Certain uncertainties

Natural History, Oct, 1998 by Neil de Grasse Tyson

When reporting scientific discoveries, the popular press hardly ever conveys the uncertainties inherent in the data or in the interpretation. This seemingly innocent omission sends a subtle, misguided message: If it's a scientific study, the results are exact and correct. These same news reports often declare that scientists, having previously thought one thing, are forced by new data to think something else; or must return to the mythic drawing board in a stupor. The consequence? If you get all your science from press accounts, then you might be led to believe that scientists arrogantly, yet aimlessly, bounce back and forth between one perceived truth and another without ever contributing to a base of objective knowledge.

But let's take a closer look.

New scientific ideas are wrong much of the time because the frontier of discovery is a messy place. But well-trained research scientists know this and are trained to quantify their level of ignorance with an estimate of the level of uncertainty for any experiment or observation. (The famous "plus-or-minus" sign in reported polling results is, perhaps, the most widely recognized example of such estimates.)

In person, scientists have been known to completely ignore their uncertainties because, for the most part, scientists are people too. There are arrogant ones, lovable ones, loud ones, soft-spoken ones, and boneheaded ones. In their published research papers, however, they are always circumspect. A scientist typically publishes a tentative result based on a shaky interpretation of poor data. Six months later, different, equally bad data may become available from somebody else's experiment, and a different interpretation emerges. This stage can drag on for years or even decades. Eventually, excellent data become available and a consensus emerges.

During the long stage of uncertainty, news stories implying certitude get written anyway. Epidemiological studies of environmental health risks or the effects of food consumption on diseases and longevity are especially susceptible to exaggerated reporting. The financial and emotional consequences of such news stories can be staggering.

Fortunately, most of the comings and goings of astrophysicists have so little impact on how people conduct their daily lives that I can spend more time joking about the problem than crying about it.

When a published scientific finding is confirmed and reconfirmed and re-reconfirmed, further confirmation becomes less interesting to scientists than working on new problems. At that point, the repeatedly confirmed nuggets of knowledge are justifiably added, with little or no uncertainty, into the basic textbooks of the day. Consistency and repeatability are the hallmarks of a genuine scientific finding, for if the laws of physics and chemistry were unpredictably different from lab to lab, then scientists could all just pack up and go home.

Modern astronomy textbooks say that the Sun occupies the central region of our Solar System. You can bet that five hundred years from now, textbooks will still be saying the same thing. Today's textbook, however, will speak only tentatively about the formation of galaxies in the early universe, or the nature of the ubiquitous dark matter, because major uncertainties remain in these areas. Suppose one day someone discovers that dark matter in the universe is actually made of chocolate pudding. Despite all the problems this would create in theoretical astrophysics, no consensus would be overthrown, because no consensus exists.

Consider the origin of the Moon's craters. All modern textbooks describe them with certainty as being caused by high-speed collisions with rocks and other debris from interplanetary space. But a century ago, they were described as volcanic calderas. If the scientific community changed its mind once before, then why should you believe us now? Because last century, the volcanic caldera hypothesis (although a leading idea) had not achieved consensus and was thus not presented as a certainty in responsible scientific writings. A chapter in The Heavens Above, a popular handbook of astronomy written in 1882 by two academics (J. A. Gillet, a professor of physics at City College of New York, and W. J. Rolfe, headmaster of Cambridge High School, Massachusetts) described the lunar surface as follows:

The smaller saucer-shaped formations on

the surface of the moon are called craters.

They are of all sizes, from a mile to a

hundred and fifty miles in diameter; and

they are supposed to be of volcanic origin.

The words "supposed to be" don't quantify the uncertainty, but they are an excellent literary substitute for a popular book. And as late as 1923, Sir Richard Gregory, a professor of astronomy at Queens College, London, wrote in the popular book The Vault of Heaven:

The origin of the lunar craters is still

obscure. Analogy suggests that the forces

which cause volcanic eruptions on the earth

have been at work on the moon ...

[although] some astronomers and geologists