Transcript 9

KITPC/ITP-CAS:
Beijing (27/05/07)
Concordance Cosmology: Is It
Correct?
Question Answered:
• Really Great Progress
• Two Ways Physical Models are Tested/Falsified
– A) Dramatic findings which overturn a paradigm; eg
the late time acceleration of the galaxies.
– B) Incremental Progress which exposes anomalies
that will not go away; eg advance of the perihelion of
Mercury.
– -----------------------------------------------------------The first, A, is not happening. Everything coheres.
And experiments underway are reaching the
precision to tell us if the second, B, will happen.
Now to the details. Presented historically..
Rumours of Great Progress…
• We know the component pieces: Photons,
Neutrinos, Baryons, Dark Matter & Dark
Energy.
• We know the history: Inflation, Baryogenesis,
Dark Matter Domination, Growth of Structure,
Dark Energy Domination.
• We know the parameters: “Precision
Cosmology”.
Foundation and Pillars..
• Homogeneous, Isotropic, Big Bang.
–
–
–
–
–
large scale uniformity (1930s -> present)
Hubble law (1930s -> present)
light element nucleo-synthesis (1960s -> present)
temporal evolution observed directly (1960s -> present)
black body radiation field (1960s, COBE -> present)
• Baryons, Photons, Neutrinos, DM & DE.
– Lyman alpha clouds, CBR spectrum (1960s -> present)
– dark matter in clusters and halos (1930s, 1970s -> present)
– supernovae show acceleration (2000s -> present)
Pillars contd…
•
Nearly Scale Invariant (n~1) Spectrum.
– dimensional analysis (Harrison, Peebles & Zeldovich)
(1960s)
– inflationary (or ekpyorotic) theory(1980s -> present)
– Fourier analysis of large scale structure(2000s)
•
Geometrical Flatness (total = 1).
– Simplicity and dimensional analysis (1960s)
– CBR spectrum, direct measurement of parts (2000s)
Each piece is supported
by multiple arguments
and measurements.
Edifice is robust!
Foundations: General
Relativity in an
Homogeneous Isotropic
Universe
The Universe is an Initial Value
Problem…..
• Globally, the universe evolves according to
the Friedman equation:
a  8G
k 

H HH
m crit  2 
2 2  
3
3
a
a
2
Hubble constant
2
density parameter
cosmological
constant
In Dimensionless Form
1   m   k  
Pillars:
Observational
Cosmology, 1920s > 1970s
The Dawn of the Modern
Era:1920-1950
• Harlow Shapley, Edwin Hubble, Walter Baade, Albert
Einstein.
• We live far off center in our galaxy.
• The spiral nebulae are galaxies like our own Milky Way
and are made of stars.
• The galaxies are moving away from one another with a
velocity proportional to the separation.
• The laws of General Relativity rule in this domain.
The data would only have convinced a visionary!
The Heroic Era: 1950-1975
• Optical Observers use big telescopes to
estimate the cosmological parameters.
• Radio observers detect the cosmic
background radiation field.
• Theoreticians compute the cooking of the
primal elements in the big bang.
• Theoreticians speculate on the origins of
structure.
Holmdel NJ: 1965 Penzias and Wilson discover a
cosmic radio buzz in their antenna.
Calculations of
the primal
“cooking” of
the chemical
elements predict
He
D
Hydrogen
Helium
Lithium
etc, correctly!
Li
A New Component - Dark
Matter:1975-1995
• Clusters of Galaxies are Dark Matter
Dominated (Zwicky: 1937).
• Galaxy Halos are Dark Matter Dominated
(Ostriker and Peebles: 1973).
• Galaxy Rotation Curves require Dark
Matter (Rubin:1978 ).
• Perturbations Observed by COBE Satellite
require Dark Matter (Mather: 1991).
Coma Cluster:
1000 galaxies
(only center
shown), 1000km/s
held together by
gravity from dark
matter!
The Evidence from our Galaxy
and other spirals shows that the
total mass increases rapidly
with increasing radius to far
outside the visible galaxy.
Visible
galaxy
1975-2002: Dark Energy,
another New Component
• The Universe must be older than the stars
within it!
• A “flat” universe, withtot = 1, is attractive and
means m + e = 1.
• Observations of distant supernovae indicate
that the Universe is accelerating.
• These arguments point to Dark Energy.
Supernova Observations show that the
universe is accelerating!
The Inventory of the Universe
Ordinary Chemical Elements
Dark Energy
Dark Matter
0
Omega
1
1950
0
1
0
1
0
1
1975
2000
The COBE (1991) satellite confirmed the basic prediction of the
big bang theory: the universe is filled with “black body radiation”.
