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History of the Universe. Inflation, the Problem Solver. A. Horizon Why is the CMB radiation so isotropic? Flat Universe Why is the density of the Universe so close to critical? Structure Where does structure come from? GUTs suggest that Universe did undergo inflation.

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History of the Universe

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History of the Universe

Inflation, the Problem Solver

A. HorizonWhy is the CMB radiation so isotropic?

Flat UniverseWhy is the density of the Universe so close to critical?

StructureWhere does structure come from?

GUTs suggest that Universe did undergo inflation

Inflation, the Problem Solver

Milky Way

Solar System

phase transition

strong nuclear force separates

extreme pressure overwhelms gravity


Inflation Solves Horizon Problem

A. Horizonwhy is the CMB radiation so isotropic?

observe … temp is 2.725 K with variation of 1 part in 100,000

in BB … two points in opposite directions could look different

 Universe tiny in past

Inflation Solves Horizon Problem

smaller than


cannot observe A+B

can observe A+B

Inflation Solves Flatness Problem

B. Flatnesswhy is the density of Universe so close to critical?

observe … matter density is 27% critical

in BB … no reason why density close to critical

 Universe HAS to look flat if you inflate fast

Flatness Problem Solved

Inflation Solves Structure Problem

C. Structurewhere does structure come from?

observe … CMB not completely uniform

observe … galaxies/clusters exist

in BB … quantum ripples in early Universe much too small

 inflation superstretches ripples into macro sizes

Quantum Fluctuations Expand

Clusters on Sky

Hubble’s Law

Redshift Map

Redshift Map

Redshift Map

Structure Simulated


1.0 Byr

3.5 Byr

13.7 Byr

Dark Matter: Rotation Curves

Dark Matter: Holding Gas

Dark Matter: Cluster Motions

Virial Theorem: for stable, self-gravitating, spherical

distribution of equal mass objects:

KE = –1/2 PE

KE per galaxy = 1/2 mgv2

KE of N galaxies = 1/2 Nmgv2 = 1/2 Mcv2

PE per galaxy = –1/2 Gmgmg/R

PE of N galaxies = –1/2 GNmgNmg/R = –1/2 GMc2/R

Assume random orbits (no preferred rotation):

1/2 Mcv2 = 1/4 GMc2/R

Mc = 2 v2R/G yields “Virial Mass”

(with lots of galaxies, can see how VM changes with radius)

Dark Matter: Quad Quasar

Dark Matter: Gravitational Lenses

Dark Matter: Yields Structure

Dark Matter: 3D Map

HST/ACS images of 8X full moon

ground-based opt/ir/rad +

space-based XMM-Newton

measure shapes of half million galaxies

to reveal “weak lensing”


dark matter clumps over time


Future Universe


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