Scientists make potential breakthrough in search for dark matter
https://www.reuters.com/science/scientists-make-potential-breakthrough-search-dark-matter-2026-09-01/61
u/philhellenephysicist 2d ago
In case anyone wants more context, here's the original article by Lawrence Berkeley Lab along with the LZ experiment website, which has slides from the TeV particle astrophysics talk in Japan and an (eventual) arXiv preprint.
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u/Tall-Link-8792 2d ago
ok but can we talk about how wild it is that we might be on the verge of solving one of the biggest mysteries in physics? like damn
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u/z0mb0rg 2d ago
Can we? Yes please. What is the implication if it is indeed a WIMP?
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u/danielravennest 2d ago
For the moment, nothing.
Galaxies act through gravity like they are about 6 times heavier than the light from stars and such can account for. Since the missing 5/6ths doesn't produce light, it got labeled "dark matter". Since the 1970's or so, scientists have been trying to figure out what dark matter is made of.
"Weakly interacting massive particles" (WIMPs) are one of the theories of what dark matter is made of. But with a single particle detection we can't tell if it is all the dark matter, or only some of it, and if the WIMPS come in one flavor or many.
The Xenon atom it bumped into may tell us which direction the particle came from (I haven't read the paper yet). With enough directional collisions, you can map out where the WIMPS are coming from. If that matches where we see dark matter from gravity effects, then it could explain all the dark matter. If the directions don't line up, then there is still more to figure out.
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u/OneRougeRogue 2d ago
But what are the physics implications, specifically? Like the Higgs Boson discovery made a bunch of theoretical physics models that relied on it suddenly valid, but what Theories rely on WIMPs in great numbers?
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u/Astrokiwi 1d ago
There's a bunch of ways to extend the Standard Model to put in WIMPs. Discovery of WIMPs in general won't narrow things down much, but isolating exactly what kind of WIMP this is (what its mass is etc) would pin us down to certain families of models, and give strong hints on what particles to look for next.
Currently we're in a bit of an awkward position because the Higgs Boson was a hole that was predicted to be filled. If the LHC had found nothing, that would have been interesting - our theories were wrong, and we need to make new theories without that hole. If the LHC had found the Higgs Boson and something else that would also have been interesting - our theories were right, but incomplete, and then we would have strong hints on where to go next. But instead they found only the Higgs Boson, which confirmed what we already thought, without giving any new clues on where to go next. So any new particle detection will help a lot in opening up where to progress.
But really it's more the other way around - it's more about confirming our models of cosmology, the evolution of the universe on large scales. Galaxy evolution simulations just give the wrong answer if they don't have dark matter in them, so you need to add dark matter (or something that behaves a lot like dark matter). Dark matter is nice and elegant. It's just another particle, so it follows known laws of particle dynamics; dark matter has mass and momentum and velocity and density, it flows around like anything else, even if it doesn't interact electromagnetically (which isn't unusual - neutrinos don't either). There's also all these natural ways to expand the standard model of particle physics which include a lot of WIMP dark matter candidates. Modifying gravity is a bit less convincing - extensions to General Relativity don't "naturally" solve dark matter, it feels like more of an arbitrary fudge factor and you don't have the same level of constraints; you're changing the laws of physics rather than adding something which obeys existing laws of physics (and therefore is more testable and predictable). There's also a good few arguments where simulations with modified gravity don't quite fit observations as well as WIMP dark matter does.
But the debate really can't be settled until we actually find some WIMPs. Even if cosmologists strongly lean towards WIMP dark matter over modified gravity, it's not unreasonable to lean towards modified gravity. It's an alternate theory, and probably less likely to be true, but it's not crackpot flat-earth climate change denial, and there is some reasonable room for debate until we really build a body of strong evidence.
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u/iamthewhatt 1d ago
That's the neat part, we don't know yet. Until we can tell for certain what Dark Matter is, we can't assume how it will affect our models besides some random guessing. And thus far I have yet to see anyone release any "potential" updates to any models based on any suggested findings. That's why this is so exciting
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u/honuworld 3h ago
You forgot the part about objects behaving oddly even WITH dark matter factored in so they invented dark ”energy”. But objects STILL acted weirdly so they decided that dark energy CHANGES in ways we don’t know, can’t see and can’t measure. In other words, we have no fucking idea.
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u/danielravennest 32m ago
I didn't forget about dark energy. It is simply a different subject than the original news article in the post.
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u/Tall-Link-8792 1d ago
Right?! If it's a WIMP, that basically means we've finally caught a particle that only interacts through gravity and the weak force. It would confirm a huge chunk of our dark matter models and completely change how we understand the universe's structure. It's like finding a ghost that we knew was there but could never touch.
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u/just4nothing 1h ago
The weak force being the interesting part - which means we can potentially produce it in colliders (in ways other than via the Higgs). If more events are found in the remaining, recorded data, we are for sure going to intensify the searches at ATLAS and CMS
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u/murderedbyaname 2d ago
The facility has tours if you're ever in the area, Lead SD, by Deadwood.
