[plasticchris]

This, ether, and dark matter. The equations don’t agree with observations so we invent a thing we have not observed to explain it. I wish it would be explained like this in popular science, went to a planetarium and they presented dark matter as absolute fact.

[Nevermark]

> The equations don’t agree with observations so we invent a thing we have not observed to explain it.

Yes, and then implications of the invention are followed up on and dark matter has passed a lot of tests and has strong explanatory power (i.e. parsimony, Occam's Razor) over a variety of phenomena, from small dark galaxies up to the matter web structure of the observable universe.

So it has very very strong evidence behind it, at this point. With an unbroken trend of accumulated evidence.

The reason for remaining questions stem from the fact that the small scale nature of dark matter is not yet characterized. Which differs from all other gravitationally active materials we know of - i.e. all the particles in the standard model.

But we don't know the fine structure of space either, and we don't count that against General Relativity. In both cases the large scale properties of each phenomena, that we can measure and model, provides clear reasons why investigating the small scale properties has been challenging.

In both cases, it is the extreme weakness of gravity at small scales, and the low, if any, alternative interactions with the standard model particles we know well.

[prerok]

The problem I have with dark matter is the name. If I understand it correctly, its existence cannot be predicted. We observe strange results, so we explain it by inventing some strange new concept of mass that's otherwise non interactive.

For example, the dark matter might be mass gathering of otherwise non reactionary particles like neutrons, it could be wrinkles in spacetime that have a similar effect as massive normal matter bodies have, or they could be advanced civilizations that learned how to hide their star systems from the rest of the universe.

We simply don't know. I suppose we had to name it somehow, but the name just sounds wrong. It might not be matter at all. It is also not dark, it's non-reactive.

Why did they not rather choose something like spacetime wrinkles?

[Nevermark]

We know we can't see it (dark, as in not emitting or otherwise interacting with light), and it creates and responds to gravity in the exact same way the matter particles we know do (matter).

The two word choices can be quibbled with, but they form an accurate shorthand for what we know.

If the fine structure is discovered to be wrinkles in space I expect there will be a renaming during a time of great celebration by the future Nobel Prize winners! Especially if that also shone light on space-time's ultimate structure!

Edit: I will humbly propose a name for your postulated tiny space wrinkles: Wrinky-dinks!

[SJC_Hacker]

Angela Collier (astronomy post-doc) takes the position that dark matter isn't an theory, but an observation

https://www.youtube.com/watch?v=PbmJkMhmrVI&t=15s&pp=ygUaZGF...

[dotnet00]

For the average person, dark matter should be presented as absolute fact. It's the leading explanation that best explains most of the associated phenomenon, and the average person has repeatedly shown themselves to be unable to understand what a scientist means when they call something a theory.

Emphasizing that we haven't explicitly discovered what dark matter actually consists of inevitably leads to people who don't understand the evidence dismissing it as "made up" and instead pushing explanations that have a much higher burden of proof (eg modified gravity or modified light speed, which struggle on the point that there are structures which have more or less "extra mass" than usual).

[Buttons840]

What's more engaging?

"We know the facts. We have it all figured out." Then the facts change years later.

Or "There's a great mystery here, a secret we haven't yet found. We're still looking, but here's some ideas that seem to explain 90% of what we're seeing."

The second is so much more engaging and would promote more interest and science funding.

[Mountain_Skies]

It would also help retain public belief that science is a process for neutral seeking of the truth rather than a self-interested force with rapidly dropping credibility. Some revision is inevitable but it doesn't need to be routinely due to having been intentionally misleading.

[Tagbert]

The second is how I have normally seen dark matter presented. The first is only used as ridicule.

[bryanlarsen]

And then we lose those people completely when the "facts" change. Better not to call them facts in the first place.

[jjk166]

The facts don't change. Apples fell to the ground when we thought newtonian gravity was correct, they still fall to the ground now that general relativity is the accepted explanation. Theories are explanations of factual observations. The observation of the phenomenon we're calling dark matter is as factual as apples falling to the ground. The explanation is subject to change as we learn more, but the facts won't.

[bryanlarsen]

dotnet00 said we should call dark matter an "absolute fact".

[jjk166]

And I concur. It's as absolute a fact as earth having a core.

[alganet]

> the average person has repeatedly shown themselves to be unable to understand what a scientist means when they call something a theory

The average person consumes science from news, not from scientists.

A lot of news outlets and "science communicators" have been repeatedly dumbing down scientific subjects for non-scientific purposes. Clickbait, ideology, lazyness.

The nature of dark matter should be presented to the public as it is. If we dumb it down too much, it's the same as not presenting it at all, or misrepresenting it.

