INTRODUCTION

While the 19th century had seen a fundamental change in the way scientists view life processes, the first half of the 20th would prove even more of a shock. The old certainties of classical physics, largely unchanged since Isaac Newton, were about to be thrown away, and nothing short of a new way to view space, time, and matter was to replace it. By 1930, the old idea of a predictable Universe had been shattered.

A new physics

Physicists were finding that the equations of classical mechanics were producing some nonsensical results. It was clear that something was fundamentally wrong. In 1900, Max Planck solved the puzzle of the spectrum of radiation emitted by a “black box”, which had stubbornly resisted classical equations, by imagining that electromagnetism travelled not in continuous waves, but in discrete packets, or “quanta”. Five years later, Albert Einstein, a clerk working at the Swiss Patent Office, produced his paper on special relativity, asserting that the speed of light is constant and independent of the movement of source or observer. After working through the implications of general relativity, Einstein had found by 1916 that notions of an absolute time and space independent of the observer had gone, to be replaced by a single space-time, which was warped by the presence of mass to produce gravity. Einstein had further demonstrated that matter and energy should be considered aspects of the same phenomenon, capable of being converted from one to the other, and his equation describing their relation – E = mc² – hinted at an enormous potential energy locked inside atoms.

Wave–particle duality

Worse was to follow for the old picture of the Universe. At Cambridge, English physicist J J Thomson discovered the electron, showing that it has a negative charge and is at least a thousand times smaller and lighter than any atom. Studying the properties of the electron was to produce new puzzles. Not only did light have particle-like properties, but particles had wave-like properties, too. Austrian Erwin Schrödinger drew up a series of equations that described the probability of finding a particle in a particular place and state. His German colleague Werner Heisenberg showed that there was an inherent uncertainty to the values of place and momentum, which was initially thought to be a problem of measurement, but later found to be fundamental to the structure of the Universe. A strange picture was emerging of a warped, relative space-time with particles of matter smeared across it in the form of probability waves.

Splitting the atom

New Zealander Ernest Rutherford first showed that an atom is made mostly of space, with a small, dense nucleus and electrons in orbit around it. He explained certain forms of radioactivity as the splitting of this nucleus. Chemist Linus Pauling took this new picture of an atom and used the ideas of quantum physics to explain how atoms bonded to one another. In the process, he showed how the discipline of chemistry was, in reality, a subsection of physics. By the 1930s, physicists were working on ways to unlock the energy in the atom, and in the USA, J Robert Oppenheimer led the Manhattan Project, which was to produce the first nuclear weapons.

The Universe expands

Up to the 1920s, nebulae were thought to be clouds of gas or dust within our own galaxy, the Milky Way, which comprised the whole of the known Universe. Then American astronomer Edwin Hubble discovered that these nebulae were in fact distant galaxies. The Universe was suddenly enormously bigger than anyone had thought. Hubble further found that the Universe was expanding in all directions. Belgian priest and physicist Georges Lemaître proposed that the Universe had expanded from a “primeval atom”. This was to become the Big Bang theory. A further puzzle was uncovered when astronomer Fritz Zwicky coined the term “dark matter” to explain why the Coma galaxy cluster appeared to contain 400 times as much mass (as seen from its gravity) as he could explain from the observable stars. Not only was matter not quite what it had been thought to be, but much of it was not even directly detectable. It was clear that there were still major holes in scientific understanding.