Chapter 18: Chapter 18: Cosmology

WHAT DO YOU THINK?

What does the universe encompass? Is the universe expanding, fixed in size,

or contracting?Will the universe last forever?

You will discover…You will discover…

cosmology, which seeks to explain how the universe began, how it evolves, and its fate

the best theory we have for the evolution of the universe—the Big Bang

how astronomers trace the emergence of matter and the formation of galaxies

how astronomers explain the overall structure of the universe

our understanding of the fate of the universe

Cosmological RedshiftCosmological Redshift

Expanding Cake AnalogyExpanding Cake Analogy

Just as all the chocolate chips move apart as the cake rises, all the superclusters of galaxies recede from each other as the universe expands.

Bell Labs Horn AntennaBell Labs Horn Antenna

Arno Penzias (right) and Robert Wilson

In Search of Primordial PhotonsIn Search of Primordial Photons

Wilkinson Microwave Anisotropy Probe (WMAP) satellite, launched in 2001

In Search of Primordial PhotonsIn Search of Primordial Photons

The balloon-carried telescope BOOMERANG

Spectrum of the Cosmic Spectrum of the Cosmic Microwave BackgroundMicrowave Background

The Microwave SkyThe Microwave Sky

The Doppler shift across the sky is caused by the Earth’s motion through the microwave background.

Our Motion Through the Our Motion Through the Microwave BackgroundMicrowave Background

Because of the Doppler effect, we detect shorter wavelengths in the microwave background and a higher temperature of radiation in that part of the sky toward which we are moving.

Unification of the Four ForcesUnification of the Four Forces

Early History of the UniverseEarly History of the Universe

The Cause of InflationThe Cause of Inflation

Observable Universe BeforeObservable Universe Beforeand After Inflationand After Inflation

Pair Production and AnnihilationPair Production and Annihilation

Evolution of DensityEvolution of Density

Era of RecombinationEra of Recombination

Observable UniverseObservable Universe

The cosmic light horizon today is about 13.8 billion light-years away in all directions. Inset: This HST Deep Field Telescope image shows some of the most distant galaxies we have seen.

Structure of the Early UniverseStructure of the Early Universe

This Wilkinson Microwave Anisotropy Probe (WMAP) image shows temperature variations in the cosmic microwave background. Inset: Tiny temperature fluctuations, observed by BOOMERANG, are related to the large-scale structure of the universe today, indicating where superclusters and voids grew.

Galaxies Forming by Combining Galaxies Forming by Combining Smaller UnitsSmaller Units

This painting indicates how astronomers visualize the burst of star formation that occurred within a few hundred million years after the Big Bang.

Galaxies Forming by Combining Galaxies Forming by Combining Smaller UnitsSmaller Units

Hubble and Keck telescope images of two groups of stars that are believed to be protogalaxies, from which bigger galaxies grew

Galaxies Forming by Combining Galaxies Forming by Combining Smaller UnitsSmaller Units

This Chandra X-ray telescope image shows gravitationally bound gas around the distant galaxy 3C 294. The X-ray emission from this gas is the signature of an extremely massive cluster of galaxies.

Stellar Birth RatesStellar Birth Rates

Star formation continued actively for billions of years when the universe was very young.

Stellar Birth RatesStellar Birth Rates

Most of the stars in an elliptical galaxy are created in a brief burst of star formation when the galaxy is very young. In spiral galaxies, stars form at a more leisurely pace that extends over billions of years.

Creation of Spiral andCreation of Spiral andElliptical GalaxiesElliptical Galaxies

A galaxy begins as a huge cloud of primordial gas that collapses gravitationally.

A Cosmic TimelineA Cosmic Timeline

Possible Geometries of the Possible Geometries of the UniverseUniverse

The curvature is eitherThe curvature is either

(a)(a) PositivePositive

(b)(b) ZeroZero

(c)(c) negativenegative

Cosmic Microwave Background Cosmic Microwave Background and the Curvature of Spaceand the Curvature of Space

Dimmer Distant SupernovaDimmer Distant Supernova

•These HST images show the galaxy in which the supernova SN 1997ff occurred. •This supernova was dimmer than expected. •The distance to it is greater than it would be if the universe had been continually slowing down. •An outward force is acting over vast distances in the universe.

Dimmer Distant SupernovaDimmer Distant Supernova

WHAT DID YOU THINK?

What is the universe? It is all the matter, energy, and spacetime that

will ever be detectable from the Earth or that will ever affect us.

Did the universe have a beginning? Yes, it occurred about 13.8 billion years ago in

an event called the Big Bang. Will the universe last forever? Current observations support the belief that the

universe will last forever.

Key TermsKey TermsBig Bangclosed universeconfinementcosmic light horizoncosmic microwave backgroundcosmological constantcosmological redshiftcosmologydark agesdark energydecouplingera of recombinationexpanding universegrand unified theory (GUT)homogeneityhorizon problem

inflationinflationary epochisotropyisotropy problemmatter-dominated universeopen universepair productionPlanck eraPlanck timeprimordial fireballquarkquintessenceradiation-dominated universestrong nuclear forcesuperstringuniverseweak nuclear force