With fluctuations – ripples – showing the seeds for all
structure to be formed later. The height of the waves
–1/100,000 – was more evidence for dark matter.
COBE:1991
Best Fit Concordance Model
(Steinhardt, 2002)
NB: Rough fit to n=1 gaussian perturbation spectrum predicted by inlationary arguments
or simple dimensional analysis.
2002: The Model Has Passed
Observational Tests at Various
Epochs: eg
•
Z ~ 106 :
Light Element Nucleosynthesis
•
Z ~ 103 :
Cosmic Background Radiation
•
6>Z>2:
Lyman alpha cloud absorptions
•
4>Z>0:
Galaxy Formation Rate
•
Z ~ 0:
Large Scale Structure of Galaxies
WMAP (2002-2007) Gives
Initial Conditions
WMAP CBR SKY
Page et al; 2003
WMAP Spectrum
CBR:WMAP initial contributions
1) |n-1|/n << 1 = 0.01+-0.04.
-> scale invariant spectrum
2) b / | m- b| << 1 = 17.1%+-0.25%.
->dark matter dominance
3) tot = 1.02 +- 0.04.
->flat universe
4)
| hopt –hcbr | << 1 = 5%+-10%; confirmation
5)
|8cbr- 8clstr | / 8 << 1 = 0.29+-0.45; confirmation
6)
scat = 0.17+-0.04; a surprise
Spergel et al: 2003
But…
• Degeneracy in parameter estimation remains (so
other measures are essential for accurate
parameter estimation).
• Low multi-poles are too low (a real issue or
statistical fluctuations?).
• E-E correlations not initially available (needed to
confirm re-ionization result).
CBR Parameter Degeneracy
Bridle, Lahav, Ostriker and Steinhardt: 2003
Computing the Universe: locally, growth of
perturbations computed classically; numerical
hydro required to reach the current epoch
• Transformation to
comoving coordinates
x=r/a(t)
• comoving cube,
periodic boundary
conditions
• Lbox >>lnl
Lbox
Given initial conditions, compute forwards and test
Remove/reduce degeneracy.
model at low red-shift.
Physics Input
•
•
•
•
•
•
•
Newton’s law of gravitation.
Standard equations of hydrodynamics.
Atomic physics (for heating and cooling).
Radiative transfer.
[ Maxwell’s equations in MHD form ].
-----------------------------------------------Heuristic treatment of star-formation.
Galaxy (L*,E0) Formation from High Resolution
Hydrodynamic Simulation (Naab et al ‘07)
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
QSO Line Absorption from IGM
• TVDPM on Large
Eulerian grids.
• Moderate overdensity gas.
• Metals, ionization
state computed.
• Line numbers and
profiles computed.
Hot gas filaments in the intergalactic medium
Cen & Ostriker .
Simulated Spectrum
Lyman Alpha Clouds
•
•
•
•
•
•
Number of absorption lines vs redshift.
Number of absorption lines vs column density.
Velocity width distribution of lines.
Spatial correlation of line strengths.
-------------------------------------------All show good agreement:theory vs observation.
Evolution of Baryon Components
Prediction confirmed: 30% -50% of baryons are in the WHIM:
Confirmed.
Direct Observations of Galaxy Formation History
Star Formation Cosmic History
Nagamine, Fukugita
Cen and Ostriker
(2001)
Large Scale Structure Surveys: Z~0
SDSS
2000s
APO
Sloan Digital Sky Survey: 2003
200,000 galaxies
CMB
Cmbgg OmOl
CMB
+
LSS
Cmbgg OmOl
How much dark matter is there?
CMB
Cmbgg OmOl
How much dark matter is there?
CMB
+
LSS
Cmbgg OmOl
How clumpy is the Universe?
CMB
Cmbgg OmOl
How clumpy is the Universe?
CMB
+
LSS
Cmbgg OmOl
Baryon Oscillations
(Tegmark et al 2006: a marginal detection)
..but some astronomical parameters
are better determined
..and some fundamental physics
parameters are better constrained as well
Where we are now….
2007
In Detail: Best Current Cosmological
Model (prior: CDM)
•
•
•
•
•
•
•
•
tot
cdm
baryon
lambda
n
H0
8
scat
= 1 (assumption) [=1.010 +0.016-0.009]
= 0.260
± 0.037 [0.26 +- 0.02]
= 0.0486
± 0.0019
= 0.691
± 0.036
= 0.966
± 0.023 [=0.938+-0.015] <=
= 68.3
± 6.75 km/s/Mpc
= 0.894
± 0.057 [=0.751+_0.031]
=0.103
± 0.054 [=0.070+_0.027]
Tegmark et al (SDSS,2005); Spergel et al (WMAP3,2006)
“precision cosmology” ??
