The Astronomy Book

197

See also: The birth of the universe 168–71 ■ Energy generation 182–83 ■ Nucleosynthesis 198–99

ATOMS, STARS, AND GALAXIES

called the strong nuclear force, thus
creating an array of atomic nuclei.
Gamow believed that, after a few
initial “seed” nuclei had assembled
from protons and neutrons, others
might have been built up by the
successive addition of neutrons,
with some decaying to protons.
At a later time, all the nuclei might
have captured electrons to form the
atoms of the chemical elements.

Doing the math
Gamow asked an American
graduate student, Ralph Alpher,
to work out the details of his idea.
Alpher and a colleague, Robert
Herman, performed extensive
mathematical calculations. They
found that the right conditions
for protons and neutrons to come
together existed only for a short
window of time of a few minutes.
Their calculations showed that
most of the universe’s neutrons

would have ended up combined

with protons in an isotope (one

of the possible alternative forms)

of helium, helium-4. A small

number would have become other

small atomic nuclei. In addition,

there would have been large

numbers of free protons (hydrogen

nuclei) left at the end of the process,

plus some unstable nuclei, which

would have quickly decayed.

Their calculations showed that

the universe would have consisted

of about 25 percent helium, with

the rest mainly hydrogen. The

paper that Alpher and Gamow

published also argued that other

heavier nuclei might have been

created in the Big Bang through

successive additions of neutrons.

Correct predictions

It was eventually recognized

through the work of scientists such

as Fred Hoyle that heavier elements

such as carbon were created in

stars and supernova explosions.

Nevertheless, the Alpher–Gamow

theory correctly explained the

relative abundances of hydrogen

and helium, lending considerable

support to the theory that the

universe began with a Big

Bang. It also correctly predicted

the existence of the cosmic

background radiation that was

discovered in 1964 (pp.222–27). ■

George Gamow

George Gamow was born in

Odessa, Ukraine, in 1904. From

1923, he attended the University

of Leningrad, studying under

Alexander Friedmann. In 1928,

Gamow briefly stayed at the

University of Göttingen in

Germany, where he developed

a theory called quantum

tunneling. This theory was

used by others to explain how

the fusion of light atomic nuclei

might create energy inside stars.

In 1933, he defected from the

Soviet Union while attending

a conference in Brussels. At

George Washington University

in the US, he turned his

attention to the evolution

of stars. From 1954, Gamow

became interested in genetics

and biochemistry. He also wrote

a number of popular science

books and sci-fi novels.

Key works

1948 The Origin of Chemical

Elements (also called the

Alpher–Bethe–Gamow paper)

1952 The Creation of

the Universe

Atomic nuclei formed from protons and neutrons in
the first minutes of the universe. Most neutrons ended
up in helium-4 nuclei. Small amounts of helium-3 and
deuterium (an isotope of hydrogen) and tiny amounts
of lithium-7 were also made. Another isotope of
hydrogen—tritium—formed, and decayed to helium-3.
Energy was released in the form of gamma rays.

Proton

Neutron

Gamma ray

Deuterium

nucleus

Helium-4 nucleus

Helium-3

nucleus

Lithium-7 nucleus

Tritium

nucleus