concordance cosmology: is it correct? kitpc/itp-cas: beijing (27/05/07)

Concordance Cosmology: Is It Correct?

KITPC/ITP-CAS: Beijing

(27/05/07)

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.

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”.

Now to the details. Presented historically..

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:

338

2

22 Λ+±=√

↵

=

akG

aaH critmρπ&

Hubble constantdensity parameter

cosmologicalconstant

H2H2

In Dimensionless Form

Λ++= km1

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.

He

D

Li

Calculations of the primal “cooking” of the chemical elements predict

Hydrogen

Helium

Lithium

etc, correctly!

A New Component - Dark Dark MatterMatter: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 dark mattermatter!

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 EnergyDark Energy, another New Component

• The Universe must be older than the stars within it!

• A “flat” universe, withtot = 1, is attractive and means m + e = 1.

• Observations of distant supernovae indicate that the Universe is accelerating.

• These arguments point to Dark EnergyDark Energy.

Supernova Observations show that the universe is accelerating!

Omega

Dark MatterDark Matter

Dark EnergyDark Energy

Ordinary Chemical Elements

The Inventory of the Universe

0 1

0 1

0 1

0 1

1950

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 dark mattermatter.

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

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 >>nl

Lbox

Given initial conditions, compute forwards and test model at low red-shift.

Remove/reduce degeneracy.

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 aYUV420 codec decompressor

are needed to see this picture.

QSO Line Absorption from IGM

• TVDPM on Large Eulerian grids.

• Moderate over-density gas.

• Metals, ionization state computed.

• Line numbers and

profiles computed.

Hot gas filaments in the intergalactic mediumCen & 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

Nagamine, Fukugita

Cen and Ostriker

(2001)

Star Formation Cosmic History

APOSDSS

2000s

Large Scale Structure Surveys: Z~0

Sloan Digital Sky Survey: 2003

200,000 galaxies

Cmbgg OmOlCMB

Cmbgg OmOlCMB

+

LSS

Cmbgg OmOlCMB

How much dark matter is there?

Cmbgg OmOlCMB

+

LSS

How much dark matter is there?

Cmbgg OmOlCMB

How clumpy is the Universe?

Cmbgg OmOlCMB

+

LSS

How clumpy is the Universe?

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: ΛCDM)

• tot = 1 (assumption) [=1.010 +0.016-0.009]• cdm = 0.260 ± 0.037 [0.26 +- 0.02]• baryon = 0.0486 ± 0.0019• lambda = 0.691 ± 0.036• n = 0.966 ± 0.023 [=0.938+-0.015] <=• H0 = 68.3 ± 6.75 km/s/Mpc• 8 = 0.894 ± 0.057 [=0.751+_0.031]• scat =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

WL

SN, CBR

2003~ 2010

A More Critical Look at the Low Red-Shift Tests:

103 > Z > 6 6 > Z > 0.5 0.5 > Z

Photons CBR SZ Rdio Lns

Baryons CBR GalForm LEN

Dark Matter CBR StrGrth HlsClstrs

Dark Energy CBR SN Ages etc

> 20Mpc/h

CBR Clstrs 2pt SDSS

20 > >1 CBR ? Cltrs,LyA, StrGrth

GrLensing

1 > ??????? ?? XXX???

But…

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, Non-Standard, 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 aYUV420 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

concordance cosmology: is it correct? kitpc/itp-cas: beijing (27/05/07)

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