[knzhou]

Gravitomagnetism is a well-understood and experimentally measured effect. It is also a very small effect, of the order v^2 / c^2 where v is the speed of the sources. In the galaxy, stars move with v/c ~ 1/1000, which means the gravitomagnetic correction is one in a million. So while N-body simulations do sometimes account for general relativistic corrections like these, they're not nearly large enough to remove the requirement for dark matter.

The main thing the paper should do is explain why they think the correction is a million times larger than the back of the envelope estimate. But they don't. Instead, they try to solve everything analytically, never plugging in numbers or reasoning about what's big or small, leading to a forest of long combinations of special functions. That's a reliable recipe for making a mistake.

That is the simple reason the paper has been ignored by everyone in the scientific community and rejected from decent journals. Of course, this hasn't stopped hundreds of fluffy pop articles being written on it, or it getting posted every week on HN. The blind leading the blind.

[floxy]

> Instead, they try to solve everything analytically...

This seems like a common refrain it lots of things I see (not just this one paper). Can anyone give a lay man's explanation why we can't just numerically simulate general relativity? As in, plug a simulation with 100 billion stars in to a super computer and see what comes out.

[ncmncm]

It ought to suffice to simulate the motion of exactly one star, in a circular orbit, for exactly one time-step, just adding up all the effects of each of the 1e11 or so other stars, plus interstellar medium. There are two possible end states: either it follows the circle--no dark matter needed--or it swings wide.

[ncmncm]

That is not the reason the paper has been ignored. If it really were wrong, somebody would say where. But most astrophysicists are nowhere near as familiar with the maths involved as the paper's author is.

It is ignored because it is inconvenient. There is no practical consequence for continuing to be wrong, in cosmology or astrophysics. You can be wrong and publish papers, be wrong and get hired, be wrong and get tenure. Meanwhile, there is no upside in letting dark matter have no role in galactic rotation curves. Feeling smug knowing everybody else is still deluded is a solitary vice. If it's right, that will probably have to be acknowledged someday, but there is no personal benefit to getting ahead of the curve, only irritation.

Cosmology has found myriad uses for dark matter besides patching up galactic rotation. Accepting reality means you need to explain why all the dark matter you have been using for these other things doesn't clump up into galaxies; or find some other way to explain what you have been using dark matter for. Dark matter is just too convenient: like the Schmoo, it can be almost anything you like, as much as you need, wherever you need it. Your use doesn't even need to be consistent with (almost) anybody else's.

When it finally becomes necessary to accept reality, no one will be embarrassed, because everyone will have lots of company, and it will never be mentioned again, at least anywhere polite.

[knzhou]

This is why I left this site. Endless smug engineers explaining condescendingly to physicists why they’re stupid sheep, without knowing the first thing about anything. Intellectual curiosity, my ass. Do you have a reply to my concrete criticism or not?

[ncmncm]

You don't have a concrete criticism. You just have a complaint. Either the math in the paper is right, or it's wrong. If it's wrong, say where. If you can't find anything wrong, say that.

[the8472]

Thanks, I assume the same cricitcism also applies to other applying-GR-corrections papers? E.g. I saw one about gravitational self-interaction leading to concentrating gravity inside galaxies and starving the outside or something like that.

[knzhou]

The same criticism applies for any other crappy paper HN likes. Whenever I check this site, half the time the front page has something even worse. Just assume everything you see here is wrong.