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
A project called PUMA aims to transport antimatter from one CERN facility to another in order to investigate exotic nuclear phenomena
The BASE collaboration breaks its own precision measurement record of antiproton’s magnetic moment
GBAR (Gravitational Behaviour of Antihydrogen at Rest) has just had a brand new part installed – an antiproton decelerator
The first antiproton beam has been successfully injected and circulated into ELENA, the Extra Low ENergy Antiproton deceleration ring
The ALPHA experiment at CERN’s Antiproton Decelerator reports the first observation of the hyperfine structure of antihydrogen
What is the effect of gravity on antimatter? A new experiment at CERN is preparing to join the quest to find the answer to this question in physics
CERN experiment reports sixfold improved measurement of the magnetic moment of the antiproton
BASE has kept a shot of antiprotons trapped for more than one year: it is the longest-lived, coldest, known baryonic antimatter object in the Universe
The commissioning of ELENA, a new antiproton deceleration ring, has begun
In September 1995 physicists at CERN synthesised the first antihydrogen atoms, paving the way for today’s growing antimatter research