the tools of cosmology - westinghouse nuclear · 2015. 2. 27. · squared fluctuation size [ in...

The Tools of Cosmology

Andrew ZentnerThe University of Pittsburgh

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Part One: The Infant Universe

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ContentsOrientation

The Expanding UniverseThe Enormous Scale of CosmologyThe Prevailing Picture of the Universe

The Pillars of Modern CosmologyPrimordial Synthesis of Light NucleiThe Cosmic Microwave BackgroundThe Appearance of Distant SupernovaeThe Arrangement of Galaxies in the UniverseThe Arrangement of Matter in the Universe

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The Expanding Universe

The Universe Appears Nearly Homogenous and Isotropic on Large Scales

Not Homogeneous: Average Density Varies

Not Isotropic: There Appears A “Special” Direction

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The Universe Appears Nearly Homogenous and Isotropic on Large Scales

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Redshift describes the stretching of electromagnetic wavelengths from receding sources

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We measure the redshifts of objects via characteristic patterns in electromagnetic spectraThe amount of redshift gives the object’s speed

From http://stokes.byu.edu

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http://stokes.byu.eduhttp://stokes.byu.edu


Edwin Hubble made a plot of the distance to galaxies against the velocities that galaxies were recedingToday the Hubble expansion rate is 22 (km/s) for every million light years of distance

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Edwin Hubble made a plot of the distance to galaxies against the velocities that galaxies were recedingToday the Hubble expansion rate is 22 (km/s) for every million light years of distance

Hubble 1929

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Einstein was both pleased and embarrassed by the discovery of the “Hubble Expansion”

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The Expansion requires no notion of “center”All point recede from all other points

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The Scale of Cosmology

The Star Closest to the Sun is 4 light-years away, about 24,000,000,000,000 miles

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The Scale of CosmologyHubble Space Telescope

http://hst.nasa.gov

Most Distant Galaxies are ∼ 200,000,000,000,000,000,000,000 or 2 × 1023

miles away ∼ ten of Billions of light years

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http://nasa.govhttp://nasa.gov

The Contents of the Universe

4%

26%

70%

Dark Matter(suspected since 30s“known” since 70s)

“Dark Energy”(suspected since 1980s“known” since 1998)

Also Ran: Radiation (0.01%)

Normal Matter(stars 0.4%, gas 3.6%)

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4%

26%

70%

Dark Matter(suspected since 30s“known” since 70s)

“Dark Energy”(suspected since 1980s“known” since 1998)

Normal Matter(stars 0.4%, gas 3.6%)

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The Geometry of the Universe

Three OptionsThe Universe Can Be “Flat”The Universe Can Be “Open”The Universe Can Be “Closed”

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The Flat Geometry is FamiliarThe angles of a triangle sum to 180°

A

CB

A + B + C = 180°

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http://casa.colorado.edu/~ajsh

Closed: Angles Sum To > 180°

Open: Angles Sum To < 180°

FLAT (EUCLIDEAN)

Our Universe

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http://casa.colorado.edu/~ajshhttp://casa.colorado.edu/~ajsh


4%

26%

70%

Dark MatterΩDM = 0.26

“Dark Energy”ΩDE=0.70

Normal MatterΩBARYON = 0.04

The Universe is FLAT When ΩBARYON + ΩDM + ΩDE = 1

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How Do We Know This?

The Synthesis of the Light Nuclei

The Cosmic Microwave Background Spectrum

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Synthesis of the Light Nuclei

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neutronproton

electronpositronneutrino

In the very early universe (t < 1 second)Densities are very high & interactions happen very quicklyThe weak interactions interconvert protons and neutronsEquilibrium is maintained while interactions are rapid

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The Universe expands, cools, and interactions freeze outEquilibrium is lost and residual neutrons are incorporated into Deuterium, Helium, & Lithium by t=20 minutes

Deuterium

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Abundance of Light Nuclei

Abu

ndan

ce o

f Ele

men

t Com

pare

d to

H

ydro

gen

4He

Baryon Density of Universe

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Abundance of Light Nuclei

Abu

ndan

ce o

f Ele

men

t Com

pare

d to

H

ydro

gen

4He

Baryon Density of Universe

Dashed lines show range of observed values

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Forward 400,000 years

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The Cosmic Microwave Background

