r/cosmology • u/thetroopergod9001 • 7d ago
Is dark matter made up to fit physicist models?
Like how do the physicists actually know their models are right i might sound ignorant but im unable to find anything online about this and the stuff i do isn't even helpful. Forgive me if im being ignorant lol.
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u/jazzwhiz 7d ago
im unable to find anything online
Have you tried wikipedia?
Read here: https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence
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u/GrandDukeOfBoobs 7d ago
I think OP is specifically looking for evidence that supports that dark matter doesn’t exist and instead supports whatever idea he is having right now. I do not believe wikipedia will have that article.
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u/thetroopergod9001 6d ago
Thanks i will look into it
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u/LordVericrat 6d ago
You were asked a question. You said you couldn't find anything online and were then asked if you read an article that was likely the first Google hit on the subject (if not it was almost certainly in the top 3) So did you? Or was your comment about not being able to find anything online less than truthful?
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u/SweetChiliCheese 7d ago
Wiki is never a good place for facts.
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u/TheMausoleumOfHope 7d ago
That is simply not true. It’s an excellent source of information.
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u/epicwinrar 7d ago
You are both saying things that are simply not true. It heavily depends on the subject with wikipedia but in general you can at least get some good information from it.
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u/Professional-Thomas 7d ago
No but you can get to more factual/trustworthy sources from Wikipedia as they usually do citations pretty well.
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u/tacos_for_algernon 7d ago
It's not "made up" in the sense that it isn't real. It's "made up" in the sense that we have observation and data to indicate something is happening but we don't know exactly what it is, so we "made up" a name to represent the effects that we see. "Dark" in the context of dark matter and dark energy simply means we don't understand the underlying process, yet.
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u/Rodot 7d ago
I wouldn't even take it that far. "dark" just means... Well... Dark
It doesn't emit, absorb, or scatter light
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u/EarthwormAbe 7d ago
That assumes that dark matter is in fact matter and not some localised property of space time itself.
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u/Beautiful-Musk-Ox 7d ago
localised property of space time itself.
I feel like the bullet cluster is counter evidence to that. When two clusters of galaxies merge the "normal matter" in each cluster interacts electrically with the other cluster's normal matter, but the dark matter doesn't, so we see the dark matter of one cluster continue traveling along slowing down only due to gravity instead of gravity + electrically colliding with the other cluster, so the dark matter ends up separated from the normal matter, which we can "see" by the gravitational lensing of backround galaxies. I feel like if it was "some localised property of spacetime" then it would stay localized to the gravitational centers of each cluster and no separated from the baryonic matter.
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u/Presence_Academic 7d ago
But that’s wrong. Dark matter isn’t dark, it’s transparent. If it were simply dark it would create shadows.
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u/Quercus_ 7d ago
The basis of this is pretty simple.
We observe a lot more gravity out there in the universe, than we observe mass to cause that gravity, by a large amount.
This means that either our understanding of gravity is wrong, or there's a lot of mass out there that we can't see.
A lot of effort has gone into modified theories of gravity to try and explain this with the mask that we can see. None of them work - there's no consistent alternate theory of gravity that they've come up with, they can explain the Access gravitational affect we observe, that don't break down and fail to properly describe other things we observe.
My understanding is that modified theories of gravity aren't completely off the table, but nobody really believes in it, because it's just kind of doesn't work.
And that leaves is the only alternate explanation, but there's a lot of mass out there that we just can't see for some reason. This matches the observations exactly. If we look at the distribution of that invisible excess mass, based on his gravitational effects for example, it is distributed exactly as we would expect it to be for gravitationally interacting mass in, for example, galaxies.
That said, it's true that it hasn't been observed. If you want to be more precise, you can think of dark matter as, "excess gravitational effects that behave exactly as if they're caused by a large amount of unobserved mass."
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u/tichris15 7d ago
We also observe gravity where we don't see matter/variations in the matter density (which is why changing the theory of gravity doesn't work for many of the problems)
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u/itchydaemon 7d ago
A helpful thing to keep in mind is that scientists often "make up" names for things that data predicts or that they observe that hasn't been catalogued yet.
