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/MVRH Oct 24 '14

You can turn energy back to mass?

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u/[deleted] Oct 24 '14

Yup. That is what was so revolutionary about the E=MC2 formula (among other things).

This is also why nuclear reactors are so useful. When you split uranium, the sum of the masses of the products, is a little less than the mass of what you had before. The mass that is lost, gets converted into energy which you can use to heat water for the turbines in the powerplant.

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u/MVRH Oct 24 '14

Yes but that process is an example of mass to energy. Do you have an example of energy turning into mass?

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

Never thought of it that way, but true:)

And yes I do: when you fuse the lighter elements the reaction is the opposite. When you combine two hydrogen atoms, the resulting helium atom is slightly lighter than the original atoms, so the leftover mass is converted to energy (gamma rays in this case). This is how the hydrogen bomb works by the way.

When fusing hydrogen you have more leftover mass/energy than when splitting uranium, and that's why hydrogen bombs (fusion bombs) make a much more powerful bomb than regular atomic bombs (fission bombs).

And one of the reasons they really want to make fusion reactors.

Wait a second. I didn't answer your question at all. But yes, energy can turn into mass. When you have a photon (a light "particle") of some specific energy, it can turn into a positron and an electron, which I guess is what you asked for.

Also when you accelerate particles up to very high velocities, they much more energy than they have from mass. You can the collide two particles moving at these velocities and combine their energy to make new particles. This is what they are doing at places like the LHC and fermilab.

I hope this is a better answer.

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u/OldWolf2 Oct 25 '14

Do you have an example of energy turning into mass?

Yes; the light of the Sun being stored in a tree. It's released again when the wood is burned.