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[Physltest] Re: [Phys-L] Re: Basic Facts About Dark



Hello,

For 4, I think that considering dark energy as a repulsive material is
sufficient to explain the expansion of the space. We really do mean that
space itself is expanding- the spatial parts of the metric are getting
larger with time, in a manner consistent with an accelerating scale
factor.

I think it looks good,

Brian Powell

SUNY, Buffalo

On Mon, 10 Jan 2005 STRatliff@NWC.EDU wrote:

Regarding Dark Energy:

Remember, that all of these statements were prefaced by, "If dark energy
exists, it has the following properties."

1. I can change "It exists uniformly throughout the universe" to "It
exists throughout the universe."
Perhaps the main problem here is that it is not required to be uniform?
If it exists throughout the observable universe then it probably exists
throughout the universe.

2. New version: It makes up most of the energy of the observable
universe.

3. My intent with statement number 3 was to somehow explain, in simple
terms, that there is a fundamental difference between "dark energy" and,
for example, light energy or sound energy. You can build a photocell that
will directly detect light. You can build a microphone that detects sound
energy. We don't have a dark energy detector. Perhaps it would be
preferable to say that we don't have a dark energy sensor.

4. My intent with statement 4 was to explain in simple terms the idea
that dark energy, if it exists, is causing the expansion of the universe
to accelerate. As a further note, I think that when we say that the
universe is expanding, we really mean that space itself is expanding.

Any further comments?

Thank you for your help.

Sincerely,
Steven Ratliff


Steven T. Ratliff
Institutional Researcher / Professor of Physics
Northwestern College
3003 Snelling Ave. N.
St. Paul, MN 55113-1598
U. S. A.

Internet: stratliff@nwc.edu
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