Information has a half life

Essentially, information is like radioactive material: Medical knowledge about cirrhosis or hepatitis takes about forty-five years for half of it to be disproven or become out of date. 

Samuel Arbesman, The Half-Life of Facts: Why Everything We Know Has an Expiration Date (New York: Current, Penguin USA, 2012), ch. 3

[W]hile we can't predict which individual papers will be overturned, just like we can't tell when individual radioactive atoms will decay, we can observe the aggregate and see that there are rules for how a field changes over time. . . . All of these results verify the first half of a well-known medical aphorism by John Hughlings Jackson, a British neurologist in the nineteenth and early twentieth centuries: "It takes 50 years to get a wrong idea out of medicine, and 100 years a right one into medicine." 

 Id.