Much of science is performed through inference, with the readings on instruments, a flash of light in heavy water, or the results of parsing through terabytes of sensor data after a particle accelerator collision either backing up a proposed scenario or weakening its foundations.
In the case of so-called dark matter, this is even more relevant, as we are talking about a proposed form of matter whose most pertinent feature is that it doesn’t interact with anything else except through gravity. This is where the wiggling of a levitating magnet may be the key to detecting it.
In this experimental setup by Rice University and Dutch researchers at the Leiden Institute, a tiny permanent magnet the size of a grain of sand is levitated above a superconductor, surrounded by highly sensitive detectors that should be able to spot even minuscule movements. So far, they have collected a month’s worth of data, with no conclusive results yet.
Even if they don’t detect any ‘knocks’ on this tiny levitating magnet, it will still help refine existing models of what dark matter’s properties might be. For the next phase of this research, they’ll add more of these sensors, which will also make it easier to distinguish background noise from any unusual readings.
We’ve previously talked about [Vera Ruben]’s contributions to the hunt for dark matter and the mysteries that prompted the idea that it might exist.
Do you have a photo of her, or of Vera Rubens who is referred to above, to contribute?
i hope i live long enough to see a halfway decent explanation of some of cosmology’s mysteries. watching physicists chase the (imo) dead ends of dark matter / dark energy is discouraging. getting more and more esoteric in quantum mechanics without resolving any of its deeper questions is discouraging too. we’re past due for a genuine breakthrough imo
“we’re past due for a genuine breakthrough imo”
I don’t know why everyone thinks there’s no progress on this stuff. It’s incremental and slow, but it’s there. You’re not going to have a smoking gun “hey wow we found something totally unexpected.” The evidence is just going to build up slowly and steadily until it’s significant.
Directly detecting dark matter is one of those things that there’s no reason the Universe has to be nice to us. If you think it’s a dead end because we haven’t been able to do that, you don’t understand the amount of phase space you have to rule out.
But the amount of progress in mapping stuff and also galaxy formation simulations is quite large.
i said no breakthrough, you said but there’s progress. they’re refining the numbers in bad models. that’s not a breakthrough and, IMO it’s discouraging.
dark matter could turn out to be meaningful but imo (and in the face of a complete lack of evidence for dark matter) it’s no better than the cosmological constant. it’s just a fudge factor, not an explanation.
Yes, and I said there’s not going to be a breakthrough on this stuff. Not like you’re thinking. There are hints of indirect detection in lots of places, and if one of those is real, they’ll just build in significance until it’s more obvious.
In direct detection, the LZ collaboration just reported literally one observed event in a dark matter phase space – and obviously you’d look at that and say “it’s just one” but this is exactly what I mean – you’re always going to start with one when you’re scaling up.
“and in the face of a complete lack of evidence for dark matter”
This isn’t true! I don’t know why people think this is true. There’s no evidence for specific particle models of dark matter. But you can map the dark matter in galaxies and clusters, and the CMB/BBN/BAO evidence for “matter that doesn’t couple to electromagnetism” is overwhelming.
And it’s not like the idea of dark matter is nutso or something. Neutrinos would have been perfectly reasonable dark matter, it’s just that they’re not massive enough for what we know.
Science works through paradigm shifts. It’s common that scientists work for decades under one assumption and view all the evidence through that lens, especially the weak evidence or “hints”. Eventually enough discrepancies mount that they can’t explain them with the existing model, and a “breakthrough” happens.
Remember a hundred years ago: “Physics is solved, now we just got to work out the details…”
If you believe in whatever the present model is, you’ll interpret the evidence in favor. If you don’t, you interpret it against. It’s just that we have to test the paradigm until it breaks whether you believe in it or not – otherwise how would you know?
@Dude: That sort of reasoning is often used by people who can’t be bothered to find out that their ideas were already disproven within a few years of the current popular theory/theories being proposed if not before. People seem to have this idea that their ignorance is just as valuable as the collective research of generations of minds, and that no one has ever put any effort into trying to find a flaw in the current theories.
