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Cosmology: The Study of the Universe


Cosmology is the scientific study of the large scale properties of the Universe as a whole. It endeavors to use the scientific method to understand the origin, evolution and ultimate fate of the entire Universe. Like any field of science, cosmology involves the formation of theories or hypotheses about the universe which make specific predictions for phenomena that can be tested with observations. Depending on the outcome of the observations, the theories will need to be abandoned, revised or extended to accommodate the data. The prevailing theory about the origin and evolution of our Universe is the so-called Big Bang theory discussed at length in the pages linked below. This primer in cosmological concepts is organized as follows:
  • The main concepts of the Big Bang theory are introduced in the first section with scant regard to actual observations.
  • The second section discusses the classic tests of the Big Bang theory that make it so compelling as the likely valid description of our universe.
  • The third section discusses observations that highlight limitations of the Big Bang theory and point to a more detailed model of cosmology than the Big Bang theory alone provides. As discussed in the first section, the Big Bang theory predicts a range of possibilities for the structure and evolution of the universe.
  • The final section discusses what constraints we can place on the nature of our universe based on current data, and indicates how WMAP furthers our understanding of cosmology.
  • In addition, a few related topics are discussed based on commmonly asked questions.

If you have a question about cosmology that you don't see answered here, or on our FAQ page, please feel free to contact us directly.

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Last updated: Thursday, 07-13-2006 Skip Additional Sub Section and Site Navigation. Return to page top.

Cosmology 101


Foundations of the Big Bang theory

Theoretical pillars
General Relativity and the "Cosmological Principle" give rise to the Big Bang theory.
Concepts of the Big Bang theory
The Big Bang theory makes definite predictions for the structure and evolution of the universe that depend on the nature and amount of matter in the universe.

Observational tests of the Big Bang theory

Expansion of the universe
A cosmological constant and the Hubble Law.
Abundance of the light elements H, He, Li
The Big Bang theory makes definite predictions for the types and amount of matter in the universe.
The cosmic microwave background (CMB) radiation
The early universe should have been very hot. The cosmic microwave background radiation is the remnant heat leftover from the Big Bang.

Limitations and extensions of the Big Bang theory

Structure in the universe
The Big Bang theory makes no attempt to explain how structures like stars and galaxies came to exist in the universe.
Fluctuations in the cosmic microwave background (CMB) radiation
The temperature of the CMB is observed to vary slightly across the sky. What produced these fluctuations and how do they relate to stars and galaxies?
The inflationary universe
A very short, but especially rapid burst of growth in the very early universe (“inflation”) provides an elegant, yet untested, explanation of the above puzzles.

Our universe

Matter in the universe
The amount and type of matter in the universe is fundamental in determining the properties of our universe. How much matter is there? Is it mostly “ordinary” matter (composed of protons, neutrons, electrons and/or photons) or a more exotic form not yet observed in the laboratory?
Measuring expansion
How fast is the universe currently expanding? How do we measure this?
The age of the universe
We can estimate the age of the universe from its current expansion rate. We can place a lower limit to the age of the universe by estimating the age of the oldest known stars. Are these numbers compatible?
The shape of the universe
Is our universe open and infinite, closed and finite, or just hovering on the flat boundary between the two?
The accelerating universe
Rather than slowing down, the expansion of our universe appears to be speeding up! One possible source of this acceleration is a form of energy called the “cosmological constant”, or a variant of it called “quintessence.”
Life the universe
How did we get from the Big Bang to the human search for extraterrestrial life?
The fate of the universe
Will the universe continue to expand forever, or eventually collapse?

Related topics

First objects
When did the first objects form in the universe?
The Milky Way galaxy
A brief tour of our own Milky Way galaxy, with a beautiful image of it from the COBE satellite.
The life cycle of stars
Learn how stars form, live and die.

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