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u/bjohnsonarch 2d ago
I actually helped repair some of the brick headframe buildings that house the lifts that go down to the detectors. It’s an incredible facility for sure
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u/just4nothing 1h ago
Going down in the elevator is certainly an experience. Dark, wet, with water running down the shaft.
Then you step up into the lab and - you could be anywhere.
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u/MaximumZer0 2d ago
So...if there is a weakly interacting massive particle that is also a light object, does that make it a...
WIMP LO?
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u/suitcasedreaming 2d ago
We must apologize for Wimp Lo. We have purposely trained him wrong, as a joke.
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u/syngyne 2d ago
I’m decaying!
Making me the victor.
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u/DrInsano 1d ago
I'm sure that's very impressive on whatever planet you come from, but there's only one problem: this is Earth.
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u/platypodus 2d ago
Detectors are fascinating. In these types of, say, passive detectors, what does the staff do all day? It seems like a boring profession, once the device is built and set up properly.
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u/Drawemazing 2d ago
There are plenty of backgrounds in these detectors, from neutrinos to background radioactivity to cosmic muons. The detector/collaboration in question, LZ, publishes fairly often. here is a link to their list of recent publications, mostly focused on radioactivity of xenon, neutrino/muon/dark matter measurements, and detector development. Basically there is enough work to go around, dont worry.
Also these are never "done", they'll do data taking periods, and design upgrades while taking data. Then when the data taking period is over they'll shut it down and upgrade it, rinse and repeat.
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u/platypodus 2d ago
I see! Thank you.
In my mind I always envisioned them as big traps, that mostly sit around until they get triggered. (Or like the radio dishes that sit there "waiting for signals").
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u/mfb- 2d ago
Most of the work is in data analysis (in a broad sense), which can be done remotely, but there is a crew on-site to run the experiment. You have a lot of hardware that needs to be watched and fixed sometimes. The experiment regularly injects different radioactive elements for calibration which then need to be removed again. And so on.
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u/DarkMatterDetective 2d ago
This is a fun question! These detectors are incredibly complicated one-of-one machines with thousands of sensors. The detector needs to be monitored around the clock to make sure nothing has become unstable. The system itself is not just a sealed vat of xenon; all 10 tons of xenon in it need to be recirculated by large circulation pumps which also need to be extremely leak tight. It's basically a small factory's worth of high vacuum and cryogenic systems which no one has ever built before in such a configuration. Therefore, there are plenty of small problems that creep up, maintenance tasks, etc. Meanwhile the electronics systems are constantly recording events (most of them background), which are sent out for processing. Those systems need their own dedicated team to keep watch over them and conduct repairs when components fail.
You might be interested in leafing through the nearly 400-page technical design report to see how many subsystems there are and how they fit together: https://arxiv.org/abs/1703.09144
From there, you can probably imagine that many of these need ongoing maintenance.
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u/just4nothing 1h ago
oh, boy, let me tell you: Software, simulations, operations (making sure it runs correctly), managing data, fixing things when they break, running calibrations (e.g. by adding a known source) - the list goes on.
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u/AdSmart6151 2d ago
"When we observe galaxies and clusters of galaxies, we see that they behave as though they contain much more mass than the matter we can see. So although we cannot see dark matter itself, we can observe what its gravity does,"
I'm not an expert so excuse the ignorance, but how sure are we that our models on gravity and the behaviour of galaxies aren't wrong? As far as I can tell from googling, it seems that we assume that dark matter exists because it explains certain observations that don't match our expectations 9f how the cosmos works. Doesn't that just mean that our models and expectations might be wrong?
Edit: also, is their behaviour of gravity on earth that doesn't match our expectations, meaning Earth is more massive than we previously assumed because of dark matter?
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u/EndoExo 2d ago
Don't make me tap the comic.
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u/geekgirl114 2d ago
Of course there is an xkcd about it
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u/AdSmart6151 2d ago
Made me laugh, I'll stay in my own lane next time LOL
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u/haseks_adductor 2d ago
no but literally everyone has that thought at some point haha
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u/spookydookie 2d ago
And there are other areas of active research around other calculations/constants being wrong besides just gravity. Not necessarily to explain the motion of galaxies, but to explain some of the weird things coming out of James Webb. Like the way we measure the size and distance of things being flawed, or the Hubble constant or cosmological constants not actually being constant.
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u/snoo-boop 2d ago
There have been a bunch of papers trying to figure out if parameters like G and c and a lot of other "constants" are actually constant. So far, every attempt ends up with error bars that include the current best-known values.
I don't recall any JWST observations that have changed this situation. Yes, it seems that it has observed things developing earlier than we thought, but that doesn't mean that "constants" aren't constant.
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u/spookydookie 2d ago edited 2d ago
I'm an idiot, I'm not proclaiming that anything is true. All I said is that there are people researching those things. They're probably bs, but they're researching them. That's all. Didn't mean to start a fight.
One explanation would be that we aren't measuring the furthest things in the universe correctly. Why do they exist? Nobody knows. If you have the answer, a Nobel is waiting for you. ;)
Now I'm kinda starting a fight, but I'm really just poking fun.
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u/Ill_Stop_ 2d ago
Having thoughts like that is essential to the growth of knowledge and advancement of science. Without thoughts like that, we’d still think the Sun revolves around the Earth, and such.
