5 ms·

My guess... In the mathematics of the physics, gravity is a scalar field. We don't really know what gravity is, we just have various descriptions that seem to

My guess... In the mathematics of the physics, gravity is a scalar field. We don't really know what gravity is, we just have various descriptions that seem to be useful at various levels of detail. So when folks talk about gravity waves, in the maths it is a pulse traversing a scalar field, and we don't really know what is happening to the space or whatever it is that makes the pulse possible. Is space actually stretchy like elastic? Unknown. But it means that if there is no other potential field that can "bend" a moving gravitational wave's trajectory then gravitational waves will travel in absolutely straight lines. Light, on the other hand, moves through the potentials generated by the gravity field and is governed by its energy, sort of, to follow geodesics of the gravity field. So in GR light takes the curvy path around objects with gravitational potentials around them. The article doesn't mention if there were any influential masses along the journey. 1.7 secs is about 320,000 miles. Maybe the curves?

weebull 3y ago
Stellar event produces a gravity wave and a light pulse coincidentally at the source. As they travel through space together the gravity wave is compressing and expanding spacetime in the vacinity of the light pulse. I could very easily believe that interaction by itself would be enough to have measurable effects over interstellar distances.
- abdullahkhalids 3y ago
  Yes. But our explanation should argue for the direction of difference (whether light arrives first or the gravity wave).
- dTal 3y ago
  Aha! So the light pulse could be riding a kind of naturally-occuring Alcubierre warp bubble?
T-A 3y ago
> In the mathematics of the physics, gravity is a scalar field. No, it's a tensor field. https://en.wikipedia.org/wiki/Riemann_curvature_tensor https://en.wikipedia.org/wiki/Riemann_curvature_tensor
- sharpener 3y ago
  Or only for the things that experience gravity as a curved surface? Gravity, arguably, does not experience gravity as a curved surface.
  - T-A 3y ago
    How would you go about arguing that?
    - westurner 3y ago
      "Gravity as a fluid dynamic phenomenon in a superfluid quantum space. Fluid quantum gravity and relativity." (2015) https://hal.science/hal-01248015/ https://hal.science/hal-01248015/ TLDR; In SQS (Superfluid Quantum Space), Quantum gravity has fluid vortices with Gross-Pitaevskii, Bernoulli's, and IIUC so also Navier-Stokes; so Quantum CFD (Computational Fluid Dynamics).
      - T-A 3y ago
        That article describes a hypothetical microphysical model of gravity. It's an old idea which has been done better by others (see e.g. "The Universe in a Helium Droplet" [1]). Whether right or wrong, it has no bearing on your claim that > Gravity, arguably, does not experience gravity as a curved surface. Any valid microphysical model of gravity must be able to reproduce the successes of general relativity in the classical limit, including the ability to match the shape of gravitational waves produced by black hole mergers. So if you want to argue that gravity "does not experience gravity as a curved surface", you have two options: 1) show that the non-linear (i.e. self-interaction) terms of Einstein's equations do not involve curvature or 2) come up with an alternative theory of gravity which does not reduce to general relativity in the classical limit and yet manages to reproduce all its successful predictions. Which one is it? [1] https://academic.oup.com/book/11557 https://academic.oup.com/book/11557
        westurner 3y ago

weebull 3y ago

Stellar event produces a gravity wave and a light pulse coincidentally at the source. As they travel through space together the gravity wave is compressing and expanding spacetime in the vacinity of the light pulse. I could very easily believe that interaction by itself would be enough to have measurable effects over interstellar distances.

abdullahkhalids 3y ago
Yes. But our explanation should argue for the direction of difference (whether light arrives first or the gravity wave).
dTal 3y ago
Aha! So the light pulse could be riding a kind of naturally-occuring Alcubierre warp bubble?

T-A 3y ago

> In the mathematics of the physics, gravity is a scalar field. No, it's a tensor field. https://en.wikipedia.org/wiki/Riemann_curvature_tensor https://en.wikipedia.org/wiki/Riemann_curvature_tensor

sharpener 3y ago
Or only for the things that experience gravity as a curved surface? Gravity, arguably, does not experience gravity as a curved surface.
- T-A 3y ago
  How would you go about arguing that?
  - westurner 3y ago
    "Gravity as a fluid dynamic phenomenon in a superfluid quantum space. Fluid quantum gravity and relativity." (2015) https://hal.science/hal-01248015/ https://hal.science/hal-01248015/ TLDR; In SQS (Superfluid Quantum Space), Quantum gravity has fluid vortices with Gross-Pitaevskii, Bernoulli's, and IIUC so also Navier-Stokes; so Quantum CFD (Computational Fluid Dynamics).
    - T-A 3y ago
      That article describes a hypothetical microphysical model of gravity. It's an old idea which has been done better by others (see e.g. "The Universe in a Helium Droplet" [1]). Whether right or wrong, it has no bearing on your claim that > Gravity, arguably, does not experience gravity as a curved surface. Any valid microphysical model of gravity must be able to reproduce the successes of general relativity in the classical limit, including the ability to match the shape of gravitational waves produced by black hole mergers. So if you want to argue that gravity "does not experience gravity as a curved surface", you have two options: 1) show that the non-linear (i.e. self-interaction) terms of Einstein's equations do not involve curvature or 2) come up with an alternative theory of gravity which does not reduce to general relativity in the classical limit and yet manages to reproduce all its successful predictions. Which one is it? [1] https://academic.oup.com/book/11557 https://academic.oup.com/book/11557
      - westurner 3y ago