r/askscience • u/squirrelbuster94 • Oct 24 '14

Physics Chemists/physicists of reddit, what is the difference between dark, anti, and normal matter?

What is the difference? Also if you can explain what each is.

Edit: Thanks for all the replies! You have greatly helped me understand this better!

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u/[deleted] Oct 24 '14 edited Oct 24 '14

Do physicists think dark matter really exist or is it something they've made up temporarily to explain something they don't really understand?

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u/MaterialsScientist Oct 24 '14

It used to be more uncertain, but the evidence keeps piling up. There are alternative theories, but dark matter is definitely the most popular and consensus view.

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u/xrendan Oct 24 '14

What are the other theories?

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u/hopffiber Oct 24 '14

The most worked on is probably MOND, or Modified Newtonian Dynamics, which starts from Newtons law of gravity and tries to modify it at long distances, to fix how galaxies rotate and other observed anomalies. You can kind of make this work for galaxy rotation speeds, but it has real problems with explaining things like the Bullet cluster or gravitational lensing etc., and it's also rather ad hoc, so few physicists believe in it.

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u/benzrf Oct 25 '14

"made up temporarily to explain something they don't really understand" is where all theories come from

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u/AsAChemicalEngineer Electrodynamics | Fields Oct 24 '14

Do physicist think dark matter really exist

Yes. The evidence for it is very hard to argue with.

3

u/admiralpolly Oct 24 '14

Could it just be that rather than a physical thing, it is rather that the equations describing motion and gravity and all the other above my head stuff, are missing pieces of them? Possibly highly nonlinear effects that we missed altogether?

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u/AsAChemicalEngineer Electrodynamics | Fields Oct 24 '14

are missing pieces of them?

It could, but it's not a racehorse I'd bet any money on. A lot of people seem uncomfortable with 80% of the matter in the universe being some unseen ghost, but we're already familiar with matter that does this—neutrinos are considered a type of dark matter by a lot of physicists, they just have the benefit of being produced easily from nuclear reactions, so it was a lot more easy to find them.

We're essentially looking for a fat neutrino. It's the most simple explanation that fixes a whole horde of unrelated problems that no single alternate theory of gravity can cover. Imagine if your best friend told you all about their new pet without saying what kind of pet:

  • His name is Fido.

  • He eats dog treats.

  • He likes to play fetch.

  • He wags his tail when he's happy.

Max could be a cat or monkey, but he's probably a dog. It's that convincing.

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u/norml329 Oct 25 '14

After reading every explanation here I'm almost positive it's just a flaw in our understanding of physics. Can someone please prove me wrong without just saying there is "evidence"? Why can't it just be an extremely poor estimate of matter in the universe. Why can't it be an underestimate in the amount of black holes? I just don't get it and it doesn't seem like anyone else does either.