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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.
While I've bee away from dark matter physics for a while, we do have a couple of theoretical candidates for dark matter, and data from cosmology and particle accelerator, somehow describing the kind of proporties that a dark matter particle would have.
And it includes a low cross section, meaning that most likely it won't interact with light (see it as smaller than light as an over simplification). This makes detection pretty hard both in direct and indirect way
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.
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.
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
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.
I am by no mean an expert, but I When I was a master student, I spent some time exploring the modified gravity rabbithole the most popular being MOND. The big limit is that it's a ad hoc model to fit galaxy rotation curve, it works pretty well. But it doesn't work if you try to use it for a cosmological model, and doesn't explain gravitational lensing. Making it an overall weak hypothesis compared to the good old cold dark matter
The standard cosmological model with dark matter and dark energy (it's two different objets) is supported by a lot of evidences. Up to now, no alternative theory works at explaining all data we have.
Don't get me wrong, we may have a massive hole in gravity, and may at a point get the missing piece of data to find it and explain everything without using exotic particles. But as of today, both particle physicists and cosmologists agree that particle physics beyond the standard model provides the most solid candidate for dark matter and that nothing else has a solid backing
I’m mostly a layman. The only thing I know is that MOND is the leading competing explanation. I leave it for experts to decide which one is correct.
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.
i could, but she does it better https://www.youtube.com/watch?v=PbmJkMhmrVI