Phil Marshall Gravitational Lensing
<p>May 10, 2010 6:45 PM
 
PHIL MARSHALL v cool guy... British...  dry sense of humor.
 
was a postdoc at UCSB  before that a post doc at KIPAC  Kavli and befoer that
at the Cav at Cambridge.  prob abt  33.  PhD in 2003.
 
*  here is the blurb on his talk
<em>Gravitational Optics - Measuring Distances in the Universe with Galaxy-sized Lenses</em>
 
Understanding the <b>mysterious "Dark Energy</b>" that appears to be driving the expansion of the Universe is one of the biggest challenges to science in the 21st century. While offering no such new understanding, I will describe a method for <b>at least quantifying the effect of the dark energy t</b>hat is both new and old. Old because the <b>time delays between the multiple images of gravitationally lensed quasars have long been known to enable a measurement of the Hubble constant,</b> and new because we have recently shown how with careful modeling of enough high quality data we can achieve comparable accuracy to other, complementary, better known cosmographic probes. After introducing and describing this experiment in some detail, I will discuss how we plan to build on it in t<b>he next decade, using LSST to find, measure and select large numbers of suitable systems.</b> Hunting for a few hundred needles in a haystack is not easy - but we have some good ideas!
 
I was late...
 
His program is this ...
 
1) find a QUAD ....  an image of a distant object (like a Quasar) that has been LENSED into
4 separate images.
 
2)  for some reason,  the the 4 images will not vary simulataneous.
(you make these observcations over eg 200 days)
 
3)  based on the differences in time of varying,  you can figure out how far away and
fast the lensing object  (galaxy) is moving away from you.
 
4)  do this with hundreds of objects to get a really sharp  (< 1%)  precise measurement
of the Hubble constant  H naught = Ho.
 
5)  use this very precise Ho  to constrain theories of dark matter.
 
*
 
very tricky math....
 
try to compute a model of the gravitational lens by doing this ...
 
Bayesian statistics    probab (parameters of model | data)
 
time delay to the distant galaxy  =  D / c prime
 
c prime is the altered speed of light  (like a refractive index)
D  is distance.
 
Need to know the mass of the lensing galalxy.
need other line of site structures.
 
best guess if that  WMAP5  +  B1608  =  69.7  km/sec  per megaparsec.
 
Decadal survey... there are 7000 astronomers.
 
some guy is producing solar energy using concentrators based on telescopes... get $1 per watt.
 
wee rehnu.com
 
LSST  is basically making a TEN YEAR MOVIE of the ENTIRE SOUTHERN SKY!!!!
ETENDUE.
 
Look at LSST Science Book.
 
LSST will detect abt 8000 quasars.  of which abt  12-16% will show QUAD images
(best for  doing his calcs)
 
Finding Lenses in the galaxy...  GALAXY ZOO !!!!
250k people are doing it.
have amateurs find lenses.
 
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