Taking the Universe

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Taking the Universes Baby Picture

• David Spergel
• Princeton University

• Houston Lecture
• November 15, 2008

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The Big Bang Model

• Two Pillars
• General Relativity
• Matter tells space how to curve
• The curvature of space tells matter how to move
• Space is not absolute but defined in terms of
  relative distance between two objects
• Large scale homogeneity
• Implication
• We live in an expanding universe!

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Mass Density / Geometry of the Universe
MAP990006
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Discovery of the Expanding Universe
4.0
3.5
Log Velocity
3.0
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m (pg)
Edwin Hubble
V H0 D
Mt. Wilson 100 Inch Telescope
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The Cosmic Microwave Background
Microwave Receiver
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Quick History of the Universe

• Universe starts out hot, dense and filled with
  radiation
• As the universe expands, it cools.
• During the first minutes, light elements form
• After 300,000 years, atoms form
• After 100,000,000 years, stars start to form
• After 1 Billion years, galaxies and quasars

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Open Questions in 1982

• Why is the universe so big and so old?
• Why is the total energy of the universe so close
  to zero? (What is the fate of the universe?)
• How did galaxies form?
• What is the universe made of?

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Cold Dark Matter (1980s)

• Most of the mass in galaxies and clusters are not
  in the form of stars, gas or dust
• Structure formation would work if non-interacting
  particles (CDM) filled galaxies
• Abundance of Helium and Deuterium implied that
  atoms did not make up most of the universe
• Particle physics models suggest the existence of
  new particles (searches continue!)

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1980s Inflationary Model

• Developed in 1980s Guth, Linde, Steinhardt,
  Albrecht
• Posits that the universe underwent a period of
  rapid expansion (inflation) driven by the
  energy of empty space (vacuum energy)
• Predictions
• A flat universe (zero energy)
• A large universe
• Small fluctuations in density that grow to form
  galaxies

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Early 1990s Astronomers see a Low Density
Universe

• The density in ordinary matter accounts for only
  5 of the critical density
• There is strong evidence for dark matter that
  makes up 30 of the critical density
• Universe appears to be open
• Has the inflationary model failed??

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Vacuum Energy Last Refuge of the Desperate
Theorist

• Empty space can have energy and curve space
• Dubious history
• Evoked several times to explain discrepancies
  between observation and theory
• Disliked by astronomers and particle physicists.
  This model implies that atoms make up only 5 of
  the universe and 2 (!) forms of exotic matter
  (dark matter and dark energy) dominate the
  universe.
• Virtues
• Saves inflation
• Makes clear predictions
• Age of universe
• Brightness of distant sources
• Geometry of the universe

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Supernova Probes of the Distant Universe

• Supernova appear to be ideal standard candles
• Bright
• Uniform
• Common
• Development of large cameras enable big redshift
  surveys

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Cosmic Microwave Background Snapshot of the
Early Universe

• Five Hundred Thousand years after the big bang,
  atoms formed and the universe became transparent
• Variations in density of the universe imprint
  fluctuations on the cosmic microwave background
• characteristic size (distance that a photon can
  travel in 500,000 years)
• Inflation makes very specific predictions about
  the fluctuation spectrum

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Wilkinson Microwave Anisotropy Probe
A partnership between NASA/GSFC and Princeton
Science Team
NASA/GSFC Chuck Bennett (PI) -gt JHU Michael
Greason Bob Hill Gary Hinshaw Al Kogut Michele
Limon Nils Odegard Janet Weiland Ed Wollack
Brown Greg Tucker
UCLA Ned Wright
Princeton Chris Barnes Norm Jarosik Eiichiro
Komatsu Michael Nolta
Lyman Page Hiranya Peiris Rachel Bean David
Spergel Olivier Dore Licia Verde Jo
Dunkley
Chicago Stephan Meyer
UBC Mark Halpern
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David Wilkinson 1935-2002
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WMAP Spacecraft
upper omni antenna
back to back
line of sight
Gregorian optics,
1.4 x 1.6 m primaries
60K
passive thermal radiator
focal plane assembly
feed horns
secondary
90K
reflectors
thermally isolated
instrument cylinder
300K
warm spacecraft with
medium gain antennae
- instrument electronics
- attitude control/propulsion
- command/data handling
deployed solar array w/ web shielding
- battery and power control
MAP990422
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June 30, 2001
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K - 22GHz
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Ka - 33GHz
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Q - 41GHz
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V - 61GHz
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W - 94GHz
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W - 94GHz
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5º
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A BABY PICTURE OF THE UNIVERSE
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What Have We Learned?