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u/DanielCraigsAnus 2d ago
Wait....I'm not the center of the universe?
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u/LevelSevenLaserLotus 1d ago
Well depending on how your perspective of infinity works, technically anywhere could be validly marked as the center, as each point has the same infinite distance from the "edge". Which means... you are the center. So am I, but you too.
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u/WhatsTheHoldup 2d ago
Appreciate the humility but those are the exact right questions to ask! Next time ask another great question and any scientist worth their salt will be hyped you're actually curious and asking this stuff.
People study science because we wanna learn how things work, that curiosity exists at the frontiers of science sure, but it's sustained by the curiosity of laymans such as yourself.
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u/askingforafakefriend 2d ago
I got one. The Big bang... birth of a black hole with all the matter energy whatever blowing into other spatial dimensions.
Not a physicist, just an idiot. Obviously.
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u/WhatsTheHoldup 2d ago
I believe you're describing a subfield of a theory known as a "holographic universe".
My professor made some contributions to the field!
We describe a braneworld description of cosmology with both 4d induced and 5d bulk gravity (otherwise known as Dvali-Gabadadze-Porati, or DGP model), which exhibits this feature: The universe emerges as a spherical 3-brane out of the formation of a 5d Schwarzschild black hole. In particular, we show that a pressure singularity of the holographic fluid, discovered earlier, happens inside the white hole horizon, and thus need not be real or imply any pathology. Furthermore, we outline a novel mechanism through which any thermal atmosphere for the brane, with comoving temperature of 20% of the 5D Planck mass can induce scale-invariant primordial curvature perturbations on the brane, circumventing the need for a separate process (such as cosmic inflation) to explain current cosmological observations. Finally, we note that 5D space-time is asymptotically flat, and thus potentially allows an S-matrix or (after minor modifications) AdS/CFT description of the cosmological big bang.
https://arxiv.org/abs/1309.1487
Imagine navigating the surface of a sphere. It has latitude and longitude but no depth. This is kinda similar to the event horizon of a black hole, when studying these event horizons it can be found that entropy/contained information seems to scale with the 2D surface area as opposed to 3D volume.
Now if you can, project that to a higher dimension. Imagine our 3D universe as a shell around a higher dimensional black hole.
You could see if it leads to testable predictions we could verify/disprove.
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u/devAcc123 2d ago
This was the absolute perfect comment to run into right after hitting the ol weed pen and turning the light off before bed
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u/BitterTyke 2d ago
yeah, i can read the words but their meaning remains uncertain.
On the other hand I can lift heavy things.
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u/sceadwian 2d ago
The professionals have been seriously trying to poke holes in this one for yyeeaarrss. They simply can't close the possibilities.
There has to be something outside of known physics going on it's just very subtle and could be in several different places all while inconveniently being very hard to observe except the unavoidable gravity signals.
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u/snoo-boop 2d ago
Appreciate the positive reply! Next time, you might choose to be more careful with "it seems that we assume" ... because we aren't.
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u/DrMonkeyLove 2d ago
To be fair, Galileo and Copernicus kinda thought the same way in their time, so...
I think there is an important distinction between the two questions "does gravity work differently at large scales?" and "is the current model wrong?" Those are different questions. The answer to the second one, historically has been, "almost certainly".
Newton's theory of gravity worked well for a while until new observations were made that required relativity to explain. It seems likely that there is potentially more beyond even relativity needed to explain gravity given our new observations, right?
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u/BitterTyke 2d ago
heres a good one for you then:
do gravity waves behave like sounds waves? IE do some reinforce and amplify whilst some reduce or cancel - could the reinforcement be responsible for the other 5/6ths effects?
discuss,
(as there are lagrange points I do think gravity could behave like sound waves)
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u/as_a_fake 2d ago
The fact that this exists and is being used in reply to exactly what it's talking about is amazing.
Other "relevant XKCD" moments aren't usually this specific lol
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u/Uzofugs2112 2d ago
I remember, in my sophomore year of undergrad physics, running whatever iteration of MONDs I’d theorized past one of my professors who was a cosmologist.
She just sort of smiled and laughed and congratulated me on the milestone.
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u/snoo-boop 2d ago
Ha ha, yeah, hopefully next time you'll notice that dark matter was observed close enough 100 years ago such that MOND couldn't possibly explain all of the dark matter data.
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u/msx 1d ago
Now i'm nobody, but i see there are scientists exploring alternative explanations and models that don't require dark matter, and they're no farther from confirming their theory then the dark matter supporters (albeith i recognize they're the vast majority).
Also, in the past there were many cases of scientists introducing some hypotetical substance to explain a phenomenon, to invariably get disproved. See phlogiston, caloric, luminiferous aether, miasma etc.
So i'm a bit skeptical (but ready to accept eventual evidences like this one when confirmed)
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u/DanielNoWrite 1d ago
There is always somebody researching radical alternatives to mainstream theory. And that's a great thing, but it doesn’t mean the mainstream theory is weak.
The fact is they are further from explaining their theories, because most scientists do not beleieve the alternatives fit all of the available evidence.
