Redefining Reality - The Intellectual Implications of Modern Science

Einstein thought, there would be local bumps in the curvature
of space-time, but from a cosmological perspective, the
universe had to have a smooth and constant curvature.
The only way to get this smoothness and not have the universe
expanding or contracting was to add a term to his equations,
which came to be known as the cosmological constant.
There was nothing in physics or observation that demanded
this term. It was required only to ensure that the picture of
reality as regular could be maintained.
Younger physicists objected. The Russian Alexander Friedmann
produced a solution to Einstein’s equations that showed an expanding
universe. Georges Lemaître, a Belgian physicist and Catholic priest,
also found the general theory of relativity to require an expanding
universe. But Einstein refused to accept their solutions. The idea
that there were large-scale changes happening violated the basic
idea that we live in a stable universe.
But in 1929, the universe told us otherwise. Edwin Hubble,
working on the newly built telescope at the Mount Wilson
Observatory in California, discovered other galaxies outside the
Milky Way. Hubble also noted that the farther away these galaxies
were, the faster they were moving and the more likely they were to
be moving away from us. From these facts, Hubble concluded that
the universe is expanding.
All stars work according to the same mechanism: They turn
hydrogen into helium. Each element has a set of telltale frequencies
of light it emits because of the structure of the atoms. Thus, the
light from all stars and all galaxies should look the same.
But light is subject to the Doppler effect. Light waves move at
the same speed, no matter the state of motion of the light source,
but the number of peaks per second changes based on the relative
41