In the hunt for dark matter, are axions our best bet? | Hacker News Reader

In the hunt for dark matter, are axions our best bet?

space.com

26 pointsgmays17 comments

Wild theory of the day.... organic matter particles in the inter-stellar void have become an electret somewhere in their history, and are thus shielding some of the gravity between stars.

Have you read _Schlock Mercenary_?

Cool theory.

The actual only obligatory xkcd for this site: https://xkcd.com/1758/

How can an unspecified new theory of gravity not be able to fit the data?

Yeah Munroe is wrong on this one. Non-newtonian gravity fits more data.

http://astroweb.case.edu/ssm/mond/mondvsDM.html

Which one of those rows does the Bullet Cluster fall under?

It falls under "don't treat science like a bunch of gotchas". There's a lot of shit we don't know. There's a reasonable argument that the observed lensing might be refractive index distortions from increased gas density in the bow shocks, aka, "actual lensing".

Okay, but if it's even questionable at predicting that, why then does everyone keep saying that dark matter is such a great explanation of a million phenomena and their grandmothers and especially the Bullet cluster? I thought that was supposed to be one of the things that gave the theory widespread legitimacy and now I'm hearing that I've been basically hearing fake news this whole time? I'm really confused.

Scientists are bad at their job? I don't know.

I remember in ninth grade physics class we did an experiment where we measured gravity and used excel to do an R^2 fit on the parabola to a second order plot. One very smart (not being sarcastic) student discovered that she could get a perfect fit with a seventh order equation (we had seven data points). I did not have the vocabulary to explain to her why she was wrong. She now sells healing crystals. Sure, the fit explained more things, but it was not a good model. Explaining a million things is not powerful when each thing you explain has a unique parametrization that you can use to "get it to work".

Mond predicted something called the external field effect, a researcher went looking for evidence it wasn't there, and then changed his mind when the evidence showed there was an efe. So there are at least some good scientists out there.

Pretty good summary of what he’s getting at:

https://www.explainxkcd.com/wiki/index.php/1758:_Astrophysic...

Whoa. Dark matter = possibly an unknown type of star too dim to see. https://en.m.wikipedia.org/wiki/Massive_compact_halo_object

Never thought about that. I always heard that dark matter was a particle that interacts gravitationally but not electromagnetically. The dim star theory seems at least worth considering.

But that raises all kinds of questions, like how is it a star if it’s not emitting light?

I like how some salty physicist added “Therefore, the missing mass problem is not solved by MACHOs” a few paragraphs in. :)

I have been, rather annoyingly, been downvoted quite often in the past for being really clear on "dark matter," which is to say that astronomers study --broadly-- stars and their assemblages, things that emit light. Dark matter can encompass anything that doesn't shine like a star, be it exotic particles or just cold interstellar gas, little black holes, whatever. It isn't necessarily some Star Trek shit. It is just stuff we can tell exists by its gravitational signature on things that do shine -- light matter, aka stars.

It's not just that it doesn't emit light, it doesn't appear to reflect or absorb light either. If it did, we should be able to pick it up through spectral analysis.

I think the usual place MACHO theories struggle to match observation is lensing events. If there were enough dark stars / planets / whatever out there to be the missing mass, we'd see characteristic blips in the light curves of stars when they wander between us and the star.

The true nature of dark matter is an additional variable parameter used to fit observations that otherwise don’t agree with current theory.

That’s just the definition of the concept. The true nature is what cause the theory to fail so that we need additional parameters.

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