[extropy-chat] WMAP Results - Cosmology Makes Sense
russell.wallace at gmail.com
Mon Mar 20 18:45:30 UTC 2006
On 3/19/06, Lee Corbin <lcorbin at tsoft.com> wrote:
> First, why multiply terms? Secondly, "dark energy" might mean ordinary
> matter that is simply invisible (e.g. Earth-sized particles floating
> between the stars). I once read an astronomer speculating that dark energy
> could turn out to be just that. Well, let's drop vague terms for specific
> ones if we can! (I.e., if we agree that, as in the equation above, they
> the same thing.)
No, that's dark matter - baryonic dark matter in this case.
The reason for the multiplying of terms is that they have different
connotations. "Vacuum energy" just means the stuff that produces the Casimir
effect, without any implication of nonzero gravitational effect. If you're
interested in the accelerating expansion of the universe you can Google
"dark energy" without getting lots of Casimir references cluttering up the
results; "dark energy" specifically connotes vacuum energy in a context
where it exerts a repulsive gravitational effect.
> Though I'm still curious about that business of gravity becoming repulsive
> > when the relative speed gets to 0.57c (quoting the figure from memory,
> > mightn't be exact), I'm curious as to whether that might explain at
> > some of the accelerating expansion.
> So far as I know, "negative gravity" joins "dark energy" in proving
> false the idea that physicists COULDN'T POSSIBLY COME UP WITH WORSE
> TERMS than "up", "down", "charmed", and "truth".
> It's *just* vacuum energy! Yes, the term "negative energy" works for
> discussing the curvature of space, but Jesus Christ, it certainly clashes
> with the everyday use of the term "gravity" as a force easily measurable
> between two massive bodies.
The repulsive gravity effect I was referring to there is a slightly
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