Is that a fact?

What we think we know as fact changes over time. What was once accepted as true is often shown to be plain wrong. “Studies of the frequency of citations of scientific papers show they become obsolete at a predictable rate. Harvard mathematician Samuel Arbesman calls this ‘the half-life of facts’. Just as with radioactive decay, you can’t tell when any one ‘fact’ will reach its expiry date, but you can predict how long it will take for half the facts in any discipline to do so. In medicine, for example, ‘truth’ seems to have a 45-year half-life. Some medical schools teach students that, within a few years, half of what they’ve been taught will be wrong – they just don’t know which half. In mathematics, the rate of decay is much slower: very few accepted mathematical proofs get disproved.” QI