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universe.” Einstein first called his
work “suspicious,” but six months
later acknowledged that his results
were correct. However, this was
Friedmann’s final contribution as he
died two years later. In 1924, Edwin
Hubble showed that many nebulae
were galaxies outside the Milky
Way. The universe had suddenly
become a lot bigger.
The expanding universe
Later in the 1920s, Lemaître entered
the debate about the large-scale
organization of the universe.
He had worked at institutions
in the United States, becoming
aware of Vesto Slipher’s work on
receding galaxies and Hubble’s
measurements of galaxy distances.
A competent mathematician, he had
also studied Einstein’s field equations
and found a possible solution to
the equations that allowed for an
expanding universe. Putting these
various threads together, in 1927,
Lemaître published a paper that
proposed that the whole universe
is expanding and carrying galaxies
away from each other and from
Earth. He also predicted that
galaxies that are more distant from
us would be found to be receding
at a faster rate than closer ones.
Lemaître’s paper was published
in an obscure Belgian journal, and
as a result, his hypothesis failed to
attract much attention at the time.
He did, however, communicate
his findings to Einstein, telling
him of the solution he had found
to the field equations allowing
for a universe that expands.
Einstein introduced Lemaître to
Friedmann’s work, but remained
ambivalent about Lemaître’s idea.
Famously, Einstein is said to have
said: “Your calculations are correct,THE BIRTH OF THE UNIVERSE
but your grasp of physics is
abominable.” However, the British
astronomer Arthur Eddington later
published a long commentary on
Lemaître’s 1927 paper, describing
it as a “brilliant solution.”
In 1929, Hubble released
findings showing that there was
indeed a relationship between the
remoteness of a galaxy and how
fast it was receding, confirming
for many astronomers that the
universe was expanding, and that
Lemaître’s paper had been correct.
For many years the credit for the
discovery of the expansion of
the universe was given to Hubble,
but today most agree it should be
shared with Lemaître and possibly
also with Alexander Friedmann.The primeval atom
Lemaître reasoned that, if the
universe is expanding and the
clock is run backward, then far
back in time, all the matter in the
universe must have been much
closer. In 1931, he suggested that
the universe was initially a single,
extremely dense particle containing
all its matter and energy—a
“primeval atom” as he called it,
about 30 times the size of the sun.
This disintegrated in an explosion,Running the clock backward, in the distant past,
galaxies must have been closer in a small, dense region.Space is expanding.The universe began from an explosion of
matter on “a day without yesterday.”General relativity allows
for a universe that is
expanding.Galaxies outside the Milky
Way are shown to be
moving away from it
at tremendous speed.The radius of space began at
zero, and the first stages of
the expansion consisted of a
rapid expansion determined
by the mass of the initial atom.
Georges Lemaître