History of Cosmology
There is evidence that some primitive forms of astronomy have existed ever since the earliest civilisations were able to record their observations of the sun, moon and stars. Four thousand years ago, the Babylonians were able to predict the motion of objects in the night sky, e.g. Sun, moon, planets and stars, even though they would have only had limited understanding of their nature. Later, the ancient Greek philosopher-scientists developed some of the earliest cosmological models within which they attempted to explain the observed motions within the night sky.
By the 4th century BC, the Greeks had developed the idea that the stars were fixed on a celestial sphere which rotated about the spherical Earth, once every 24 hours, while Sun, Moon and the planets moved in the ether between the Earth and the stars. However, we might initially try to condense the entire history of cosmology into one simple table that reflects the perceived age and size of the universe along with the speed of light:
|Ancient||<104 years||108 km||Infinite|
|Now||13.7*109 years||>1023 km||3*108 m/s|
Today, Aristotle is recognised as one of the first to try to develop a logical model of the universe, albeit that this model was possibly more of a rationalised philosophy than verified science. However, the following table is reflective of the long historical timeline of developments that have attempted to build on the model handed down by the Greeks and although this list is not exhaustive, it tries to represent some of the most significant scientific events:
| 220 -
Ptolemy lays the basic mathematical foundations
of the geocentric model
1543 - Copernicus forwards a scientific rationale for the heliocentric model
1643 – Galileo - Dialogue ` provides the arguments for the heliocentric model
1609 - Kepler publishes his laws of planetary motion
1687 - Newton publishes Principia contain laws of motion and gravitation
1755 - Kant publishes his ‘Theory of the Heavens’
|1905 - Einstein proposes the
Special Theory of Relativity
1915 - Einstein proposes the General Theory of Relativity
1922 - Slipher publishes his findings on galactic redshifts
1922 - Friedmann publishes a solution to Einstein's field equations
1927 - Lemaître proposes a creation event as a result of an expanding universe
1929 - Hubble demonstrates a linear redshift-distance relation
1933 - Milne names and formalizes the cosmological principle
1934 - Lemaître links cosmological constant to a vacuum energy.
Bondi, Gold, & Hoyle propose a steady state
1948 - Alpher, (Bethe) & Gamow introduce the concept of inflation
1948 - Gamow predicts cosmic microwave background radiation
1950 - Fred Hoyle derisively coins the term `Big Bang`.
1965 - Penzias and Wilson discover the 2.7K microwave background radiation
1968 - Carter speculates on need for a strong anthropic principle
1969 - Misner outlines the Big Bang horizon problem
1969 - Dicke outlines the Big Bang flatness problem
1981 - Guth proposes the inflationary universe to solve the horizon and flatness problems
The timeline above is divided into three periods of historical developments, i.e. prior to the 20th century plus pre/post 2nd World War. However, because the developments prior to the 20th century have already been essentially covered, .i.e. see History, the discussion will now focus on the later developments.