Gravitational Lenses as Standard Rulers in Cosmology

The accelerating expansion of the Universe is a great challenge for both physics and cosmology. From the observational point of view, it is crucial to have various methods to assess cosmic expansion history, which can be alternative to standard candles (Sonia in cosmological context). Strongly gravitationally lensed systems create such a new opportunity by combining stellar kinematics with lensing geometry. Using strong gravitational lenses as probes of cosmic expansion is becoming attractive in light of ongoing surveys like SLACS based on different protocols than older searches focused on potential sources. In this approach, pursued recently by the authors, strongly lensed systems with known central velocity dispersions act as '' standard rulers '' - Einstein radius being standardized by stellar kinematics. (authors)