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rapid pace, it should not be surprising that many facts people learned in school have been overturned and are now out of date.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 half-life—the time required for half the atoms of a given amount of a radioactive substance to disintegrate. For example, the half-life of the radioactive isotope strontium-90 is just over 29 years. Applying the concept of half-life to facts, Arbesman cites research that looked into the decay in the truth of clinical knowledge about cirrhosis and hepatitis. "The half-life of truth was 45 years," he found.

In other words, half of what physicians thought they knew about liver diseases was wrong or obsolete 45 years later. Similarly, ordinary people's brains are cluttered with outdated lists of things, such as the 10 biggest cities in the United States.

Facts are being manufactured all of the time, and, as Arbesman shows, many of them turn out to be wrong. Checking each one is how the scientific process is supposed to work; experimental results need to be replicated by other researchers. So how many of the findings in 845,175 articles published in 2009 and recorded in PubMed, the free online medical database, were actually replicated? Not all that many. In 2011, a disquieting study in Nature reported that a team of researchers over 10 years was able to reproduce the results of only six out of 53 landmark papers in preclinical cancer research.

In 2005, the physician and statistician John Ioannides published "Why Most Published Research Findings Are False" in the journal PLoS Medicine. Ioannides cataloged the flaws of much biomedical research, pointing out that reported studies are less likely to be true when they are small, the postulated effect is likely to be weak, research designs and endpoints are flexible, financial and nonfinancial conflicts of interest are common, and competition in the field is fierce. Ioannides concluded that "for many current scientific fields, claimed research findings may often be simply accurate measures of the prevailing bias." Still, knowledge marches on, spawning new facts and changing old ones.

Another reason that personal knowledge decays is that people cling to selected "facts" as a way to justify their beliefs about how the world works. Arbesman notes, "We persist in only adding facts to our personal store of knowledge that jibe with what we already know, rather than assimilate new facts irrespective of how they fit into our worldview." All too true; confirmation bias is everywhere.

So is there anything we can do to keep up to date with the changing truth? Arbesman suggests that simply knowing that our factual knowledge bases have a half-life should keep us humble and ready to seek new information. Well, hope springs eternal.

More daringly, Arbesman suggests, "Stop memorizing things and just give up. Our individual memories can be outsourced to the cloud." Through the Internet, we can "search for any fact we need any time." Really? The Web is great for finding an up-to-date list of the 10 biggest cities in the United States, but if the scientific literature is littered with wrong facts, then cyberspace is an enticing quagmire of falsehoods, propaganda, and just plain bunkum. There simply is no substitute for skepticism.

Toward the end of his book, Arbesman suggests that "exponential knowledge growth cannot continue forever." Among the reasons he gives for the slowdown is that current growth rates imply that everyone on the planet would one day be a scientist. The 2010 Scientometrics study also mused about the growth rate in the number of scientists and offered a conjecture "that the borderline between science and other endeavors in the modern, global society will become more and more blurred." Most may be scientists after all. Arbesman notes that "the number of neurons that can be recorded simultaneously has been growing exponentially, with a doubling time of about seven and a half years." This suggests that brain/computer linkages will one day be possible.

I, for one, am looking forward to updating my factual knowledge daily through a direct telecommunications link from my brain to digitized contents of the Library of Congress.