The job descriptions for some professions require little explanation. It's pretty much self-evident that butchers are going to deal with dead animals, accountants are going to do something with money, and doctors are going to help you get better when you're sick.
But the job of a chemist is perhaps not so obvious; just what does a chemist do?
One could say a chemist studies chemistry, but what then is chemistry?
Chemistry is sometimes defined as being the study of matter. However, this is not an overly helpful definition, as it then requires one to define the term "matter".
The Oxford English Dictionary defines matter as "That which has mass and occupies space". I hesitate to argue with such a venerable text, but in this case it is wrong; there is something else that has mass and that occupies space: antimatter.
Matter is composed of atoms, which themselves comprise positively charged protons, neutral neutrons and negatively charged electrons. However, in 1928, the English physicist Paul Dirac postulated that the electron could have a positively charged counterpart of identical mass, and this particle, named the positron, was duly observed in 1932.
Likewise, the negatively charged counterpart of the proton, the antiproton, was discovered in 1955, and the antineutron in 1956. These particles are examples of antimatter, which can be thought of as a "mirror image" of ordinary matter. For example, whereas an atom of hydrogen would be made up of a single proton and a single electron, an atom of antihydrogen comprises an antiproton and a positron.
Antimatter is not something you or I would encounter in our everyday lives, for the very compelling reason that whenever antimatter comes into contact with matter, both are instantly annihilated, with the release of enormous amounts of energy.
However, last month, a team of scientists working at CERN (Conseil Européen pour la Recherche Nucléaire) in Switzerland reported they had managed to prepare and trap antihydrogen atoms for 1000 seconds, a quite remarkable achievement, and one that may have significant implications for our understandings of the origin of the universe.
The Big Bang was the source of all the matter in the universe.
However, present theories predict an equal amount of both matter and antimatter should have been produced in the Big Bang, begging the question of why they didn't just instantly annihilate each other. Given our known universe appears to consist predominantly of matter, there is either something wrong with the present theories, or matter and antimatter are not exact mirror images of each other.
The experiments at CERN will doubtless allow us a greater understanding of the properties of antimatter.
Antimatter does have at least one important application with which some of you may be familiar. A Positron Emission Tomography (or PET) scan involves the emission of a positron (the antimatter equivalent of an electron) by particular atomic nuclei which are introduced into a specific area of the body.
When this positron encounters an electron, the two particles are annihilated, with the production of two gamma rays travelling in opposite directions. Detection of these gamma rays and subsequent computer analysis allows a three-dimensional image of the area of interest to be obtained.
So while the very name "antimatter" sounds like something out of science fiction, it is very much science fact. And its as yet undiscovered properties will amaze us.
• Dr Blackman is an associate professor in the chemistry department at the University of Otago.