The current “model” for dark matter isn’t really a model. It’s the equivalent of a spherical cow. It’s not intended to be correct. It’s intended to be wrong so we can figure out, from what’s wrong, what’s really going on.
Except it just keeps working. The fact that there’s no actual more physical model just tells you the Universe isn’t making things easy.
No one “believes” in the current model. It’s not a physical model. It’s phenomenological.
People also have this idea that just because someone is spending tremendous amounts of money and effort on something, they’ll automatically validate whatever idea you have.
Dark matter is a kind of “god of the gaps” idea, which is the first one they came up with, and when they can’t think of anything better they fall back on that default – which isn’t saying it must be correct. It’s just this concept of some mystical “stuff” that has all sorts of weird and seemingly impossible properties, yet it conveniently explains all the observations at once IF you believe it exists as such.
It’s the best explanation we have, the only problem is that it isn’t explaining anything because all the things that might be dark matter are continuously being shot down as “not it”.
Sound familiar? It’s kinda like ether theories back in the late 19th century. It seemed to explain everything, yet the more they looked into it the more it became apparent that this stuff just does not exist, and then everyone was forced to accept that empty space has properties other than being empty.
Except what is “working”, what “dark matter” is, is just a re-statement of what’s missing: there’s lots of it, we can’t see it, and it doesn’t interact with anything else except through gravity.
There’s a problem, so the solution must be the shape of the problem. That’s obvious, but calling it “dark matter” isn’t really saying what the solution IS.
That’s literally the point!
It’s a phenomenological model. It’s not physical. It’s not real. No one thinks it’s real. It’s there to model the phenomena. Hence the name.
You use the model to set bounds on the unknown physics, and then find the places it doesn’t agree to determine what you don’t know.
The direct detection methods like this are entirely decoupled from the observations. None of the direct detection things have to work. It’s entirely possible it’s just not possible to observe it practically.
Pat – Dude managed to get you to put your finger on what i’m looking for :) “No one “believes” in the current model.” that’s the breakthrough i’m looking for, something to believe in.
Well, so far they’ve detected no hints for Dark Matter.
“Well, so far they’ve detected no hints for Dark Matter.”
Yes, they have. That’s literally what the model is. That’s what you’re doing when you map the gravity of a region and subtract out the luminous matter. That’s why we have maps of dark matter in areas. And “inferring” the existence of something isn’t anything new. You do the exact same thing in particle physics when you’re reconstructing invisible tracks from particles that don’t interact electromagnetically.
What we don’t have hints for is an interacting particle explanation for it. And there’s no reason to believe that they are going to be interacting.
The difficulty with dark matter is that physicists really, really hoped that the “WIMP miracle” was a hint, rather than a coincidence, and at this point it’s pretty obvious if it’s the latter. So we had literally decades where physicsts had convinced themselves that detection was going to be right around the corner.
But there’s no fundamental reason that dark matter has to have non-gravitatational interactions. There’s no reason to believe that the fundamental structure of the physics in the Universe is discoverable at planet-scale.
It could also be that there was nothing to find experimentally in the first place, but rather that a theory with strong support, was in fact partly erroneous and led the community onto false predictions. This is what would MOND theories would argue about. This has happened in the past (ether which actually did not exist, the discovery of Neptune: in which case it was the possibility of the existence of a new body was doubted, along with the validity of newtonian theories). Science doesn’t have a single path, but there is always one that is more strongly supported, and sometimes a system based on a tradition of strong evidence will be proven wrong by a case that tests its limits.
MOND is past a dead end at this point – Milgrom’s even basically said that his most recent models would still need dark matter, just… not as much. At which point you say “wtf is the point.”
Dark matter as a theory has been built up over decades not because it’s an idea that people like. It’s because it’s the only one that’s survived. Originally people thought it was just unaccounted for gas in galaxies. Didn’t work because you can measure gas other ways. Then there was a fight between particle dark matter and massive compact objects (like black holes or something), and searches for compact objects failed to the point where they couldn’t work at all.
And then the CMB results came, the BAO results came, lensing studies came, etc., and at this point we need massive things that interact with gravity but not light and baryons, but not neutrinos either, which can clump separately from normal matter and doesn’t self-interact strongly.
