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



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

Dear PHYS-L,

I've been thinking about dark energy, and have come up with a simple list
of its properties. I am trying to come up with a list of properties that
is both correct but also in simplified form for non-scientists to
understand.

Would you please comment on the statements below and let me know if I have
left anything out, or made any mistakes.

If dark energy exists, it has the following properties:

1. It exists uniformly throughout the universe.

No possible observation can confirm this "property".

2. It makes up most of the energy of the universe.
OK if by "energy" you are including the energy equivalence of
mass and by "universe" you mean the "locally observable universe"


3. Unlike other forms of energy (visible light, sound, radio waves,
etc.), it cannot be directly detected.

It is as "detectable" as are, for example, distant masses that
give rise gravitational lensing. "Detect" is not a very precise vern.

4. It causes empty space to repel itself.

Nonsense. We have no experience with "empty space". "Dark
energy" is just a catchy code phrase for the observation that the
expansion of the Universe is apparently accelerating - according to the
most recentt measurements. The observation can be "explained" by invoking
Einstein's "cosmological constant". The difficulty, for many theorists,
is that there is no a posteriori justification known for the observed
value of the constant.


Thank you,
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



--
"Trust me. I have a lot of experience at this."
General Custer's unremembered message to his men,
just before leading them into the Little Big Horn Valley
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