Dark matter is not something that we really know anything about. It's just the name given to a series of discrepancies between our cosmological models and our observations.
this post was submitted on 17 Nov 2025
51 points (98.1% liked)
No Stupid Questions
44362 readers
774 users here now
No such thing. Ask away!
!nostupidquestions is a community dedicated to being helpful and answering each others' questions on various topics.
The rules for posting and commenting, besides the rules defined here for lemmy.world, are as follows:
Rules (interactive)
Rule 1- All posts must be legitimate questions. All post titles must include a question.
All posts must be legitimate questions, and all post titles must include a question. Questions that are joke or trolling questions, memes, song lyrics as title, etc. are not allowed here. See Rule 6 for all exceptions.
Rule 2- Your question subject cannot be illegal or NSFW material.
Your question subject cannot be illegal or NSFW material. You will be warned first, banned second.
Rule 3- Do not seek mental, medical and professional help here.
Do not seek mental, medical and professional help here. Breaking this rule will not get you or your post removed, but it will put you at risk, and possibly in danger.
Rule 4- No self promotion or upvote-farming of any kind.
That's it.
Rule 5- No baiting or sealioning or promoting an agenda.
Questions which, instead of being of an innocuous nature, are specifically intended (based on reports and in the opinion of our crack moderation team) to bait users into ideological wars on charged political topics will be removed and the authors warned - or banned - depending on severity.
Rule 6- Regarding META posts and joke questions.
Provided it is about the community itself, you may post non-question posts using the [META] tag on your post title.
On fridays, you are allowed to post meme and troll questions, on the condition that it's in text format only, and conforms with our other rules. These posts MUST include the [NSQ Friday] tag in their title.
If you post a serious question on friday and are looking only for legitimate answers, then please include the [Serious] tag on your post. Irrelevant replies will then be removed by moderators.
Rule 7- You can't intentionally annoy, mock, or harass other members.
If you intentionally annoy, mock, harass, or discriminate against any individual member, you will be removed.
Likewise, if you are a member, sympathiser or a resemblant of a movement that is known to largely hate, mock, discriminate against, and/or want to take lives of a group of people, and you were provably vocal about your hate, then you will be banned on sight.
Rule 8- All comments should try to stay relevant to their parent content.
Rule 9- Reposts from other platforms are not allowed.
Let everyone have their own content.
Rule 10- Majority of bots aren't allowed to participate here. This includes using AI responses and summaries.
Credits
Our breathtaking icon was bestowed upon us by @Cevilia!
The greatest banner of all time: by @TheOneWithTheHair!
founded 2 years ago
MODERATORS
What does it mean when light hits something? Is light "hitting" the air around you? If so how can you see at all?
For light to measurably change when it interacts with a particle or group of particles, there has to be a separation of electrical charges. The light also has to be close to the energy of an available energy state transition. There's lots of diffferent types, but remember electron orbitals? Most visible light interactions involve electrons jumping to higher energy orbitals or falling to lower energy orbitals. There are only very specific interactions that are possible with specific wavelengths of light. Fortunately, visible light spans a wide range of wavelengths that interact very strongly with the forms of matter that surround us.
There are lots of things that won't interact with light at all. Nuetrons and neutrinos don't have a charge separation and don't interact with light at all. You could shine very strong lasers through a cloud of neutrinos, and as far as the beam path would indicate, it would be identical to vacuum. They have to be studied by how they interact with other matter that does interact with light. It may sound counterintuitive, but single free charges like a bare hydrogen nucleus or free electron also don't absorb or emit photons. It is only when charges can interact with eachother that we get light interactions.
So nothing measurable happens when light propagates through a volume where dark matter is. There is no mechanism by which the two can interact, except gravitational lensing.
It passes right through. It only interacts with gravity. Which can indirectly bend light, however, by bending spacetime.
dark matter is not a "thing", it's a problem
Can you explain this a little more?
dark matter is a stand in, not a known type of particle. astronomers realized, that in galaxies there had to be way more mass than is visible due to the movement of stars within. but since it couldn't be detected in any other way than through its gravitational influence, it was called dark matter.
this person has given the best answer so far. there is no thing we could identify as dark matter. the concept of it is more like a roadmap, a question to be answered.
