A peculiarity of Dirac’s equation is that it can be solved using either positive or negative numbers—meaning that it has two possible solutions. Dirac understood this to mean that for every particle in the universe, there must exist an equal and opposite particle. He described these opposite particles as ‘antimatter’ and theorized that the universe must contain equal quantities of matter and antimatter, which would have been produced simultaneously during the Big Bang. Furthermore, Dirac imagined that while our sun and Earth are made up of matter, there could be entire galaxies, solar systems and planets composed entirely of antimatter.
A central issue with Dirac’s theory is the relative lack of observable primordial antimatter in the universe. When matter and antimatter come into contact, they annihilate each other in a flash of energy. If the universe contains equal amounts of matter and antimatter, each with the power to completely extinguish the other, it’s surprising that from our observations of the natural world, the universe appears to consist almost entirely of matter.
In a picturesque mountainous setting in rural Switzerland, scientists at the CERN laboratory are working to answer this and other fundamental questions by exploring the composition of the universe. Using incredibly advanced tools such as particle accelerators and detectors, particle physicists have been able to glimpse the behaviour of the fundamental particles that dictate the laws of nature. Much of this research involves the use of antimatter, which CERN scientists have been successfully creating since 1995 for use in their experiments.
The production of antimatter typically begins in a device known as the ‘Antiproton Decelerator’, and involves the bombardment of metal blocks with high-energy proton beams. As the protons collide with the metal, the resulting bursts of energy have the potential to create pairs of protons and antiprotons—which happens roughly once in every million collisions. Antiprotons are then separated and directed using a complex system of magnetic fields, and slowed by passing them through clouds of electrons. Once sufficiently slowed (newly created antiprotons travel at close to the speed of light), the antiprotons are ready to be studied. In some experiments, antiprotons are slowed by passing them through clouds of cold positrons, resulting in the formation of antihydrogen—the simplest atom of antimatter.