Scientists have examined the evidence from many different angles, and it only seems to make sense if dark matter is a real physical thing.
Somebody may eventually prove that wrong, but this is not an instance of scientists jumping the gun or inventing new matter as a convenience, it's simply all that fits.
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u/Bensemus 1d ago
They are further than lambda CDM. There’s a reason that’s the main leading theory. It has the most evidence supporting it and fits our observations the best.
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u/nicuramar 2d ago
Dark matter is the simplest explanation, but just go read about it on Wikipedia. The behavior of gravity on earth does match expectations.
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u/Blahkbustuh 2d ago
I used to be skeptical too, but there are things that really stood out to me that align with dark matter:
The first is that stars in a galaxy orbit around the center like a wheel turning rather than like the planets in the solar system where the inner ones orbit much much faster than the outer ones. The 'rotating like a wheel' means there's a lot more gravitational mass and it is distributed in a disperse and far out way rather than being the visible stuff or a giant black hole in the center.
We can measure the mass of galaxies by how they distort light around them of objects far behind them. Gravitational lensing is common and they can back out the mass of the closer object from it. They can tell how much and where the mass is that is doing the lensing and this lines up with what we know about dark matter.
Scientists have found a small number of galaxies that appear to have no dark matter. They've also found galaxies that have collided where the two regions of mass kept on trucking through (didn't collide) but the visible stuff got smashed up and left at the collision point.
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u/marvinsface 2d ago
> They've also found galaxies that have collided where the two regions of mass kept on trucking through (didn't collide) but the visible stuff got smashed up and left at the collision point.
That’s wild. The mystery stuff imparts gravity, so it has mass, but when blobs of it are set to collide it acts like nothing is there and just carries on? Like it’s just pure gravity without the mass?
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u/MozeeToby 2d ago
Mass yes, interactions no. That's what WIMP means: weakly interacting (so they don't bump off each other or anything else) massive (still have mass though) particles.
The weakly interacting part also makes them very hard to detect, hence the excitement of a possible detection. They are also only one proposed explanation for dark matter so detecting them can really answer some open questions.
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u/SenorTron 2d ago
Disclaimer: not a scientist, this is all based on reading other people's explanations of this over the years.
Well it has mass, however that doesn't mean it has to physically interact with other things.
As an example, think of Neutrinos. They mostly pass through the matter we are familiar with as if it isn't there, only very very rarely colliding. However they still have mass.
Maybe Dark Matter is made of a particle type (or multiple particle types) that don't interact at all other than with gravity. Or maybe, if we're lucky it does interact but just incredibly rarely. Maybe as rarely compared to a neutrino as neutrinos do to us. In that scenario it would be incredibly tricky to detect, but not necessarily impossible, and maybe we can find ways to do so.
That type of rarely interacting particle is referred to as a Weakly Interacting Massive Particle, or WIMP, and it's the type of thing that the experiment in the OP is designed to try and detect.
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u/chipstastegood 2d ago
Why are neutrinos not what dark matter is?
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u/Flatulant_Tapir 2d ago
They are too lightweight, meaning they will move to fast to behave the way dark matter would have to to explain the data. It's called the cdm theory as in cold dark matter with the particles moving much slower than the speed of light. A we can detect them and the amount they have is not enough to be the dark matter
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u/cjameshuff 1d ago
Well, they literally are a type of dark matter, which makes the argument by incredulity against dark matter particularly dumb...they are a direct, known counterexample. The types of neutrino that we have detected are too light/fast moving to account for any significant fraction of dark matter (they would escape galaxies instead of forming halos), but the Standard Model suggests that "sterile neutrinos" might exist that would be candidates.
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u/Bensemus 1d ago
They are hot dark matter. They don’t have the right properties to explain the cold dark matter scientists are searching for. There also just isn’t enough of them. We know of neutrinos and can detect them.
WIMP are the leading candidate. They are a particle with a fuck ton of mass but they only interact via gravity and the weak nuclear force. Like neutrinos this makes them extremely hard to detect. Neutrino detectors are massive tanks of water usually with like thousands of tons. Every now and then a neutrino interacts with a molecule and this creates a photon that is then picked up by the detectors that surround the tank.
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u/chipstastegood 1d ago
Follow up question - if we can detect hot dark matter like neutrinos which have very little mass, why can’t we detect cold dark matter which have a lot more mass? One would think that more mass means it is easier to detect?
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u/Vanacan 1d ago
If they do exist, we have been detecting them for a while through their mass. That’s why we have thoughts about them possibly existing.
This experiment is to try and get corroborative evidence to prove that they exist physically, through interactions that aren’t just gravitationally.
(Using XKCD as my source here so forgive me if I’m wrong,) To put some numbers into perspective, for the amount of dark matter we think is in the solar system, if it were uniformly distributed, there would be the equivalent to a single squirrel’s mass of dark matter on the earth. The fact that theres even a possible detection is pretty wild.
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u/Fractal_Soul 1d ago
When normal matter "bumps into" other normal matter, it's generally the electrons of one repelling the electrons of the other. Dark matter doesn't interact via electro-magnetism, so the particles(?) just skate right past each other.
