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Comment by kloch | Hacker News Reader

> For dark matter, we keep those standards. The evidence for some kind of dark matter, that there is something that can’t be explained by just the Standard Model and Einstein’s gravity, is at this point very strong.

Option 1: Do more research on Gravity to see what we might be missing there. The difficulty in measuring G, and the flyby anomaly would be good places to start.

Option 2: Make up fully unconstrained variable 'X' that can take any value you want at any location or time in the universe[1]. This is amazing because it can perfectly solve so many difficult problems!

Obviously many people will and should be skeptical of throwing full confidence at option 2 in it's current state.

[1] Unlike neutrinos or black holes, there is no theory for what dark matter is made of, and how it is created or destroyed. Thus there are no constraints on how much you can have at any given location or time.

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The point of the article is that dark matter is the result of doing 1, not 2. What's this "fully unconstrained" nonsense? We have outrageous amounts of data that need to be fit. Why is "the flyby anomaly" a useful place to start and not a century's worth of galactic rotation and mass estimates?

Dark Matter persists precisely because it's the best theory that fits the available observations. Arguments against it are the bits predicated on squishy stuff like "aesthetics".

No one thinks we have all the answers, but demanding we throw out the best model we have is going backwards.

being "skeptical of throwing full confidence at option 2 " is not the same as "demanding it be thrown out". It just means show us something more than "magic variable 'X' fits all curves."

You want... more from a theory than that it fit the data? That's not how theories work.

I think what you're asking for is a lab-testable prediction from a dark matter theory. And no, we don't have that. It would be nice if we did, but we don't. We don't have it from MOND either, though, so I still don't get your denialism. If you don't want us to do science to figure this out, what are you asking for?

If your theory isn't testable, it's not a scientific theory. Period. It's either a hypothesis or it's faith. When you go around denouncing people for asking you to make a testable prediction it just makes you look bad.

Evolution wasn't testable for decades after Darwin's death. Continental drift's predictions are still awaiting results that won't come for another few thousand years. Newton's gravity took hundreds of years before it could be directly tested.

All those theories were merely fitting to data. Do you genuinely claim they were "unscientific"?

I repeat: the desire to reject a theory for aesthetic reasons is the "faith" side of this argument. It's OK to prefer a better theory if you have one. It's not OK to sling insults at the people who point out that it's the best theory we have.

Fitting any arbitrary measurement is trivial via regression. The hard and useful part is making predictions.

Cosmology is not amenable to either predictions or engineering. There’s not even anything to deny.

> Arguments against it are the bits predicated on squishy stuff like "aesthetics".

I disagree with that. The biggest hurdle people have (in my experience is) is the claim that 85% of the universe is made of something that no one has ever observed directly. We believe it exists because of the behavior of the matter we can observe and our understanding of gravity. It's the best theory we have, and yet it smells a little like epicycles, phlogiston and ether.

> is the claim that 85% of the universe is made of something that no one has ever observed directly.

The only thing anyone has ever observed directly is the contents of their own mind. All empirical work, without exception, is mediated by instruments, whether they're retinas or telescopes or 50,000 metric tons of purified water hooked up to a photomultiplier tube. Low-energy electromagnetic interactions happen to be the channel we're naturally best-equipped to use in our daily lives, but they have no special epistemic significance.

I take your point, but I would argue that retinas and brains are categorically different than telescopes and photomultiplier tubes.

But the point you make brings up an interesting analogy though. If we consider optical illusions — where the mental model our brains create at a preconscious level lead us to incorrect conclusions about reality (insofar as an objective reality can exist) — can that inform our understanding of the models we use to interpret our astronomical observations?

But until someone comes up with a heliocentric model of dark matter we're going to remain here. What we can do at this point is collect more data with better precision, and if we're lucky at some point someone will see a relationship in two otherwise uncorrelated events and use that to make model that makes accurate predictions.

>The point of the article is that dark matter is the result of doing 1, not 2.

The article may claim or argue this, but supports this claim rather poorly.

Look the fact that dark matter is even a topic, is because our models are wrong somehow. Dark matter is a convenient theory, but essentially a non-testable one, and one that has yet to have any real predictive power (outside of it accurately predicting things where our models fail at predicting things - but this isn't a real case, as it's essentially circular reasoning when it's existence is inferred from the errors in our model in the first place).

The dark matter explanation for the Bullet Cluster is exactly doing 2, not 1.

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