infinitesimus:

In the late 1920s, Paul Dirac had thought that it was possible for electrons to have both a positive charge and negative energy, and while his paper on the idea didn’t explicitly state that there would be a new particle to fit the idea, the door was left open for someone to discover such a particle, and it wasn’t too long until it was found.

American physicist Carl David Anderson allowed cosmic rays to pass through a cloud chamber and a lead plate, and a magnet surrounding the apparatus would cause particles to bend in different directions according to their charge. It was this apparatus, and the image shown above, that would lead to the first piece of evidence for the antiparticle, the black curved line in the image being an ion trail that matched the mass to charge ratio of an electron, but with a positive charge - the Positron.

As with many other discoveries, Anderson wasn’t the first to have witnessed the result, but was the first to know what it was. Soviet physicist Dmitri Skobeltzin and Chinese physicist Chung-Yao Chao had observed the signs of an electron but charged positively, but chalked them up to anomalous results - Anderson himself said that if Chung-Yao Chao’s work had been followed up, the positron would have been discovered two or three years earlier.

With the discovery of the Positron came the new world of antimatter, an area of much research to this day, and long into the future.

Image: Cloud chamber photograph of the first Positron, Carl David Anderson