More than about 13.7 billion years ago, the Big Bang occurred. The start of the Universe. Our Universe.
It is believed that one moment there was just a tiny hot ball containing everything in the universe and then a moment later, the universe burst into existence with the biggest explosion of all time, separating into basic forces such as electricity and gravity—so big that everything is still hurtling out from it—even today.
At first, the entire universe was a hot ball tinier than an atom and much hotter than any star. This swelled much, much faster than the speed of light, growing to the size of a galaxy in just a tiny fraction of a second.
As the universe expanded, it began to cool and tiny particles of energy and matter—each of them much smaller than atoms—began to form a thick, soup-like material.
After about 3 minutes, gravity started to pull the particles together. Atoms joined together to make gases such as hydrogen and helium, and the thick ‘soup’ began to clear and thin out. By the ends of the third minute, the matter that surrounds us today had been created.
Over time, as the young universe grew larger, the gases clumped into clouds. After several hundred million years, the clouds began to form stars and galaxies.
The seeds for the new view of the Universe were planted in 1916 when Albert Einstein published his theory of general relativity, from which the Dutch astronomer Willem de Sitter developed an imaginary expanding Universe. The idea became reality in 1929, when Edwin Hubble showed the Universe is expanding, which means that it was once smaller and denser. It has, however, Belgian Georges Lemaitre’s suggestion, in 1931, that the Universe’s origin was a primeval “cosmic egg” that exploded, creating an expanding Universe, which served as the first Big Bang model.
In the 1940s, Fred Hoyle together with Americans Hermann Bondi and Thomas Gold, put forward an alternative view of the Universe. The “Steady State” theory they proposed that the Universe appears the same in every location and at all times. It has no beginning or end, and matter is commonly created.
In 1948, George Gamow outlined how the relative proportions of the hydrogen and helium in today’s Universe could be produced in a Big Bang Universe. The case for the Big Bang strengthened after 1955, when Martin Ryle showed that the distant, older radio galaxies were more numerous and densely packed than those nearby. This disproved the vital characteristic of the hypothetical Steady State Universe, in which density would always stay the same.
Direct evidence for the Big Bang came a decade later. George Gamow had predicted that a remnant of the Universe’s initial radiation would remain: the microwave background that would have permeated all space, before starting to cool. This was detected in 1946 by Arno Penzias and Robert Woodrow Wilson, confirming that the Universe was intensely hot in the past.
