- 1576 – Thomas Digges modifies the Copernican system by removing its
outer edge and replacing the edge with a star-filled unbounded space - 1610 – Johannes Kepler uses the dark night sky to argue for a finite
universe - 1720 – Edmund Halley puts forth an early form of Olbers’ paradox
- 1744 – Jean-Phillipe de Cheseaux puts forth an early form of Olbers’
paradox - 1826 – Heinrich Olbers puts forth Olbers’ paradox
- 1917 – Willem de Sitter derives an isotropic static cosmology with a
cosmological constant as well as an empty expanding cosmology with a
cosmological constant - 1922 – Vesto Slipher summarizes his findings on the spiral nebulae’s
systematic redshifts - 1922 – Alexander Friedmann finds a solution to the Einstein field
equations which suggests a general expansion of space - 1927 – Georges Lema”tre discusses the creation event of an expanding
universe governed by the Einstein field equations - 1928 – Harold Robertson briefly mentions that Vesto Slipher’s redshift
measurements combined with brightness measurements of the same galaxies
indicate a redshift-distance relation - 1929 – Edwin Hubble demonstrates the linear redshift-distance relation
and thus shows the expansion of the universe - 1933 – Edward Milne names and formalizes the cosmological principle
- 1934 – Georges Lema”tre interprets the cosmological constant as due to
a vacuum energy with an unusual perfect fluid equation of state - 1938 – Paul Dirac presents a cosmological theory where the
gravitational constant decreases slowly so that the age of the universe
divided by the atomic light-crossing time always equals the ratio of
the electric force to the gravitational force between a proton and
electron - 1948 – Ralph Alpher, Hans Bethe(“in absentia”), and George Gamow
examine element synthesis in a rapidly expanding and cooling universe
and suggest that the elements were produced by rapid neutron capture - 1948 – Hermann Bondi, Thomas Gold, and Fred Hoyle propose steady state
cosmologies based on the perfect cosmological principle - 1951 – William McCrea shows that the steady state C-field can be
accommodated within general relativity by interpreting it as a
contribution to the energy-momentum tensor with an unusual equation of
state - 1961 – Robert Dicke argues that carbon-based life can only arise when
the Dirac large numbers hypothesis is true because this is when burning
stars exist; first use of the weak anthropic principle - 1963 – Fred Hoyle and Jayant Narlikar show that the steady state theory
can explain the isotropy of the universe because deviations from
isotropy and homogeneity exponentially decay in time - 1964 – Fred Hoyle and Roger Tayler point out that the primordial helium
abundance depends on the number of neutrinos - 1965 – Martin Rees and Dennis Sciama analyze quasar source count data
and discover that the quasar density increases with redshift - 1965 – Edward Harrison resolves Olbers’ paradox by noting the finite
lifetime of stars - 1966 – Stephen Hawking and George Ellis show that any plausible general
relativistic cosmology is singular - 1966 – Jim Peebles shows that the hot Big Bang predicts the correct
helium abundance - 1967 – Andrei Sakharov presents the requirements for a
baryon-antibaryon asymmetry in the universe - 1967 – John Bahcall, Wal Sargent, and Maarten Schmidt measure the
fine-structure splitting of spectral lines in 3C191 and thereby show
that the fine-structure constant does not vary significantly with time - 1968 – Brandon Carter speculates that perhaps the fundamental constants
of nature must lie within a restricted range to allow the emergence of
life; first use of the strong anthropic principle - 1969 – Charles Misner formally presents the Big Bang horizon problem
- 1969 – Robert Dicke formally presents the Big Bang flatness problem
- 1973 – Edward Tryon proposes that the universe may be a large scale
quantum mechanical vacuum fluctuation where positive mass-energy is
balanced by negative gravitational potential energy - 1974 – Robert Wagoner, William Fowler, and Fred Hoyle show that the hot
Big Bang predicts the correct deuterium and lithium abundances - 1976 – A.I. Shlyakhter uses samarium ratios from the prehistoric
natural fission reactor in Gabon to show that some laws of physics have
remained unchanged for over two billion years - 1977 – Gary Steigman, David Schramm, and James Gunn examine the
relation between the primordial helium abundance and number of
neutrinos and claim that at most five lepton families can exist - 1980 – Alan Guth proposes the inflationary Big Bang universe as a
possible solution to the horizon and flatness problems - 2003 – NASA’s WMAP takes first detailed “baby picture” of the universe.
The image reveals the universe is 13.7 billion years old (within one
percent error) and that the inflationary theory is correct.
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