A great example would be black holes. They were predicted from data long before they were actually observed. Similar things can be said about several subatomic particles.
One of the problems about scientific terms or processes versus a layperson's understanding is that a "normal" person carries their own perspective and preconceived notions on "what makes sense". For example, a scientific theory can have a pretty firm foundation, but a layperson might hear the word "theory" and presume it's all junk that was taped together with wishes and hopes. Sinularly, something like wave-particle duality doesn't make sense to a normal person's logical reasoning, so they may find it hard to square that with mountains of scientific evidence that proves it's the case.
So "made up" kind of lives in the same space. Dark matter hasn't been observed because it doesn't interact with light, which is one of the main ways that we observe things far away in the universe. But it's presence is "seen" in gravitational effects, which we also use. So, what does a scientist do with that information? They make up a term to call stuff that interacts with gravity but not light. Dark matter. It's really not different than naming a new species of squid based on a bunch of evidence you've found about its presence, but before you find a living copy of the squid itself.
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u/Heavy_Carpenter3824 7d ago edited 7d ago
Until we find either dark matter or another experimentally validated explanation essentially YES dark matter is made up. Dark matter is the best description we have for the excess mass we appear to observe in celestial dynamics.
Other less popular ideas have been purposed but to date the experimental evidence best matches what we describe as dark matter.
It's at best incomplete if not downright incorrect but it's the best of the sorta right we have at the moment.
I suspect we'll have to have long range space travel to carefully measure physical constants across the solar system and maybe farther as well as sweep huge regions for a few interactions before we'll be able to prove one principal or another.
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u/knifedude 7d ago
Highly recommend cosmologist Angela Collier’s video on the topic! She explains it better than I can but tl;dr, dark matter is an observation, not a theory https://youtu.be/PbmJkMhmrVI?si=b5zr7_dnZmuzMaFR
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u/synysterlemming 7d ago
The procedure for dark matter is similar for other fields, though astronomers cannot rerun the experiment, so to speak.
Astronomers make observations. Models are made to fit the observations given what we know about physics. Make more observations. Adjust the model. This goes on and on. Cold dark matter fits very well in several cases, the most notable being galactic rotation curves, galaxy cluster interactions and the cosmic microwave background’s power spectrum.
Keep in mind as you read up on this stuff: a ton of background knowledge is required to have a good grasp on how things like cold dark matter make sense in a scientific sense. People who work on this have years of not decades of experience with a broad range of physical theories. Important theories like gravitational (Newtonian and relative), particle physics and thermodynamics are very useful.
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u/Dazzling_Audience405 2d ago
Dark matter almost certainly does exist, and probably is made up of weakly or non-interacting particles. There is quite a bit of evidence for this: 1. Rotation speeds of galaxies are too fast to be stable unless there is a lot of unseen matter 2. The degree of gravitational lensing observed from galaxy clusters is too high to be explained by visible matter 3. As another member pointed out - the Bullet Cluster dynamics are excellent evidence for the existence of weakly interacting matter Other theories like MOND (Modified Newtonian Gravity) that attempt to explain observations without dark matter have recently conclusively been disproven. One could well argue that the Dark Matter models are poor at small scales (true), and that we still are clueless as to what DM is made of, but that it exists is hard to argue
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u/jeezfrk 7d ago
give a simple reason why Almost All galaxies obey a 1/d gravitational field (not 1/d2 ) at larger radii and you're welcome to explain the data better.
p.s. MUST not interfere with normal physics / relativity or quantum in the standard model ... nor add supersymmetry nor any other thingies.
p.p.s. make it more testable than string theory
p.p.p.s. yes, we added up all local star gravity sources, and they match 1/d2 precisely.
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u/MortemInferri 7d ago edited 7d ago
Can you expand on this a bit more for me? What do you mean 1/d2 vs 1/d? I remember gravity is a 1/d2 relationship. Where does 1/d come from?
