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Starlevel004

Well, any other theory would have to explain all of the following better than cold dark matter does:

1. Galactic rotation curves (galaxies spin too fast)

2. Galactic gravitional lensing (galaxies bend too much light)

3. The shape of the cosmic microwave background (it only matches if you have dark matter)

4. The bullet cluster (visible matter collided, but the gravitional lensing kept going)

Non-electromagnetically interacting matter solves all of these, and the same ratio of matter:dark matter solves all of them. That would be one hell of a coincidence.

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It also has to do so without destroying a bunch of other exceptionally well tested theories - it's very easy to explain something if you ignore other requirements, like being compatible with relativity - which has been a big problem for MOND but is no problem at all for dark matter (because it's just extra matter being normal out in space).

I don't understand why it has to be non-electromagnetically interacting. Can we honestly say we should be able to resolve all the matter in a galaxy with our current sensing technologies? Why can't it just be the equivalent of non-light-emitting asteroids and planets. We can barely detect whether a star has planets in our own galaxy. And according to Wikipedia the amount of matter we would be missing in a sphere with radius from the sun to Neptune is 10^17 kg or approximately a large asteroid. Which seems like a rounding error. But my knowledge of astronomy is definitely minimal.

> I don't understand why it has to be non-electromagnetically interacting

Because we have zero evidence of it electromagnetically interacting. We have evidence of other particles like this, like neutrinos.

> Why can't it just be the equivalent of non-light-emitting asteroids and planets

Because they've been ruled out: https://en.wikipedia.org/wiki/Massive_compact_halo_object

You are not proposing anything new. Your ideas have been thought of before, and discarded because they lack evidence.

Hah. I didn't think I was proposing anything new. I was telling you how it sounds to someone who isn't an astronomer.

Do you honestly think you've come up with a clever idea that none of the researchers in the field already considered?

You are describing MACHOS, which was one hypothesis for dark matter. https://en.wikipedia.org/wiki/Massive_compact_halo_object

The thing is, we've looked for them. If they were small (asteroid sized), the amount required would be visible as dark clouds obscuring the objects behind them. If they were large (brown dwarf or bigger), we'd see gravitational lensing from them. We don't really see either of those on the scale required to explain the gravitational effect.

shit man. I was asking a question. So much for curiosity at HN.

Curiosity is one thing, but in practice "just asking questions about dark matter" is uncomfortably close to pseudoscience and a lot of us are sick of it. It's similar to if you had accidentally said something similar to a young-earth creationist.

Did you just compare CDM-Lambda to the age of the of earth?

That implies far more evidence than actually exists. The science on the age of the Earth is far more grounded in experimental results simply because, well, we live on the Earth.

This doesn't mean CDM-L is incorrect in any way, but saying that questioning it is similar to being a YEC is ridiculous.

There's confident and there's cocky, I think you veered too much in one direction there.

I plainly did not say they're equivalent, no. But the difference in mindset among the proponents is often one of degree, not kind. Bear in mind that I only brought it up to explain to someone why their honest questions might have been accidentally conflated with that mindset.

Personally I'm still holding out the possibility of something like MOND being true, even if it looks more and more like it will have to coexist with DM at best. That doesn't stop me from noticing that most of the people who believe in it look exactly like cranks, and many of them actually are. And I'm going to keep pointing this out where it's relevant.

HN is less hackers than it is pedantic VC lackeys training for their aspirational role as a wealthy-and-opinionated Twitter personality.

I think it's the "can we honestly say" phrasing that got you flamed here. It reads as "those stupid scientists don't know what they're doing".

Oof. Like I said. Just fyi, for any of the HN'ers left "can we honestly say" is just a colloquialism for "is it reasonable to say, given..." Pretty sure my "given" wasn't nutso anti-science. Especially considering I am a scientist. HN was fun while it lasted. Peace out.

It's probably just a terminology mismatch. But practicing scientists take a lot of care to honestly say what they're saying, so it doesn't land well as rhetoric.

Thank you. That's the exact understanding I was missing. I appreciate that.

Unfortunately it is very common for people to spend 10 minutes using their "common sense" to find some simple explanation that seems to have defied the Scientist, rather then spend that time to read a quick article that explains the foundamentals.

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