282 OBSERVING THE CMB
to the inflationary model of the
early universe proposed by
American Alan Guth.
The CMB is a flash of radiation
that was released about 380,000
years after the Big Bang, at
the time the first atoms formed
(pp.196–97). The expanding
universe had cooled enough for
stable ions (positively charged
nuclei) of hydrogen and helium
to form, and then, after a little
more cooling, the ions began to
collect electrons to make neutral
atoms. The removal of free electrons
from space led to the release of
photons (particles of radiation).
Those photons are visible now
as the CMB. The CMB comes from
the whole sky, without exception.
It has redshifted (the wavelengths
have stretched), and it now has
wavelengths of a few millimeters,
while the original radiation’s
wavelengths would be measured
in nanometers (billionths of a meter).IN CONTEXT
KEY ASTRONOMERS
George Smoot (1945 –)
John Mather (1946–)BEFORE
1964 The cosmic microwave
background—an echo of the
Big Bang itself—is discovered.1981 Alan Guth proposes
cosmic inflation, a theory in
which fluctuations of energy
density were locked into space
during the Big Bang.1983 Redshift surveys show
that galaxies are clustered
around voids of nothingness.AFTER
2001 Wilkinson Microwave
Anisotropy Probe is launched
to refine the map of the CMB.2015 The Planck observatory
studies the CMB to refine the
age of the universe to 13.813
billion years +/- 38 million years.
Combining this with other data,
the latest estimate is 13.799
billion years +/- 21 million years.T
he Cosmic Microwave
Background, or CMB,
was discovered in 1964.
This is the afterglow of the Big
Bang and it is as near as scientists
can get to observing the event
that brought the universe into
existence, 13.8 billion years ago.
Linking the structures observed
in the universe to the features
discerned in the CMB remains
a key challenge for cosmologists.Wrinkled time
The first great breakthrough
came from the Cosmic Microwave
Background Explorer, known as
COBE, a NASA satellite launched
in 1989. The detectors on COBE,
designed and run by George
Smoot, John Mather, and Mike
Hauser, were able to find the
oldest structures in the visible
universe, described by Smoot as
“wrinkles in time.” These wrinkles
in otherwise uniform space were
once dense regions containing the
matter that would form stars and
galaxies. They correspond to the
large-scale galaxy superclusters
and great walls seen in the
universe today, and add weightThe Cosmic Microwave
Background Explorer (COBE)
spent four years in space collecting
information about the CMB, scanning
the celestial sphere every six months.I always think of
space-time as being the
real substance of space,
and the galaxies and the
stars just like the foam
on the ocean.
George Smoot