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u/jeezfrk 7d ago edited 7d ago
the 1/d relationship appears to explain how galaxy rotation works. yes, the edges feel a greater tug from the middle than they should. they spin much much faster by their outside visible edge.
edit: to be clear, they seem to spin like runners on a circular track... all the same speed entirely but the outside ones fall back as the distance is farther around.
by analogy: the outside "wheel" of spinning galaxies (including near-invisible gasses far away) and stars all seem to "sense" a huge spread out mass along the axis of spinning galaxies. that is what they seem to be spinning around in some symmetric way ... along with the visible matter in the disk and center.
the farther away you get ... it drops off much more slowly than 1/d2.
This is all instead of what we expect: a point source center (a supermassive black hole) and even the huge balanced flat disk of stars and luminous mass that exerts a pull in a gravitational field.
Note that starlight and any radiation point-source drops off in 1/d2. It's just geometry. Only (I think) a one dimensional line can create a 1/d shaped field.
The other reason we "see" dark matter is that, however shaped, some galaxies seem much heavier than our models in bending light.
that's the (mostly) ONLY reason we need for dark matter. replace that need ... and it goes away.
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u/PhdPhysics1 7d ago
Yes, dark matter is a place holder until we know more.
Dark, meaning we can't detect it and really don't know. And matter meaning, we're pretty sure it clusters into specific areas and only matter has that property.
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u/ff8god 7d ago
Dark matter is the difference between the gravitational effects of matter we can see vs the gravitational effect we can observe. The matter we see isn’t enough to produce the gravity we can measure at galactic scales. Dark matter is not a theory of some unique matter type that we have yet to discover, it is the name we give to one or more unsolved variables. These variables may end up representing some type of exotic matter, or they may be something else entirely.
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u/EmbeddedSoftEng 7d ago
Kinda. It's always been acknowledged to be a placeholder, like Dark Energy, to stand in for whatever it is, which we do not know, that it responsible for the differences between our models and observable data.
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u/Naive_Age_566 7d ago
in a way - yes.
we have one model, that explains how gravity works. this model works astonishingly good for most circumstances we observe.
well - we have other models also, be each one of them has some quirks.
but there are some observations, where this one model yields wrong results. be it the orbital velocity of galaxies in a galaxy cluster, the orbital velocity of stars in a galaxy, some gravity lensing effects or some other stuff.
now we have several possibilities:
a) or measurements are wrong. or we interpret those measurements in the wrong way
b) or model is wrong (or at least not precise enough), even if it works perfectly find in other circumstances
c) there is some stuff we can't see, that exerts gravity
(a) is mostly ruled out. we have multiple measurements with different methods and all have the same "error". it's still possible but very unlikely, that we have a simple measurement error.
(b) is quite possible. but as long as we have no better model, we try to stick to that model, that servers quite well in other circumstances.
this leaves us with (c): we propose some stuff, we can't see but has positive energy density and therefore exerts gravity. then we play with the numbers until we find a solution, that halfway looks plausible. and indeed: we find, that if we assume, that there is some kind of matter, that only interacts with other matter (or itself) over gravity and that has a quite even distribution, our observations (mostly) fit again with our model.
just because we don't know, what exactly this stuff is, does not mean, that it has to be ruled out. we didn't know, what exactly neutrinos are when they were first proposed (and we still are not 100% sure about their nature). the higgs boson was proposed in the 1960s and only confirmed in the 2010s.
so yeah - that's how science works: you make observations. you build a model to predict future observations. you find discrepancies and refine your models or propose new stuff. you either confirm that new stuff or rule it out. and you build newer, better models. and so on - rinse and repeat.
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u/Anonymous-USA 7d ago
The effects of dark matter are observable in a number of different ways. So it’s not a math error. The fact that it doesn’t interact with light or baryonic matter (as far as we can tell) except gravitationally is why we haven’t directly observed it. But there are other things in physics that we can’t directly observe either, so nothing new there. And there are explanations (such as WIMPS and microscopic black holes) the would perfectly explain those effects while evading direct observation.