The early 20th century saw many years of certainty in science overthrown by two new theories: relativity, and quantum theory. Since the time of Newton, scientists had believed that the universe and all it contained could be described in mechanistic terms, obedient to his law of gravitation and three laws of motion. All events – or at least those involving objects and forces – could be counted as predetermined, and therefore predictable.

But although for most practical purposes Newton’s laws still ruled, they were now shown to be neither absolute nor universal. According to Einstein’s theory of relativity, at speeds approaching that of light, neither time nor mass remain constant. Time and space belong to the same continuum. Both space and light can be bent by gravity.

Again, at the subatomic scale, quantum theory showed that Newton’s laws no longer applied. It showed that light, and other forms of electromagnetic radiation, are neither waves nor particles, but both waves and particles simultaneously. Other certainties also crumbled. Under Newtonian mechanics the position and momentum of any object can in theory be accurately measured at the same time. Quantum mechanics showed that at the subatomic scale you cannot measure both the position and momentum of a particle simultaneously, because making the observation itself alters the outcome.

These counter-intuitive theories – shattering our views of space, time and the very concept of cause and effect – may appear to come from an Alice-in-Wonderland world. Yet many aspects of both have been proved by observation and experiment. Quantum theory accounts for a range of phenomena, from how the eye detects light to the workings of semiconductors, a key technology in modern computers. And Einstein’s famous equation, E = mc² (where c is the speed of light), shows that mass (m) may be converted into energy (E), and is thus fundamental to both nuclear power and nuclear weapons.

The 20th century also saw revolutionary transformations in other fields, from transport, power generation and medicine to agriculture, bioengineering and computing. Scientists provided an explanation of the molecular structure of DNA and hence how genetic characteristics are inherited, and made significant progress in understanding the workings of the brain. As a result of such discoveries, the status of science soared. By the 1950s scientists had become the heralds and guarantors of progress, as engineers had been in the 19th century.

‘The unleashed power of the atom has changed everything save our modes of thinking and we thus drift toward unparalleled catastrophe.’

A horde of reporters surrounding Professor Albert Einstein in the lounge of the S.S. Belgenland as he arrived in New York City (1930)

REVOLUTIONS IN SCIENCE