Hacker News Reader

Comment by Twisol | Hacker News Reader

Yes; the "dark" in these terms reflects our lack of understanding about both topics, not that they share some "dark" aspect in common. They're names for holes in our models, not for entities predicted by them.

View on HN

They're both "dark" because neither interacts with electromagnetic radiation.

I share the opinion that they're names for holes, not entities; but I'm not qualified to defend that opinion.

That's true but even more than that, we're not really sure dark matter is actual particles at all. Modified gravity for example is one alternative explanation that don't require a new particle or field.

So it is something but we don't know what, right? Is it safe to say it's not something from the periodic table or we simply don't know at all?

And, in order to understand a something, do we always need that something to interact with EM radiation?

Neither "dark matter" nor "dark energy" can be made from atoms (i.e. from the periodic table), because atoms interact with photons. I think to say "it is something" is a strong claim, requiring strong evidence.

Dark energy, in particular, can't be a kind of "stuff".

We could "understand" something that doesn't interact with EM; but we'd have trouble observing it.

I don’t know about dark energy, but dark matter isn’t called such because it’s a “hole in our models”. The theory is it doesn’t react electromagnetically with other matter. So it’s quite literally, “dark” matter.

Is that theory or observation? My understanding is that we know it doesn't react electromagnetically with other matter because we (failed to) observe that behavior, not because we expected it to behave that way a priori.

If modified Newtonian (MOND) theories won out, the theory would explain this observation by saying that there was no matter there to begin with. If neutrino theories won out, the theory would explain this observation by saying that dark matter is electromagnetically neutral. But those are two entirely different theories, trying to explain the same observations, and trying to fill the hole in our currently accepted models in different ways.

EDIT: Per a child comment, you might mean "theory" as "idea", as in "the [idea] is that it doesn’t react electromagnetically with other matter." In which case, yes!

There seems to be a lot of evidence for dark matter, that's how I understand it as an outsider. What it means is that there is a lot of consistency in observations, things add up, to the dark matter theory.

I usually agree with your understanding of dark matter/dark energy as placeholders for missing knowledge.

Ah; I think we might only be disagreeing on terminology at this point, then. A physical "theory" is a coherent model that makes testable predictions in its own right, as in the "theory of gravitation". A hypothesis is an explanatory idea, like dark matter.

There's definitely lots of evidence for dark matter, yes~!

a priori is the wrong term because our physical theories are not a priori.

Dark matter has lots of reasons to be assumed but a common one is that when we try to explain the gravitational effects of galaxies based on a quantification of observable matter, there is a huge shortfall. That creates a space for something with a gravitational effect that is unobservable otherwise.

That many of the objects of our physics are theory laden is true, but that they are therefore “unreal” or merely an artefact of theory does not necessarily follow.

Just to be pedantic, I’ll point out that’s literally “transparent” matter and we use the term “dark” which is really more appropriate for something that absorbs EM radiation because it also implies the mystery of the holes in our knowledge. English is great.

Reply on news.ycombinator.com