This book continues our exploration of cosmology,
the science of the universe as a whole.
Here we examine four critical and somewhat mysterious phenomena that
have shaped our universe and the science of cosmology: Inflation, the
Cosmic Microwave Background (CMB) radiation, Dark Matter, and the
Inflation was an extremely brief period of extremely rapid expansion,
occurring just after the Big Bang. While not derived from any
fundamental principle, Inflation has become an indispensible part of
cosmology. It was added to address problems in the original Big Bang
theory, including “fine tuning” of the geometry, uniformity, and
large-scale structure development.
CMB, first seen as irritating noise, was discovered accidentally, but
has become the most definitive evidence of the Big Bang and a
cornerstone of cosmology. The CMB has revealed more about our universe
than almost any other scientific discovery.
Dark matter comprises over 80% of all the matter in our universe, and
has dominated both the expansion of the universe and the formation of
stars and galaxies. Yet, we are barely beginning to understand this
invisible, nearly inert substance.
The Cosmological Principle asserts that our universe is the same
everywhere and in every direction. We will examine the evidence that
supports it, and the critical importance of it being almost but not
Inflation, the universe expanded by an incredible amount, and at an
exponential rate. As the figure above illustrates, the space created at
t=0 probably expanded to become vastly larger than our observable
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