 Now, let's take a look at some of the new particles that sent the world physics into never-before-seen territory. In 1932, Carl David Anderson began investigations into cosmic rays and encountered unexpected particle tracks in his cloud chamber photographs. The 6 mm thick lead plate in the chamber is designed to slow particles down. This particle came up from the bottom and is curving counterclockwise, indicating that it has a positive charge. You'll note that its curvature increases after passing through the lead plate. This curvature indicates that its mass is the same as an electron. This was the discovery of the positron. In 1928, four years before Anderson discovered the positron, Paul Dirac predicted the existence of antimatter and proposed that all particles had antiparticles and that they would annihilate each other if they came into contact. The positron is the antiparticle of the electron. This is an example of converting matter to energy.