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u/marvinsface 1d ago
That’s interesting. Would the dark matter particles have their equivalent of “electrons”, like dark electrons? Electrons have mass right? If so, and if the dark electrons have mass, what stops these particles from bumping into each other? Or like you said, maybe it’s the charge traits that do the repelling, and since I think I heard atoms are mostly empty space, I guess there’s enough empty space inside the normal mass and dark mass such that it all could “collide” without actually touching? Talking out of my ass as a layman who’s just fascinated by the topic, pls excuse anything ignorant
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u/Bensemus 1d ago
No. Atoms have electrons. Particles don’t. Neutrinos are a known type of dark matter. They interact via gravity and the weak nuclear force. We have detectors that detect the weak interactions.
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u/cjameshuff 2d ago
Scientists have found a small number of galaxies that appear to have no dark matter.
Also some that appear to be almost entirely dark matter. Candidate Dark Galaxy 2 appears to be four globular clusters orbiting within a dark matter halo that contains little or no other stars.
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u/zeperf 2d ago
Have we observed small areas of space where there is gravitational lensing without standard matter being present? To say it inversely, can't we essentially just observe concentrated volumes of space that must contain blobs of dark matter?
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u/Dry_Button_3552 2d ago edited 2d ago
Yes we have actually, the Bullet Cluster is the premium example of this
https://en.wikipedia.org/wiki/Bullet_Cluster
The major components of the cluster pair—stars, gas and the putative dark matter—behave differently during collision, allowing them to be studied separately. The stars of the galaxies, observable in visible light, were not greatly affected by the collision, and most passed right through, gravitationally slowed but not otherwise altered. The hot gas of the two colliding components, seen in X-rays, represents most of the baryonic, or "ordinary", matter in the cluster pair. The gases of the intracluster medium interact electromagnetically, causing the gases of both clusters to slow much more than the stars. The third component, the dark matter, was detected indirectly by the gravitational lensing of background objects, as calculated using the best available theory of gravity in general relativity. This provides support for the idea that most of the gravitation in the cluster pair is in the form of two regions of collisionless dark matter, which bypassed the gas regions during the collision.
Modified gravity theories can't adequately explain not just this cluster, but other similar clusters that have also since been found. In fact, one of the original proponents of MOND (MOdified Newtonian Dynamics), said that the results of studying the Bullet cluster could be explained by matter that's there but we can't see. In his case he says it would be "cold, dense hydrogen clouds" instead of "dark matter".
At any rate, this isn't the only observational evidence that modified gravity theories have to account for, and the problem is that while modified gravity theories can be used to explain most or all the observational evidence, no single modified gravity theory can explain all of them simultaneously; it ends up being "well this theory for that observation, an this other theory for this other observation", etc.
Which is where Dark matter comes in. It's not a perfect solution to EVERY observation, but so far it's the main one that checks the most boxes.
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u/Blahkbustuh 2d ago
Here's the Bullet Cluster. It's two galaxies that had a head-on collision.
Look at the pictures in that article. In this one, the red/pink is normal matter (the visible stuff) that is glowing in X-rays because of all the collisions and compression from the galaxies colliding.
The blue is calculating where the mass is located based on the gravitational lensing of farther away stuff behind this galaxy. That is to say, the blue areas are where the mass of the dark matter is.
This means the dark matter of each galaxy passed through the other and just kept on going--because it doesn't collide with anything--it can only tug on things through gravity. The visible, regular matter of the galaxies can't pass through each other and so collided and the gases and dust between the stars got compressed and became hot enough to glow in X-rays and the collisions slowed it down so that the plumes of regular matter slowed down while the dark matter which didn't collide more or less kept on going leaving the regular matter behind.
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u/AdSmart6151 2d ago
I used to be skeptical too
Nice way to phrase it like you're about to start sharing the Gospel XD
But that's pretty interesting, especially the last part that there's some galaxies that defy our expectations about gravity, yet not all. So there is definitely something out there influencing gravity that isn't affecting all galaxies but only a part of them, it's not just our models being wrong. Good to know :)
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u/Blahkbustuh 2d ago
Here, found it--for the colliding galaxies. I wrote my comment quickly.
I was skeptical because it would make more sense to me that we've only worked with gravity on 'small' scales and there could be some part of gravity we're missing that only becomes a factor at huge distances before there needing to be stuff that only interacts with gravity we haven't otherwise detected, but the evidence like what I linked points in the direction of the later explanation--dark matter that only interacts via gravity, it doesn't interact with the other forces so it can't emit energy and "collapse" into denser objects like how matter forms planets, stars, and black holes. Dark matter particles are forever stuck as a cloud moving around the center of gravity.
What you wrote isn't how it would be. Dark matter doesn't influence gravity, it's stuff that is largely invisible to us but interacts with visible matter through regular gravity, and this only shows up at the scale of galaxies. The mass of galaxies is like 5/6 dark matter and that's pretty consistent except for a small number of weird galaxies. Even our own galaxy by mass is mostly dark matter arranged as a big spherical cloud and the visible galaxy is only a small disk in the middle.
