[shiroiuma]

The dark matter hypothesis has always seemed like BS to me, like the simple product of a math error. I think the observational results are caused by something else that's not understood or seen yet.

What's funny to me is how people can be so confident about astrophysics theories, when we're just a primitive race that hasn't even ventured beyond our own moon and fighting brutal wars over whose imaginary god is correct.

[kadoban]

> I think the observational results are caused by something else that's not understood or seen yet.

Since it's not seen or understood, we could say it's "dark" for brevity. And since it's clearly affecting gravity let's just say "matter" for short.

[naasking]

Nah that already presumes that it's a separate thing. It could be a modification of gravity instead.

[kadoban]

It could at one point have been, but that's basically been ruled out by further observations.

It's hard to say why only _some_ galaxies have their gravity modified without it being caused by some sort of substance.

[naasking]

> It could at one point have been, but that's basically been ruled out by further observations.

It really hasn't. The same standard of evidence that would rule out modified gravity would also rule out dark matter.

[throwawaymaths]

We could also call it the "Jesus Christ effect" too. Certainly that wouldn't suggest any sort of mechanism or bias interpretations of what could cause it

[aeturnum]

If you're interested in learning more I recommend you watch "dark matter is not a theory"[1]. We consistently, across many measures, observe the effect of substantially more mass than we expect using traditional understandings of dynamics. People have been aware of it, under different names, for about 90 years now.

[1] https://www.youtube.com/watch?v=PbmJkMhmrVI

[throwawaymaths]

This is terrible. Of course dark matter is a theory. Saying it's just a bundle of observations is like saying "1) lee Harvey Oswald had interactions with the CIA and 2( he killed JFK", and claiming "hey man, just making two innocent factual observations". No, of course not. By shoving different things together you are implying a causal connection, which is exactly a hypothesis.

This kind of a wordplay shell game is really bad for science

[aeturnum]

Things fall towards the earth. You can check that they do right now by dropping something. That things fall towards the earth isn't a theory - it's an observation. Gravity - the most popular explanation for why that happens - is a theory!

"Dark matter" comes from a group of observations that consistently suggest there is more mass in the universe than we can account for. The fact that we keep observing it is not the same thing as an explanation for the observations. There are also theories that try to explain dark matter! But the fact that people observe it is not a theory.

[throwawaymaths]

I'm going to repeat, clearly. The observations themselves are not a theory. Grouping them together is.

> That things fall towards the earth isn't a theory.

Actually, it is.

Any given object falling once is an observation. Noticing more than one thing falling consistently is a theory.

[shiroiuma]

"he killed JFK" isn't an observation: there's no witnesses that ever testified to this. You don't know that he killed JFK, and in fact new evidence casts serious doubt on it (it was here on HN recently I think).

[Pxtl]

There's a good cosmology YouTuber who basically explains: dark matter is not a theory, it's a set of observations. Galaxies behave like there's a halo of invisible mass surrounding them, one that varies in density per-galaxy. The halos even perturb as expected in galaxy collisions. But nobody's got a coherent theory on what that halo is.

https://m.youtube.com/watch?v=PbmJkMhmrVI&pp=ygUbZGFyayBtYXR...

[nimish]

This is maybe half true. Dark matter is required to explain these under the current lambda-cdm model, but the behavior of galaxies is not evidence for it in a constructive sense. It's only evidence that the current model is untenable.

Galaxy rotation curves are better explained by applying general relativity without the severely restrictive assumptions required in lambda cdm. You don't even need the full thing, just the first order linear approximation that allows for gravitational waves (and thus is causal), as Ludwig showed a few years ago. You need at least this because gravitational waves exist, and those cannot occur in the singular newtonian limit used mostly for convenience.

It doesn't take much to then question the need for dark matter as if it is compensating for poor models in one case, it probably is doing the same in others.

[naasking]

> Galaxies behave like there's a halo of invisible mass surrounding them,

No they don't. Galaxies exhibit anomalous velocity curves according to existing gravitational theory as applied in a specific cosmological model. That's the observation. This could be explained by a halo of indivisible stuff or it could be explained by a misunderstanding of gravity or a different cosmological model.

I'm general, we should not explain observations in terms of speculative theories, because this carries a presumptive bias.

> The halos even perturb as expected in galaxy collisions.

They actually don't. Dark matter would explain part of the bullet cluster (lensing), but it can't explain the high collision velocities observed.

[aeturnum]

Haha - I simultaneously wrote my own comment that recommended the same video! I think acollierastro makes really good, accessible physics content.

[TheBigSalad]

I think almost everyone realizes dark matter is a placeholder for the unknown. It doesn't mean we shouldn't explore the possibility of special dark matter particles that don't interact with regular matter. In fact, there's not much else to do.

[benreesman]

I think this is the most honest-sounding reply to a layperson.

Our data doesn’t fit GR with the boundary conditions that make sense more locally. Positing a bunch of non-interacting mass/energy is closer to observations than doing nothing.

Calling it a placeholder seems honest, reasonable, and productive.

Getting pushy about WIMPs and stuff (which is deeply intertwined with the refusal to give up on supersymmetry because, careers) in a world where Michio Kaku is on TV talking about quantum computing and AI in a way that’s less scientific than Matt Gaetz yelling about UFOs on C-SPAN to distract from the child-trafficking charges is icky.

[throwawaymaths]

There are two historical dark matter theories in early cosmology. Neptune and Vulcan. One of them turned out to be real. It would do to remember that the other one did not.

[nobody9999]

>fighting brutal wars over whose imaginary god is correct.

Especially when they're the same imaginary god[0].

[0] https://en.wikipedia.org/wiki/Abrahamic_religions

[shiroiuma]

Many Christians vehemently disagree that the Muslim god is the same as theirs. What a bunch of academics have to say on the matter is irrelevant; religion is just someone's personal belief and completely unfalsifiable, so you can't say they're "wrong".

[nobody9999]

Why should I care one way or another what a bunch of folks (whichever bunch, I'm not picky) who worship some imaginary sky daddy think?

Are you claiming that one group is less wrong about their fake deity than another? That's rich.

[shiroiuma]

No, I'm criticizing the people who claim that one group is less wrong about their fake deity than another. I see this all the time when religious violence flares up: "they're not following their religion correctly!", coming from people who aren't even in that religion but think they're experts on that religion's teachings (and ignoring the fact that so many believers have incredibly different ideas of what those teachings are). It really annoys me, so I feel the need to call it out. If someone claims that their religion tells them to murder children, then I believe them; it's all made-up anyway, so it's ridiculous for some outsider to say they're doing their religion wrong.

[sph]

Way to derail the thread.