Random gravitational lensing

A simple three-dimensional approach to calculate the probability of observing gravitational lensing, caused by a chance superposition of lens and source, is presented. The formalism is then used to estimate the lensing probabilities in a number of astrophysical situations. As indicated in earlier works, we find that the chance of random gravitational lensing being detected locally is small, and the chance at extra-galactic distances is large.