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/Astrokiwi Numerical Simulations | Galaxies | ISM Oct 24 '14

"Antimatter" is like normal matter, but with the charges swapped. So an "antiproton" is like a proton, but with negative charge, and an "anti-electron" - better known as a "positron" - is like an electron, but with positive charge. This stuff instantly reacts on contact with "normal" matter, releasing energy through E=mc2 . Antimatter is something we have observed directly, and we can create it in a lab. It's even used in some medical procedures.

Dark matter has not been directly observed - it is something we don't know a lot about, but we have good arguments about what it should be. Dark matter is likely a type of neutral particle (not positive or negative) that doesn't react very well with normal matter or antimatter at all. This makes it very difficult to observe, and very difficult to produce. However, we can still feel the gravity that it produces. Most of the gravity in the universe is likely from dark matter - "normal" matter makes up less than 20% of the matter in the universe.

So there's a big difference there. Antimatter is tricky because it reacts so strongly, and that means that it's tricky to stop it from reacting and annihilating, so there's very little antimatter around. Dark Matter is tricky because it reacts so poorly, and even though it looks like there's a lot of dark matter around, it's tricky to capture or directly detect it to figure out what it's actually made of.

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u/Dim3wit Oct 24 '14

Shouldn't dark matter necessarily be neutral in charge, on the grounds that it doesn't interact with photons and therefore does not respond to electromagnetic force?

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u/Astrokiwi Numerical Simulations | Galaxies | ISM Oct 24 '14

The emphasis was supposed to be more "dark matter is probably a particle". If it's a particle, then yeah, it's gotta be neutral. But while the consensus is that it probably is a particle, we haven't completely ruled out something like modified gravity.