Comment by worik | Hacker News Reader

Comment by worik | Hacker News Reader

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> * DM particle haven't yet been found.

We do not know that dark matter exists

> * The current best theory of the structure formation and galaxy evolution involves dark matter and critically depend on it to reproduce observations.

The stories we like to tell require dark matter. Otherwise our stories are wrong

> * There is a broad variety of Dark matter models that are consistent with simulations.

We have a lot of stories using dark matter. We really like it

> * It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.

Our stories are just stories but it is all we have

> * There are a few cases where you can find tensions with the existing DM based paradigm.

Our stories are not internally consistent.

> * A final point. Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.

We really like stories with dark matter

I love Astrophysics! Pure math with constraints. Do not confuse it with reality

All theories are stories. All communicated information is stories. Stories is just a word, it has pejorative meaning in context. Bible Stories are not like physics stories. A lot of physics stories are subject to test, null hypothesis, disproof.

The stories which persist are useful. Calling them theorems or theory helps us rei-fy stories into propositions which can be used to do science. Science is about modelling things, understanding things, and testing things. It is a valid proposition to argue DM is defined by stories which remain untestable, but the proposition there are better alternatives ignores that to construct stories without DM which are better will demand addressing the problems DM has to exist, to define the blank spaces in other, testable stories. You think Absolute zero exists? It's just a story. We haven't got there, we got close, we observe what happens, but this mythical zero point.. What good is it, if we can't get there? I love temperature, the whole thing depends on a fantasy...

Do not confuse your projection of "what is reality" with reality. I love HN, where people make asserts which don't mean what they think they mean!

> A lot of physics stories are subject to test, null hypothesis, disproof.

Nothing in astrophysics is like that, is there?

I'm not an astrophysicist. But I note, had Oppenheimer not died before it was confirmed at least one of his theories predicted black holes. He would have got a Nobel on it.

To me, thats a strong indication the fundamentals of mass, energy as modelled, were projected in advance of radio-telescopes confirming the theory. isn't that what Astrophysics does?

Perhaps there are better examples. Personally, I find the main sequence circular logic reasoning, but its a model for spectral colour, distance, age and size. I'd kind of like it if we flew a mission to hold a Pantone colour wheel up close, and measure the damn thing properly for size and colour but age is very hard. You're back in models of decay of mass/energy outcomes and how we believe half-life in C14 analysis.. except done as spectral lines at a distance based on one solar mass we have close by to model things on. Plus, we don't know how to make pantone colour stable across 20,000 years of flight time to measure a star up close and by then Humans will have 29 eyeballs seeing into the infrared like mantis shrimps.

Gravitational lensing is pretty cool. I think it was initially theoretical, and it was a long time being proved.

Gravity waves defy detectors. If we can get detectors working that will be immensely cool. I may have stepped off the scienting engine by wanting an outcome, which arguably is not aligned to null hypothesis testing. Maybe we can't detect gravity waves and they remain theory?

Look, its rude. I apologize in advance. I do kinda think you're trolling. Are you trolling? Maybe Dang will be upset at my asking. It's ok to ignore.

Wat... "Like" implies preference. You're using the word "story" to imply someone pulled it out of their imagination. What they said was "we currently have no plausible theories that doesn't require dark matter". These theories have to be consistent with other theories and observations.

plausibility is a bayesian prior

Different people have different priors. For some dark matter is more unlikely.

If they don't agree with the hole in the other theories which use DM to reconcile observations, thats an issue worth exploring. If they just don't like the DM label on those holes, its a fine point. What do you want to call the emerging shape in theory which is a hole, in otherwise very fine, testable propositions?

Indeed. That's why claiming that dark matter exists OR not exists is wrong. We do not know. The consensus is that it's more likely that it does.

I don't understand your point. You could say that about pretty much anything.

We really like to tell stories where 2+2=4, etc.

How do you not understand?

We know 2+2=4. We do not know that dark matter exists.

No, but we have a theory that predicts several things, including something like dark matter. It has been tested for several of it’s large scale predictions involving the movement of matter. Now we are testing it’s prediction of physical dark matter.

2+2=4 is only true under certain assumptions. We also do not know that dark matter does not exist, which is the claim of the article.

We do know that dark matter, as constituted, in all its variations, requires observations grossly incompatible with what we, in fact, find.

Pop science cosmology presentations never, ever mention these contradictions. But it is, exactly, embracing contradictions like these that would make it science, not religion. Presentations without them actively mislead the public as to what science is and is for.

Trotting out details found (or made) consistent with DM amounts to indulging confirmation bias. An honest presentation describes the current favored theory, which summarizes a collection of observations, and then whatever is inconsistent with it. Sweeping inconsistent facts under the rug is the opposite of science.

Every substantial advance has come from embracing contradictions of current favored theories. Young people are inspired not by sweeping, broad-brush stories of how the universe is, but by mysteries that remind us how much is left to be discovered.

Biologists understand this. It is very easy to get a biologist to say "nobody knows". Every non-moribund field revels in what is still wholly unknown. Only cosmology circles the wagons against contradictory evidence.

I don't think i have ever heard anyone claim we know for sure. I have heard lots of physicists claim that its the best theory they are aware of given evidence they have seen, which is a really different claim.

> Biologists understand this. It is very easy to get a biologist to say "nobody knows"

Depends on what you ask them about.

Most things you can ask them, they have no answer for. They revel in it.

No one (here) is claiming that we know dark matter exists...

> We know 2+2=4

Which is why we really like telling stories about it.

My point is, we tell stories about literally everything, so i don't know what point you are trying to make.

If your criticism applies equally to basic facts, it is a bad criticism.

Anything which gives good prediction power is useful.

Given we can't observe reality directly, since we ourselves see it though a model, We can adapt the above list to everything.

The question isn't "is it a story" the question is "is it useful for prediction"

Much of astrophysics has been.

We do not know that reality exists.

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