Clegg - Quantum Theory: a Crash Course

This lack of fixed values for properties of particles did not sit comfortably for some of the earliest scientists involved in quantum theory at the beginning of the twentieth century. Notably, both Max Planck, who came up with the basic concept that light could be quantized, and Albert Einstein, who showed that this quantization was real and not just a useful calculating tool, hated the intrusion of probability into what they felt should be the fixed and measurable reality of nature. Einstein was convinced for his entire career that beneath the apparent randomness and probability there was some structure, something that behaved like the ordinary physical world. Yet all the evidence is that he was wrong.

The younger players, starting with Niels Bohr, and people such as Erwin Schrdinger, Werner Heisenberg, Paul Dirac, and Max Born, quantified probability-driven quantum behavior during the 1920s. Their progress was remarkable. These were theoreticians who had little time for experiment. Their ideas could be described as inspired guesswork. And yet the mathematics they developed matched what was later observed in experiments with impressive accuracy.

From the 1930s to the present day, there were a whole string of technological advancements in electronics, the development of the laser, the increasing employment of superconductivity, and more, each of which made direct use of the supposedly weird behavior of quantum particles. It is hard to deny something exists when you build it into gadgets found in every home. And the trigger for quantum physics to move from obscurity to center stage would be World War II.

Many of the key players in the second and third generation of quantum physicists, from Niels Bohr to Richard Feynman, played a significant role in World War II. Their involvement primarily revolved around nuclear fission. In 1938, German physicist Otto Hahn and Austrian physicist Lise Meitner demonstrated radioactive decay, a quantum process, subject to the same influence of probability as other behaviors of quantum particles. In itself, nuclear fission was interesting, but the importance of the process became clear when combined with the idea of the chain reaction. It could either run as a controlled reaction, generating heat, or given its head, it could run away with itself in an ever-increasing cascade, producing a nuclear explosion.

As the world headed unsteadily toward all-out war, there was a fear that Germanywith Denmark and Austria key centers for quantum physicswould produce a nuclear weapon, giving it a terrifying military advantage. In response to this threat, one of the first of the familiar names in the quantum theory story to become involved was Albert Einstein. Einstein was a lifelong pacifist, and it had not occurred to him that the intersection of E = mc2 and nuclear decay could produce a devastating bomb. He was asked to sign letters to the US authoritiesand President Roosevelt was persuaded into action, setting up the Manhattan Project, which saw the United States produce and deploy the first atomic bombs in 1945.