**HEAD 2000, November 2000**

*Session 26. Deep Surveys*

Display, Wednesday, November 8, 2000, 8:00am-6:00pm, Bora Bora Ballroom
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## [26.22] Smooth Energy: Cosmological Constant or Quintessence?

*S. Bludman (DESY, Hamburg & University of Pennsylvania), M. Roos (University of Helsinki, Finland)*

For a flat universe presently dominated by smooth energy,
either cosmological constant (LCDM) or quintessence (QCDM),
we calculate the asymptotic collapsed mass fraction as
function of the present ratio of smooth energy to matter
energy \mathcal{R}. Identifying the normalized collapsed
fraction as a conditional probability for habitable
galaxies, we observe that the observed present ratio
\mathcal{R} ~ 2 is likely in LCDM, but more likely in
QCDM. Inverse application of Bayes' Theorem makes the
Anthropic Principle a predictive scientific principle: the
data implies that the prior probability for \mathcal{R}
must be essentially flat over the anthropically allowed
range. Interpreting this prior as a distribution over {\em
theories} lets us predict that any future theory of initial
conditions must be indifferent to \mathcal{R}. This
application of the Anthropic Principle does not demand the
existence of other universes.

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