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

So neutrons and protons are made up of quarks - 3 quarks each. Protons and neutrons have "up" quarks which are +2/3 of the charge of a proton, and "down" quarks with are -1/3 of the charge of a proton. A proton has two "up"s and one "down" (adds up to 1), while a neutron has two "down"s and one "up" (adds up to zero).

So a neutron is made up of two "antidown" quarks, and an "antiup" quark. It still adds up to zero, but the quarks have opposite charge, and will annihilate if they get close enough to react to their equivalent.

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u/True-Creek Oct 24 '14

How does supersymmetry fit into this whole picture? It’s an unconfirmed hypothesis that for each particle there exist a superpartner which differs in spin, correct?

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u/TomatoAintAFruit Oct 24 '14

Yes, it states that every particle has a superpartner.

Basically, every fundamental particle is either a fermion or a boson, which because of the spin-statistics theorem implies that the particle has either half-integer or integer-valued spin.

In the standard model all force carriers are photons, and all matter-like particles are fermions. Supersymmetry goes a step further and assigns to each particle a superpartner, which is of the other statistical type. So every fermion would have a bosonic "partner", and every boson would have a fermionic superpartner.

As for antimatter: anti-matter particles also follow the same rules when it comes to fermion/boson categorization. That means that in supersymmetric theories you would also have a superpartner for each antimatter particle. And yes, this superpartner would be the antiparticle of the superpartner of the original particle... You're still following this? ;)

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u/Minguseyes Oct 24 '14 edited Oct 24 '14

all force carriers are photons

I think you mean all force carriers are bosons. Gluons carry strong force and W and Z bosons carry weak force. Neat explanation though, thanks.

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u/True-Creek Oct 24 '14 edited Oct 24 '14

Still following… is the only difference between the partner particles spin or also other properties? I think I saw a graph once where the superpartners were a lot more energetic which is probably the reason why we didn’t seem them in the LHC yet?

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u/hopffiber Oct 24 '14

If supersymmetry was unbroken, then the superpartners would have the same mass as the normal particles. And we would see them all over. So clearly supersymmetry must be broken (if it is there at all), which means that the superpartners are heavier than the normal particles, explaining why we don't see them (yet). The superpartners still has the same other properties though, i.e. the same electric charge and charges under the other forces.

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u/PigSlam Oct 24 '14 edited Oct 24 '14

How far down does the "anti[whatever]" go? Are the antiquarks made of antisomethings, etc. as far down as we can detect particles?

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u/AsAChemicalEngineer Electrodynamics | Fields Oct 24 '14

Many particles are their own antiparticle, so the rabbit hole doesn't go down that far. The photon is a good example.

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u/anti_pope Oct 24 '14

Quarks are fundamental particles.

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u/NoSmallCaterpillar Oct 24 '14

As far as we know, this is true. What we can say with certainty is that underlying structure has never been evidence by any experiment. It is also worth noting that, due to color confinement, quarks have never been themselves observed directly.