- Broida 1640
Tommaso Treu - UCSB
What is the universe made of? What is the origin of cosmic acceleration? Strong gravitational lenses where the background source is variable in time and the foreground deflector is a massive galaxy can be used very effectively as cosmic "standard rods" to measure the geometry and content on the universe and help answer those questions. Gravitational time delays constrain primarily the Hubble Constant and - in combination with other techniques - the equation of state of dark energy, flatness of the universe, and neutrino masses. I will illustrate recent advances in modelling techniques and data quality that enable a 7% measurement of the Hubble Constant from a single gravitational lens as well as constraints on the equation of state of dark energy and flatness comparable to those obtained with the best probes. A measurement of the Hubble Constant with absolute precision of <4% is in progress. I will show the first results and their implications. I will conclude by discussing the bright prospects of gravitational time delays as cosmographic probe.