242
THE RADIUS
OF SPACE
BEGAN
AT ZERO
GEORGES LEMAÎTRE (1894–1966)
T
he idea that the universe
began with a Big Bang,
expanding from a tiny,
superdense, and extremely hot
point in space, is the basis of
modern cosmology, and one that is
often said to have originated with
Edwin Hubble’s 1929 discovery
of cosmic expansion. But the
precursors of the theory predate
Hubble’s breakthrough by several
years, and first sprang from
interpretations of Albert Einstein’s
theory of general relativity as it
applied to the universe as a whole.
When formulating his theory,
Einstein drew on the available
evidence of the time to assume
that the universe was static—IN CONTEXT
BRANCH
AstronomyBEFORE
1912 US astronomer
Vesto Slipher discovers
the high redshifts of spiral
nebulae, suggesting they
are moving away from Earth
at high speeds.1923 Edwin Hubble confirms
that the spiral nebulae are
distant, independent galaxies.AFTER
1980 US physicist Alan Guth
proposes a brief period of
dramatic inflation in the early
universe to produce the
conditions we see today.1992 The COBE (Cosmic
Background Explorer) satellite
detects tiny ripples in the
cosmic microwave background
radiation (CMBR)—hints of the
first structure that emerged in
the early universe.