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1965ApJ...142..419P

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The Wilkinson Microwave Anisotropy

Probe

http://map.gsfc.nasa.gov

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http://map.gsfc.nasa.govhttp://map.gsfc.nasa.gov


A Map of the CMB on the sky is extremely smoothThe CMB has a thermal spectrum with T=2.726 K = -454.7 °F

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Turning up the contrast on the map reveals fluctuations of 1 part in 100,000 or temperature changes of ~ 0.00003 K

WMAP http://map.gsfc.nasa.gov

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Producing the CMB

In the Early Universe, temperatures are highElectrons cannot join protons (or Helium nuclei) to form atoms because photons are energetic enough to knock them offPhotons don’t travel far before interacting

proton

electron

helium

photon

deuterium

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Producing the CMB

When the temperature drops, energies are not high enough to prevent electrons from joining nuclei to form atomsPhotons no longer interact with the electrically-neutral medium and they move freely through the universe from then on

hydrogen

helium

photon

deuterium

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Observing the CMB

This Cosmic Microwave Background light transmits an image of the infant universe frozen as it was at decoupling

http://map.gsfc.nasa.gov

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Observing the CMB

In the early universe the gravity of density fluctuations tries to compress dense patchesThe pressure of the photons pushes backThis results in small oscillations in the local density and temperature

proton

electron

helium

photon

deuterium

http://background.uchicago.edu/~whu

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Observing the CMB

In the early universe the gravity of density fluctuations tries to compress dense patchesThe pressure of the photons pushes backThis results in small oscillations in the local density and temperature

baryonsphotonshttp://background.uchicago.edu/~whu

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Observing the CMB

Hot & Cold patches reflect the time needed to compressHot & Cold patches have a typical physical sizeThe angle subtended by such patches on the sky is a function of the geometry of the space

OpenFlat

Flat

Closed

ISW

Observer

Early

Late

sound horizon

LastScattering Surface

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Observing the CMBhttp://map.gsfc.nasa.gov

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Observing the CMB

WMAP http://map.gsfc.nasa.gov

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Observing the CMB

10 100 500 10000

1000

2000

3000

4000

5000

600090° 2° 0.5° 0.2°

Squa

red

Fluc

tuat

ion

Size

[ in

(0.0

0000

1 K

)2 ]Angular Size

Large Small

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Observing the CMB

10 100 500 10000

1000

2000

3000

4000

5000

600090° 2° 0.5° 0.2°

CompressionPeak

RarefactionPeak

CompressionPeak

Primordial Fluctuation

Squa

red

Fluc

tuat

ion

Size

[ in

(0.0

0000

1 K

)2 ]Angular Size

Large Small

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Observing the CMB

10 100 500 10000

1000

2000

3000

4000

5000

600090° 2° 0.5° 0.2°

Peak Positions Appropriate for a Flat Universe

Squa

red

Fluc

tuat

ion

Size

[ in

(0.0

0000

1 K

)2 ]Angular Size

Large Small

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Observing the CMB

10 100 500 10000

1000

2000

3000

4000

5000

600090° 2° 0.5° 0.2°

Relative Peak Height Provides Alternative Mearure of Baryon

Abundance and Agrees with Light Element Synthesis

Squa

red

Fluc

tuat

ion

Size

[ in

(0.0

0000

1 K

)2 ]Angular Size

Large Small

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Summary

Light Element Synthesis & Cosmic Microwave Background Studies:

Support Extrapolation of Expanding Universe Picture to a time 13.7 Billion Years Ago!

Provide Measurements of the Geometry and Total Matter Content of the Universe!

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Summary

http://casa.colorado.edu/~ajsh

Closed: Angles Sum To > 180°

Open: Angles Sum To < 180°

FLAT (EUCLIDEAN)

Our Universe

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http://casa.colorado.edu/~ajshhttp://casa.colorado.edu/~ajsh

Summary & Next Step

4%

26%

70%





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Summary & Next Step

4%

26%

70%





WHY?

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Summary & Next Step

4%

26%

70%





WHY?

WHY?

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the tools of cosmology - westinghouse nuclear · 2015. 2. 27. · squared fluctuation size [ in...

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