Transcript COMING HOME - 2006 Mitchell Symposium

COMING HOME
Michael S. Turner
Kavli Institute for Cosmological Physics
The University of Chicago
Some Cosmological
Observations from Afar
No Chinks in “The
New Cosmology”
(i.e., CDM + Dark Energy + Inflation)
•
•
WMAP + SDSS + 2dF + HST Key Project +
DASI + ACBAR + CBI + t0 + SNe …
Smaller error bars, consistency remains
– σ(n): 0.1 to 0.02; σ(Ω0): 0.03 to 0.01; σ(w): 0.2 to
0.1
•
•
Hubble constant has been constant for 5
years! H0 = 72 ± 7 km/s/Mpc
Looking better than ever – almost ready for a
real name!
Precision Cosmology is
Harder than Theorists’
projections
• “Bits & bites”
• l = 2 to 5
• Optical depth:
τ = 0.17 to 0.09
Serious testing of
Inflation has begun
Key Predictions
1. Flat Universe
2. Almost scale-invariant, Gaussian perturbations:
|(n-1)| ~ 0.1 and |dn/dlnk| ~ 0.001
1. Gravity waves: spectrum, but not amplitude predicted
Key Results
1. Ω0 = 1.0 ± 0.01
2. (n-1) = 0.96 ± 0.017*; dn/dlnk = -0.1 ± 0.05; no
evidence for nonGaussianity
3. r < 0.55 (95% cl)*
*Depends significantly upon the priors assumed
Cosmic Acceleration
Dark Energy
•
•
•
Evidence for cosmic acceleration has
gotten stronger (HST, CFHTLS, Essence,
WMAP, XMM/Chandra…)
Still no understanding – “theorists continue
to explore phase space”
No evidence that dark energy is not the
energy of the quantum vacuum
–
•
w = -1 ± 0.1 (from ± 0.2); no evidence for time
variation
Very significant probes on the horizon:
–
JDEM, LSST, …
Loose Ends
1.
2.
3.
4.
5.
6.
7.
Precision test (few percent) using baryon density:
BBN (D/H) vs. CMB (odd/even) unrealized
Consistency of BBN light element predictions (He
– D – Li tension)
σ8: lack of consistency
Cosmic variation of α
Excess power at l ~ 2000
“LSND 4th neutrino”
DAMA, e+ excess, …
What Do We Really Know
About Cosmic Acceleration
Charles A. Shapiro & Michael S. Turner,
astro-ph/0512586
Much of What We Know About
Cosmic Acceleration Traces to
Model Assumptions (ΛCDM, wCDM)
• ΛCDM, wCDM are much better fits than
models w/o “dark energy” (CDM or
OCDM)
• … but, the acceleration history is fixed:
recent acceleration, past deceleration
• In addition, the correctness of Friedmann
equation is assumed (what if gravity theory
is part of the solution?)
Assumptions & Inputs
• Metric theory of gravity with Robertson-Walker
metric
• “Friedmannless” analysis
• Reiss et al’s Gold Set of Supernovae (adding
CFHT Legacy doesn’t change things much)
• Flat Universe (can be relaxed – more later)
• Piecewise constant acceleration histories
• Principal component analysis for q(z)
Robust Conclusions
• Universe may not be accelerating today:
Model with deceleration since z = 0.3 is
acceptable at 10% cl
• Very strong evidence that Universe once
accelerated (5σ) (from best determined
mode)
• Strong evidence that q(z) was larger in the
past (other well determined modes)
• Weak evidence that Universe decelerated
in the past
Deceleration
6 Most Well Determined Principal Components
Redshift
2 Best Determined Modes
ΛCDM
Without Friedmann Equation Best
Evidence for Flatness is Lost
(i.e., CMB Anisotropy)
• Might be able to determine spatial curvature
independently:
dV = r2drdΩ / [1 - kr2]1/2
r(z) = coordinate distance to object with redshift z
|k|-1/2 = curvature radius
• Determine r and dr (e.g., SNe) and dV (e.g. number
counts), infer k
My List of Burning Issues
1. Cosmic Acceleration/Dark Energy: “Most
Profound Mystery in all of Science”
2. Dark Matter: 3 pronged approach – space,
accelerators, and underground expt’s – the
prize is within sight!
3. Testing the predictions of inflation – inflation is
knocking at the door to become part of
“standard cosmology”
4. Using the consistency and crosschecks now
afforded by precision cosmological data (BBN,
SDSS/2dF, WMAP, SNe…) to test General
Relativity in new regimes