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communications. In 1964, it was
being used by two radio astronomers,
Robert Wilson and Arno Penzias,
who were trying to detect a halo
of cold gas around the Milky Way.
Penzias and Wilson were looking
at the 2¾-in (7-cm) range, but they
could not get rid of a stubborn
low-level hiss that was ruining
their measurements.
The pair painstakingly eliminated
potential sources of interference,
dusting down plugs and checking
circuits. At first, they thought that
the noise was coming from New
York, but pointing their telescope
away from the city did not help.
Then they thought it might be high-
altitude static from a nuclear bomb
test or an unknown radio source in
the solar system but, over the course
of the year, the signal never varied
its ceaseless soft hiss. In desperation,
they even removed a nesting pair
of pigeons and chipped away an
accumulation of “white dielectric
material” (bird droppings).
Stumped, Penzias contacted a
colleague, who directed him to James
Peebles at Princeton. Taking the call
for Peebles, Dicke knew immediately
what the Bell Laboratories scientists
had found. He hung up the telephone
and said to his colleagues, “Well,
boys, we’ve been scooped.”The only way is up
The discovery of the cosmic
background radiation is one of
the three experimental pillars
of the Big Bang theory—the other
two being Hubble’s Law and
the cosmic abundances of the
elements hydrogen and helium
(pp.196–97). Big Bang theorists
had predicted exactly what had
now been found: radiation coming
from all directions at 3 K.
The Big Bang had until then
been a highly contested idea, and
many scientists—including Penzias
and Wilson—still favored FredSEARCHING FOR THE BIG BANG
Hoyle’s Steady State model, in
which an expanding universe
essentially remains unchanging
due to the constant creation of
matter. According to this theory,
the universe does not change in
appearance over time.
Steady State theorists suggested
that the microwave background
was the result of scattered starlight
from distant galaxies. To demonstrate
to a sceptical physics community
that the signals were indeed the
relic fireball radiation predicted by
Big Bang theory, it was necessary
to confirm Alpher’s and Herman’s
condition that the radiation should
match that of a theoretical black
body. This required measuring the
CMB at different frequencies. The
next obvious move was to take an
even more accurate determination
of the spectrum by launching a
space-based receiver.
During the 1970s and 1980s,
Herb Gush, a physicist at the
University of British Columbia,
fired sounding rockets into space
in order to observe the CMB
without interference from Earth’s
atmosphere. This indicated that theRobert Wilson and Arno Penzias
pose in front of the Holmdel Horn
antenna following the announcement
in 1978 of their Nobel Prize for
discovering the CMB.All of our best physical
theories are incomplete.
James PeeblesScience is a series of
successive approximations.
James Peebles