• Simple model fits a wide range of data (only 5
  numbers)
• Age of universe13.7 Gyr
• Composition
• Atoms 4
• Matter 23
• Dark Energy 73
• Scale Invariant Fluctuations seed growth of
  galaxies
• First Stars formed 200 Myr after the big bang

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A Picture is worth 6 numbers.
Density of Atoms 2.273 /- 0.062
Density of Matter 0.1099 /- 0.0062
Age of Universe 13.69 /- 0.13 Gyr
Amplitude of Density Fluctuations 0.796 /- 0.036
Slope of Density Fluctuations 0.963 /- 0.015
Epoch of Star Formation 11.0 /- 1.4
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From Baby Pictures to Todays Universe
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EVOLVING THE UNIVERSE FORWARD IN TIME
Computer simulation of the growth of structure,
in a box 80 million light years on a side.
Courtesy Renyue Cen.
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Sloan Digital Sky Survey Taking a picture of the
universe today
The telescope can view a region of sky 35 times
bigger than the full Moon. It is located at
Apache Point Observatory in Southeast New
Mexico. It observes without a dome it is
protected from wind buffetting and stray light by
a comoving light baffle structure.
Connie Rockosi at the telescope
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The Apache Point ObservatorySunspot, New Mexico
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SDSS imaging camera, built by Jim Gunn et al.
Shown here mounted on the telescope.
Interior view of the camera, showing the filters
on the corrector plate.
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SDSS spectrographic cartridge mounted on
telescope and mated to spectrograph.
We take spectra of 640 objects at a time, with
typical exposure times of one hour.
Resolution ?/??2000 Coverage 3800-9200 Å
Spectrographs built by Alan Uomoto et al.
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From Baby Pictures to Todays Universe

• Assume that galaxy clustering is determined only
  by initial conditions (from CMB) and gravity
• Predict the universe today

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We have now found the equivalent peak in the
clustering signal of galaxies, demonstrating
unambiguously that galaxy distribution grew by
gravity from the CMB fluctuations.
Eisenstein92 et al.
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All of the pieces seem to fit.

• Supernova distance
• Hubble Constant
• Age of Universe
• Cluster Properties

• Cosmic Abundances
• Gravitational Lensing
• Absorption Line Statistics

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Cosmology Now Has A Standard Model

• Basic parameters are accurately determined
• Many can be measured using multiple techniques
• All of the pieces fit
• The universe is very strange
• Atoms make up only 5 of the universe
• Dark matter dominates galaxies
• Dark energy (74 of the universe fills space)
• Soon after the big bang, the universe underwent a
  very rapid period of expansion.

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Is Cosmology Done?

• Big Open Questions
• What is the dark energy?
• What is the dark matter?
• How did the universe begin?
• Next Steps
• New ideas from particle physics PCTS
• New experiments ACT, HSC, LSST

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THANK YOU !
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Is the Universe Finite or Infinite?
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Topology
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Two Torus
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Other Tilings
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Three Torus
Same idea works in three space dimensions
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Infinite number of tiling patterns
This one only works in hyperbolic space
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Spherical Topologies
This example only works in spherical space
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Dodecahedral Space
Tiling of the three-sphere by 120 regular
dodecahedrons
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Homogeneous Isotropic Universe
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The microwave background in a multi-connected
universe
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Matched circles in a three torus universe
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If the universe was finite
Cornish, Spergel, Starkman, Komatsu
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What we see in the WMAP data
UNIVERSE IS BIG!
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Conclusions

• Cosmology is in a golden age!
• Advances in technology are enabling us to probe
  the physics of the very early universe and the
  birth of structure
• So far, the standard model appears to fit the
  data, but stay tuned!

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Spherical Topologies
This example only works in spherical space
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Dodecahedral Space
Tiling of the three-sphere by 120 regular
dodecahedrons
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Homogeneous Isotropic Universe
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The microwave background in a multi-connected
universe
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Matched circles in a three torus universe
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If the universe was finite
Cornish, Spergel, Starkman, Komatsu
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What we see in the WMAP data
UNIVERSE IS BIG!
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Conclusions

• Cosmology is in a golden age!
• Advances in technology are enabling us to probe
  the physics of the very early universe and the
  birth of structure
• So far, the standard model appears to fit the
  data, but stay tuned!