waynehu
Professor,
Department of Astronomy and Astrophysics
University of Chicago
Summary of Key Concepts
Overview
Cosmology:
origin, evolution, fate of material universe
Wrinkles in the energy of primordial light
Basic Principles
Big Bang: the universe began hot and dense
and thereafter expanded and cooled.
Gravitational Instability: Stars, galaxies,
clusteres of galaxies ("Structure") formed from the
gravitational pull of small density wrinkles in the early
universe
Cosmological Expansion
Recession of the galaxies: distant objects
appear to be moving away from us.
Cosmic Microwave Background: we are bathed
in primordial light.
Properties of the Cosmic Light
3 degrees above absolute zero (-270 degrees
celcius)
400 photons per cubic centimeter
10 trillion photons per second per squared
centimeter
A Brief History
Looking at
distant objects, we look backwards
in time.
Galaxies formed when the universe
was a few billion years old
Microwave background radiation was emitted
when the universe was about 300,000 years old
Before 300,000 years, the universe was a nearly smooth particle soup.
Gravitational Instability
Wrinkles represent "hills" and "valleys"
Matter falls into and accumulates in valleys
Dense objects such as galaxies form
in the valleys
Cosmic Inflation
Inflation stretches fluctuations at the
elementary particle into galaxy-large wrinkles.
Cosmological horizon the distance beyond which
we cannot look. An important concept in structure formation
Temperature Sky Maps
Temperature anisotropies: small variations in the
temperature of the microwave background from one direction on the sky to
the other.
Temperature map: representation of the 3 dimensional
sky in a 2 dimensional plane.
COBE: a satellite which detected the large features
in the microwave background sky in 1992.
Small Angle Anisotropies
Small angle anisotropies come from ripples that
are smaller than the horizon when the microwave photons started traveling to
us.
structure formation.
Small scale ripples have already participated
in the process of structure formation and carry important information
as to its nature.
Seeing Sound
Sound waves: small scale ripples in the
microwave background reflect sound waves in the early universe.
Spectrum: the sound spectrum carries
information about the origin of fluctuations and the fate of
the universe.
Music of Inflation
Fundamental mode of sound waves is related to
the size -- in the microwave background context, the horizon.
Overtones based on the fundamental mode form
a pattern of sound that identifies its origin -- in the cosmological
context the ultimate source of perturbations from inflation.
Spatial Curvature
Curvature of space is equivalent to gravity and
is a measure of the amount of matter in the universe.
Curvature is measured by its lensing effect on
spots in the microwave background sky.
If the universe has a large curvature it is massive enough to
recollapse ending the universe in a big crunch.