The antiproton is the proton's twin, only with a negative charge. When such a twin approaches a nucleus, it doesn't just bounce off: a whole dance of attraction and repulsion unfolds between them. Physicists at CERN have learned to calculate this dance for the lightest nuclei — deuterium (proton plus neutron), tritium, and helium-3.
The method is like assembling a picture from building blocks. The nucleus is described as a set of protons and neutrons, each with its own position and spin (internal rotation). The antiproton is added as another block, but with a different rule: it doesn't need to be exchanged with the nucleus's particles because it isn't identical to them. This simplifies the calculation without sacrificing accuracy. The scientists computed how strongly the antiproton scatters, how the energy levels in the bound system change, and where annihilation most often occurs — the flash when a particle and an antiparticle vanish, turning into other particles.
The main difficulty is the forces between the antiproton and nucleons at short distances. They are very stiff, like a compressed spring. To describe such a spring, you need many blocks: that is, a huge number of basis states. This requires powerful computers and patience. The scientists found a way to get by with fewer blocks without losing accuracy.
Such calculations will help interpret future experiments with antihydrogen — an atom where an antiproton replaces the proton and a positron replaces the electron. If we learn to precisely predict how antimatter interacts with ordinary matter, we can look for the slightest differences between them. What if the antiworld is just a bit different from ours?
When an antiproton and a proton meet, they annihilate, releasing enough energy to boil a drop of water.
In the series Star Trek, antimatter engines use the annihilation of protons and antiprotons to propel the ship.