Thanks for the answer, and might I be so bold as to ask what your current research is?
You might also find it interesting that two photons cannot interact directly. They’re only able to do so through the creation of a virtual electron-positron pair. And as Chronos says this requires a very large energy density – at reasonble energy densities this doesn’t happen at all.
Fascinating stuff, Chronos. If this were true, it seems to me that it would have some odd implications. If I observe two nuetrinos going faster than I am, they’ll both be left-handed, ordinary neutrinos. However, from the neutrino’s perspective, won’t one neutrino always be left handed and the other right handed if they’re going at different velocities? In other words, two left-handed neutrinos would always be anti-particles of each other unless they’re going at the same speed.
It’s on the implications of neutrino mass on Hawking radiation. The main reason neutrino helicity is relevant is that it changes the number of different ways a neutrino can be emmitted. Since there’s no particular reason to belive that gravitational interactions have a preferred parity (as does the Weak interaction), a black hole can presumably produce both right and left handed neutrinos.
Truth Seeker, what you say would only be true if the two neutrinos were moving in the same direction to begin with, and only relevant if one is catching up to the other. Even then, that’d take an awfully long time, since neutrinos are typically produced at very close to the speed of light. Also, you shouldn’t think of neutrinos meeting antineutrinos as being anything particularly dramatic. The annihilating-to-gamma-rays thing only happens with particles which interact primarily electromagnetically, such as electrons and positrons. Protons interact mostly by the strong interaction, for instance, so you’re likely to get a few pions when proton meets proton, and those will then decay to photons and assorted leptons. Neutrinos, meanwhile, interact only via the Weak force (and gravity, but that’s almost always negligable), so there isn’t even anything that’s likely to happen. You might have something like [symbol]n[/symbol] + [symbol]n[/symbol] --> Z --> 2[symbol]g[/symbol], but that’d be rare.
But if they’re virtual particles, doesn’t the uncertainty principle allow their energy to exceed the energy of the photons?
Another question from a tyke: Does antimatter only exist in subatomic particle form, or can it exist theoretically in atomic and molecular forms? In other words, is there an anti-hydrogen, an anti-oxygen, an anti-water, and so on?
If so, does this mean that if the balance of matter and anti-matter were reversed (more anti-matter than matter) than our universe would be composed of anti-matter instead? (Which I assume we would refer to as matter from that frame of reference, and what we call matter now would be anti-matter in such a universe.)
Making any sense?
As I understand it - YES.
From my freshman physics textbook as best as I can remember it - “an Anti-egg would taste the same to an anti-man as an egg tastes to us”
There is at least anti-hydrogen. It was first produced at CERN in 1995 (cite). Since then it has been reproduced elsewhere. I seem to remember that Fermilab also made anti-helium, but I have no cite for thar.
Correct. It is possible for two photons of any energy to interact in this way. You get a couple of photons of, say, an eV each colliding, and producing an electron and a positron, with a total energy of 2 eV. Then, though, the electron and positron go “Oh, dang! We’ve got energy less than our mass! That ain’t allowed!”, and promptly re-annihilate to two photons again. Of course, the closer you get to the “real” mass, the easier this becomes.
Well, without the anthropomorphization, but that’s the gist of it.
I’ll note that a PET scan uses positrons, or anti-electrons (I used to call them negatrons to be silly). So antimatter not only exists, but has usefulness in many people’s daily lives.
Besides anti-hydrogen, there is a substance called positronium, which is an electron/positron pair which can be bound together. I was involved in a project ostensibly to look for it in a jet of energy and matter streaming out from the center of an elliptical galaxy (M87 for those keeping score at home) using Hubble. We didn’t expect to see it, but knew that our images had lots of other uses, so the project was accepted by the people who grant telescope time.
There may very well be positronium in the jet, but it was way too weak to detect, and the light from the jet itself swamped everything else. Oh well. It was still neat working with the data, and I was able to solve a pernicious calibration porblem we had with the camera. 
Slight Hi-jack
E=mc^2…Energy equals mas times speed of light squared.
According to Dirac(?), the square root of this equasion gives
solutions for matter and antimatter.
-E=?
What is the structure of exotic matter?