Phys 56608

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Astrophysical Limitations on Meaningful
Measurements of Dark Energy

• Phys 566-08
• Lawrence M. Krauss

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DARK ENERGYThe Problem

• The only truly fundamental question of interest
  at this point is Is w ? -1?
• THE MOST reasonable theoretical prediction is
  w-1, via a cosmological constant.
• The most sensible alternatives predict w -1
• Observations suggest w -1
• Measuring w -1 therefore tells us nothing.
• Incorporating realistic uncertainties does not
  leave much room for optimism. (i.e. supernovae)

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Bound on w
-1.2 lt w lt -0.8
Looks a lot like w -1...
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Dark Energy and SN
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(No Transcript)
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• UNCERTAINTIES... MAG.
• Canonical m STATISTICALuncertainty assumed
  0.15/sn..

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Uncertainties
Observable for SN
PROBLEM SHOW THIS
where
we model
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Uncertainties
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Uncertainties
EXAMPLExt
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Limits on w for sigma_m 0.15

• statistical uncertainty in w approx .04-.09 for
  300-3000 SN!
• Is this good enough?
• too good to be true?

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Actual Ground-based uncertainties!LMK, D.
Huterer, K. Smith
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Actual Ground-based uncertainties!

• 300 Supernovae.. 100 from z0.03 to .08

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Actual Ground-based uncertainties!

• SNAP 3000 Supernovae.. 100 from z0.03 to .08

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Watching your waist Looking for dark matter..
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Watching your waist Looking for dark matter..
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Watching your waist Looking for dark matter..
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Watching your waist Looking for dark matter..
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But it is worse!...
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Actual Ground-based uncertainties!

• We do not know z dependence of w... therefore
  uncertainty larger..., and parameter dependent!

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Ruling out a Cosmological Constant?

• What would it take to unambiguously establish
  that w?-1 and/or w? constant?
• take w w_0 w_a z/(1z)

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Model Independent w Principle components

• piecewise w(z) over i intervals
• covariance matrix for given measurement
• Invert it..

• W decorrelation matrix, eigenvectors e

• eigenvalues give uncertainty

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Ruling out a Cosmological Constant?

• Principle Component Test

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Lambda or not?LMK, D. Huterer, K. Jones-Smith
astroph/0701692

• parametrize w(z)

• compare w(z) to w-1

• calculate standard deviations

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Ruling out a cosmological constant..
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Ruling out a cosmological constant..
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Ruling out a cosmological constant..
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THE BAD NEWS

• 3000 SN SNAP survey..

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Other Methods SN Redshift, Galaxy Cluster Number
counts

• Fisher Matrix.. allowing central redshift as
  additional nuisance parameters..

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Redshift uncertainties SN
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Redshift uncertainties SN
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Redshift uncertainties Number counts
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Redshift uncertainties Number counts
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Redshift uncertainties Number counts
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Dark Energy Summary

• w -1
• cosmology of no help?
• need theory...

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CONCLUSIONS

• NEED ACCELERATORS AND PARTICLE THEORY
• COSMOLOGY GREAT FOR DISCOVERY,
• ...But not for much more?
• DISCOVERIES ALREADY MADE?

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The End of Science?
Galaxies Never Form?
Maybe this is telling us something?
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Anthropic Mania
IF there are many different universes, and the
energy of empty space can vary in each one, then
only those in which it is not much greater than
what we measure will galaxies form... and only
then will stars and planets form, and only then
astronomers....
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Why Stop There?
The Constants of Nature and the Puzzles of Modern
Physics

• Gravity The weakest force in nature...
• Proton 2000 times heavier than the electron
• Three generations of elementary particles... who
  ordered them...
• ....
• A theory of anything?

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The Landscape of Nothingness
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The Fundamental Anthropic Problems?

• An idea based on ignorance
• One never knows what variables are anthropically
  selected (or not).
• One never knows what the set of possibilities
  is.
• It is never compelling, only suggestive.
• It has been wrong before!

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Which is the best Anthropic Measure?
VASTLY DIFFERENT RESULTS DEPENDING UPON CHOICE!
P d (x - )
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A Different Anthropic Measure?

• Not Number of Galaxies hospitable to life? (i.e.
  Dark Matter per Baryon)
• Total Number of Observations (observers)
  maximum total number of computations...
• Favors a cosmological constant lt 10-4 present
  value...

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Typicality is Everything!!Maor, LMK, Starkman 07
What Really Matters is
Define 3 conditional probabilities
We have no idea of 2, but fix ß 1
Then, R is still small over most of parameter
space!
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Boltzmann Idiots! Anti Evolution
Boltzmann Brains If the Landscape has Universes
that expand exponentially forever Life like us
will arise by spontaneous fluctuations...
Therefore we are not typical!
But we arent typical in any long-lived
universe.. as we have shown..
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The Landscape of Nothingness
IS THIS SCIENCE?