Things behave in ways that can’t be explained by our current understanding of physics.
For example, galaxies rotate faster than we would expect. It’s as if there’s more matter in the galaxy than we could see. Scientists use the name ”dark matter” for this phenomenon.
Scientists don’t know if dark matter really exists, or if there’s other ways to explain this phenomenon. Another explanation is that there’s no extra matter, but that this is just how gravity behaves in large scales.
What’s interesting is that different galaxies has different amounts of ”dark matter”. Some have almost no ”dark matter” at all.
What physicists and astronomers do, is they look at how things work here on earth and where we can observe things.
For example, we can observe that the earth orbits the sun, we know that orbit takes a year, and it's pretty stable. And from that and the speed and orbit of other planets, we can calculate the mass of each. And with the same math, we can do it for our galaxy.
But when we look way, way deeper into the universe, we can only see: electromagnetic things, that is light and radio. And by observing that or how it behaves, in the case of black holes, we can say where things are, what they're like and how they move. Including how big they are, how massive, we can calculate how much mass is required to keep a galaxy together.
The problem is the movement we can see, doesn't match the calculated weight and gravity of the things we can see.
The solution is that we assume that things do behave as we think they do, we just can't see it. The weight that we can directly or indirectly observe accounts for about 5% of the effect we can see. So we make up the rest. That's "dark matter". Not because it's different from what we know, but because we can't observe or "see" it.
Or we're wrong about the rules that we use to calculate stuff or things are happening we don't understand yet.
And we recently discovered a clump of dark matter big enough to form a gravitational lens - we could actually see it curving light.
This helps show that dark matter isn't evenly distributed, it's not that we just need to add a multiplier to some equation; it's something that 'exists'.
Personally, I'm a big fan of "there are unknowns in the universe", so imo they found lens, which could be a gravitational lens ;)
Cool nontheless.
That is literally what dark matter is.
Parts of the universe don’t behave according to the laws of physics established by experimentation done nearest to us. Dark matter is a placeholder until we figure out why this is happening.
You know that idea of putting "here be dragons" on a map to indicate that that area is unknown? "Dark matter" is Physics for "here be dragons"
I like this analogy
I think what they mean is that "dark matter" is just a name that scientists gave to a phenomenon they have yet to understand. It's a variable in a math problem that represents something that's there, that influences the whole system, but we don't quite yet know what it is.
If my memory is correct, one of these problems is the mass of the universe. It doesn't quite all add up. So they made up this dark matter to explain it. It's the missing matter that we can't quite observe but makes it all make sense.
It’s an unknown something with a question mark on it.
"Dark matter" is just an elegant term for "we don’t know".
It just passes through.
Interesting little detail: Even though the light doesn't interact directly with the dark matter, so in a sense it just passes through, the light can still be affected by the dark matter indirectly. Because the dark matter does have mass, or at least interacts gravitationally like it has mass, it actually deforms space-time. This deformation can cause light to travel through a longer path than one might expect.
This has been used to create dark matter "maps", to show where there is more and where there is less dark matter. It also shows up in gravitational lensing.
it doesn't. light hitting e.g. a helium atom is an electromagnetical interaction. if dark matter does only interact gravitationally, it wont get hit by light.
Not a physicist, but pass through unaffected would be the obvious answer?
Yeah, it just doesn't hit it.
Gravity does work with dark matter tho, so we can't really say "unaffected" because the dark matter would still bend the light due to gravity. I'm not sure if we can detect that bend, but I remember something relatively recently about how dark matter can interact via gravity, and I'm assuming bending light would have been the easiest way to test that.
I'm not sure if we can detect that bend
I guess we could, if only we knew where our dark matter is :)
Maybe once they find it, they can figure out how it interacts with the material world. They haven't found it yet. Knowing how it interacts, would actually help find it.