Antimatter Explained: How CERN Makes It, Traps It and Why SF Gets It Wrong

What antimatter is

For almost every particle of ordinary matter there is an antiparticle with the same mass and opposite electric charge. The electron has the positron, the proton has the antiproton, and so on. When a particle meets its antiparticle they can annihilate, converting their mass into other particles and energy, often high-energy gamma rays.

Paul Dirac's equation for the electron, published in 1928, implied such partners. Carl Anderson found the positron in cosmic-ray tracks in a cloud chamber in 1932. The antiproton followed in 1955, discovered by Owen Chamberlain, Emilio Segrè and colleagues at the Bevatron accelerator in Berkeley, work that earned the 1959 Nobel Prize in Physics.

Antimatter is already around you

Antimatter sounds exotic, but small amounts appear in everyday settings.

• Medical imaging: positron emission tomography (PET) uses tracers such as fluorine-18, which emit positrons. The scanner detects the gamma rays produced when those positrons annihilate with electrons in the body.
• Natural radioactivity: potassium-40, present in foods such as bananas, very occasionally decays by emitting a positron.
• Cosmic rays: high-energy particles striking the atmosphere create positrons and other antiparticles constantly.
• Thunderstorms: space telescopes have detected signs of positrons produced in powerful bursts of gamma rays above thunderstorms.

In each case the antimatter lasts only a moment before meeting ordinary matter. The hard part is not making antiparticles, it is keeping them.

How CERN produces antiprotons

CERN's antimatter programme starts with protons from the Proton Synchrotron, accelerated to a momentum of 26 GeV/c and fired into a metal target. Most collisions produce ordinary particles, but a tiny fraction create proton-antiproton pairs. Magnets pick out the antiprotons, which emerge at around 3.5 GeV/c, far too fast for any experiment that wants to hold them still.

They go into the Antiproton Decelerator (AD), a ring operating since 2000. Instead of speeding particles up, it slows them down, using stochastic and electron cooling to squeeze the beam while reducing its energy to about 5.3 MeV. Since then a second, smaller ring called ELENA (Extra Low ENergy Antiproton) has been added. It decelerates the antiprotons further, to about 100 keV, so that experiments can capture a much larger share of them.

How antimatter is trapped

Antiprotons cannot touch any wall, so they are held in Penning traps, which combine a strong magnetic field with electric fields to confine charged particles in a vacuum. Positrons, usually collected from a radioactive source, can be stored the same way.

Antihydrogen, an antiproton bound to a positron, is harder. It is electrically neutral, so electric fields cannot hold it. Experiments such as ALPHA use magnetic traps that exploit the atom's tiny magnetic moment, which only works if the atoms are extremely cold. The milestones show how difficult this is.

• 1995: the first antihydrogen atoms were made at CERN's earlier LEAR ring, but they flew away at high speed.
• 2002: the ATHENA and ATRAP experiments produced large numbers of cold antihydrogen atoms.
• 2010: ALPHA reported trapping antihydrogen, 38 atoms in its first published result.
• 2011: ALPHA held antihydrogen for about 1,000 seconds.
• 2023: the ALPHA-g experiment reported that antihydrogen falls downward under gravity, as general relativity predicts.

Why it matters

The research is not about energy production. It is about one of the largest open questions in physics: the Big Bang should have produced matter and antimatter in equal amounts, yet the observable universe appears to be made almost entirely of matter. Something tipped the balance, and the known differences between matter and antimatter are not large enough to explain it.

So CERN experiments compare the two with extreme precision. If antihydrogen's spectrum, the antiproton's magnetic moment or antimatter's response to gravity differed even slightly from ordinary matter, it would point to new physics. So far every measurement agrees with the predictions, which is itself an important result. Experiments such as BASE also work on transportable traps, with the aim of moving antiprotons to quieter laboratories for even more precise measurements.

There is also a link to everyday technology. Experiments on antimatter push the limits of vacuum systems, superconducting magnets, particle detectors and precision lasers, and these skills feed back into other fields. The direct medical use of positrons in PET scanning is a reminder that antimatter physics is not only a question for cosmologists: the same annihilation that limits storage at CERN is what lets a hospital scanner locate a tumour.

Why science fiction misuses it

The annihilation of matter and antimatter converts mass to energy completely, so on paper it is the densest energy source imaginable. One gram of antimatter meeting one gram of matter would release about 1.8 x 10^14 joules, roughly the energy of a 43-kiloton explosion. That number is why antimatter fuels so many starship engines and doomsday devices.

The reality is different. Production is extraordinarily inefficient: far more energy goes into the accelerators than could ever come back from the antiprotons. CERN has noted that if all the antimatter it has ever made were annihilated at once, the energy would light an ordinary light bulb for only a few minutes. Storage is limited to small numbers of particles in delicate traps. Antimatter is not a fuel; it is at best a battery with a catastrophic charging loss.

Popular fiction also tends to treat antimatter as a single substance that can be poured into a tank. In practice, what exists is a few antiprotons, a few positrons or a few antihydrogen atoms, each held under precise conditions. Making bulk solid or liquid antimatter, and keeping it away from every container wall, is far beyond any known technology.

How a writer can use antimatter plausibly

1. Treat it as a storage medium, not a source. A civilisation would need a huge energy supply, such as large solar collectors close to a star, to make antimatter in the first place.
2. Make containment the drama. A failing magnetic trap, a power cut or a vacuum leak is a far more credible threat than a villain with a canister.
3. Use small quantities. Milligrams or micrograms can still matter, for example as a trigger or a precision propulsion aid, without breaking physics.
4. Use the real mystery. A story built around why the universe prefers matter, or around a surprising measurement, can carry tension without explosions.
5. Respect the logistics. Transporting antimatter means transporting a working trap with power, vacuum and cooling, and that is a plot in itself.

The interesting thing about antimatter is not how much energy it holds. It is how hard humanity has to work to hold even a few atoms of it.

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Massimo Marino Author Editorial Team

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