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Tests of Big Bang Cosmology

The Big Bang Model is supported by a number of important observations, each of which are described in more detail on separate pages:
The expansion of the universe
Edwin Hubble's 1929 observation that galaxies were generally receding from us provided the first clue that the Big Bang theory might be right.
The abundance of the light elements H, He, Li
The Big Bang theory predicts that these light elements should have been fused from protons and neutrons in the first few minutes after the Big Bang.
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.

These three measurable signatures strongly support the notion that the our universe evolved from a dense, nearly featureless hot gas, just as the Big Bang model predicts.

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Last updated: Tuesday, 09-26-2006 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 in 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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Expansion

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