strong gravitational lensing

[Sorry for the lack of posts; I have been on vacation since Monday.]

Last Monday (the 20th), I gave our informal lunch talk on the uses of strong gravitational lenses (multiply imaging or very high magnification systems) in cosmology. I am a bit suspicious that strong lensing will be crucial in the coming era of cosmology, but the talk gave me an opportunity to highlight some places where I think it might be important:

• Strong lenses might put robust limits on the radial profiles and evolution of collapsed objects, when simulations and theory become good enough to make the relevant predictions. As it is, there is an interesting lack of low-redshift gravitationally lensed arcs from massive clusters.
• High magnification lenses can be used to find very faint, very high-redshift sources. There are already some quasi-believable redshift 10 candidate galaxies out there, and some definite redshift 6 galaxies.
• Well-understood lenses lensing variable quasars can be used to make measurements of distances (times distance ratios) to pin down the world model.

All of these projects are immature now, but I got the opportunity to quip that as we transition from precision cosmology to accurate cosmology (Ben Weiner's joke), we might need one or more of these techniques. Lensing is a blunt tool, but it does do some things very well.