In 1928, British physicist Paul Dirac wrote down an equation that combined quantum theory and special relativity to describe the behaviour of an electron moving at a relativistic speed. The equation – which won Dirac the Nobel prize in 1933 – posed a problem: just as the equation x2=4 can have two possible solutions (x=2 or x=-2), so Dirac's equation could have two solutions, one for an electron with positive energy, and one for an electron with negative energy. But classical physics (and common sense) dictated that the energy of a particle must always be a positive number.
Dirac interpreted the equation to mean that for every particle there exists a corresponding antiparticle, exactly matching the particle but with opposite charge. For the electron there should be an "antielectron", for example, identical in every way but with a positive electric charge. The insight opened the possibility of entire galaxies and universes made of antimatter.
But when matter and antimatter come into contact, they annihilate – disappearing in a flash of energy. The big bang should have created equal amounts of matter and antimatter. So why is there far more matter than antimatter in the universe?
Check out this timeline for an overview of antimatter research
At CERN, physicists make antimatter to study in experiments. The starting point is the Antiproton Decelerator, which slows down antiprotons so that physicists can investigate their properties.
Not all accelerators increase a particle's speed. The AD slows down antiprotons so they can be used to study antimatter
Antimatter experiments at CERN
In the antimatter hall at CERN, numerous experiments are using antiprotons from the Antiproton Decelerator to investigate the properties of antimatter.
ACE brings together an international team of physicists, biologists and medics to study the biological effects of antiprotons
AEGIS uses a beam of antiprotons from the Antiproton Decelerator to measure the value of Earth's gravitational acceleration
ATRAP compares hydrogen atoms with their antimatter equivalents – antihydrogen atoms
ALPHA makes, captures and studies atoms of antihydrogen and compares them with hydrogen atoms
ASACUSA compares matter and antimatter using atoms of antiprotonic helium
Featured updates on this topic
ALPHA reports a measurement of the electric charge of antihydrogen atoms, finding it to be compatible with zero to eight decimal places
The ASACUSA experiment at CERN has succeeded for the first time in producing a beam of antihydrogen atoms
Help the AEGIS experiment at CERN to work out how antimatter is affected by gravity. Just join the dots!
TEDed and CERN physicist Chloé Malbrunot team up to test the principle of universality of free fall for antimatter
Latest measurements from the AMS experiment unveil new territories in the flux of cosmic rays
A ground-breaking ceremony today marked the start of construction of an extension to CERN's antimatter facility
The ALPHA collaboration has published a paper describing the first direct analysis of how antimatter is affected by gravity
The LHCb collaboration has made the first observation of matter-antimatter asymmetry in the decays the B0s
The ATRAP experiment presents most precise measurement yet of the antiproton magnetic moment
An international team of collaborators are manipulating 'fat' antiatoms at the AEGIS experiment at CERN's Antiproton Decelerator
The recently installed AEGIS experiment will examine the effect of gravity on antimatter
At CERN today, the experiments at the Antiproton Decelerator presented updates on their work in 2012, and their hopes for 2013