Quasar spectra and the gravitational lens hypothesis

Quasar spectra have been used to identify gravitational lens candidates, often in the absence of other evidence, and it has even been suggested that they can be used as reliably as fingerprints to uniquely identify individual objects. In the paper the authors point out that quasar spectra are sufficiently similar that, in the presence of noise, it can be extremely difficult to distinguish between different objects solely from spectral characteristics. (author)