The Big Bang theory is a wide-ranging, and as yet incomplete, explanation of how the universe came into being that holds sway with a large part of the modern scientific community. In broad terms, it describes how – some 13.8 billion years ago, according to the most accurate current calculations – the cosmos was born when a tiny ‘primordial atom’ exploded, setting free a vast quantity of energy and undergoing a phase of rapid super-expansion. Then a period of cooling brought about the appropriate conditions to begin the long evolution of our universe as we know it today.
In terms of popularizing the Big Bang theory, there has been no greater figure than Stephen Hawking. His work since the late 1960s (and his capacity to communicate it) has helped consolidate the idea of a period of cosmological super-expansion in the nano-seconds following the creation of the universe – a phenomenon that helps to explain why physically distant regions of the sky look similar, since they were originally in close contact with each other.
Along with James Hartle, Hawking also developed the ‘no-boundary theorem’ that draws on quantum theory and Einstein’s General Theory of Relativity in a bid to show that it is senseless to talk of time before the universe began (not least because the General Theory proved space and time are not absolutes). Querying what predated the Big Bang, Hawking has suggested, is like ‘asking for a point south of the South Pole’.
Hawking may be the poster boy of the Big Bang theory but he is just one of an army of scientists who continue to labour to understand better its exact nature.
Birthing the big bang
The man usually considered to have come up with this extraordinary thought was, somewhat unexpectedly, a Belgian priest by the name of Georges Lemaître. He was working in the 1920s, a period in which scientific observations (notably by the British astronomer Edwin Hubble) strongly indicated that the universe is expanding, and at pace. As it became clear that galaxies are hurtling away from us in every direction, Lemaître pondered the existence of a primeval atom as the point of origin of everything. It was an idea that other scientists eagerly seized upon, developing and elucidating the theory. They envisaged a massively dense and ferociously hot mass of energy and matter no more than a few millimetres across but which contained the building blocks of the cosmos – a sort of cosmological flat-pack kit, if you like.
Yet not everyone was convinced. One significant alternative school of thought championed the Steady State Theory, which suggested that as the galaxies travel apart, new matter is created in order to maintain a constant average density across the universe. If this idea was right, the universe must stay basically the same (on the large scale) across all of time – making the Big Bang moment an impossibility. However, by the mid-1960s the pendulum was swinging towards the Big Bangers. In particular, in 1965, cosmic microwave background radiation was recorded for the first time – confirming a phenomenon long predicted by adherents of the Big Bang.
‘The Big Bang is our modern scientific creation myth. It comes from the same human need to solve the cosmological riddle.’
Carl Sagan