Hawking & Hertog: String Theory Can Explain Dark Energy
In order to explain gravitational effects in the universe, physicists have proposed a concept called dark energy. Quantum field theory allows for dark energy, in a quantity known as the "cosmological constant," but predicts a value 120 orders of magnitude greater than that indicated by observations.
Cosmologist Andrei Linde of Stanford University, along with colleagues, showed in 2003 that string theory allows for such a force without specifying the exact value of the cosmological constant. Except there are 10,500 possible values and no obvious reason why it would settle on the one observed in nature. Critics point out that this is an example of string theory's inability to make useful predictions.
The Hawking/Hertog paper (due in an upcoming issue of Physical Review D) tackles this problem. It allows for a method to make testable predictions about the nature of the universe, which would help us determine the necessary properties of dark energy. Their model proposes that the universe as a whole follows multiple "branches," as Feynman's interpretation of quantum mechanics dictates. Our present universe is the "sum" over these different branches. This sum would include all initial conditions, including all possible values of the cosmological constant.
Working from the present as a starting point, you can sum the possible trajectories over the past, ignoring the trajectories which have a negligible probability of applying to our universe. The following example from Hertog is from an American Institute of Physics press release:
... knowledge that our universe is very close to being flat could allow one to concentrate on a very small portion of the string theory landscape whose values for the cosmological constant are compatible with that flatness. That could in turn lead to predictions that are experimentally testable. For example, one could calculate whether our universe is likely to produce the microwave background spectrum we actually observe.
If such a procedure were employed and the results matched our current universe, it would indicate that the application of this principle is a valid model within the structure of string theory.
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I like your articles AZJ you clearly do a lot work digging them up .
Ray
The cosmological constant equals the implicit prediction of the inter universe force concluded as the square of diameter in http://www.arXiv.org/pdf/gr-qc/0507130. Square of the universe diameter (60 orders of magnitude in Planck lengths) is 120 orders of mangitude compared to gravity.
http://www.arXiv.org/physics/0210040 v1 has already predicted in 2002 that all coupling constants are increasing with time.