Why Is There Anything at All? The Universe Should Have Cancelled Itself

For every kind of particle there exists a partner with the same mass and the opposite electric charge and opposite values of certain other properties. The partner of the electron carries a positive charge, the partner of the proton a negative one, and the neutral particles have partners too, distinguished by other properties rather than by charge. When a particle meets its partner both are destroyed and their entire mass is converted into energy, usually as high-energy light, which is the most complete conversion of mass to energy that occurs anywhere and is the reason the subject has such a grip on the imagination.

The discovery followed prediction, which is unusual and was persuasive:

• •Paul Dirac's 1928 equation had solutions with negative energy
• •He interpreted those in 1931 as particles of opposite charge
• •Carl Anderson found such a track in cosmic rays in 1932
• •The partner of the proton followed in 1955 at an accelerator
• •Whole antihydrogen atoms were first made in 1995
• •Those atoms were trapped and studied from 2010 onwards

The problem is stated simply and has not been solved. Energy converting into particles produces matter and its counterpart in equal quantities, so the early universe should have contained equal amounts of both, which should then have annihilated completely and left nothing but light. Instead there is a universe of matter with only traces of the counterpart, created in collisions and in certain decays. The leading explanation is a slight asymmetry in the laws themselves, favouring matter by roughly one part in a billion, and small asymmetries of exactly that kind have been observed in the decay of certain particles since 1964. The observed asymmetries are far too small to account for the imbalance.

The reputation as an energy source survives the arithmetic badly. The conversion is complete, so a gram would release an enormous amount of energy, and that is the whole of the case for it. Against that, none exists naturally in usable quantity, so every particle must be manufactured in an accelerator at an energy cost vastly greater than what it would later release, which makes it a very poor battery rather than a fuel. Production rates are measured in nanograms per year across all facilities combined. Storage requires holding charged particles in a vacuum by magnetic fields indefinitely, since contact with any wall destroys them.

Despite its reputation as an exotic fuel, the real applications are medical and analytical. Positron emission tomography injects a substance containing an atom that emits the electron's counterpart, and when each one annihilates with a nearby electron it produces two photons travelling in exactly opposite directions, which detectors around the patient record, allowing the point of origin to be calculated and an image of metabolic activity to be built. That is a routine hospital scan performed millions of times a year. Research facilities use the counterparts to test whether the laws really are symmetrical, including measuring whether antihydrogen falls downward, which was confirmed in 2023.

Every particle has a partner of opposite charge, and contact destroys both and converts their entire mass to energy. Dirac predicted it in 1931 and Anderson found it in 1932. Equal amounts should have been made in the early universe and annihilated completely, and the slight asymmetries observed since 1964 are far too small to explain why anything survived. The practical use is the hospital scanner.