The Astronomy Book

283

One of the key observations of
the CMB came in the 1970s, and
removed any doubt that it was an
echo of the Big Bang. This was
the discovery that the thermal
spectrum of radiation from the
CMB tallied very closely with that
of a theoretical black body (p.225).

Black bodies
Black bodies do not really exist—
they cannot be made and no object
observed in the universe functions
as black bodies do in theory.
However, the CMB is the closest
match that has ever been found.
A black body absorbs all
radiation that hits it. Nothing is
reflected. However, the absorbed
radiation adds to the thermal
energy of the object, and this
is released as radiation. In 1900,
German Max Planck, the founding
figure of quantum physics, showed
that the spectrum of radiation
released by a black body is entirely
dependent on temperature.
In an everyday example of
radiation varying with temperature,
an iron bar glows red when first

See also: The birth of the universe 168–71 ■ Searching for the Big Bang 222–27 ■ Cosmic inflation 272–73 ■
Redshift surveys 274–75 ■ Tegmark (Directory) 339

THE TRIUMPH OF TECHNOLOGY

These fluctuations, or

“wrinkles in time”, are the oldest structures

ever found and represent the formation

of the first stars and galaxies.

The CMB’s wavelength

shows how hot the

universe was when the

CMB was emitted.

The CMB is not

smooth and uniform, but

contains tiny fluctuations

in temperature.

heated. Heating it more makes it

orange, and eventually the bar will

glow “blue hot.” Metalworkers learn

to roughly judge the temperature of

iron by its color. The metal is not

particularly close to a black body in

the theoretical sense, but stars and

The cosmic microwave background

is a flash of radiation produced

380,000 years after the Big Bang.

other astronomical objects are a

much closer match to a black body,

and so the color, or wavelengths of

their emissions, can be compared

to the thermal spectrum of a

theoretical black body to give

a relatively precise temperature. ❯❯

George Smoot After a childhood in Florida and

Ohio, Smoot began his career as

a particle physicist working at

MIT. His interests switched to

cosmology and he moved across

the country to the Lawrence

Berkeley National Laboratory.

It was there that Smoot studied

the CMB and developed ways

of measuring its radiation.

Smoot’s early work involved

fitting detectors to high-altitude

U2 spyplanes, but in the late

1970s, he became involved in the

COBE project to take his detector

into space. After his success with

COBE, Smoot cowrote Wrinkles in

Time with Keay Davidson

to explain the discovery.

Smoot won the Nobel Prize in

2006, along with John Mather,

for his work on COBE. He

reportedly gave his prize

money to charity. However,

three years later, Smoot won

an even greater sum when he

bagged the $1 million jackpot

on the TV game show A re You

Smarter Than a 5th Grader?

Key work

1994 Wrinkles in Time (with

Keay Davidson)