We explore how light behaves near massive objects, and show that for gravitational lenses, gravitational redshifts and black holes, the main concepts can be understood in general terms from Einstein's oft-quoted equation, E=mc^2. Light paths are changed as they pass close to the sun and to massive galaxies, so giving us the idea of gravitational lenses which can change the appearance of distant galaxies and quasars. Some examples of multiply imaged quasars and lensed galaxies are given. Gravitational redshifts of light from compact stars have been measured. In the extreme case of very compact objects - black holes - no light can escape at all. There are compelling reasons for believing that massive black holes reside near the centers of many galaxies, and particularly the center of the Milky Way.



Professor Carswell was invited to Swinburne under the Board of Research Visiting Professor Grant Scheme, and this lecture was presented as part of the PVC(R) Visiting Professor Lecture Series.