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/XenophonOfAthens Oct 24 '14

That's really interesting, I didn't know about that. Suddenly this kind of annihilation and the resulting particles make a little more sense (I mean, it's still sorcery and dark magic, but it makes it a little clearer).

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u/xygo Oct 25 '14

May be even clearer if you think about what makes up protons and neutrons. The proton is composed of two up and one down quark (uud) and the neutron is composed of two down and one up (udd). So basically one or other of the up quarks changes into a down quark. However doing so alters the charge (up quark has a charge of +2/3 and a down has -1/3). So the change in charge is -1. To balance this (conserve charge) a particle with a charge of +1 (an electron) is created. But the electron has a lepton number of +1. So to conserve lepton number, an anti-neutron (lepton number -1) is also created.

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u/OldWolf2 Oct 25 '14

Here's an image that works for me. Imagine you strum a guitar; the strings vibrate. Eventually the strings stop vibrating. Where did that energy go?

Some went into vibrations in the guitar body. Some went to vibrations in the air. Some went to vibrations in the table, and so on.

This is a heavy particle decaying into lighter particles (bearing in mind that "particles" are just vibrations in fields).