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Vesto Slipher determined that most spiral galaxies were receding from Earth. -
In Einstein's General Relativity establish and it was found to admit no static cosmological solutions, in Big Bang's theoretical underpinning, the universe was either expanding or shrinking. -
The idea of an expanding universe began when American astronomer Edwin Hubble began observing the phenomenon known as redshift. -
Russian mathematician Alexander Friedmann derived the expanding-universe solution to general relativity field equations. -
Alexander Friedmann used Friedmann equations to describe the Friedmann–Lemaitre–Robertson–Walker (FLRW) universe. -
Belgian astronomer and cosmologist Georges Lemaitre first proposed the expanding model for the universe to explain the observed redshifts of spiral nebulae.
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Edwin Hubble concluded that the universe was expanding calculated from their observed red-shift. -
Hubble and Milton Humason formulated the empirical Redshift Distance Law of galaxies--The Hubble's Law
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The war had provided a stimulus for industry and for economic activity in general. The collapse of the global economic system in 1929.
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Lemaître proposed in his hypothesis of the primeval atom that the universe began with the "explosion" of the "primeval atom" – what was later called the Big Bang. -
Georges Éduard Lemaître imagine the early universe was extremely dense, He proposed the idea that the universe began with this explosion, called the "primordial atom."
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The impact of the Second World War cancelled all the plans for the science investigations and experiments, engrossed everything into the field of weapon and war.
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The most advanced two countries started their own competition in the space. During the time, the development of the astronomy and the attentions and assistances of the military was highly increased. The fastest development in the 20th century happened.
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Gamow was the first to establish the idea of the Hot Big Bang, which is the idea close to Big Bang.
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The remnant cosmic background radiation from the explosion discovered and detailed observation provided by Arno Penzias and Robert Woodrow Wilson.