167
See also: The theory of relativity 146–53 ■ Stellar composition 162–63 ■ Energy generation 182–83 ■ Nucleosynthesis 198–99
ATOMS, STARS, AND GALAXIES
dense gas. The answers he obtained
were a good match for observations
of both giant and dwarf stars.
Gas laws and relativity
The physical laws governing the
relationships between the pressure,
volume, and temperature of a gas
were well understood. Since they
all have widely spaced molecules,
gases behave in similar ways—for
instance, Boyle’s law (formulated by
Irish chemist Robert Boyle) states
that, at a constant temperature, the
product of the pressure and volume
of a given mass of gas is constant.
Eddington used these laws to
calculate that the temperature
at the center of the sun is about
29,000,000°F (16,000,000°C), with
a density 150 times that of water.
To understand what was going
on in the sun’s center, Eddington
now needed Einstein’s equation
E = mc^2 (pp.149–50). This equation
states that energy is equal to mass
multiplied by the square of the
velocity of light. It was the key to
unlocking the mystery of the source
of the sun’s energy, as it showed
how mass could be turned into
energy. The conditions at the solar
center were sufficiently hot and
dense to allow nuclear reactions to
take place and mass to be destroyed,
thus producing the energy that
Einstein’s equation predicted.
At first, physicists suggested
that individual electrons or hydrogen
atoms might be the mass thatIt is sound judgment to hope
that, in the not too distant
future, we shall be competent
to understand so simple
a thing as a star.
Arthur EddingtonArthur Eddington Arthur Eddington was born into a
Quaker family, and was educated
in mathematics and physics at
the universities of Manchester
and Cambridge. In 1905, he
joined the Royal Observatory,
Greenwich, but a few years later
he returned to Trinity College,
Cambridge, becoming Plumian
Professor in 1913 and director
of the Cambridge University
Observatory in 1914. He lived
there for the rest of his life.
In 1919, Eddington sailed
to Príncipe Island, West Africa,
to observe a total solar eclipse
and test Einstein’s predictionabout the bending of starlight
by the sun. He was a brilliant
astronomer and mathematician,
and able to communicate the
most difficult physical idea in
a simple and elegant language.
This made his books extremely
popular, especially his
explanations of relativity
and quantum mechanics.Key works1923 The Mathematical Theory
of Relativity
1926 The Internal Constitution
of the Starswent into Einstein’s equation. In
1931, Welsh astrophysicist Robert
Atkinson showed that a process in
which four hydrogen atoms were
fused into one slightly less massive
helium atom fit the data from the
sun. This process is very slow and
produces energy to fuel the sun for
billions of years. Here also was
evidence of the transmutation
of the elements, showing how
the composition of the universe
changes with time. ■Since all gases obey the same laws,
assuming that the sun is not only
gaseous at the surface but throughout
allows the calculation of the temperature
and pressure at the center.