One day 20 years ago, Thomas Gehrmann had a lot of mathematical expressions on his computer screen.
He was trying to figure out the odds of three jets of elementary particles bursting from two particles smashing together. Physicists often do bread-and-butter calculations to check whether their theories match the results of their experiments. Gehrmann was going big, though, because of the longer calculations.
He had sketched diagrams of hundreds of possible ways the colliding particles could interact before shooting out three jets. Adding up the individual probabilities of those events would give a better idea of the outcome.
Gehrmann needed software to tally the terms in his formula. Is it possible to computing it? He said to raise the flag of surrender and talk to your colleagues.
Fortunately for him, one of his colleagues knew of a still-unpublished technique for shortening this kind of formula. Gehrmann saw terms merging together and disappearing by the thousands. The future of particle physics was glimpsed in the 19 computable expressions that remained.
The Laporta algorithm is the main tool for generating precise predictions about particle behavior. Matt von Hippel is a particle physicist at the University of Copenhagen.
The inventor, Stefano Laporta, remains obscure despite the spread of the algorithm. He doesn't command a lot of researchers and rarely attends conferences. A lot of people assumed he was dead. Laporta is living in Bologna, Italy, which is where he came up with the method for assessing how the electron moves through a magnetic field.
One, two, many.
The challenge in making predictions is that there are many things that can happen. An electron that is just minding its own business can spontaneously emit and return a photon. There can be more particles in the photon. The busybodies interfere with the electron's affairs.
Particles that are before and after an interaction become lines leading in and out of a cartoon sketch, while those that briefly appear and then disappear form loops in the middle. The diagrams were translated into mathematical expressions where loops became summing functions. There are more likely events with fewer loops. Physicists need to look for subtle signs of novel elementary particles that may be missing from their calculations when making the kinds of precise predictions that can be tested in experiments. With more loops comes more integrals.
The illustration is for a magazine.
