... Matter's evil twin
“If A is any particle and this particle has no attributes other than linear and angular momentum (which include energy and spin), then A is its own anti-particle--one of the constituents of antimatter. For example, the photon is its own anti-particle. If a particle has other attributes (such as an electric charge Q), then the anti-particle has the opposite attributes (or a charge of -Q). The proton and neutron have such attributes.”— Maria Spiropulu – Professor of physics at the California Institute of Technology and ex CERN researcher.
Opposites have an innate, childish appeal. Light has dark, yin has yang, positive has negative and Spock has mirror-Spock. This might seem like nothing other than a result of our tendency to explain and attempt to understand the differences inherent in nature, but physics tells us that opposites are actually fundamental elements of the universe. The subatomic building blocks of matter have mirror images – and those anti-particles can form into anti-atoms and in theory, those anti-atoms could form into an anti-you. Electrons replaced with positrons, protons replaced with anti-protons and neutrons replaced with anti-neutrons; anti-matter is like ordinary matter staring into some invisible, universal mirror.
In the early 20th century, the world of physics was developing at an alarming pace. Einstein told us that mass is merely a concentrated form of energy (e=mc2) and published his theory of special relativity, and then quantum mechanics came along and showed everybody how thoroughly mind-boggling the subatomic world was. Paul Dirac set out to describe the electron according to the laws laid down by Einstein and the rules of quantum mechanics, and in 1928 he managed it. However, his equation had a little catch – it also allowed for the existence of an (ordinarily negative) electron with a positive charge, the positron.
Dirac postulated that all of the building blocks of matter have these twins with opposite characteristics. Particles are classified through things like their “spin” and their electric charge – and these qualities are the exact opposite in anti-matter. In essence, a proton is bound to an electron because they have opposing electromagnetic charges, so in the same way an anti-proton could have an orbiting positron – so anti-atoms are completely possible.
This isn’t all theory – in 1932 Dirac’s prediction was shown to be correct, with Carl Anderson actually finding a positron. Its opposing charge was confirmed by its behaviour in a magnetic field, and since then the anti-proton and numerous other anti-particles have been discovered. The main aim of experimental researchers now is assembling anti-atoms (such as anti-hydrogen), and this was first accomplished at CERN in 1995.
Produced in Pairs, annihilated in Pairs
When energy condenses into mass, it produces both matter and anti-matter. You don’t get a proton without an anti-proton, and both of them should function according to the same laws of physics. This is merely a theoretical assumption, though, and testing it in practice is extremely challenging. You see, when matter and anti-matter meet, physicists use the term “annihilation” to describe what happens. This essentially tells you everything you need to know – they go back from mass into pure energy, in the form of an explosion.
Jeff Hangst from Denmark’s Aarhus University works against this process in his experiments on anti-hydrogren atoms. He explains, “What we'd like to do is see if there's some difference that we don't understand yet between matter and antimatter,” but keeping the anti-hydrogen locked in one place isn’t easy. They’ve had to map the electromagnetic “character” of the atom and create what they describe as a magnetic “bottle” to hold it. It still doesn’t last very long though, disappearing after a fraction of a second. Professor Paul Nolan from Liverpool University is still impressed, though, “In physics terms, a fifth of a second is a long time.”
The big bang problem
If matter and anti-matter are created together from condensed energy, and they annihilate each other when they come into contact, the creation of any kind of matter presents a big problem. Theoretically, equal amount of matter and anti-matter would have been created in the big bang, and then it would have all been destroyed when they came back into contact. The universe should contain no matter at all. What we’re faced with now is a universe with predominantly matter, and hardly any anti-matter aside from that created during radioactive decay. Something is obviously awry.
The main theory that has been suggested to explain this is that our universe had a slight imbalance of matter to anti-matter at the big bang, somewhere in the order of one extra matter particle for every billion matter and anti-matter particles created. What ensued in the early universe would then be a cacophony of annihilation, leaving a scrap of debris behind. That debris represents the subatomic particles which make up all of the galaxies, stars and planets in the universe and every single atom in your body.
The DZero experiment at Fermilab involved smashing a lot of protons and anti-protons together in a particle accelerator. The collisions create both pairs of muons and anti-muons, but the researchers found a 1 percent difference in favour of muons – the ordinary matter. This hints at a solution to the problem, but it’s only a hint. Researcher Dr. Guennadi Borissov commented, “This beautiful result provides important input to understanding the matter dominance in the Universe.”
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