The Embarrassing Menagerie – Part Three
The quest to understand the true nature of the atom soon left scientists awash in a menagerie of particles that did little to enlighten them. In fact the results of these atom-smashing experiments became more and more difficult to understand, and even more difficult to explain. The dream of finding a simple model to explain the constituents of the atom quickly faded in the gloom of the cloud chambers in which these collision experiments took place.
The first indication of the complexity that was to come occurred in 1928 when a British theoretical physicist named Paul Dirac produced a theoretical proof demonstrating the existence of a positively charged nuclear particle. At first it was assumed that he had come up with a theoretical proof accounting for the existence of the proton. Closer examination however revealed that this was not the case, as Dirac’s theoretical particle had the wrong mass.
Although Dirac’s hypothetical particle was hardly taken seriously at the time, a young American physicist named Carl Anderson discovered just such a particle some years later while investigating certain effects of cosmic radiation. Anderson called this particle a “positron”, since it was similar in mass to an electron, but carried a positive electrical charge. Anderson’s particle was in fact the exact opposite of the electron, and for this discovery he was awarded the Nobel prize in 1936.
With the experimental confirmation of the existence of Paul Dirac’s theory of anti-electrons, it was natural for physicists to look next for negative protons. These negative protons needed to be identical to protons in mass, but carry a negative charge. In 1955, proof of the existence of just such a particle was confirmed in a collision experiment. This was followed one year later by the discovery of anti-neutrons.
Physicists then found that for every particle of known charge, there existed in nature an exact counterpart with an opposite charge. So for every particle there existed an anti-particle. While particles combined together to form matter, anti-particles combined together to form what was described as “anti-matter”. And whenever particles of matter and anti-matter collided, they were found to annihilate each other in a vivid burst of light, or electromagnetic radiation.
As more and more of these collision experiments were undertaken, with particles accelerated to speeds that came ever closer to the speed of light, more and more strange new particles began to be discovered. Not only were the existence of these particles hitherto unsuspected, but they appeared to be every bit as elementary as the elementary particles out of whose collisions they were formed.
As more and more particles came to be seen in their cloud chambers and observed on photographic plates, physicists like Robert Oppenheimer began to wonder:
“We do not know whether to say of these objects that they are ejected from nuclear matter or created by the encounter.” (Science and the Common Understanding)
There was, in addition, an even more extraordinary discovery. Some of the particles that emerged from these collisions were just as large as the original particles involved. it was as if two billiard balls collided together, and out of this collision four other balls emerged, two of which were the same size as the original billiard balls! Clearly something absurdly paradoxical seemed to be taking place in front of the eyes of startled physicists.
The particles that emerged out of these collisions had two main characteristics. They were all unstable, and they all existed for incredibly short periods of time. Some particles in fact lasted mere trillionths or even quintillionths of a second. And whereas the proton, neutron and electron were stable and existed freely in nature, the newly created elementary particles did not maintain their identity, but broke down spontaneously into yet other particles.
Scientists soon became embarrassed by this dazzling array of unexpected wealth. Whereas the original scattering experiments had been conducted in the hope of discovering the secret of the atom, which was initially thought to consist of just three particles, physicists now found themselves with a menagerie of over two hundred mysterious particles! This menagerie was referred to by Kenneth Ford, former Director of the American Institute of Physics, as “the particle zoo”.
As the British mathematician and physicist Banesh Hoffmann, who was later to become the biographer of Albert Einstein, mourned in his book “The Strange Story of the Quantum“:
“To add to the woes of the theorist, he has been overwhelmed by a veritable flood of new fundamental particles discovered in the last few years. They have mocked any hopes he may once have entertained that the structure of matter was on the verge of being clarified.”
The atom could no longer be pictured as a tiny sun surrounded by a host of electrons orbiting around it, for the nucleus bore no resemblance at all to the nature of the sun. Not only was the nucleus not solid, but it was found to be composed of numerous other particles, and that these particles did not remain intact, but changed into other particles whenever they collided with each other.
The solid atom of Democritus was now seen to be a dazzling interplay of energy, where particles were continuously being created and destroyed. In the words of Gary Zukav:
“The subatomic world is a continual dance of creation and annihilation, of mass changing into energy and energy changing to mass. Transient forms sparkle in and out of existence creating a never-ending, forever newly-created reality.” (The Dancing Wu Li Masters)
