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James Webb Space Telescope finds evidence for alternate theory of gravity

(thedebrief.org)
355 points jchanimal | 8 comments | 16 Nov 24 18:33 UTC | HN request time: 0.001s | source | bottom
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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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1. twothreeone ◴[17 Nov 24 00:28 UTC] No.42160861[source]▶
GR says spacetime is curved by mass, right. So what's the basis for explaining the curvature of space (which can be measured, e.g., LIGO) in MOND?
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2. MathMonkeyMan ◴[17 Nov 24 04:49 UTC] No.42162034[source]▶
MOND has nothing to say about the curvature of spacetime, since MOND is Newtonian (MOdified Newtonian Dynamics). It goes back to "F=ma and gravity is a force" and modifies the rules so that gravity grows weaker faster at a certain scale.

The fact that MOND fits a lot of the data troubled cosmologists, because they know that a General Relativistic theory is needed to explain pretty much the rest of gravity.

TeVeS is an extension to General Relativity that reduces to MOND in the non-relativistic limit. For comparison, General Relativity reduces to Newtonian gravity in the non-relativistic limit. The non-relativistic limit is when speeds and spacetime curvature are small.

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3. oneshtein ◴[17 Nov 24 08:43 UTC] No.42162873[source]▶
> GR says spacetime is curved by mass, right.

Wrong. GR says that gravitation can be modeled as acceleration.

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4. mog_dev ◴[17 Nov 24 09:32 UTC] No.42163063[source]▶
General Relativity states that mass-energy curves spacetime, and objects follow the straightest possible paths (geodesics) through this curved geometry. The equivalence principle relates gravity and acceleration, but it's not the main description of gravity in GR.
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5. Gooblebrai ◴[17 Nov 24 10:20 UTC] No.42163240[source]▶
How does MOND deal with the effects of time dilation and length contraction? Do we have to go back to Newton's time where there's a universal time?
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6. naasking ◴[17 Nov 24 14:30 UTC] No.42164360[source]▶
MOND is an effective theory, it only describes observations and doesn't put forward any explanation of what's really going on.
7. oneshtein ◴[17 Nov 24 15:44 UTC] No.42164753{3}[source]▶
Spacetime is model.
8. MathMonkeyMan ◴[18 Nov 24 00:33 UTC] No.42168630{3}[source]▶
I don't know if Newtonian gravity can be reconciled with Special Relativity. First thought is "no, that's why Einstein arrived at General Relativity." But I'm not in the field, so I don't know.