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u/cjameshuff 2d ago
especially the last part that there's some galaxies that defy our expectations about gravity, yet not all. So there is definitely something out there influencing gravity that isn't affecting all galaxies but only a part of them, it's not just our models being wrong. Good to know :)
More that it's a lot easier to explain the outliers as having different amounts of dark matter (especially since the differences from normal matter mean there's plenty of ways to separate the two) than it is to justify having different laws of gravity for each galaxy.
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u/smokefoot8 2d ago
Our theory of gravity is General Relativity, and it has been so successful that it is hard to modify it without messing up all the successful predictions it has.
Dark matter is diffuse enough that it doesn’t modify Earth’s mass - I’ve seen estimates that about a gram is inside Earth at any one time. That also means that it doesn’t impact the orbits of the planets noticeably. It is only at the scale of the galaxy where the combined mass of the dark matter filling what looks like empty space has enough cumulative impact to be noticeable
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u/hdufort 2d ago
There has been a lot of proposals to "fix" the measurements, for example the MOND family of gravity models.
One thing for sure, the way we measure galactic rotation is accurate. More accurate than other things we measure in the observable universe. We calculate the difference in redshift/blueshift in stars on both sides of the galaxy (this works better for galaxies that we observe from the side, obviously).
So this is one of the very few things in the universe were we can't really care doubt over the methodology, measurements and calculated values. But... this calculation also depends on how we estimate the diameter of a galaxy. See below.
So where do we go from there? The galaxies are spinning way faster than they should, the further we move away from their center.
Maybe our theory of gravity is wrong in some situations. But why? If an extension if gravity is needed, we need to justify it. Nov just patch the formula with arbitrary parameters until it fits the model.
Maybe there is hidden matter causing the increase in rotation. Why is this special invisible matter only present at the outer edge of galaxies? Why is this excess matter not obscuring the view? Why isn't it falling or migrating inwards?
Why are some galaxies more impacted than others? The discrepancies aren't uniform.
If another of our measurements is wrong, maybe our sizing of galaxies is wrong. There are issues in how we calculate distances in space. If a galaxy is 2x closer than we thought, then it's 2x smaller than we thought. Then our calculation of rotation speed will also be wrong. Could it be a factor?
Some have suggested there is some kind of "ether" in space. It would slow down stars, not make them go faster.
Some have suggested that a quantum gravity model would round up small values (quanta equivalent), causing a stronger than expected pull in low density regions. Maybe.
So many possibilities and open questions.
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u/reasonably_plausible 2d ago
Doesn't that just mean that our models and expectations might be wrong?
This is essentially where everyone first lands on the topic, because mentally is just feels more elegant. There's also plenty of scientists who have worked on different models of gravity to try to account for the observations that have been made.
The problem is that nothing we have come up with has ever explained the various experimental data that we have accumulated better than the existence of matter that doesn't interact with electromagnetic radiation. If you want to modify gravity over a large scale, you have to also explain why different galaxies show different levels of discrepancy between their visible mass and the gravitational adjustment necessary. Eventually, all alternate theories end up needing to implement fudge factors themselves accounting for something that is out there interacting gravitationally.
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u/DrMonkeyLove 2d ago
To be fair, our current models are what, about 80 or 90 years old, and every model prior to these have been wrong. I can see why someone could assume the current models are wrong too.
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u/Brainth 2d ago
Models aren’t wrong, but incomplete. A model is a framework that can be used to predict the behavior of nature around us. If something contradicts the model, we say it’s outside of its scope.
Newtonian physics works great for everyday stuff, for example. It’s not wrong just because it doesn’t accurately predict the orbit or Mercury.
It sounds meaningless, but models aren’t supposed to be the way nature actually works, only predict it. If we were to map nature to a model one-to-one, it would likely be a model as complex as the universe itself.
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u/BountyBob 2d ago
If we were to map nature to a model one-to-one, it would likely be a model as complex as the universe itself.
I remember a video where someone confidently claimed that they 100% knew there is a theory of everything. The rest of the guests seemed surprised in this confidence. They further explained that the problem is that it might not be a simple theory but could end up being what you said and might be a theory we can never calculate.
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u/DrMonkeyLove 2d ago
So are you saying Ptolemy's celestial spheres model was just incomplete? It's just semantics. Models can absolutely be wrong.
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u/I_Love_That_Pizza 2d ago
It is possible. That line of thought is often referred to as Modified Newtonian Dynamics, or MONDO for short. The gist is, as I understand it, "maybe gravity words very differently over large distances."
But we have no evidence of this, except the models of galactic behaviours. We can't say for certain that it's not the culprit, but we know that on smaller scales, the effects of gravity are well understood.
Dark matter, as in literal matter we can't see, is one possible explanation for the so-called "dark matter problem," and MONDO is another. Dark Energy has the same naming trouble, where really it's the "dark energy problem," for which perhaps the answer is literal energy we can't see.
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u/Woodtoad 2d ago
Where does the last “O” comes from? Or is it there just to make it sound cooler?
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u/Uzofugs2112 2d ago edited 2d ago
It’s a dark O that needs to be added modified Newtonian dynamics models to help them fit the data. We aren’t entirely sure what it is but can theorize its existence comfortably.
