Thursday Throughput: The Dark Matter Is Still Missing Edition
[ThTh1] All normal matter — at least all normal matter outside of a black hole — emits light. Regardless of what it is composed of or what its temperature might be, it emits light. That’s basic thermodynamics.
However, starting in the 1930s, we began to see hints that the light in the universe may not trace all the matter; that there may be matter that is fundamentally different from the stuff we deal with every day and that emits no light at all. This stuff — dubbed Dunkle Materie by Fritz Zwicky, has now been indirectly confirmed by at least a dozen different approaches. We see that galaxies rotate so fast, they would fly apart were it not of the invisible matter binding them. Galaxies in clusters move so fast, only dark matter could keep them bound. For a while, it was thought that maybe the laws of physics were wrong. But the Bullet Cluster seems to have put a bullet in that theory.
But while the indirect evidence for the existence of dark matter is strong, the direct evidence is weak at best. The current theory is that dark matter is kind of subatomic particle like neutrinos — something that exists in massive numbers but rarely interacts with normal matter or itself. So, we’ve tried to detect dark matter the same way we detected neutrinos — building massive vats of chemicals and waiting for a particle of dark matter to hit something.
So far, only one experiment has claimed a signal — the DAMA experiment in Italy claims not only to have detected a signal of dark matter but to have shown seasonal variation as the Earth move around the Sun. This claim, however, has been controversial, with disputes over methodology and interpretation.
This week, another paper from the COSINE group, which uses a similar experiment, reported that they failed to replicate DAMA’s results. This follows a result early this year from the ANAIS collaboration which similarly failed to find the signal claimed by DAMA. The suggestions are that DAMA is measuring a bias in their data analysis.
More experiments are planned so we should get a definitive answer on this soon. But it’s somewhat disappointing to see this claim contradicted. It’s been 88 years since Zwicky first reported the possible existence of dark matter and forty years since Vera Rubin confirmed it. In that time, the case for dark matter’s existence has grown stronger with each passing year — its presence is etched into the very structure of the universe itself. But we have yet to detect one single particle.
Until that happens, dark matter remains the great unknown. And the possibility that we misunderstand a giant fraction of the universe remains.
[ThTh2] Even as the Delta variant has spread out from the epicenter in southern states, the partisan gap between death rates and infections rates continues to grow. I cannot begin to express how frustrating it is to see pandemic response politicized this way.
[ThTh3] Here’s a visualization of all the binary black hole systems LIGO has detected.
We love this new #GWTC3 animation, by @NUCIERA's @actualdrdoctor, showing cartoons of our new #O3b merger events! Can you spot the #NeutronStar #BlackHole merger candidates #GW191219_163120 and #GW200115_042309? For lots more #GWTC3 goodies, check out https://t.co/43rLJ247SR pic.twitter.com/M0T4GY8rsF
— LIGO (@LIGO) November 8, 2021
[ThTh4] HPV vaccines have now been shown to cut cervical cancer rates by 90%. Doing this globally will take some work — different strains of HPV circulate in different populations. But we could be looking at hundreds of thousands of lives saved every year.
[ThTh5] A new study out of South Korea shows dramatic reductions in COVID transmission rates on public transport when masks are used.
[ThTh6] Astronomy’s Decadal Survey, which tries to map out the next ten years of research, dropped last week. Plans include three new space telescopes, two new ground-based telescopes and efforts to increase diversity in the field. Now let’s see if the funding shows up.
[ThTh7] Pfizer’s antiviral pill — built on similar principles to anti-HIV meds — is showing stunning effectiveness in preventing serious illness and death. Though I will repeat what I said with Merck’s antiviral pill — this is a supplement to vaccination, not a replacement.
With Dark Matter (the stuff, not the commenter), I can’t help but wonder if one of the base assumptions is wrong.Report
The problem is that it’s no longer one assumption. It’s a bunch of them. The structure of the universe kind of demand dark matter be present.Report
I know the math regarding Dark Matter is much more developed, but it still strikes me as a modern incarnation of aether. Which makes me wonder about base assumptions (especially regarding gravity) and if we have something wrong.Report
Then is the whole problem that the answer is unsatisfying? Let’s say the answer is that there is a kind of matter (or something whose closest analogy is matter) that has mass but doesn’t interact in any other way. If that would satisfy the equations, it doesn’t have to satisfy the physicists. I guess I’m asking if there’s any problem with undetectability.Report
Yes, because if it’s undetectable, then the theory can’t be falsified except by the development of a competing theory with more evidence to support it.Report
What if the nature of dark matter is that it’s only detectable by its gravitational effect? Not “really hard to spot”, but by definition able to interact with normal matter only through gravity. If the math backs up the observed gravitational effect and the lack of any other effect, wouldn’t that meet the criteria of falsifiability?Report
That would put us in “invisible fairies” territory. Or external to the universe Lovecraftian aliens pushing on the fabric of the universe trying to get in.
We need to figure out what Dark Matter is. Particle? How is it that we can’t reproduce it, study it, fine it, or describe it?
Can it be eaten by a black hole? If yes, then shouldn’t we see it being ripped apart and/or interacting with the black hole? Adding mass to it if nothing else. If no, then wtf?
