Dark Matter, Dark Energy, and the Current State of Cosmology

Nick Kaiser

Institute for Astronomy

University of Hawaii

Fritz Zwicky

The Coma Cluster

Zwicky & the Missing Mass

• Measured galaxy speeds in Coma

• Virial theorem: M/L ~ 500 M_sun/L_sun

• The “missing mass”

• An outstanding problem in cosmology– 90-98% of the universe is in a mysterious form– detectable only by its gravitational attraction

The Dark Matter Puzzle

• Where is it?

• How much is there?

• What is it?

Cosmology in a nutshell:

• The old cosmology– Friedmann; Einstein; de Sitter ….

• The New Cosmology– Inflation - scalar fields

• The Hot Big Bang

• Structure Formation

The Friedmann Model

• Scale factor R(t)• mass density and

curvature of space• problems

– horizon

– flatness

Inflationary Cosmology• In the beginning there was the field….

• Vector, tensor and scalar fields

• Weinberg-Salaam:– unified theory - the Higgs field

• The “inflaton”– central to inflation– solves the old problems– predicts a flat universe =1– quantum fluctuations structure formation

The Hot Big Bang

• The cosmic kitchen– big bang nucleosynthesis

• Abundance of “baryons” baryons ~ 0.02

• Relics– cosmic background– neutrinos

Structure Formation• Quantum fluctuations

• gravitational instability

• dark matter

• the “cosmic web”

The Cosmic Web

The history of the Universe

Inventory of Dark Matter

• Galaxies– luminous parts M/L ~ 1-5– flat rotation curves M/L ~ 30

• Pairs … Groups … Clusters– M/L ~ 100-500

• Super-Cluster Dynamics = 1?

Galaxies

Gravitational Lensing

• Gravity bends light rays– probe of dark matter– highly versatile

• microlensing - “machos”

• galaxy lensing

• lensing by cluster

• lensing by superclusters

Theory of gravitational lensing

Lensing by galaxies

Lensing by clusters

MACSJ2243

Cosmic Microwave Background

• Relic from the big bang

• Probe of structure @ t ~ 100,000 yr

• COBE– large angle

• BOOMERANG– small angles– flat Universe

COBE Satellite

The COBE Sky

From COBE to BOOMERANG

The Universe is flat!

What is the Matter?

• Neutrinos?– No longer popular

• Axions or other fields?

• WIMPs?

• Etc etc etc….

• Plenty of theory - scarce observations

Dark Energy

• Consensus model: ~ 0.3

• CMB = 1

• resolution: the accelerating Universe– expansion history from supernovae– fainter than expected– universe is being accelerated - dark energy– “late time inflation” - yet another field?

The Nearest GalaxiesThe Nearest GalaxiesLMC

SMC

February 22, 1987February 22, 1987

Expansion History from SN

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The Current Status of Cosmology

• A “working model” for creation of the Universe and the structure therein

• Impressive concordance with current observations

• Embarrassing number of ingredients– luminous baryons; dark baryons; neutrinos;

dark matter; dark energy….

• Epicycles?