[extropy-chat] WMAP Results - Cosmology Makes Sense
Lee Corbin
lcorbin at tsoft.com
Sun Mar 19 20:37:16 UTC 2006
Amara writes
> A few days old news, but still important :-) See a discussion,
> with links to more details on the cosmic variance blog:
> "WMAP Results- Cosmology Makes Sense!"
> http://cosmicvariance.com/2006/03/16/wmap-results-cosmology-makes-sense/
Penrose, for what *he's* worth, criticizes this graph a lot.
In particular the very broad band of uncertainty at the left
hand end. At his talk that I attended he even went so far as
to say that most of the time when this graph is presented,
data for multipole moment l=0, 1, 2, and 3 is simply dropped
because it doesn't fit the theoretical expectations! (I'm not
sure if l=0 is even meaningful.)
Maybe the fact that this is just a few days old means that better
data really is available to counter him on this; but I see the
blue band of uncertainty on the graph still looking large.
> Excerpts:
> # Here is the power spectrum: amount of anisotropy as a function of
> angular scale (really multipole moment l), with large scales on the
> left and smaller scales on the right. The major difference between
> this and the first-year release is that several points that used to
> not really fit the theoretical curve are now, with more data and
> better analysis, in excellent agreement with the predictions of the
> conventional LambdaCDM model. That's a universe that is spatially
> flat and made of baryons, cold dark matter, and dark energy.
His other big cow was the use of the term "dark energy", with
which I totally agree with him. He complained: "I knew what the
cosmological constant was *long* before the nineties, when this
awful term was coined. And that's all it is!"
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.)
"Dark energy" should be abolished, says I, adding my weighty opinion
to that of Penrose.
Lee
> # The best-fit universe has approximately 4% baryons, 22% dark
> matter, and 74% dark energy, once you combine WMAP with data from
> other sources. The matter density is a tiny bit low, although
> including other data from weak lensing surveys brings it up closer
> to 30% total. All in all, nice consistency with what we already
> thought.
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