Yeah, that's the one.
>we read a book called The Spirit Catches You
>and You Fall Down by Anne Fadiman (excellent read by the way - I
>totally recommend it if you're interested). The book tells the true
>story of a young Laos girl named Lia (who's family was associated with
>the Hmong culture) who has severe epilepsy. Fadiman is a reporter who
>investigated all the events, hospitalizations, cultural clashes, etc.
>that went on during this young girl's short life.
>
Kim
---------------------------------------
"The tragedy [with autism] is not that
we're here, but that your world has no
place for us to be. How can it be
otherwise, as long as our own parents
are still grieving over having brought
us into the world?"
— Jim Sinclair "Don't Mourn For Us"
One of my main current interests is using the avalanche of new data to raise the ambition level beyond cosmological parameters, testing rather than assuming the underlying physics. My battle cry is published here with nuts and bolts details here and here.
Photos of the cosmic microwave background (CMB) radiation like the one to the left show us the most distant object we can see: a hot, opaque wall of glowing hydrogen plasma about 14 billion light years away. Why is it there? Well, as we look further away, we're seeing things that happened longer ago, since it's taken the light a long time to get here. We see the Sun as it was eight minutes ago, the Andromeda galaxy the way it was a few million years ago and this glowing surface as it was just 400,000 years after the Big Bang. We can see that far back since the hydrogen gas that fills intergalactic space is transparent, but we can't see further, since earlier the hydrogen was so hot that it was an ionized plasma, opaque to light, looking like a hot glowing wall just like the surface of the Sun. The detailed patterns of hotter and colder spots on this wall constitute a goldmine of information about the cosmological parameters mentioned above. If you are a newcomer and want an introduction to CMB fluctuations and what we can learn from them, I've written a review here. If you don't have a physics background, I recommend the on-line tutorials by Wayne Hu and Ned Wright. If you already work on CMB, visit my experiment compilation or my data analysis center. CMB experiments have already revolutionized cosmology, but I think the best is yet to come. For instance, NASA's MAP satellite will publicly release measurements of unprecedented quality in December 2002. Two new promising CMB fronts are opening up --- CMB polarization and arcminute scale CMB, and are likely to keep the CMB field lively for another decade.
Large-scale structure: 3D mapping of the Universe with galaxy redshift surveys offers another window on dark matter properties, through its gravitational effects on galaxy clustering. This field is currently being transformed by the 2dF Galaxy Redshift Survey and the Sloan Digital Sky Survey (SDSS). The SDSS, where I am part of the large-scale structure analysis team, will finish mapping a million galaxies in the nearby Universe over the next few years, and complementary surveys such as DEEP and VIRMOS will map high redshifts and the evolution of clustering. The abundance of galaxy clusters, the largest gravitationally bound and equilibrated blobs of stuff in the Universe, is a very sensitive probe of both the cosmic expansion history and the growth of matter clustering. Many powerful cluster finding techniques are contributing to rapid growth in the number of known clusters and our knowledge of their properties: identifying them in 3D galaxy surveys, seeing their hot gas as hot spots in X-ray maps or cold spots in microwave maps (the so-called SZ-effect) or spotting their gravitational effects with gravitational lensing.
Yet another probe of dark matter is offered by gravitational lensing, whereby
its gravitational pull bends light rays and distorts images of distant objects.
The first large-scale detections of this effect were reported
by four groups
(astro-ph/0002500,
0003008,
0003014,
0003338)
in the year 2000, and
I anticipate making heavy use of such measurements as they continue to improve,
partly in collaboration with
Bhuvnesh Jain here at Penn.
Lensing is ultimately
as promising as CMB
and is free from the murky bias issues
plaguing LSS and LyAF measurements, since it probes the matter density directly via
its gravitational pull. I've also
dabbled some
in the stronger lensing effects caused by galaxy cores,
which offer additional insights into the detailed nature of the
dark matter.
Supernovae 1a:
If a white dwarf (the corpse of a burned-out low-mass star like our Sun) orbits another dying
star, it may gradually steal its gas and exceed the maximum mass with which it can be stable.
This makes it collapse under its own weight and blow up in a cataclysmic explosion called
a supernova of type Ia. Since all of these cosmic bombs weigh the same when they go off
(about 1.4 solar masses, the so-called Chandrasekhar mass), they all release roughly
the same amount of energy - and a more detailed calibration of this energy is possible by measuring
how fast it dims, making it the best "standard candle" visible at cosmological distances.
The supernova cosmology project
and the
high z
SN search team
mapped out how bright SN 1a looked at different redshifts found the first evidence in 1998 that
the expansion of the Universe was accelerating.
This approach can ultimately provide a direct
measurement of the
density of the Universe as a function of time,
helping unravel the nature of dark energy - I hope the
SNAP project gets funded.
The image to the left resulted from a different
type of supernova, but I couldn't resist showing it anyway...
The so-called Lyman Alpha Forest, cosmic gas clouds backlit by quasars, offers yet
another new and exciting probe of how dark has clumped ordinary matter together, and is sensitive
to an epoch when the Universe was merely 10-20% of
its present age. Although relating the measured absorption to the densities of
gas and dark matter involves
some complications,
it completely circumvents the Pandora's of galaxy biasing.
Cosmic observations are rapidly advancing on many other fronts as well,
e.g., with direct measurements of the cosmic expansion rate and the cosmic baryon fraction.
----- Original Message -----From: Lewis MehlMadronaSent: Tuesday, December 16, 2008 5:55 AMSubject: Re: I ain't afraid of no ghost