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It Will Be A SNAP.

Dear list members:
NASA will soon be launching SNAP (Super Nova/Acceleration Probe)
which should provide conclusive data with regard to acceleration of the
expansion rate of our Universe. The SNAP satellite should allow us to make a
determination as to which of the favored mechanisms for cosmic acceleration
is at work. The SNAP Satellite utilizes a sophisticated CCD array developed
at Berkeley lab which, unlike most CCDs will be sensitive to infrared
frequency light and be radiation resistant. This will allow the observation
of as many as 2000 type 1a supernova per year. With this data it should be
possible to determine the scale factor of the Universe at different times.
The two leading candidates are a positive cosmological constant and the
dark energy hypothesis, dubbed Quintessence by Paul J. Steinhardt of
Princeton University.
Dark energy is related to the cosmological constant but unlike CC it is
coupled to matter and energy density of the Universe so problematic fine
tuning is not required to account for the parameters of the observed Universe.
General Relativity predicts the following relationship:


Where p is mass density, a is the scale factor and P is pressure. To
conserve mass energy P must be negative to account for the positive vacuum
energy. Given that P is negative and has a sufficient magnitude, the above
equation predicts a positive value for da^2/dt^2 indicating an accelerating
expansion rate. SNAP should allow us to plot the scale factor as a function
of time with great accuracy. If the acceleration is due to a positive CC we
will see a very high acceleration rate. If dark energy is the driving
mechanism, then we will find a lower acceleration rate. Finally if there is
no actual acceleration underway we should be able to determine that also.
Assuming the success of SNAP we should know in the next few years if dark
energy or a positive cosmological constant is at work in our Universe.

Bob Zannelli