Ref: http://map.gsfc.nasa.gov/m_uni.html
Foundations of the Big Bang theory

Theoretical pillars
http://map.gsfc.nasa.gov/m_uni/uni_101bb1.html
General Relativity and the "Cosmological Principle" give rise to the
Big Bang theory.

Concepts of the Big Bang theory
http://map.gsfc.nasa.gov/m_uni/uni_101bb2.html
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
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest.html

Expansion of the universe
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest1.html
General Relativity and the "Cosmological Principle" give rise to
the Big Bang theory.

Abundance of the light elements H, He, Li
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest2.html
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.

The cosmic microwave background (CMB) radiation
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest3.html
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
http://map.gsfc.nasa.gov/m_uni/uni_101bblimit.html

Structure in the universe
http://map.gsfc.nasa.gov/m_uni/uni_101structures.html
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
http://map.gsfc.nasa.gov/m_uni/uni_101Flucts.html
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 "fine tuning" of the universe
http://map.gsfc.nasa.gov/m_uni/uni_101tuning.html
The universe we live in appears to be very "unlikely" in the context
of the standard Big Bang theory. Is there some mechanism that forces
it to be that way?

The inflationary universe
http://map.gsfc.nasa.gov/m_uni/uni_101inflation.html
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
http://map.gsfc.nasa.gov/m_uni/uni_101ouruni.html

Matter in the universe
http://map.gsfc.nasa.gov/m_uni/uni_101matter.html
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
http://map.gsfc.nasa.gov/m_uni/uni_101expand.html
How fast is the universe currently expanding? How do we measure
this?

The age of the universe
http://map.gsfc.nasa.gov/m_uni/uni_101age.html
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
http://map.gsfc.nasa.gov/m_uni/uni_101shape.html
Is our universe open and infinite, closed and finite, or just
hovering on the flat boundary between the two?

The accelerating universe
http://map.gsfc.nasa.gov/m_uni/uni_101accel.html
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."

The fate of the universe
http://map.gsfc.nasa.gov/m_uni/uni_101fate.html
Will the universe continue to expand forever, or eventually
collapse?

Related topics
http://map.gsfc.nasa.gov/m_uni/uni_101topics.html

First objects
http://map.gsfc.nasa.gov/m_uni/uni_101firstobj.html
When did the first objects form in the universe?

The Milky Way galaxy
http://map.gsfc.nasa.gov/m_uni/uni_101mw.html
A brief tour of our own Milky Way galaxy, with a beautiful image of
it from the COBE satellite.

The life cycle of stars
http://map.gsfc.nasa.gov/m_uni/uni_101stars.html
Learn how stars form, live and die.