Colloquium Detail

Gravitational Optics - Measuring Distances in the Universe with Galaxy-sized Lenses

Date: 5/10/2010

Phil Marshall
Stanford UniversityUnderstanding the mysterious "Dark Energy" 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 at least quantifying the effect of the dark energy that is both new and old. Old because the time delays between the multiple images of gravitationally lensed quasars have long been known to enable a measurement of the Hubble constant, 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 the next decade, using LSST to find, measure and select large numbers of suitable systems. Hunting for a few hundred needles in a haystack is not easy - but we have some good ideas!