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Published Online May 4, 2006
Science DOI: 10.1126/science.1126231

Research Articles

Submitted on February 14, 2006
Accepted on March 28, 2006

Why the Cosmological Constant Is Small and Positive

Paul J. Steinhardt 1* and Neil Turok 2

1 Joseph Henry Laboratories, Princeton University, Princeton, NJ 08544, USA.
2 DAMTP, CMS, Wilberforce Road, Cambridge, CB3 0WA, UK.

* To whom correspondence should be addressed.
Paul J. Steinhardt , E-mail: steinh{at}princeton.edu

Within conventional big bang cosmology, it has proven to be very difficult to understand why today's cosmological constant is so small. In this paper, we show that a cyclic model of the universe can naturally incorporate a dynamical mechanism that automatically relaxes the value of the cosmological constant, taking account of contributions to the vacuum density at all energy scales. Because the relaxation time grows exponentially as the vacuum density decreases, nearly every volume of space spends an overwhelming majority of the time at the stage when the cosmological constant is small and positive, as observed today.






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