Helium consists of 2 protons, 2 neutrons, and 2 electrons

[FeDeX_LaTeX]

An element of helium consists of 2 protons, 2 neutrons, and 2 electrons.

I have been told that anti-helium can exist if instead of 2 protons there are 2 antiprotons, instead of 2 neutrons there are 2 antineutrons, and instead of the 2 electrons there are 2 positrons. Is this true?

Also, will the "anti-helium" exhibit different properties? Can we apply all of our laws of atomic physics to anti-matter as we do with normal matter?

Thanks.

 

[Bob S]

Yes, anti-helium would have two anti-protons, two anti-neutrons, and two positrons. It would have the same properties as helium (in anti-matter), and obey the same laws of atomic physics. One of the most convincing signatures of anti-matter in the universe would be detecting anti-alpha-particle (anti-helium nuclei) cosmic rays above the atmosphere.

Bob S

 

[DaveC426913]

Yes, that's simply anti-matter.

"Simply" should be quoted though, because it's rare to find atomic antimatter - not sure if it occurs in nature.

It would have the same properties as helium (in anti-matter), and obey the same laws of atomic physics.

To elaborate:

Anti-helium would in principle behave the same as helium - if it were in an antimatter environment. For example, if it were surrounded by anti-nitrogen and anti-oxygen, it would be buoyant.

If it were not in an anti-matter environment, it would annihilate.

 

[FeDeX_LaTeX]

Thanks for clearing that up guys.

So is it true that, for every normal matter there exists a corresponding anti-matter? Where can anti-matter usually be found?

 

[DaveC426913]

Thanks for clearing that up guys.

So is it true that, for every normal matter there exists a corresponding anti-matter?

It is more accurate to say: for every normal particle of matter there can exist a corresponding particle of antimatter.

Note that even this is loose. Photons are their own antiparticles. (They're not matter, but they can be considered particles.)

Where can anti-matter usually be found?

It's not found in any quantity or for a significant duration to be much use. And even then, we're talking subatmouic particles here, not atoms.

Wiki:

Antiparticles are created everywhere in the universe where high-energy particle collisions take place. High-energy cosmic rays impacting Earth's atmosphere (or any other matter in the solar system) produce minute quantities of antimatter in the resulting particle jets, which are immediately annihilated by contact with nearby matter.

http://en.wikipedia.org/wiki/Antimatter#Origin_and_asymmetry

 

[Fightfish]

Where can anti-matter usually be found?

Indeed, antimatter is a very very rare occurrence in our universe. Most of it undergoes annihilation with matter once it is formed. If significant amounts of anti-matter exist...we wouldn't be here in the first place!

This problem of matter-antimatter asymmetry (missing antimatter, if you would have it) is a big one in cosmology. A slight excess of matter over antimatter during the Big Bang is the reason why planets and whatnot, including us, exist today. Otherwise, our universe would just comprise loads of photons if antimatter and matter were present in equal amounts.