february 16, 2009scott dodelson, aaas meeting gravitational waves as a probe of the early universe
TRANSCRIPT
February 16, 2009 Scott Dodelson, AAAS Meeting
Gravitational Waves as a Probe of the Early
Universe
February 16, 2009 Scott Dodelson, AAAS Meeting
Consider the United States in 1790
•Over-densities of order 50
•Concentrated in East
•Vast Voids with low density
February 16, 2009 Scott Dodelson, AAAS Meeting
Consider the United States Today
• Over-densities of order 10,000
• Concentration in coasts
• Traces of primordial density (Boston-Washington; East > West)
• Vast Voids
February 16, 2009 Scott Dodelson, AAAS Meeting
The story of this evolution is the story of the United States
When we understand the evolution from one map to another, we can understand • the sociological, economic, and political forces acting on the US• the people, or the constituents, of the US
February 16, 2009 Scott Dodelson, AAAS Meeting
Less parochially, we rely on cosmic maps
WMAP
Sloan Digital Sky Survey
Today, there are huge overdensities: the density in this room is 1030 larger than in an average spot in the Universe
This map of the Cosmic Microwave Background (CMB) shows that the photon/baryon distribution was smooth to one part in 10,000 at t=400,000 years.
February 16, 2009 Scott Dodelson, AAAS Meeting
Less parochially, we rely on cosmic maps
This map of the Cosmic Microwave Background (CMB) shows that the photon/baryon distribution was smooth to one part in 10,000 at t=400,000 years.
WMAP
Sloan Digital Sky Survey
Today, there are huge overdensities: the density in this room is 1030 larger than in an average spot in the Universe
Modern Cosmology quantitatively explains this evolution: Gravitational Instability
February 16, 2009 Scott Dodelson, AAAS Meeting
Quantifying Cosmic Evolution has led to great Discoveries
Kravtsov et al.
Cosmic WebDark Sector
Galaxy Formation
February 16, 2009 Scott Dodelson, AAAS Meeting
Lingering Question
Who/what planted the seeds of structure?
February 16, 2009 Scott Dodelson, AAAS Meeting
Was it even possible?
Hubble Radius (Distance light travels as the Universe doubles in size) at t=400,000 years
How are these two spots correlated with one another?
February 16, 2009 Scott Dodelson, AAAS Meeting
The Horizon ProblemD
ista
nce
Time
Distance between 2 spots in CMB
t = 400,000 yrs
Hubble Radius
February 16, 2009 Scott Dodelson, AAAS Meeting
The Horizon ProblemD
ista
nce
Time
Distance between 2 spots in CMB
t = 400,000 yrs
Hubble Radius
February 16, 2009 Scott Dodelson, AAAS Meeting
The Horizon ProblemD
ista
nce
Time
Distance between 2 spots in CMB
t = 400,000 yrs
Hubble Radius
Be careful extrapolating backwards …
February 16, 2009 Scott Dodelson, AAAS Meeting
Expansion is Governed by the Constituents of the Universe
• Early times correspond to large energies
• The Standard Model of Particle Physics has been tested up to ~100 GeV
• Higher energies/earlier times might bring new particles/forces
February 16, 2009 Scott Dodelson, AAAS Meeting
Probe Unification of Physics at High Energy
George Rieke
LHC
Tevatron
Seeds of Structure
February 16, 2009 Scott Dodelson, AAAS Meeting
Dis
tan
ce
Time
Distance between 2 spots in CMB
t = 400,000 yrs
Hubble Radius
Inflation Solves the Horizon Problem
Inflation
February 16, 2009 Scott Dodelson, AAAS Meeting
The Seeds of Structure
Einstein’s Theory of General Relativity associates over-dense regions with distortions in the fabric of space-time.
What was distorting Space-Time during Inflation?
February 16, 2009 Scott Dodelson, AAAS Meeting
Quantum Mechanical Fluctuations
Ubiquitous on the sub-atomic level …
Inflation stretches them to astronomical sizes
February 16, 2009 Scott Dodelson, AAAS Meeting
Seeds of Structure
Quantum mechanical fluctuations generated during inflation Perturbations freeze out when distances get larger than horizon Evolution when perturbations re-enter horizon
Dis
tort
ion
s in
Sp
ace-T
ime
February 16, 2009 Scott Dodelson, AAAS Meeting
Sealing the Deal & Identifying the Physics
Einstein’s theory allows for different types of distortions in the fabric of space-time. Seeds of structure are scalar or density perturbations. There are also tensor perturbations or gravitational waves.
Scalar/Density
Tensor/Gravitational Waves
February 16, 2009 Scott Dodelson, AAAS Meeting
Gravitational Waves are Produced, e.g., in Collisions of
Black Holes
But they are also produced microscopically due to quantum mechanics … just like density perturbations.
February 16, 2009 Scott Dodelson, AAAS Meeting
How can we detect Primordial Gravitational Waves?
Back
er, Ja
ffe, L
om
men
20
03
Primordial Signal
Measure Polarization of Cosmic Microwave Background
February 16, 2009 Scott Dodelson, AAAS Meeting
Compton scattering of unpolarized anisotropic radiation produces
polarization• Require
Quadrupole (small before t=400,000 yrs)
• Require Compton scattering (rare after t=400,000 yrs)
• Signals factor of 10 smaller than temperature anisotropies
February 16, 2009 Scott Dodelson, AAAS Meeting
Polarization field decomposed into E- and B- modes
Mis
sion
Con
cep
t S
tud
y: T
heory
20
08
February 16, 2009 Scott Dodelson, AAAS Meeting
Polarization field decomposed into E- and B- modes
Mis
sion
Con
cep
t S
tud
y: T
heory
20
08
Density perturbations produce only E-modes
February 16, 2009 Scott Dodelson, AAAS Meeting
Polarization field decomposed into E- and B- modes
Mis
sion
Con
cep
t S
tud
y: T
heory
20
08
Density perturbations produce only E-modes
Gravity waves produce E- and B- modes
February 16, 2009 Scott Dodelson, AAAS Meeting
ResultsS
am
tleb
en
, Sta
gg
s, & W
inste
in 2
008
E-modes have been detected: their spectrum agrees with theoretical prediction
February 16, 2009 Scott Dodelson, AAAS Meeting
New QUAD Results
Pryke et al. 2008
February 16, 2009 Scott Dodelson, AAAS Meeting
Scientists are voting with their feet
February 16, 2009 Scott Dodelson, AAAS Meeting
Scientists are voting with their feet
February 16, 2009 Scott Dodelson, AAAS Meeting
We have sharpened questions that have been asked for
millennia …“Who Created These?”Isaiah 40:26
… and we have real hopes of answering them over the coming decade.
What physics drove inflation in the early universe, thereby producing the seeds of structure?