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Comment by glimcat | Hacker News Reader

"Dark" is a typical label for unobservables (see also, "Dark Ages").

The fact that dark matter is specifically unobservable via electromagnetism just makes it funny. Well, a little bit, if you're a cosmologist.

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It's dark, but is it matter? If it's not definitely matter, name it something else that doesn't bias the search for a solution.

Basically, there are some knowns: The universe expands according to the fried,am equation. Different percentages of matter, energy give rise to different expansion rates. Expansion history of the universe is known via looking at supernova (which are equally bright at the source). Knowing matter is mostly hydrogen/helium and energ is mostly photons allows us to calculate the density of matter/energy in the universe. These don't match the terms found from measuring supernova leading the differences to be called dark matter/dark energy. Additionally, gravitational lensing is seen by objects which can't be seen. Meaning, they have mass, but don't appear to absorb/reflect light. Additional additionlly, similar effects are seen affecting the formation of galaxies: extra matter is needed to give the structure we see, but we apparently can't see that matter. So it was originally dark because we knew nothing about it, but the name stuck once it appeared we could not see it. It is definitely matter.

It is definitely matter.

The whole point of the article that we're commenting on is that it might not be matter. The root problem is that the observed doesn't line up with the expected. Is the problem with the observed or with the expected? We don't know. You're assuming the problem is with the observed. This article is saying we can modify our expected values with a tweak to the model.

We should name the phenomenon after the problem, not after one of the not-yet-proved-but-expected-to-be solutions.

It is matter, in that it behaves gravitationally the same way that ordinary matter does. (Unlike dark energy, which does not behave the same way ordinary matter does; dark energy is actually poorly named because it does not behave like ordinary energy.) Basically, the dark matter hypothesis can successfully explain a wide variety of unexplained phenomena if there exists a substantial number of weakly-interacting, but otherwise ordinary particles.

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