Re: Dark Energy Project First Light

[Stupendous Man <richmond@stupendous.cis.rit.edu>]

  Chris A. asked:

> I figure I'm not the only one wondering how you are going
> to photograph dark energy.  Could you post a 15 second exective
> summary on how they get from dark energy to IR photons?
> I'm sure once you have the photon everyone on the TASS list would
> understand.  It's that first step that seem inpossible

  The basic idea is that the cosmological parameters have a strong
enough effect on the formation of structure early in the universe
that they might leave detectable features in the resulting
universe today.

  For example, suppose that the overall density of matter
is very high.  Then, early in the universe, gravitational collapse
forms relatively large structures: giant clusters of galaxies,
and the galaxies within these clusters.  These large concentations
of mass lead to strong clustering on very large scales --
so that galaxy clusters are more likely to be found near
other galaxy clusters, and so that the large-scale distribution
of galaxies looks "lumpy."

  On the other hand, if the density of matter is low in the
early universe, then structure formation is delayed.  That
means that the large-scale structure we might observe today
would be more uniform, with fewer big blobs of matter and fewer
empty voids.

  The "Dark Energy Camera" really just observes ordinary 
visible and infrared light from the stars in the local universe,
and from stars and galaxies in the more distant universe (which
we see as they were long ago, when the universe was young).
There are several ways that one can use observations of galaxies
on local (current) and distant (long-ago) scales to infer 
how structure probably formed ... which in turn, through 
the lens of theory, tells us something about the density of
matter and the cosmological constant (aka "dark energy").

  That's the basic idea.  There are plenty of astronomers
using ground-based and space-based telescopes to do this
sort of analysis already; the Dark Energy Camera will just
do a particularly good job.


                                       Michael Richmond