Tuesday, January 25, 2011

Antimatter matters

One of the biggest mysteries of physics (and life, the universe, and everything)  is this: why is anything even here?

In physics, the question crops up at two levels. First, why did the Big Bang happen? Second, once the Big Bang did happen, matter and antimatter were, per theory, created in equal quantities. So: why didn't the universe's matter and antimatter eradicate each other and leave behind nothing but energy? 

(I'm not complaining that we're here. Merely puzzled.)

I have no answer for either question, but I admit to an interest in all things antimatter. When matter and antimatter (of matched particles, like proton/antiproton or electron/positron) meet, the result is horrific explosions. Mass and energy stand in a fixed relationship, per what is perhaps the best-known equation in physics -- E = mc squared (sorry I can't enter a superscript on blogspot) -- so we know exactly what radiation results: gamma rays with very specific energies. (It's a bit more complicated for proton/antiproton annihilation -- some secondary particles are produced along with the gamma rays. For electron/positron encounters, though, the byproduct each time is simply a photon carrying 511 KeV of energy.)

SF writers like antimatter because matter/antimatter annihilation is the most compact way to store energy -- whether for superweapons or to fuel interstellar travel. The challenge is in having any antimatter to store. Antimatter has to be created one antiparticle at a time.  E = mc squared being a symmetric relationship, we have to provide a lot of energy to create a little antimatter. Then we have to store that antiparticle without it touching anything  ... or boom.

Antimatter is produced, antiparticle by antiparticle, in extremely high energy collisions of regular-matter particles inside huge particle accelerators. Using magnetic fields, the (for example) positrons are captured from the subatomic debris. The antimatter is then held isolated by magnetic traps -- if the antimatter touches the wall of a physical container: bye-bye, antimatter.

As you might expect, antimatter produced this way doesn't come cheap. In a 1999 article, NASA said they could produce antimatter for $1.75 quadrillion an ounce. (Passing note: industrial-scale antimatter production plays a big part in my novel InterstellarNet: New Order.)

So here is a truly keen recent headline: Antimatter caught streaming from thunderstorms on Earth. Positrons, to be specific: the tell-tale gamma rays of their subsequent destruction have been caught in  satellite observations.

Alas, capturing antimatter in the middle of an upper-atmosphere lightning storm doesn't seem practical.


Erik said...

Good read. Determining what is possible is the job of a scientist, but determining how to turn 'possible' into 'practical' is the job of an SF writer.

Off topic question: who came up with the idea of using hyper-drives to wipe out GP hulls? Was it you or Niven? I find it hard to believe that humans hadn't figured it out earlier (they had both technologies for a long time). I guess they didn't know about the power plant, and the hyper space bubble is fairly small, but someone must have at least recognized that the bubble could cut the GP hull?

Edward M. Lerner said...

Thanks, Erik.

As for inventing ways to destroy the all but indestructible GP hulls, except for antimatter (as per Larry's old story, "Flatlander") I'm the guilty party.