It might be “organism” and maybe big invisible creatures actually tug gently on things far away from one another.
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u/Desperate-Lab9738 2d ago
We've also observed galaxies that don't seem to have dark matter at all, which makes mond unlikely since you wouldn't expect to see those with mond
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u/opisska 2d ago
No, the point is that if you measure gravity at Earth and extrapolate to galaxies, ot doesn't work with the visible matter. There is no darl matter component to Earth, because the (presumed) dark matter is.moreorless evenly spread in galaxies. If there was dark matter in everything, we would just now it as "normal gravity" and wouldn't see a problem.
That having said, the discrepancy in gravity for galaxies can also be explained by changes in properties of gravity on very, very large scales - because the galaxies are just so much bigger than the Earth or Solar System so if the extrapolation is just a tinsy bit wrong, then it would have the observed effect. Some observations (weak lensing etc...) are very hard to explain without dark matter though. But to be fair, the current mainstream cosmology with dark matter also has some pretty big discrepancies when conpared to real world. More people believe dark matter than modified gravity, but it's not settled. Well unless they actually found the WIMPs!!!
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u/throwawaygoawaynz 2d ago
They have found some galaxies that appear to rotate according to their visible light mass, indicating they might not have dark matter, and thus putting a lot more doubt over gravity modification theories.
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u/Bensemus 1d ago
No. We’ve found galaxies with no dark matter to galaxies that are almost entirely dark matter. We’ve also found galaxy collisions where the visible matter is all clumped together but there are tow galaxy mass things on either side like the dark matter just kept on going.
This is why other theories haven’t gained much traction. They can explain one type but are then even worse at explaining the rest.
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u/opisska 1d ago
At the same time, lambda-CDM cosmology continues to fail to produce the current universe in large-scale simulations, with the typical issue being a vast overproduction of dwarf galaxies that are nowhere to be found around us. The fact is that both theories have pretty large issues and the MOND people can list thebissues with dark matter for hours (believe me, it's hard to stop them). DM is currently much more popular and I think the examples you listed are quite helping that, but a significant part is just herd mentality. In my opinion, the tribalism here is pretty harmful to actual science - it also leads to DM being routinely presented as far more settled than it really is.
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u/Axentoke 2d ago
I think it was Sean Carroll who made the point that even if you introduce some kind of effect that makes gravity behave differently at large scales, it needs to have some kind of particle to mediate it…and since it would be an unknown particle, you’re just back to a different kind of dark matter.
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u/PinkynotClyde 2d ago
Dark matter isn’t being labeled something specific. It would mean that we can’t see it because light isn’t interacting in a way that allows us to.
So, technically we use light to give us a story in the first place. Not meeting expectations of how the cosmos work with gravity, I think that’s what you’re saying, but you’re instead heading in the direction of questioning the story light is giving us.
Dark matter is saying we don’t understand why light doesn’t interact with this matter, and looking for more in the universe than what light can directly explain.
So people hypothesize different things. Like what if it’s tiny black holes that light falls into but the effect is too small for our instruments to detect, yet there’s so many that formed long ago seperate from the star method, and they circle each other without merging too much. If lensing happens maybe it just cancels out mostly by the end, since light takes all paths and the black holes are so small. I just made that up but it’s fun to think about.
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u/LitLitten 2d ago
think less “it’s specifically dark matter” and more “it’s dark matter because we don’t know what x additional mass is, so this is the closest recognizable placeholder for that lack of clarity”
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u/Paratwa 2d ago
There has been theories for that, that gravity eventually becomes repulsive instead of pulling, though I’m not sure how the heck that was supposed to solve anything. :) I’m sure whoever babbled about it was far smarter than me though.
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u/SenorTron 2d ago
The problem with that type of explanation is that the effects we see aren't consistent in different galaxies.
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u/Uninvalidated 2d ago edited 1d ago
Doesn't that just mean that our models and expectations might be wrong?
They might very well be. As they've been many times before. I mean, we got stuff like the cosmological principle which were based on the lack of observations. Hubble and JWST has knocked some massive holes in that theory but still it isn't discarded (the inventors of the theory has said it's dead a long time ago though) In this field we tend to stick to old models even when they are outdated due to lack of replacement theories. In the case of dark matter we simply don't have an answer that works with out observations, hence something was invented to fill the gap, just as inflation filled a gap in the big bang theory even though there isn't any evidence for it. Neither is this detection on its own evidence. As we say in my country directly translated to English, one occurrence is no occurrence. We need to see a lot more of these detections and we have to rule out it's not cosmic rays, radioactive decay or something else as well.
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u/PicardovaKosa 2d ago
We are not sure of anything. There are multiple explanations for every problem currently in physics.
The point is you start with the most probable and most testable hypothesis.
You cant really test on earth modified gravity, but you can search for dark matter so you do that.
Hypothesis and models are only as good as they are testable. Famous example is string theory, a model that is amazing mathematically, but completely untestable so basically useless.
Most models that would explain our observations of galaxies are either introducing more problems or are untestable.
Plus, suggesting a new particle is responsible for something is a very popular and easy way to explain the unexplained. Also, its very testable so popular for publication.
