The State of the UniverseDavid Weinberg, Ohio State University

The State of the Universe (as we know it)David Weinberg, Ohio State University

The State of the Universe (as we think we know it)David Weinberg, Ohio State University

Bottom Line

A wide range of current data are well explained by a cosmological model with

• A spatially flat Universe

• Dominated by cold dark matter and a cosmological constant

• ≈ 0.75, m ≈ 0.25, b ≈ 0.05, H0 ≈ 70 km s-1 Mpc-1

• Gaussian, adiabatic, primordial fluctuations that are

approximately (but not perfectly) scale-invariant.

Ongoing/planned experiments will substantially improve the

precision of cosmological tests and could poke holes in this picture.

How Far We’ve ComeIn the mid-’80s, the main data to be explained were:

• galaxy clustering

• properties of galaxies

• existence of high-redshift quasars

• upper limits on CMB anisotropy

How Far We’ve ComeToday: We argue about the parameters of flat inflationary cold dark matter models.

The Path to CDM• COBE: Gravitational instability is right, inflation OK.

The Path to CDM• COBE: Gravitational instability is right, inflation OK.

• Improving galaxy clustering and H0 data: harder to accommodate with m=1.

The Path to CDM• COBE: Gravitational instability is right, inflation OK.

• Improving galaxy clustering and H0 data: harder to accommodate with m=1.

• Ly forest: Explains phenomenon not designed to explain.

The Path to CDM

• COBE: Gravitational instability is right, inflation OK.

• Improving galaxy clustering and H0 data: harder to accommodate with m=1.

• Ly forest: Explains phenomenon not designed to explain.

• Type Ia supernova Hubble diagram: direct evidence for cosmic acceleration.

Riess et al. 1998

The Path to CDM

• COBE: Gravitational instability is right, inflation OK.

• Improving galaxy clustering and H0 data: harder to accommodate with m=1.

• Ly forest: Explains phenomenon not designed to explain.

• Type Ia supernova Hubble diagram: direct evidence for cosmic acceleration.

• BOOMERANG/MAXIMA: Flat universe, clear acoustic peak. Strengthens supernova evidence for dark energy.

Jaffe et al. 2001

Developments since 2000

• Substantial improvements in precision and dynamic range of measurements (WMAP, DASI, CBI, ACBAR; 2dFGRS, SDSS; larger and more distant supernova samples; precise Ly forest measurements)

• Addition of: Weak lensing, CMB polarization, CMB/BBN consistency on b.

• “Vanilla” CDM, with tot=1, w=-1, free parameters m, b, h, ns, As, looks close to consistent with all current data, though some tension on parameter values.

Dark Matter• The Silver Bullet Cluster: qualitatively new evidence for dark matter vs. modified gravity.

Clowe et al. 2006; fig. courtesy Doug Clowe

Dark Matter• The Silver Bullet Cluster: qualitatively new evidence for dark matter vs. modified gravity.

• Small scale problems of cold dark matter:

• Excess of small scale structure (satellite galaxies).

• Wrong rotation profiles of disk galaxies.

My take: The case that these problems are related to dark matter not baryonic physics isn’t strong enough, and probably won’t become so.

• Ly forest lower limit on dark matter particle mass: 2.5 keV for thermal equilibrium decoupling, 14 keV for sterile neutrino (95% confidence; Seljak, McDonald, & Trac 2006)

Seljak, Mcdonald, & Trac 2006 (astro-ph/0602430)

Ly forest flux power spectrum: cold dark matter vs. 6.5 keV sterile neutrino

WMAP

Spergel et al. 2006 l ≈ 100 degs /

WMAP

Spergel et al. 2006

3-yr data vs 1-yr data:

Smaller error bars throughout.

Key difference is new polarization measurement, changing central value and error bar on optical depth.

Changes central values on m

and 8: a lighter, less clustered universe.

Substantially reduces degeneracies among cosmological parameters.

WMAP + SDSS LRGs

Tegmark, Eisenstein et al. 2006

SDSS adds turnover scale, tilt, and acoustic oscillation scale measured in km/s at z ~ 0.35.

WMAP + SDSS LRGs

Tegmark, Eisenstein et al. 2006

WMAP + SDSS LRGs

Tegmark, Eisenstein et al. 2006

WMAP + SDSS LRGs

Tegmark, Eisenstein et al. 2006

Supernova Hubble Diagram

Riess et al. 2004

Astier et al. 2006

Supernova Hubble Diagram + SDSS BAO Scale

Astier et al. 2006

Developments since 2000

• Substantial improvements in precision and dynamic range of measurements (WMAP, DASI, CBI, ACBAR; 2dFGRS, SDSS; larger and more distant supernova samples; precise Ly forest measurements)

• Addition of: Weak lensing, CMB polarization, CMB/BBN consistency on b.

• “Vanilla” CDM, with tot=1, w=-1, free parameters m, b, h, ns, As, looks close to consistent with all current data, though some tension on parameter values.

Game Over?

Game Over?The tyranny of vanilla:

Will we be cursed by a successful standard model with key elements that we don’t understand?

Game Over?

Things we might find with improved data: • w = -0.9• w = -1.1• dw/dz|0.5 = 1, or (z=10) = 0.1.

• Inconsistency of gravitational and distance constraints on w: modified gravity, not dark energy.• tot = 1.02

• r = 0.1 (gravity waves), dns / d ln k = -0.03

• Primordial fluctuations have non-Gaussian or isocurvature component

Future Experiments

Improved measurements of supernovae, weak lensing, galaxy clustering/baryon oscillations, Ly forest, CMB temperature and polarization anisotropies

An incomplete list:Current: SDSS-II, CFHT Legacy SurveyNear Future: PAN-STARRS, Planck, South Pole TelescopeMedium Term: Dark Energy Survey, SDSS-IIILong Term: LSST, Square Kilometer Array, JDEM, CMBPOL

Bottom Line

A wide range of current data are well explained by a cosmological model with

• A spatially flat Universe

• Dominated by cold dark matter and a cosmological constant

• ≈ 0.75, m ≈ 0.25, b ≈ 0.05, H0 ≈ 70 km s-1 Mpc-1

• Gaussian, adiabatic, primordial fluctuations that are

approximately (but not perfectly) scale-invariant.

Ongoing/planned experiments will substantially improve the

precision of cosmological tests and could poke holes in this picture.