COMING HOME
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Transcript of COMING HOME
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COMING HOMECOMING HOME
Michael S. Turner
Kavli Institute for Cosmological Physics
The University of Chicago
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Some Cosmological Some Cosmological Observations from AfarObservations from Afar
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No Chinks in “The No Chinks in “The New Cosmology”New Cosmology”
• 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!
(i.e., CDM + Dark Energy + Inflation)
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Precision Cosmology is Precision Cosmology is Harder than Theorists’ Harder than Theorists’
projectionsprojections
• “Bits & bites”
• l = 2 to 5
• Optical depth:
τ = 0.17 to 0.09
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Serious testing of Serious testing of Inflation has Inflation has begunbegun
Key Predictions1. Flat Universe2. Almost scale-invariant, Gaussian perturbations: |(n-1)| ~ 0.1 and |dn/dlnk| ~ 0.0011. Gravity waves: spectrum, but not amplitude predicted
Key Results1. Ω0 = 1.0 ± 0.012. (n-1) = 0.96 ± 0.017*; dn/dlnk = -0.1 ± 0.05; no
evidence for nonGaussianity3. r < 0.55 (95% cl)*
*Depends significantly upon the priors assumed
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Cosmic AccelerationCosmic AccelerationDark EnergyDark 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, …
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Loose EndsLoose Ends
1. Precision test (few percent) using baryon density: BBN (D/H) vs. CMB (odd/even) unrealized
2. Consistency of BBN light element predictions (He – D – Li tension)
3. σ8: lack of consistency4. Cosmic variation of α5. Excess power at l ~ 20006. “LSND 4th neutrino”7. DAMA, e+ excess, …
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What Do We Really Know What Do We Really Know About Cosmic AccelerationAbout Cosmic Acceleration
Charles A. Shapiro & Michael S. Turner,astro-ph/0512586
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Much of What We Know About Much of What We Know About Cosmic Acceleration Traces to Cosmic Acceleration Traces to
Model Assumptions (Model Assumptions (ΛΛCDM, wCDM)CDM, 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?)
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Assumptions & InputsAssumptions & 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)
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Robust ConclusionsRobust 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
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6 Most Well Determined Principal Components
Dec
eler
atio
n
Redshift
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ΛCDM
2 Best Determined Modes
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Without Friedmann Equation Best Without Friedmann Equation Best Evidence for Flatness is Lost Evidence for Flatness is Lost
(i.e., CMB Anisotropy)(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
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My List of Burning IssuesMy 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