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

neutron

deuterium

3H

4He

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

electronplasma“soup” traps photons

electrons attached to atoms, photons stream through

last scattering surface

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 percentmatter densitygeometrybaryon densityexpansion 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.