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355 points jchanimal | 1 comments | | HN request time: 0.209s | source
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samsartor ◴[] 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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throwawaymaths ◴[] No.42160543[source]
> My hangup with MOND is still general relativity.

Fwiw, we know for a fact also that for edge cases GR is wrong because it doesn't agree with quantum mechanics (unless QM is wrong), so it's maybe not right to take GR as gospel, especially for a theory that only seems to also change GR in edge cases, and the only reason why "it doesn't agree" might amount to "the math is hard and the physicists haven't put enough work in yet"

To wit, accepting a mond-ified GR is probably not going to change how GPS works so the claim that "GR has withstood the test of time and engineering" is not a totally solid refutation of MOND

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scotty79 ◴[] No.42161818[source]
> because it doesn't agree with quantum mechanics

I don't think it doesn't agree. It's just that we never managed to neither formulate quantum mechanics on 4 dimensional space time nor quantize gravitational force. So we simply have no idea what happens in small scale in significant gravitational fieldd.

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1. throwawaymaths ◴[] No.42176195[source]
> I don't think it doesn't agree. It's just that we never managed to neither formulate quantum mechanics on 4 dimensional space time nor quantize gravitational force. So we simply have no idea what happens in small scale in significant gravitational fieldd.

I don't think MOND dosen't agree with GR. It's just that we never managed to formulate MOND in a spacetime compatible with GR. So we simply have no idea what happens on the galactic scale in a significant gravitational field.