We compute the expected value of the cosmological constant in our universe
from the Causal Entropic Principle. Since observers must obey the laws of
thermodynamics and causality, the principle asserts that physical parameters
are most likely to be found in the range of values for which the total entropy
production within a causally connected region is maximized. Despite the absence
of more explicit anthropic criteria, the resulting probability distribution
turns out to be in excellent agreement with observation. In particular, we find
that dust heated by stars dominates the entropy production, demonstrating the
remarkable power of this thermodynamic selection criterion. The alternative
approach - weighting by the number of "observers per baryon" - is less
well-defined, requires problematic assumptions about the nature of observers,
and yet prefers values larger than present experimental bounds.Comment: 38 pages, 9 figures, minor correction in Figure