We’re in this weird area where it both clearly exists and every test to measure it says it doesn’t exist.Report
Lovecraftian aliens can be measured, but only by consulting the unnatural writings of the Mad Arab which are contained in the monstrous tome known by those who dare whisper of such things as the Necronomicon.
My question is, do tests to measure dark matter fail to confirm its existence, or do they confirm its undetectability outside of gravity? By all means we should try to understand it better, and if it’s one of those things that exists just about everywhere for an incredibly short amount of time or something that only interacts with gravity and neutrinos, then there’s value in learning that. But if it’s characterized by, say, mass but no volume, or for some reason only affects dimensions we can’t measure, then it could be explained as fully as we can.Report
I’m not current with this but last I checked we have some clues which round to nothing after the margin of error.
So other than gravity we’ve got nothing for sure (although if wiki disagrees with me I’d believe wiki).
Darn right. Rewriting the law of gravity is one of the few ways we might come up with a star drive.
I don’t actually have much hope for this, if we’re mis-measuring mass or mis-approximating gravity then the old theory will stay put and we’ll just change the rest.Report
I don’t think it’s undetectable so much as “difficult to detect”.
The Higgs Bosun was difficult to detect, for instance, but not exactly aether.
Dark matter is a bit of a placeholder — lots and lots of different observations basically say “We’re missing a lot of matter and energy here, stuff that seems to refuse to interact in any real way with anything but gravity (but we can see it’s gravitational shadow in multiple, independent ways). WTF is it even? Let’s call it “dark” matter and “dark” energy because of it’s refusal to interact with the EM field”.
I mean there are some possible solutions that side-step the need for it, but at the moment it fits Occam’s razor better to say “There’s a subatomic particle we’re missing from our models — because it hates to interact with the EM field” than “All our models are hugely wrong in some key facet, despite being incredibly predictive everywhere else”.
Because our current model is highly explanatory, and there are a number of ways (WIMPS for instance) there could be a particle we struggle to detect except gravitationally, and adding a new particle is…not exactly as huge a deal as overturning the applecart.
That said, Einstein and Newton, you know?Report
I guess the question is (and particle physics is not my forte), do we have a model of fundamental particles that has room for a particle that can handily ignore the EM force, but not gravity?
Or, do we just not understand gravity at the macro level as well as we think we do? I mean, last I checked, we don’t even know how gravity works. Is it mass bending space time, or a messenger particle (gravitons, anyone?), a combination of, or a dual nature?
This is what I mean by the underlying assumptions. We think gravity behaves so, because our observations and equations say so, but what if we are missing some terms in those equations? We got the Euler Equations, instead of the full Navier-Stokes?Report
Oh, the commenter has been wrong in his base assumptions on occasion as well. 😉
Big picture, if the theory requires invisible undetected things to make it work and we can’t find those things, then the theory is probably wrong.
Ergo The Theory of Gravity is probably Wrong.
Nobel Prize for you if you can resolve the issue.Report
I’ll get right on that, just gotta brush up on my Modern Physics…Report
The thing that really convinced me of dark matter was the bullet cluster result. I might make a video or something about it. A really elegant experiment showing that gravity does not follow the light.Report
Please!Report
Yes please. More cool science stuff!Report
ThTh6: I see that they’re asking for three new space-based telescopes. Related to that, I found it interesting that when I went through my usual news sources this morning, I didn’t see a word about SpaceX successfully launching another crew headed for the ISS last night. I believe this was the 24th Falcon 9 launch this year. How quickly things become routine.Report
Did you read the bit about SpinLaunch?Report
Yeah. Let’s see ’em scale it. Parts of the US military won’t accept the lateral stress on the payload from SpaceX’s horizontal integration technique, and have required SpaceX to add a vertical integration (“stacking”) capability. What are the lateral stresses on the payload sitting out at the end of a centrifuge arm?Report
It’s certainly novel, but I’m wondering if it would be more practical as a satellite killer than a satellite launcher.Report
THTh2:
This fact is a good companion to Dennis’ essay, for anyone wondering how to reach the Trumpists. There is a shockingly high percentage of people who, when faced with a choice between a lifesaving vaccine and their political cult, choose the cult even to the point of death.
The idea that they will change their minds when presented with a calm reasoned set of facts needs to be retired.Report
My wife’s 102 Grandma didn’t take vaccine. She got Covid.
She lived, but almost died. Sounded like it was a coin flip.
I don’t hear the anti-vac arguments out of that branch of the family any more. Made believers out of them.
They’ll change their minds, but it will take a stupid amount of time and too many people will die.Report
For examples, one can view the subreddit, HermanCainAward. There is extreme cognitive dissonance on display by the worst of the worst.Report
https://www.reddit.com/r/HermanCainAward/Report
[ThTh4] Speaking of politicizing public health.
https://www.csis.org/blogs/smart-global-health/politics-hpv-vaccine-debateReport
That link is 10 years old. That vaccine is a lot more widespread and accepted now. The disease is greatly reduced.Report
Yes, and that’s all great. Maybe 10 years from now we’ll say the same about Covid and the Right will have a new vaccine to attack.Report