Coming Soon: Industrial Strength
Surveys in Advanced Planning
•
•
•
•
•
•
•
Better CBR Experiments (eg Planck/ACT)
Better Baryon Oscillations (eg SDSS3)
Better SNI Constraints (eg LSST)
Better Weak Lensing ( eg DES)
Large SZ Surveys (eg APEX, SPT…)
+++++++++++++++++
=> Real “Precision Cosmology” ?
OR
• => Real Challenges to the “Concordance Model”
SZ
~ 2010
2003
WL
SN,
CBR
A More Critical Look at the Low Red-Shift Tests:
But…
103 > Z > 6
6 > Z > 0.5
0.5 > Z
CBR 
SZ 
Rdio Lns 
CBR 
GalForm 
LEN 
Dark Matter
CBR 
StrGrth 
HlsClstrs
Dark Energy
CBR
SN 
Ages etc 
Clstrs 2pt 
SDSS 
Cltrs,LyA,
StrGrth 
?? 
GrLensing
Photons
Baryons
l > 20Mpc/h CBR 
20 > l >1
1>l
CBR ?
???????
XXX???
Is Something Wrong Here?
Is the CDM paradigm wrong at small scales ?
•Too many small galaxies predicted?
•Central galaxy densities predicted too large?
•Too many satellite galaxies predicted?
•Too many galaxies in voids predicted?
•Etc……..
Or is it simply that it is too hard to compute correctly in the extreme non-linear domain?
Will the Problems Give Clues To
The Nature Of The Dark Matter ?
•
•
•
•
•
•
•
•
•
Standard: Weakly Interacting Cold Dark Matter (CCDM).
Variant: Strongly Self-Interacting Dark Matter (SIDM).
Variant: Warm Dark Matter (WDM).
Variant: Decaying Dark Matter (DDM).
Variant: Repulsive Dark Matter (RDM).
Variant: Self-Annihilating Dark Matter (SADM).
Variant: Fuzzy Dark Matter (FDM).
Variant: Massive Black Holes as dark matter (BH).
Etc, etc,…
Conclusions
• Uniform, Isotropic, Hot Big-Bang Model is
a Very Good Fit to Suite of Observables.
• Inflationary Origin for Perturbations Fits
Large Scale Structure Observations.
• Cold Dark Matter Paradigm Works Well.
• Flat, K = 0, Model is Satisfactory.
• “New”, Repulsive Force, Cosmological
Constant or Quintessence Seems Required.
Do We Understand the Cosmos?
• The general picture that we have works well.
• Apart from some (important) details, all
predictions match our improving observations.
• But, we have said this before!
• Each time, some apparent detail has been a
clue to a basic omission. Something ignored.
• My view: this will happen again. AND
Big Questions Remain Unanswered
• Re the Past: What was the origin of the
perturbations that gave rise to structure in
the universe? What happened before the big
bang, and does the question make sense?
• Re the Present: What is the dark matter? The
dark energy?
• Re the Future: Will there be surprises?
• Re Us: Do we matter? Does the “anthropic
principle” make sense?
The Truth is More Complex…
• We Know Some of the Components, But There Are Huge
Gaps in Our Knowledge!
• We Understand Some of the Phases, But Calculate Others
Incorrectly, and for Others there Are Equally Valid, NonStandard, Alternatives!
• We Know Some Parameters to Percents, Others to Factors
of Two and Others Are Uncertain to Order of Magnitude!
The Nature of the DM is Unknown: All Tests are on Small
Scales and are Problematic!
• Shortage of Visible Satellite Galaxies: baryonic physics a plausible
explanation.
• Number of Small Galaxies: understood from baryonic physics.
• Absence of Dwarf Galaxies in Voids: probably ok given baryonic
physics.
• ======================================
• Dark Matter in Dwarf Systems: incomprehensible at present.
• Shortage of DM Satellite Systems: a potential problem.
• Absence of DM Cusps in Galaxies: a serious problem.
WMAP3 Best Fit Parameters:
http://lambda.gsfc.nasa.gov/product/map/current/parameters.cfm
Ansatz: LCDM (k = 0, w = -1)
Data: WMAP3 + All data
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
WMAP Parameters:
http://lambda.gsfc.nasa.gov/product/map/current/parameters.cfm
Ansatz: LCDM (k = 0, w = -1)
Data: WMAP3 + All data