The Beginning of Time:
Evidence for the Big Bang &
the Theory of Inflation
A Brief History of the Universe
 <10-43 seconds: Planck era

before the Planck time (all known laws of
physics break down and we can’t say
anything about what conditions were like)
 10-43 - 10-38 seconds: GUT era

all four forces are “unified” (have the same
strength)
 10-38 -10-10 seconds: electroweak era

the electromagnetic and weak force become
distinct.
the particle era
 10-10 - 0.001 seconds: particle era
plasma of fundamental particles (matter
and anti-matter)
 for some unknown reason, there must have
been slightly more matter than anti-matter,
at least in our corner of the Universe

 at
the end of the particle era, matter
and anti-matter annihilate, leaving
mostly matter. Photons outnumber
protons by a billion to 1.
Big Bang Nucleosynthesis
 0.001 seconds– 3 minutes: nucleosynthesis
temperatures of 109 K allow hydrogen nuclei
to fuse into helium nuclei.
proton
deuterium
neutron
4He
3H
the density of baryons
 deuterium is formed in the course of
fusing hydrogen to helium, and some is
still left over
 the observed ratio of deuterium to
hydrogen and helium tells us the density
of baryons (protons and neutrons) during
the era of nucleosynthesis
 observations of deuterium abundance
show that the density of baryons is about
5 % of the critical density
 at very high temperatures (>1011 K) protons and
neutrons can change into one another
 as the Universe cools, protons (which are slightly
less massive) become favored
 ratio of protons to neutrons at the time when
nucleosynthesis begins is predicted to be 7 to 1.
prediction:
hydrogen 75 %
helium 25%
Recombination
 3 minutes – 500,000 years: recombination
hydrogen and helium nuclei capture
electrons and become neutral atoms. The
Universe becomes transparent to photons.
Stars and Galaxies
 the plasma of neutral atoms gradually cools
and protogalactic clouds form.
 The first stars form out of the hydrogen and
helium, make heavy elements, etc.
 planets
 life
 astronomers
 etc…
Light from the Big Bang
 in 1965, Penzias and Wilson discovered an
unexpected signal at microwave frequencies
 this signal looked the same in all directions,
and could not be attributed to any particular
source
 Penzias and Wilson thought there must be
something wrong with their experiment!
Penzias & Wilson
Cosmic Microwave Background
 it was soon realized that this radiation came
from the hot Universe soon after the Big
Bang!
 cosmological redshifting over the huge
distance this light has traveled has shifted
the wavelength from the visible to the
microwave
last scattering surface
electrons
attached
to atoms,
photons
stream
through
electron
plasma
“soup”
traps
photons
COBE satellite
The COBE experiment
 COBE showed that the CMB is an almost
perfect blackbody (thermal) spectrum with a
temperature of 2.73 K
 the CMB is incredibly uniform in all
directions; but COBE detected variations
from place to place of one part in 105
Spectrum of the CMB
Temperature of the sky
Implications of COBE results:
 the temperature and spectrum of the
CMB measured by COBE is very strong
confirmation of the hot Big Bang theory
 the small temperature differences
detected by COBE provide direct evidence
that the Universe was lumpy on small
scales at early times
The Boomerang experiment
Constraining the Geometry
of the Universe
The MAP satellite
All sky temperature map:
predicted results from MAP
in the next few years…
 results from MAP and other new CMB
experiments will allow us to determine the
values of all of the cosmological
parameters to an accuracy of 10 percent
 matter
density
 geometry
 baryon density
 expansion rate (Hubble parameter)
 and much more…
Some remaining questions
 where did those lumps come from (needed to
seed structure formation)?
 why is the Universe so smooth on large
scales?
 why is the Universe so close to a flat
geometry (implying that the density of matter
and energy is very close to the critical
density)?
Isotropy problem
Inflation
 the theory of inflation is an attempt to solve
all of these problems
 this theory says that the Universe went
through a brief period of very rapid
expansion soon after the Big Bang –
perhaps growing by as much as a factor of
1030 in 10-36 seconds.
 perhaps caused by the “freeze out” of the
strong force from the GUT “super-force”
The observable Universe
quantum fluctuations
Inflated quantum ripples
 quantum
fluctuations get
expanded to the size
needed to seed
structure formation –
and variations seen
in the CMB
Inflation would have
“expanded away”
any curvature that
the Universe may
have once had
the flatness problem
We are here because, more than ten billion
years ago, the Universe borrowed energy from
the vacuum to create vast amounts of matter
and anti-matter in nearly equal
quantities…Your body is a collection of the
atoms that were created billions of years ago
in the interiors of stars, the fraction of a
fraction of a percent of normal matter that
escaped annihilation in the first microsecond
of the Universe.