Whatever the answer turns out to be, it’s very likely going to look approximately like the basic “cold dark matter” right now, because the only other option is that there’s more than one thing explaining those observations, and that’s just more unlikely than a single explanation.
My pet weird theory is that dark matter is matter in a “parallel” universe, where parallel means it’s located here in three dimensions but separated by some distance along an extra dimension – so the matter can feel each other’s gravity but they don’t interact otherwise because they’re not occupying the same space.
Kinda like having two magnets on both sides of a table top. Move one and the other moves with.
Can’t be identical: we already know it has minimal self interactions. That’s the Bullet Cluster data – the dark matter passed right through itself and the regular matter collided and heated up.
A completely decoupled dark sector is what they’re testing here, except the only phase space that’s testable is very heavy particles.
nothing is a dead end until we can see the end. that’s the joy and the agony of not knowing, all sorts of whackadoodle things might turn out to be true. we don’t know what we’ll find when we unwrap that present. who knows, maybe dark matter will be convincing some day :)
“nothing is a dead end until we can see the end.”
The guy literally created the theory as an alternative to dark matter, and when evidence was presented that his theory wouldn’t work for, he then said well okay maybe there’s *some” dark matter but not as much.
Which makes it a dead end. He can go off and find a way to measure his weird fictitious different gravity and everyone else will look for the dark matter he still says is there.
I do understand that there’s not much difference to the Christian God.
Then you don’t understand.
Astronomers aren’t searching for dark matter. They know where it is. They can, and do, map it. It’s not the same everywhere. There are clumps and voids, some of which lines up where other matter does and some doesn’t. Broadly those distributions look like what you’d expect from a non-interacting ideal gas that’s relatively cool. They map it using gravity, which is exactly the same as inferring a particle’s existence by missing momentum, which is how it was done for years.
Studying dark matter on astrophysical scales is easy. Studying it on laboratory scales – that’s something else. The fact that physicists can’t see dark matter interactions yet says nothing about the astrophysical evidence, because they’re looking for physics beyond what astronomers see.
The dark matter interactions astronomers see are so minimal – on a lab scale – that it’s entirely possible there’s no practical way to study it. It’s possible. Nature doesn’t have to be kind.
This also isn’t any different than having to go to insane scales to study neutrinos, either. And if dark matter interacts even weaker than them (and gravity is that weak), you might need absurd scales to observe it.
How did it go in the Simpsons, when professor Frink made the particle accelerator that proved they need a bigger particle accelerator.
“… either backing up a proposed scenario or weakening its foundations …”
Yup. Perfectly captures the attitude of cosmologists seeking funding.
None of this falsifiability nonsense, thank you very much.
So you’re levitating a magnet with a strength able to overcome 1G of gravity AND keep the magnet from sliding off the superconductor. I foresee issues isolating potential atomic forces from the forces needed to keep the magnet levitating. Moving the base will cause a dampened movement in the magnet, so you should be able to determine and measure that correlation, but the scales are vastly different.
The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes.
Meitner was an earlier pioneer in nuclear fission, of which she should have shared the Nobel prize with Otto Hahn (as well as Fritz Strassmann). With her nephew Otto Frisch, their 1939 paper in Nature coin the term fission. Even earlier her experiments with Alpha particles led Ernest Rutherford to predict the nuclear atom. She also captured the first image of a positron, and her experimental data also suggested the existence of neutrinos.
I think her legacy is pretty solid.
Note that this was a response to another person’s comments, which appears to have been deleted and how just looks like some random point.
I’m not familiar with the details of this experiment, but I did work in superconductivity for awhile. It is very likely that the reason they are using a superconductor here is to levitate the magnet without any external currents via the Meissner effect. Thus, there would be no “noise” in the control algorithms. Still, the small size of the magnet will give this experiment a very low cross-section for detection, even with the high density of the material.
I’m curious how they rule out other external forces and magnetic fields.
They put an emdrive in the same chamber and make sure it produces no thrust
I think the obvious assumption would be that dark matter is something out in space and does not typically enter a terrestrial laboratory, but assumptions should be tested and verified anyway