every PhD there is an equal and opposite PhD." Ginsberg's theorem is a set of adages based on the laws of thermodynamics. Godwin's law, an adage in Internet culture: "As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one." Coined by Mike Godwin in 1990. Gompertz–Makeham law of mortality: the death rate is the sum of an age-independent component and an age-dependent component. Goodhart's law: When a measure becomes a target, it ceases to be a good measure. Gossen's laws are three laws in economics relating to utility and value, formulated by Hermann Heinrich Gossen. Graham's law, a gas law in physics: the average kinetic energy of the molecules of two samples of different gases at the same temperature is identical. It is named for Thomas Graham (1805–1869), who formulated it. Grassmann's law: A dissimilatory phonological process in Ancient Greek and Sanskrit which states that if an aspirated consonant is followed by another aspirated consonant in the next syllable, the first one loses the aspiration. Named after its discoverer Hermann Grassmann. Grassmann's law (optics), an empirical result about human color perception: that chromatic sensation can be described in terms of an effective stimulus consisting of linear combinations of different light colors. Greenspun's tenth rule: Any sufficiently complicated C or Fortran program contains an ad hoc, informally specified, bug-ridden, slow implementation of half of Common Lisp; coined by Philip Greenspun. Gresham's law is typically stated as "Bad money drives good money out of circulation", but more accurately "Bad money drives good money out of circulation if their exchange rate is set by law." Coined in 1858 by British economist Henry Dunning Macleod, and named for Sir Thomas Gresham (1519–1579). The principle had been stated before Gresham by others, including Nicolaus Copernicus. Grimm's law explains correspondence between some consonants in Germanic languages and those in other Indo-European languages. Discovered by Jacob Grimm, (1785–1863), German philologist and mythologist and one of the Brothers Grimm. Grosch's law: the economic value of computation increases with the square root of the increase in speed; that is, to do a calculation 10 times as cheaply you must do it 100 times as fast. Stated by Herb Grosch in 1965. Grotthuss–Draper law: only that light which is absorbed by a system can bring about a photochemical change. Named for Theodor Grotthuss and John William Draper. Gustafson's law (also known as Gustafson–Barsis's