[dotnet00]

I tend to agree about science communication, but on the other hand, I've also seen how frustrating it can be to constantly have to correct the same fallacious arguments over and over again because people misinterpret the ideas and have a bad case of Dunning-Kruger.

So presenting things as is doesn't really work because people still have only partial information relative to those who work in the field. Thus being the same in effect as misrepresentation.

I think I was too harsh in saying that it should be presented as absolute fact, ideally I'd rather the average person be much better educated in their understanding of the scientific process, such that they'd have enough humility to recognize that watching a documentary does not give them all the facts. But that doesn't seem realistic, so it's a difficult issue.

[alganet]

> I'd rather the average person be much better educated in their understanding of the scientific process

Yes! However, I don't know how realistic this is.

[thatguy0900]

"For the average person, dark matter should be presented as absolute fact." This is how you end up with a crises where noone trusts experts or institutions anymore

[TheLoafOfBread]

Dark matter and dark energy is a gap in knowledge and should not be presented like a fact, but as a temporary constant added to human models of universe to make them actually work.

It is like a boy calculating physics homework, only to be 30% off, so he will add some constant to get to result he wants. It sounds ridiculous, does it? Well dark matter/energy is that constant to get result we expect.

[prerok]

One reason for dark matter explanation that I heard is that it is used to explain the same angular speed of star systems in the galaxies.

To me, that seems far fetched. Would it not be more likely that our formula for large distance gravity interactions should change?

[jjk166]

But the thing is it's only the angular speed of star systems in some galaxies. We have also found galaxies that behave differently, as if they have no dark matter. This is very easily explained with dark matter theory - they actually don't have dark matter. Any theory that modifies gravity needs to explain why we only sometimes modify gravity.

Further, while that was the observation dark matter was originally introduced to explain, there are a lot of other observations it has since explained. For example we can see regions of space with high gravity that do not appear to have any substantial amounts of regular matter in them. Again, stuff we can't directly detect as it doesn't interact with light but still has mass is a really simple explanation.

And from a theoretical perspective, there's no reason to think dark matter is weird. There is no law that says all particles need to interact with the electromagnetic force, indeed we know of many particles that don't even though none of the ones we know are particularly good candidates for dark matter. That there is a particle we don't know about specifically because it's most important property is that it is hard for our instruments to directly detect is far more likely than that one of our most successful theories which has an extremely firm foundation and has correctly predicted numerous observed phenomena with incredible accuracy has been wrong this whole time.

[prerok]

Thank you for the explanation.

What I don't like about this, is that we take the observations, apply some custom guesses as to why the spacetime is folded differently and... there you go, your formulas now match. It smells too much like the explanation of geocentric system, where they invented that planets also circle around a perceived dot on their trajectory path and that happily coincides with the Earth's rotation.

I think what we are missing is that these behaviors need to be predictable. We don't know where these anomalies in spacetime curvature will be and why they are there. And as I stated in another comment here, I think dark matter is a bad name for the unexplained spacetime curvatures (warpings?, wrinkles?).

[jjk166]

Again, you're focusing on one small sliver of what dark matter is observed to do, and coming up with alternative explanations for that particular observation. There are a whole host of different observations of dark matter, and any reasonable competing theory needs to explain all of them. Modified gravity is the inelegant epicycle explanation, while dark matter is the simple alternative explanation in your analogy.

> I think what we are missing is that these behaviors need to be predictable. We don't know where these anomalies in spacetime curvature will be and why they are there.

But we do! We can see galaxies that have been stripped of their dark matter and we can find nearby the dark matter that was stripped. We can predict, based on our theory of dark matter where these gravitational anomalies will be, then we look there and lo and behold we see them. We aren't applying custom guesses to match our observation, the universe just happens to match exactly what we'd expect it to look like if it contained a bunch of matter that didn't interact with the electromagnetic force.

> I think dark matter is a bad name for the unexplained spacetime curvatures (warpings?, wrinkles?).

Dark matter isn't the space time curves, which aren't particularly special. All massive particles produce such warping, and we just call it gravity. Dark matter is matter (stuff that interacts with gravity) which is dark (does not interact with light). We would expect it, assuming it exists, to produce such warping of spacetime, which again is exactly what we see.

[plasticchris]

It should be presented as this is what we think, there are some gaps we filled in here, and these gaps are usually where the next big advance comes from. No need to even use the word theory, just explain in simple words and people can get it.

[8note]

I think presenting the evidence for dark matter is much more engaging and useful than the conclusion of dark matter.

Stuff like baryon acoustic oscillations are interesting enough on their own