Compton’s 1932 cosmic ray surprise revealed antimatter and reshaped physics forever

It looked like an electron but carried the opposite charge

In 1932, Arthur Compton’s cosmic-ray experiments using a cloud chamber uncovered a particle that matched an electron’s mass but flipped its electric charge. The striking image offered early experimental proof of antimatter, challenging existing assumptions about matter. The discovery didn’t just change physics—it also laid groundwork for modern medical imaging such as PET scans.