# Antimatter

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.

# The Antiproton Decelerator

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

ACE brings together an international team of physicists, biologists and medics to study the biological effects of antiprotons

# AEGIS

AEGIS uses a beam of antiprotons from the Antiproton Decelerator to measure the value of Earth's gravitational acceleration

# ATRAP

ATRAP compares hydrogen atoms with their antimatter equivalents – antihydrogen atoms

# ALPHA

ALPHA makes, captures and studies atoms of antihydrogen and compares them with hydrogen atoms

# ASACUSA

ASACUSA compares matter and antimatter using atoms of antiprotonic helium

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## Featured updates on this topic

### ALPHA experiment shows antihydrogen charge is neutral

21 Jan 2016 – ALPHA shows the most accurate measurement yet of the electric charge of antihydrogen atoms in a new Nature paper

### ALPHA experiment takes antimatter to a new level

22 Aug 2018 – The ALPHA collaboration has observed a new electronic transition in the antihydrogen atom

### LIVE: Inside CERN’s antimatter factory

26 Apr 2018 – On Thursday 26 April 2018 at 4pm CEST, join the CERN Facebook live from our unique Antiproton Decelerator

### A new era of precision for antimatter research

4 Apr 2018 – The ALPHA experiment at CERN has measured a light-induced transition in antihydrogen with unprecedented precision

### Making antimatter transportable

7 Mar 2018 – A project called PUMA aims to transport antimatter from one CERN facility to another in order to investigate exotic nuclear phenomena

### A more precise measurement for antimatter than for matter

19 Oct 2017 – The BASE collaboration breaks its own precision measurement record of antiproton’s magnetic moment

### GBAR’s antiproton decelerator installed

24 Aug 2017 – GBAR (Gravitational Behaviour of Antihydrogen at Rest) has just had a brand new part installed – an antiproton decelerator

### First antiprotons in ELENA

4 Aug 2017 – The first antiproton beam has been successfully injected and circulated into ELENA, the Extra Low ENergy Antiproton deceleration ring

### The ALPHA experiment explores the secrets of antimatter

3 Aug 2017 – The ALPHA experiment at CERN’s Antiproton Decelerator reports the first observation of the hyperfine structure of antihydrogen

### Raising the (G)bar for antimatter exploration

17 Mar 2017 – 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

### BASE precisely measures antiproton’s magnetic moment

18 Jan 2017 – CERN experiment reports sixfold improved measurement of the magnetic moment of the antiproton