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u/junktrunk909 2d ago
I'm not understanding why we would consider any particle that interacts with regular matter like xenon to be dark matter. I thought the whole definition of dark matter is that it's matter that has no interactions with regular matter other than through gravity. This article says they think this particle may be WIMP but doesn't help explain what that really is, why it's a candidate for dark matter, etc. I'm left less informed than I was before reading this article.
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u/lemmingsnake 2d ago
WIMP stands for "weakly interacting massive particle", weak in this context meaning the weak force. That means a particle that has mass (and so interacts gravitationally) and interacts via the weak force, but not the electromagnetic force--so no light.
Neutrinos fit the bill here, but for other reasons (too hot mostly, also not enough of them) aren't a good dark matter candidate otherwise. Neutrinos are detected in the same way, since they have a weak force interaction they can collide with the nucleus of an atom, which we can observe the effects of in these detectors.
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u/junktrunk909 2d ago
Interesting. So my understanding of the definition of dark matter was wrong. It's not that there are no interactions other than gravity, but rather there's no interactions other than gravity and weak force?
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u/lemmingsnake 2d ago
It's more "no EM interactions", since we can't see it when we look where it should be (galaxy halos). It doesn't have to have a weak interaction and some proposals don't (like sterile neutrinos), but those are basically impossible to build a detector for, so best we can do is look for the options we might be able to see.
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u/esituism 2d ago
The only way we know how to interact with / observe it currently is through gravity. It doesn't seem to exist on or interact with the electromagnetic spectrum at all - which is odd because as far as we can tell all other matter does.
By interact with, everything with matter we seem to be able to bounce or otherwise observe light / radio / X-ray / infra / other waves coming off it - thus making it interact with our EM spectrum.
We can't seem to 'hit' DM with anything, but we can tell it's there because of the effects of its gravity on the stuff around it.
Whether or not all of that is caused by dark matter being a wimp is yet to be seen.
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u/Uninvalidated 2d ago
So my understanding of the definition of dark matter was wrong
There's so many dark matter theories and papers written on the subject everyone is getting fed up hearing about it to be honest.
You're not wrong. You're not right either. It all depend on who you ask and which dark matter theory they're in favour of. Some of the theories require several types of dark matter even.
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u/rocketsocks 2d ago
Weakly interacting doesn't mean non-interacting. It just means it reacts with gravity and some other weak force, which could be the weak-nuclear force (as is the case with neutrinos) or perhaps a force which is currently unknown (to be expected if its a very weak force).
And, actually, the most important aspect of dark matter interactions is that they interact wiht themselves only extremely weakly. Most of the time dark matter particles are looping around a galaxy on big eccentric orbital paths and they are never passing through anything of substance at all.
However, there are plenty of dark matter candidate theoretical particles that would react through already known forces, just not very much.
We already know of one whole family of weakly interacting particles in the form of neutrinos. Every day septillions (trillions of trillions) of neutrinos from the Sun and elsewhere stream through the various neutrino detectors on Earth, and of all of those only a few hundred undergo a reaction with matter that allows them to be detected. The odds of a dark matter particle interaction are far, far lower than that.
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u/NOS4NANOL1FE 1d ago
What kind of breakthroughs or scifi tech can come from doscovering dark matter?
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u/BonzoTheBoss 2d ago
"Potential breakthrough" = "potential not breakthrough"
Boy I hate journalists sometimes.
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u/Fuzzy_Paul 2d ago
So anxious to find it that any unknown reading points towards it. Let's relax and wait for more confirmation before the shout out.
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u/Decronym 2d ago edited 28m ago
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| JWST | James Webb infra-red Space Telescope |
| LIGO | Laser Interferometer Gravitational-wave Observatory |
| LZ | Landing Zone |
| Jargon | Definition |
|---|---|
| cryogenic | Very low temperature fluid; materials that would be gaseous at room temperature/pressure |
| (In re: rocket fuel) Often synonymous with hydrolox | |
| hydrolox | Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer |
Decronym is now also available on Lemmy! Requests for support and new installations should be directed to the Contact address below.
4 acronyms in this thread; the most compressed thread commented on today has 6 acronyms.
[Thread #12666 for this sub, first seen 2nd Sep 2026, 04:47]
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u/WaffleBlues 2d ago
"potential breakthrough" is the same as saying "maybe a breakthrough" which is close enough to "maybe not a breakthrough"....
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u/rocketsocks 2d ago
Yes and? If you can't stand the "maybes" stay away from science. Most of the time most of science lives in maybe land.
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u/betacarotentoo 1d ago
Yeah, once a month, a breakthrough in the search for dark matter, a concept invented for some calculations to make sense.
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u/honuworld 2d ago
Dark matter and dark energy are just excuses for the fact that we have no idea why the Universe doesn’t follow our best models of entropy and motion. “There must be something invisible affecting things in ways we can’t measure that change randomly for reasons we don’t know.”
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u/squshy7 1d ago
You just described every force prior to their respective observation.
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u/honuworld 3h ago
We NEVER described gravity as something we couldn’t detect or measure. Try harder.
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u/EndoExo 2d ago
tl;dr possible WIMP detection. Further research needed.