3 ms·
Light and gravitational waves don't arrive simultaneously
- sharpener 3y agoMy 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 agoStellar 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 agoYes. But our explanation should argue for the direction of difference (whether light arrives first or the gravity wave).
- dTal 3y agoAha! 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 agoOr only for the things that experience gravity as a curved surface? Gravity, arguably, does not experience gravity as a curved surface.
- T-A 3y agoHow 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 agoThat 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
- jasmes 3y agoThis seems intuitive, don’t photons have to interact with stuff and get dragged around by gravity and magnetic fields? I don’t think “gravitons” do that. Neutrinos can arrive before photons IIRC, simply because they don’t strongly interact. Physics is wild.
- az09mugen 3y agoOr just maybe light and gravitational waves are not created at the same time. Maybe just light is created 1.7s after. How can we be so sure what happens in the physics of a kilonova that we suppose light and gw don't travel at the same speed ?
- pbjtime 3y ago>In 2017, such an event occurred Negative. In 2017, such an event was observed.
- montjoy 3y agoI’m going to be honest with you. I too used to be pedantic like this until one day I realized it’s really fucking annoying. Now let me tell you why you are wrong. :) I’m fine with “occurred”. Because of causality the event had absolutely no impact on our local spacetime until those gravitational waves and photons showed up, regardless of how far back in time the event originated. Another way to think about it: Because the photons and gravitational waves have no mass, no time occurred from their perspective between their origination point and arriving at earth. I have no qualifications BTW. I just like physics. There’s a decent chance I’m wrong.
- Jerrrry 3y agoReddit.com is a different website.
- yetihehe 3y agoSo, it was observed but it did not occur? Could you expand this a little?
- Moldoteck 3y agoBc of travel distance, meybe they mean that it occured earlier but observed than
- yetihehe 3y agoIt did not occur at the source of event, because at source gravitational waves and light waves were probably pretty close together, so "not simultaneous arriving of light and grav waves" is an event which was observed as happening on Earth in 2017.
- Kerbonut 3y agoI believe that sentence is fine as the event in question is the lagging signals being observed. > On August 17, 2017, the signal from an event that occurred 130 million light-years away finally arrived here on Earth.
- gpsx 3y agoLight and gravitational waves travel the same speed in a vacuum, but space isn’t really a vacuum. I wonder if this makes any contribution.
- fjfaase 3y agoThere are about 4.1e14 seconds in 130 million years. The two seconds delay is thus very small. I wonder what is the role of the fact that interstellar vacum is not an absolute vacum. I read some where that there is about one atom in each square cubic cm. The number of cm in one light year is 9.4605284e17.