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James Webb Space Telescope finds evidence for alternate theory of gravity

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355 points jchanimal | 3 comments | 16 Nov 24 18:33 UTC | HN request time: 0.604s | source
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samsartor ◴[16 Nov 24 20:21 UTC] No.42158987[source]▶
My hangup with MOND is still general relativity. We know for a fact that gravity is _not_ Newtonian, that the inverse square law does not hold. Any model of gravity based on an inverse law is simply wrong.

Another comment linked to https://tritonstation.com/new-blog-page/, which is an excellent read. It makes the case that GR has never been tested at low accelerations, that is might be wrong. But we know for a fact MOND is wrong at high accelerations. Unless your theory can cover both, I don't see how it can be pitched as an improvement to GR.

Edit: this sounds a bit hostile. to be clear, I think modified gravity is absolutely worth researching. but it isn't a silver bullet

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meindnoch ◴[16 Nov 24 21:39 UTC] No.42159582[source]▶
>We know for a fact that gravity is _not_ Newtonian, that the inverse square law does not hold

[citation needed]

The consensus is that gravity - outside of extreme mass/energy environments - works just as Newton described it to many many decimal places.

Emphasized part added because people in the replies thought that I literally think that General Relativity is somehow wrong. Don't be dense. All I'm saying is that gravity at galactic scales works as Newton described it. General Relativity has extremely tiny effect at those scales.

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EPWN3D ◴[16 Nov 24 22:05 UTC] No.42159764[source]▶
You're simply wrong. There's no other way to put it. The GPS system would have been simply impossible to deploy without the general theory of relativity. There's no extreme energy or mass involved, just precision requirements that are influenced by the minuscule differences in time experienced by the surface of the earth and orbiting satellites.

Also Newton's laws famously could not account for Mercury's orbit. Mercury is just an ordinary planet orbiting an ordinary star. Nothing extreme is involved. He knew his laws were incomplete. But they were so dead-on in basically every other scenario that could be physically observed at the time that he figured there was some small tweak missing (or maybe another planetary body that hadn't been spotted yet).

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1. ahazred8ta ◴[17 Nov 24 00:06 UTC] No.42160738[source]▶
We know that spacetime is einsteinian, not euclidean, yes. But that's not what's being discussed here. The issue is whether the force of gravity deviates from the expected 1/r^2 value. Experiments, measurements and observations within the solar system have not revealed any deviation. The precession of mercury is not due to a deviation from 1/r^2; it is due to space near the sun being bent instead of flat. Ditto GPS; we have to adjust for time dilation and curved space, but not for any deviation from 1/r^2. MOND theories predict that MOND gravity is indistinguishable from normal at short ranges less than several light years; the MOND effects only show up at distances of many light years.
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2. anon84873628 ◴[17 Nov 24 17:25 UTC] No.42165429[source]▶
You seem to just be arguing about the definition of "gravity" now.
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3. mafuyu ◴[17 Nov 24 18:08 UTC] No.42165725[source]▶
That’s kinda the whole point, isn’t it? I’m just a layman, but my understanding is that the incompatibilities of GR and QM point to a need for a proper theory of gravity. Looking at the dark matter problem from a purely GR-perspective will miss that context.