physical properties.
hopler 8y ago
Ether is an independent absolute entity, and other objects move relative to it. Per GR, spacetime is an embodiment relations between objects, not an independent absolute entity.

whatshisface 8y ago

There might be some philosophical or creative writing overlap in the way the two are described, but the actual things that the theories are saying are completely different, lacking even a conceptual similarity.

bsder 8y ago

If LIGO confirmed "aether", then the measurements in the perpendicular arms would vary depending upon time (orientation of Earth in rotation, orientation of Earth around Sun, etc.). As far as I know, they very much do NOT vary--to an absolutely amazing precision. As far as I can tell, if the "aether" existed and we could detect it, we basically would have no hope of detecting gravitational waves. > Naively, spacetime and quantum fields are both forms of aether theories. Not ... really. The existence of "aether" implies a preferential frame of reference. And every experiment we have done to attempt to establish such has failed.

NotAnEconomist 8y ago
But the arms are predicted to vary in those cases by the same theory that LIGO is confirming: our rotation causes frame dragging, and there's some weird Sun-Earth orbital relativistic effects as well, right? I know the Sun-Jupiter orbit produces a large portion of the estimated 5,000 watts of gravitational emissions given off by our solar system. My mental model of this is that it perturbs the aether ("spacetime") through which it travels, radiating waves which carry energy out of the system. Is there a different one? It's just the power output in those waves is incredibly, incredibly low -- LIGO can only hear much larger events, such as large astral bodies colliding. So I'm not sure I understand -- there seems to be at least a gravitational aether.
- axilmar 8y ago
  By aether, do you mean an underlying medium that allows forces to be propagated? I guess that using that definition, there is an 'aether'. The difference with the rejected concept of aether is that this "aether" is deformable by gravity, whereas the rejected one is not.
  - raattgift 8y ago
    > 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

tntn 8y ago

Interesting article by Wilczek on the subject of aether: http://ctpweb.lns.mit.edu/physics_today/phystoday/Ether.pdf http://ctpweb.lns.mit.edu/physics_today/phystoday/Ether.pdf Einstein also gave a talk in the late 20s (?) in which he discussed how spacetime in GR could be considered a kind of aether, though stripped of most of its physical properties.

hopler 8y ago

Ether is an independent absolute entity, and other objects move relative to it. Per GR, spacetime is an embodiment relations between objects, not an independent absolute entity.