Nov 2, 2018
The Missing Antimatter Mystery
Why are we here?
The special creatures that swim in pockets of water at low tide. The husky brown freckles on a little girl’s face. Above, the clouds shaped like boughs of cedar or smoke or maybe cherry stems and pits. All these things are wondrous in their own right but are even more so when you realize that none of it is supposed to exist. Not the girl, not the clouds, not anything in this world.
Matter is a mystery that we don’t yet know how to explain. When the spectacle that we call the Big Bang occurred, our standard model predicts that there should have been an equal amount of matter and antimatter created. This would have occurred because the intense temperature and density spurred new particles, as per the famous e=mc². This equation tells us that matter and energy are interchangeable so that you can get mass from energy and energy from mass. According to physicists, it was light that became the atoms that make up our worlds. This possibility gained traction in the 90’s when researchers succeeded in turning light into matter by means of radiation beams. The radiations beams were smashed together until they resulted in two particles: matter, and antimatter.
To understand what antimatter is, simply imagine a positive number and then its negative counterpart. A positive hydrogen atom has an antimatter counterpart known as anti-hydrogen. It has exactly the same mass and, other than having an opposite charge, behaves in exactly the same way. Just as when -5 and 5 meet to create 0, so too do matter particles and antimatter particles meet to annihilate in powerful bursts of energy. After creating these particle pairs, the universe would have then cooled, awash only in plumes of radiation.
And yet here we are — a testament to the fact that every particle didn’t have an anti-particle pair, that there was an imbalance known today as baryon asymmetry.
Normal matter (although really that term is relative; if we had been made of antimatter we would have considered that to be “normal matter” and what we consider normal matter now to be “antimatter”) is made of protons and electrons. In antimatter this changes to antiprotons and positrons, respectively. Positrons and electrons are inseparable in the sense that they are the two possible outcomes of vibrations in the electron field, one outcome positive and the other negative. You can’t have one without the other just as you can’t have up without a down. When they come together, it creates the most efficient reaction known to physics.
At 100 times more effective than a hydrogen bomb, a couple of pounds of antimatter colliding with a couple of pounds of matter would cause an explosion 3,000 times more powerful than the Hiroshima bombing of World War 2. Even a single gram of antimatter would match the power of a nuclear bomb and would give us enough energy to launch a rocket into orbit. Needless to say, the potential for this material is enormous. And while we can make it in a lab, with our current technology it takes a billion times more energy to make antimatter than what we can get back from it. That single gram mentioned before would cost an astonishing $25 billion to produce.
Rooms at CERN’s Antimatter Factory are filled with the constant humming of machinery. Inside there’s the cold metal structures and looming blocks of concrete set out around the machines. High energy particle collisions produce antiprotons which are then bound with positrons to create anti-hydrogen. While individual anti-particles are fairly easy to come by, it’s fully formed anti-atoms that are rare and greatly sought after. The anti-hydrogen produced in these labs is held in place by a magnetic field so it doesn’t come into contact with any matter whatsoever. The result, of course, would be annihilation. These days researchers are able to hold antimatter in place for months at a time, giving them ample room to make observations.
What physicists are hoping to find is differences between matter and antimatter that would explain the baryonic asymmetry. But so far the pairs seem to act identical to one another: they react to magnetic forces in the same way, absorb the same frequency of light, and even behave identically during the famous double-slit experiment.
However, research has shown that certain particles prefer to settle as matter over anti-matter, though there’s no clear reason for this preference. Kaons are an example of this phenomenon. When particles are presented with the possibility to become either a kaon or an anti-kaon, they choose the former much more of the time than they choose the latter, even though the chances of becoming either should be split evenly. This strange behavior is known as a CP-violation — charge conjugation parity symmetry, or the fact that the laws of physics should be the same for matter and antimatter atoms. Almost two decades later (kaons were discovered in 1964) particles called B mesons were found to also be capable of CP-violation. These discrepancies, along with certain conditions and aspects of thermodynamics present during the Big Bang, could be responsible for the asymmetry we see today. A theorized set of particles and their anti counterparts with different decay channels would also help explain why there’s a bigger inclination for matter over antimatter.
The search for antimatter is now 50 years old. It began in the late 1920’s when it was mathematically theorized during Paul Dirac’s attempt to reconcile quantum mechanics and general relativity. And CERN isn’t the only place antimatter can be found. It’s also present in cosmic rays and flowing out from the center of our own Milky Way galaxy.
It’s strange to imagine entire galaxies made from antimatter — some elusive, dangerous material. And yet it’s entirely possible. Antimatter can gather just as matter does to form planets, stars, and even people. Maybe, just maybe, there exist constellations and cosmic bodies out beyond our current reach that would annihilate us upon contact. Some theoretical physicists do believe this mystery can be solved by exploring unknown regions of the universe. Someday.
But if this were the case, the point at which matter and antimatter met in the intergalactic medium would be a place of extreme violence and energy as the two came into contact. We don’t see this sort of activity anywhere in the universe, even on a smaller scale. It shows us that, as far as we can tell, 99% of the universe is made of matter.
The reason for our existence — the existence of anything — remains a fascinating unknown even in science.
