June 24, 2001

11:22 PM

These guys cool and trap anti-electrons (positrons) and at the same time cool and trap anti-protons. Why? Because they want to make cold anti-hydrogen and compare its properties with ordinary hydrogen. Pretty cool all round, really.

"Any difference between antimatter and matter would be extremely interesting since we do not yet understand why we have a universe made of matter. We would expect that the big bang that originated our universe would create equal amounts of antimatter and matter, which would then annihilate, leaving nothing. The great mystery is why enough matter was left over that we and our matter universe could exist."
posted by lagado (11 comments total)

If, as Richard Feynman predicted, anti-particles travel backwards in time, I'm curious how someone could come up with a method of storing them. Also, if M-AM reactions lead to mass annihilation, than creating significant amounts of antimatter on Earth seems a bit risky to say the least.

(Feel free to correct my rudimentary understanding of quantum physics)
posted by dr. zoidberg at 11:34 PM on June 24, 2001

I'll let the physicists (SDB? Kris? Bueller?) do the real talking, but if I understand it well, there should be an equal amount of matter and anti-matter in the universe, and the anti-matter is not confined to some Bizarro Earth on the other side of oblivion. It's right here.

...except in my room. I have an matter/anti-matter imbalance and a bit more anti-matter could be quite useful right now in straightening up. Of course, I'm sure it would just vaporize my Miles Davis CDs and not the pizza boxes and chocolate milk bottles I'd prefer it to.
posted by fooljay at 12:05 AM on June 25, 2001

If, as Richard Feynman predicted, anti-particles travel backwards in time, I'm curious how someone could come up with a method of storing them.

I guess they store them from the moment they let them go right up until the moment when they first captured them.
posted by lagado at 12:35 AM on June 25, 2001

considering we dont understand the universe.. there is no grand unified theory.. one of these days we are gonna poke in the wrong place and someones gonna say "42!" and the earth will cease to exist.
posted by stbalbach at 6:16 AM on June 25, 2001

What's an anti-election? Oh. I get it. Sorry. Interesting!
posted by ParisParamus at 6:25 AM on June 25, 2001

We're getting to points at which experimental physics bumps into theoretical physics. Which is interesting in a cultural as well as a scientific sense, given that there's a classic Aristotle vs Plato tension between the two groups. Not that I think the two will annihilate one another, though there may be a few black eyes.
posted by holgate at 6:47 AM on June 25, 2001

I'd like a little more evidence that this thing isn't going to cause the universe to end before they go forward with this.
posted by straight at 9:30 AM on June 25, 2001

"Any difference between antimatter and matter would be extremely interesting since we do not yet understand why we have a universe made of matter. We would expect that the big bang that originated our universe would create equal amounts of antimatter and matter, which would then annihilate, leaving nothing. The great mystery is why enough matter was left over that we and our matter universe could exist."

Well, according to Stephen Hawking there is a logical explanation for why the universe contains more matter than antimatter, even if, in the beginning, the amounts were relatively the same. The properties of the strong nuclear force combined with the electromagnetic and weak forces suggest that, at low energies, anti-quarks can turn into electrons. The absence of gravity in this theory probably doesn't amount to much, considering gravity's effects are so weak that when dealing with particles of this size they can be neglected.

Now, it would seem, despite my elementary understanding of physics, that it would make more sense to trap the anti-particles and, rather than create anti-hydrogen, attempt to convert them to particles. Just a thought.
posted by Oddsea at 10:09 AM on June 25, 2001

Hawking says that? Unless there were exactly the same quantity of both types of particles, the universe would always end up with one predominating, since most would be annihilated in matter/anti-matter collisions. If the universe is 49% antimatter and 51% garden-variety-matter, then 98% will be annihilated and the remaining 2% matter will be all that's left. This is almost the standard exmple of symmetry breaking. The actual quantities would probably be much closer, of course. The only exceptions would be local concentrations of antimatter that happened to escape collisions with ordinary matter. I'm not sure what role the strong force would pay in this scenario.
posted by rodii at 11:09 AM on June 25, 2001

Why is there more matter in the universe than anti-matter is one of those Big Questions (and stbalbach, do stop being such a Henny Penny ;-j)

The ATRAP collaboration is interested in finding differences between the properties of a particle and its anti-matter equivalent. If they were in every respect symetrical in their properties and interactions then it's hard to see why there would be an asymetrical preference towards one or the other and yet there has clearly been one.

I think they state it pretty clearly here (sorry for the long quote):

Testing PCT Invariance

Comparisons of the orbital cyclotron frequencies of antiprotons and protons test the PCT invariance theorem, as do comparisons of the structure of antihydrogen and hydrogen.

Historically, P, which stands for parity, was examined first. To understand the concept, imagine conducting an experiment in which the outcome is watched in a mirror. Now suppose a second experiment is constructed that is the mirror image of the first. If parity is conserved, the outcome of the second experiment should be identical to the outcome observed as the mirror image of the first experiment performed.

Until 1956, it was believed that reality was invariant under such a parity transformation. Early that year, however, Lee and Yang, then at Columbia University and the Institute for Advanced Study in Princeton, N.J., respectively, realized that the invariance of parity in weak interactions, which are responsible for radioactive decay, had not yet been tested. Later that year Wu and her colleagues at Columbia showed that mirror-image experiments did not produce mirror-image results when weak interactions were involved. The widespread belief in parity conservation was shattered.

Faith in a new invariance, PC, rapidly replaced the discredited notion. C stands for charge conjugation, a "thought experiment" process that turns particles into their corresponding antiparticles. To test whether PC is conserved, a mirror-image experiment is constructed, and all the particles in the experiment are replaced with their corresponding antiparticles. In 1964 Cronin and Fitch, then at Princeton University, used particles called kaons to demonstrate, explicitly and unexpectedly, that PC is not conserved.

Today most physicists believe that PCT is invariant (the T stands for time reversal). Thus far theorists have yet to construct a reasonable theory in which PCT is not conserved. To test the invariance of PCT, imagine making a movie of an experiment's mirror image in which all the particles have been replaced by their corresponding antiparticles. Then a second experiment is performed to mimic what one sees in the film when it is run backward - when "time is reversed".

One consequence of PCT invariance is that the circular cyclotron frequencies of the antiproton and proton in a magnetic field should be identical. TRAP looked for differences in the measured cyclotron frequencies and found no evidence of violations of CPT invariance at the level of 9 parts in 1011. The TRAP experiment is currently one of the most accurate tests of PCT invariance, certainly the most stringent test carried out with baryons and antibaryons.

Another consequence of PCT invariance is that the structure of antihydrogen and hydrogen should be identical. This is the prediction that ATRAP intends to test at even higher accuracy. We shall see whether this invariance under PCT continues to hold.
posted by lagado at 3:39 PM on June 25, 2001

posted by fooljay at 10:14 PM on June 26, 2001