225
showed that it would have two
distinguishing features. It would
come from every direction in the
sky, and the energy curve would
have the telltale shape of an object
very close to thermal equilibrium,
a so-called black body.
Alpher and Herman stopped
there, advised that the radio
telescopes of the day would not
be able to pick up such a quiet
hiss. But Dicke thought otherwise.
During World War II, while working
on radar systems, he had built such
a machine: the Dicke radiometer,
which collects a microwave signal
and measures its power. Dicke added
a switch to filter out “noise.” The
device is still used today in space
telescopes and satellites. Choosing
a suitable bandwidth in which to
conduct the search for the radiation
was the next important stage,
since so many things produce
radio waves. For example, the sky is
filled with microwave wavelengths
around the 8¼-in (21-cm) mark,
emitted by atoms of hydrogen. It
seemed logical to start at a dark
part of the spectrum. In the spring
of 1964, Wilkinson and Roll began
looking at the 1¼-in (3-cm) band,
but they were beaten in their quest
by a piece of serendipity.
Holmdel Horn
Less than an hour’s drive from
Princeton University is the Holmdel
Horn—a giant radio antenna, built
by Bell Laboratories for satellite ❯❯
See also: The birth of the universe 168–71 ■ Beyond the Milky Way 172–77 ■
Cosmic inflation 272–73 ■ Observing the CMB 280–85
NEW WINDOWS ON THE UNIVERSE
A theoretical “black body” absorbs all the radiation that hits it, then
emits radiation at different intensities (measured as spectral radiance)
across different wavelengths, depending on its temperature, as shown here.
Robert H. Dicke
Bob Dicke was born in St.
Louis, Missouri, in 1916, but
grew up in Rochester, NY.
Fascinated by science from
a young age, he began an
engineering degree before
switching to physics. After
graduating from Princeton in
1939, Dicke worked at MIT’s
Radiation Laboratory during
World War II, developing
microwave radar. He and
his wife, Anne, returned to
Princeton following the war
and remained there for the rest
of their lives. Dicke’s research
was initially centered around
radiation, and he formulated
a new quantum theory to
explain the emission of
coherent radiation produced
by a theoretically ideal laser.
His interest in radiation led
him to team up with James
Peebles and predict the
existence of the CMB. By
the 1960s, Dicke’s interests
had spread to theories of
gravitation. He developed
high-precision experiments
to test general relativity more
robustly and produced an
alternative theory of gravitation.
An imaginative experimentalist
and a prolific inventor, Dicke
held more than 50 patents,
ranging from lasers to designs
for clothes dryers.
SPECTRAL RADIANCE
WAVELENGTH (μm)
0 0.5 1 1.5 2 2.5 3
14
12
10
8
6
4
2
0
VISIBLE
5,000 K
3,000 K
4,000 K