Fifteen positrons are emitted by a banana each day. A positron is an antimatter particle and far from being a figment of science fiction, it has been proven that it exists. However, what exactly is antimatter and why should we care?
In the late 1920s – when quantum theory was largely established and since when has yet to fail experimental testing – Paul Dirac tried to merge quantum mechanics with Einstein’s theory of relativity. The relativistic equation he produced was beautiful. His equation for the electron gave two solutions and predicted that there must be a particle identical to the electron but with a positive charge. Antimatter came from a theorist’s pen; sure enough, the positron was discovered experimentally in cosmic rays 5 years later.
Antimatter was a key player in the beginning of the universe. In order for conservation laws to be obeyed, it is believed that at the Big Bang, equal amounts of matter and antimatter were created. As these two particles come together they annihilate, releasing vast amounts of energy (0.25g of matter and 0.25g of antimatter annihilating is the equivalent of 5 kilotonnes of TNT). The annihilation produces photons of light which have enough energy to transform into a matter-antimatter pair. However, the rapidly cooling universe meant that, after a few seconds, the cosmic battle between antimatter and matter ceased. What we see around us now is a consequence of the tiny difference in the amount of matter and antimatter that existed when the universe was just one minute old. The reason for this difference is a mystery that scientists are yet to solve.
Tara Shears from the University of Liverpool describes antimatter as ‘one of the biggest questions in physics’. She is involved in the Large Hadron Collider accelerator (LHCb) where they are on the quest to prove CP violation. This is the idea that antimatter is not just an identical, oppositely charged version of matter and was first observed in 1964 – leading to a Nobel prize for James Cronin and Val Fitch. Essentially, what the LHCb is doing is isolating samples of Bs mesons then counting how many are antimatter and how many are matter. They found that the difference in number between the two types is about 25%.
Whilst these results match the current theory, it still leads to a fundamental problem: if you turn back time to the Big Bang, the prediction for how much antimatter was present is much less than expected. The amount of antimatter predicted by this theory is not half a universe but instead nearer to about one galaxy’s worth.
So this is where we are left. Perhaps it will be new physics or new particles yet to be discovered that will be the key to unlock this conundrum about antimatter and the beginnings of time. Who knows what we may find when the LHC is restarted in 2015. All I am certain of is that the anti-world matters, even if we are yet to ascertain exactly how…