The phenomenon of gravitational lensing is becoming an important tool for studying objects in the distant universe, according to an article in Time Magazine (September 4 2006). Lensing is caused by the systematic (angular deviation proportional to the impact parameter?) bending of light from a point source, as the light passes close to a massive object. Lensing can be regarded as one aspect of the small-angle scattering of light by mass --- think of the universe as a (very) large transparent medium in which is embedded a variety of small-angle scattering centres. Light in such a medium will be multiply scattered when it travels over a long enough distance. In a solid this would lead to opalescence. Is there any evidence for some kind of (red) background radiation which could be caused by such scattering? Or is the universe too small for this to be significant?