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*From*: Robert B Zannelli <Spinoza321@AOL.COM>*Date*: Sun, 25 Feb 2001 12:24:15 -0500

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:

-3*(da^2/dt^2)=4*pi*G*(p+(P/(C^2))*a

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

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