Tuesday, May 05, 2009

Why Antihydrogen and Antimatter Are Different

An excellent review of CPT theorem and the asymmetry between matter and antimatter.

If matter were made with hydrogen, the existence of antimatter would be assured by the existence of the two antiparticles (antiproton and antielectron), the existence of the antiphoton being assured by QED. As Dirac emphasized, to have matter it is necessary to have another particle (the neutron) and another glue (the nuclear glue) to allow protons and neutrons to stay together in a nucleus. This problem first comes into play in heavy hydrogen, which has a nucleus – the deuteron – made of one proton and one neutron. For these two particles to remain together there needs to be some sort of "nuclear glue". We have no fundamental theory (like QED) to prove that the nuclear antiglue must exist and act like the nuclear glue. It can be experimentally established, however, by looking at the existence of the first example of nuclear antimatter: the antideuteron, made with an antiproton, an antineutron and nuclear antiglue. If the antideuteron exists, all other antielements beyond heavy antihydrogen must exist. Their nuclei must contain antiprotons, antineutrons and nuclear antiglue. But if the antideuteron did not exist, nothing but light antihydrogen could exist: farewell anti-water and farewell all forms of antimatter.

It give a glimpse on how many (all?) of the physics that we understand are so dependent on symmetry principles, and how many new physics are being discovered via such violations.

Don't miss it!



Kurt Kohler said...

Antiphoton? Those can't exist, right?

I assume you meant antiproton.

Lapsed Physicist

ZapperZ said...

No, it wasn't me, and I believe the article DID meant to say "antiphoton", even though a photon is, via conventional understanding, its own antiparticle.

I think they are just trying to keep all the "anti" together within the antimatter.