Lecture 6: How Did Everything Begin?
planets) or because they are too small (such as the subatomic particles known
as neutrinos).Why should anyone believe this bizarre story? Because it rests on a colossal
amount of carefully tested evidence. The earliest evidence came from
Hubble’s studies of the “red shift,” which showed that the further away an
object was, the faster it was moving
away from us. This meant that the
Universe must be expanding; so at
some time in the past it must have
been in¿ nitely small.What clinched the new theory was
the discovery of “cosmic background
radiation” (CBR). Until 1965, big bang
cosmology had a rival, the “steady
state” theory, supported by Fred Hoyle and others. They argued that the
apparent expansion of the Universe was caused by the continuous creation of
new matter. Supporters of the “big bang” theory suggested that when energy
and matter separated 380,000 years after the big bang, there must have been
a huge À ash of energy that should still be detectable as a weak energy source
coming from all parts of the Universe.In 1964, two engineers, Arno Penzias and Robert Wilson, were trying to
construct an extremely sensitive radio antenna. They could not eliminate
a persistent background hum. Eventually, they realized they were hearing
the cosmic background radiation. That clinched it for the big bang theory
because no other theory could explain the source of this universal energy.There are other powerful reasons for accepting big bang cosmology. No
astronomical objects older than 13 billion years have ever been detected. As
telescopes (like the Hubble space telescope) probe deeper in space they are
also probing further into the past. What they ¿ nd is that the early Universe
was different in several respects from today’s Universe, which is what big
bang cosmology predicts in an evolving, historically changing Universe.
Models of the big bang suggest that hydrogen and helium were created in
huge amounts, and other elements in smaller amounts. Observed distributionsModels of the big bang
suggest that hydrogen and
helium were created in huge
amounts, and other elements
in smaller amounts.