For most of human history, the universe was thought to be eternal and unchanging. That picture shattered in 1929. At the Mount Wilson Observatory, astronomer Edwin Hubble pointed the 100-inch Hooker telescope toward distant galaxies. He was measuring their distances, which he then compared to their 'redshift'—the way their light stretched as they moved. What he found was astonishing: nearly every galaxy was rushing away from us. More than that, a galaxy's speed was proportional to its distance. This was the first observational proof that the universe is not static, but is dramatically expanding. Hubble’s discovery overturned the long-held belief in a static, unchanging cosmos. It also raised a profound new question: if everything is flying apart, what did it fly apart from?
The Big Bang Theory
How scientists worked out that the universe began in a hot, dense state, from Hubble's expanding galaxies to the cosmic microwave background and the COBE satellite's 1992 map.
The Runaway Galaxies
Frequently Asked Questions
Who first proposed the Big Bang theory?
In 1931, Belgian priest and physicist Georges Lemaître proposed that the universe began as a single 'primeval atom.' He argued that because the universe is expanding, it must have been smaller in the past, tracing back to a point where space and time began.
Where did the name 'Big Bang' come from?
The name was coined by astronomer Fred Hoyle on a BBC radio broadcast in 1949. Ironically, Hoyle was a critic of the theory and used the phrase 'big bang' to dismiss the idea of the universe being created in a single moment, but the catchy name stuck.
What is the strongest evidence for the Big Bang?
The 'smoking gun' evidence is the Cosmic Microwave Background, or CMB. Discovered in 1964 by Arno Penzias and Robert Wilson, it is the faint afterglow of the early universe's expansion, a uniform radiation cooled to approximately 2.7 Kelvin that fills the entire sky.
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