Samuel Arbesman

A Harvard University research fellow and scientometrics expert analyzes the changing nature of factual information to explain how knowledge in most fields evolves in systematic and predictable ways that, if properly understood, can be powerful tools for training and professional improvement.

Why Everything We Know Has an Expiration Date

The Half-life of Facts

Piet Terheyden

Scientometrics has even given bragging tools to scientists, such as the h-index, which measures the impact of a paper on other researchers. It was created by Jorge Hirsch (and named after himself; notice the h) and essentially counts the number of articles a scientist has published that have been cited at least that many times. If you have an h-index value of 45, it means that you have forty-five articles that have each been cited at least forty-five times (though you have likely published many more articles that have been cited fewer times).

As I began thinking about how to understand how discoveries get harder, I settled on size. I assumed that size is a good proxy for how easy it is to discover something: The smaller a creature or asteroid is, the harder it is to discover; in chemistry, the reverse is true, and the largest elements are the hardest to create and detect, so I used inverse size.

In fact, if you uttered the statement “Eighty percent of all the scientists who have ever lived are alive today” nearly anytime in the past three hundred years, you’d be right.

Two Australian surgeons found that half of the facts in that field also become false every forty-five years.

So too with species and many other discoveries. As mentioned earlier, when a field is young the discoveries come easily, and they are often the ones that explain a lot of what is going on—or, in the case of species, are the really big ones. Many things that we know about are incredibly common or relatively easy to know; they’re in the main portion of this distribution. But there are uncountably more discoveries, although far rarer, in the tail of this distribution of discovery. As we delve deeper, whether it’s into discovering the diversity of life in the oceans or the shape of the Earth, we begin to truly understand the world around us.

The International Bureau of Weights and Measures, which is responsible for defining the length of a meter, and for a long time maintained in a special vault the quintessential and canonical kilogram, is also in charge of providing the officially sanctioned metric prefixes. We are all aware of centi- (one hundredth), from the world of length, and giga- (one billion), from measuring hard disk space. But there are other, more exotic, prefixes. For example, femto- is one quadrillionth and zeta- is a sextillion (a one followed by twenty-one zeroes). The most recent prefixes are yotta- (1024) and yocto- (10-24), both approved in 1991.

As Jonathan Cole, a sociologist of science, argues: Science and technology are closely related, but they are not the same thing. Science involves a body of knowledge that has accumulated over time through the process of scientific inquiry, as it generates new knowledge about the natural world—including knowledge in the physical and biological sciences as well as in the social and behavioral sciences. Technology, in its broadest sense, is the process by which we modify nature to meet our needs and wants. Some people think of technology in terms of gadgets and a variety of artifacts, but it also involves the process by which individuals or companies start with a set of criteria and constraints and work toward a solution of a problem that meets those conditions.

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