Some of the most fundamental questions in cosmology are still lacking adequate answers: How big is the Universe? How old is it? How will it develop - in the long run?

The key to these problems are found in two parameters, and it is important to determine accurate values for them. The first is the expansion rate of the Universe, described by the well-known Hubble parameter. This tells us about velocities and distances and is a measure of the age of the Universe. The other is the mean mass density in the Universe, described by the Density parameter. The problems of finding accurate values for these two parameters are connected with the difficulties of determining the enormous distances in the Universe and the fact that most of the mass in the Universe consists of dark matter and is therefore not readily observable.

The most modem "astrophysical tool" available to solve these problems are Gravitational Lensing. This phenomenon is based on Einstein's determination of how light rays are bent in a gravitational field. Any mass suitably situated in front of a source, may act as a lens.
The first lens was discovered in 1979; it is a galaxy lensing the light of a distant quasar. The earlier, theoretical investigations by Sjur Refsdal were immediately recognised for their comprehensiveness and had a strong impact on both theoretical and observational research in the following years. He had shown that these lenses provide a unique opportunity to determine distances to galaxies and to find dark matter.
A common effect of gravitational lenses, in addition to the amplification, is a splitting of the distant source in two or more images. Light rays producing the images will travel along different routes and spend different lengths of time. Distances to the lensing galaxies (and the sources) can be determined by measuring the time delay between different images. Observations of some lens systems have been going on for several years. However, an accurate value for the time delay is still lacking.

The determination of time delays for some lens systems and investigations of some other highly interesting lens effects will be actively pursued in our research project. We hope thereby to obtain a fairly accurate value of the Hubble parameter and the Density parameter.