[extropy-chat] WMAP Results - Cosmology Makes Sense
lcorbin at tsoft.com
Sun Mar 19 21:11:41 UTC 2006
> > [Lee wrote]
> > [Penrose's] other big cow was the use of the term "dark energy"
> > ...He complained: "I knew what the cosmological constant was
> > *long* before the nineties, when this awful term was coined."
> I disagree. "Cosmological constant" is a term for the effect
> (without comment on the cause); "dark energy"/"vacuum energy"
> is a postulated cause of that effect.
> > Susskind in "The Cosmic Landscape" explains that the following
> > three items are just different terms for exactly the same thing:
> > vacuum energy = cosmological constant = dark energy
> > (Of course, the lambda cosmological constant is just the constant
> > added to the right part of Einstein's equation, but it serves
> > exactly the same function. The nice term "vacuum energy" on the
> > other hand, is very appropriate for depicting the concept of
> > the on-going virtual particle creation/destruction within each
> > cubic meter of space.)
> Er, "dark energy" and "vacuum energy" mean basically the same thing,
> if you think "vacuum energy" is a nice term, what have you got against
> "dark energy"?
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 mean
the same thing.)
> 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 least
> 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.
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