In 1932, a strange curve in a cloud chamber became humanity’s first proof of antimatter

As Carl Anderson investigated cosmic rays at the California Institute of Technology in August 1932, he observed some peculiar behavior of particles in a cloud chamber photo. In a cloud chamber photo, a charged particle travels through vapor as it is subjected to a magnetic force. However, there appeared to be one track that curved in such a way that it went against normal logic.Initially, it seemed like a minor scientific observation. But in the years to come, it became the first proof ever of the positron, the positively charged version of an electron. According to the American Physical Society, Anderson’s photograph recorded a particle that behaved like an electron in mass but carried a positive charge. That combination immediately ruled out an ordinary electron.This discovery marked a historic milestone in physics. It proved that nature allowed mirror images of matter.The experiment that revealed something impossibleAnderson was utilising a cloud chamber, which is an apparatus invented to cause the invisible subatomic particles to leave a visible trail as they travel through the supersaturated vapour. With the use of the curvature of these trails, physicists were able to determine the charge and momentum of a particular particle.In Anderson's research, a magnetic field causes the trajectory of the cosmic-ray particles to change in direction. While electrons, which have negative charges, curve in one direction, the unknown particle moves in the reverse direction. This fact was quite significant because it moved like a low-mass particle as opposed to a high-mass proton. NobelPrize.org states that Anderson's finding marked the discovery of the positron.It was the very design of the device that helped convince him. Anderson introduced a lead plate into the cloud chamber, which caused the particles to lose their energy while moving through it. With a comparison between the curvatures before and after the lead plate, Anderson could make assumptions about the type of particle it was. Had it been a proton, it would not have reacted the same way to energy loss.The implications were astonishing. There was an identical, but positive form of the electron in nature.A theory suddenly became realThe discovery was of great importance because it helped prove the hypothesis previously advanced by Paul Dirac, who was a theoretical physicist. His equations had implied the existence of opposite charges to particles such as the electron. Anderson’s discovery was thus very significant, for this theory had not been proved before.The positron is identified as being the first discovered antiparticle. This was an important discovery beyond particle physics. Scientists were able to prove the existence of a hidden symmetry in the universe beyond what our everyday experience would have us believe. Matter was not special anymore.The extraordinary thing about this discovery is just how inconspicuous the proof was. No bang marked the discovery. No massive machine was used to make it. A mere curve in condensed vapor brought into question what the universe held. The myth that antimatter began as science fictionModern popular culture frequently depicts antimatter as something from science fiction. In contrast, the actual discovery was based on thorough experimentation and analysis and not on entertainment.Based on what is known about antimatter, it resulted from a connection between theoretical predictions and experiments. Anderson did not assume that he had discovered antimatter. The cloud chamber provided physical evidence of antimatter due to geometric, curvilinear, and ionization properties. This explanation worked because the gathered evidence disproved any simpler hypothesis.This example demonstrates one more characteristic of a discovery in science. Innovations do not have to be large-scale discoveries or revolutionary moments. Sometimes innovation comes from a realization that some details contradict known assumptions.Why the discovery still matters todayDiscovery of the positron proved influential far beyond the context of Anderson's original experiments. As time went by, positrons became the focus of particle physics studies and of applications in medical diagnostics, for example, through the technology of PET scanning, which relies on antimatter. Reportedly, the discovery of the positron led scientists to a completely new field of study. While initially just a peculiar phenomenon observed in cosmic rays, it soon became one of the most remarkable achievements in history.Moreover, there seems to be something very human in the very narrative of the discovery. It did not come immediately as an accepted and admired fact, but rather as a peculiar line that first seemed incorrect, and then became historically important.The positron discovery stands as a testimony to how science develops through careful observation of discrepancies. One photograph taken from a cloud chamber in 1932 showed that our universe was even stranger and more symmetrical than we could have ever expected.