Half the facts you know are probably wrong: old truths decay and new ones are born at an astonishing rate.

• Author: Bailey, Ronald
• Position: Columns - Column

DINOSAURS WERE cold-blooded. Increased K-12 spending and lower pupil/teacher ratios boost public school student outcomes. Most of the DNA in the human genome is junk. Saccharin causes cancer and a high fiber diet prevents it. Stars cannot be bigger than 150 solar masses.

In the past half-century, all of the foregoing facts have turned out to be wrong. In the modern world facts change all of the time, according to Samuel Arbesman, author of the new book The Half-Life of Facts: Why Everything We Know Has an Expiration Date (Current).

Fact-making is speeding up, writes Arbesman, a senior scholar at the Kaufmann Foundation and an expert in scientometrics, the science of measuring and analyzing science. As facts are made and remade with increasing speed, Arbesman is worried that most of us don't keep up to date. That means we're basing decisions on facts dimly remembered from school and university classes--facts that often turn out to be wrong.

In 1947, the mathematician Derek J. de Solla Price was asked to store a complete set of The Philosophical Transactions of the Royal Society temporarily in his house. Price stacked them in chronological order by decade, and he noticed that the number of volumes doubled about every 15 years, i.e., scientific knowledge was apparently growing at an exponential rate. Thus the field of scientometrics was born.

Price started to analyze all sorts of other kinds of scientific data, and concluded in 1960 that scientific knowledge had been growing steadily at a rate of 4.7 percent annually for the last three centuries. In 1965, he exuberantly observed, "All crude measures, however arrived at, show to a first approximation that science increases exponentially, at a compound interest of about 7 percent per annum, thus doubling in size every 10-15 years, growing by a factor of 10 every half century, and by something like a factor of a million in the 300 years which separate us from the seventeenth-century invention of the scientific paper when the process began."

A 2010 study in the journal Scientometrics, looking at data between 1907 and 2007, concurred: The "overall growth rate for science still has been at least 4.7 percent per year."

Since knowledge is still growing at an impressively rapid pace, it should not be surprising that many facts people learned in school have been overturned and are now out of date. But at what rate do former facts disappear? Arbesman applies to the dissolution of facts the concept of...