Well, it’s not dark matter. I had that argument with a a co-worker whose father is a physics university professor, so he was sure he was right. Don’t know where the miscommunication occurred. Truth is, even though there’s almost 6 times as much dark matter as “ordinary” matter in the universe, it’s damn hard to figure out, as it only interacts gravitationally. Light passes right through it, hence the name. The “antimatter” moniker is also beautifully descriptive, but this time tells us exactly what the stuff is. It interacts with light and everything else like usual, it just happens to have the exact opposite charge. Antiprotons are the same mass as protons, but with a negative charge; antielectrons (better known as “positrons”)… well, I’ll let you guess. While “ordinary” guys like you and me are scarily underrepresented next to dark matter, there isn’t much antimatter kicking around these days. The reasons why are simple and yet puzzling.
The main reason is ANNIHILATION! FUCK yeah! When a particle and its corresponding antiparticle meet, E = mc² takes over and the bits are transformed explosively into energy, often in the form of photons. Why this happens is a little murky, but you can kind of imagine that particles want to have as little mass as possible, and photons have zero mass. Non-matched particles can’t annihilate each other because something wouldn’t be conserved, like spin or charge. The deadly doppelgangers fit just right.
The opposite can actually occur through a process called “pair production,” when a high energy photon can spontaneously turn into an electron and a positron. Holy shit! Being in close proximity to each other, the two particles usually, you guessed it, ANNIHILATE each other and exit as quickly as they entered, but when the pair is produced near the event horizon of a black hole, sometimes the antiparticle will “fall in” while the other one flies off into space and sticks around, a phenomenon called Hawking radiation. Freaky!
All right, so if matter and antimatter annihilate each other as soon as they come in contact, maybe the question isn’t “where’s all the antimatter,” but why is there… anything at all? Doesn’t it stand to reason that if both kinds of matter exist, equal amounts of each would have been created? That’s what the standard model of particle physics predicts. So why wasn’t there a Big Boom that blew all our matter into energy? Maybe the antimatter is still out there, but it’s hiding. There can’t be large chunks of it in the observable universe, or we’d be able to notice the high energy photons from the annihilation at the “boundary” with all the regular matter. It could be beyond the observable range, so far away that the light from those regions hasn’t yet reached the Earth, but why would it all be sequestered off in a corner somewhere?
If, alternatively, more matter than antimatter was created at the beginning of the universe, there must be fundamental differences between the two things we don’t yet understand. Current experiments trying to find out if antimatter reacts differently to gravity or if the magnitudes of its magnetic charges deviate from those of normal matter at all could set us on the path to provide a backdoor reason for why regular matter eked out its counterpart.
This universe ain’t big enough for the both of us. Image from physicscentral.com
Even though there isn’t much antimatter, more is produced every day! Cosmic rays smashing into the atmosphere create some through pair production. Coming from the other side, positrons are also products of certain kinds of radioactive decay. We take advantage of this process with Positron Emission Tomography, the PET scan that produces three dimensional images of functional processes in the body. And if that’s not enough, we can even whip some up ourselves! Antimatter is a not uncommon product of particle accelerators, and the wizards at the European Organization for Nuclear Research (CERN) have even been able to create and isolate entire hydrogen atoms of the stuff!
WHAT DOES THIS MEAN?
Given the tremendous amounts of energy released during matter-antimatter reactions, could we use those antiparticles for spaceship fuel or even weapons? Well, you’d have to hold it first, and even with the best vacuums in the world, those antihydrogens don’t last very long before they find a partner to shuffle off this earthly coil with. And you’d need A LOT of it. According to CERN senior physicist John Eades in a 2012 Skeptical Inquirer article, if all the antiprotons EVER produced at the laboratory over its near 60 years of operation were somehow bottled and used as an energy source… it would power a sixty-watt light bulb for eight or nine minutes. Not exactly enough to push us to the stars. Making bombs would be an even worse proposition. At the current viable bottling rate, you could muster enough antiprotons to make a hydrogen bomb-sized explosion in just about 10,000 times the age of the universe.
While we have a pretty good idea what antimatter is, why we don’t see much of it is an ongoing mystery. The paltry particles we’re able to produce won’t likely even the scales anytime soon.