Ultraviolet divergence short distances. The name comes from the earliest example of such a divergence, the "ultraviolet catastrophe" first encountered in understanding blackbody radiation. According to classical physics at the end of the nineteenth century, the quantity of radiation in the form of light released at any specific wavelength should increase with decreasing wavelength—in particular, there should be considerably more ultraviolet light released from a blackbody radiator than infrared light. Measurements showed the opposite, with maximal energy released at intermediate wavelengths, suggesting a failure of classical mechanics. This problem eventually led to the development of quantum mechanics. The successful resolution of the
Invisible ink its intended use. For example, property marking should ideally be done with ink easily read under ultraviolet light, whereas in espionage such an ink would be considered too easily detectable since a large number of letters may be screened relatively quickly using UV light. Invisible inks are inherently "insecure" against a determined and well-equipped inspector, which must be balanced against the logistical difficulty in carrying out mass-screening of posted mail. It is easier to perform large-scale undetected screening of millions of electronic communications, than to mass-screen even a small fraction of conventional mail. Apart from in dictatorships where large numbers