John Horgan [8.14.05]

All these theories are preposterous, but that's not my problem with them. My problem is that no conceivable experiment can confirm the theories, as most proponents reluctantly acknowledge. The strings (or membranes, or whatever) are too small to be discerned by any buildable instrument, and the parallel universes are too distant. Common sense thus persuades me that these avenues of speculation will turn out to be dead ends.


John Horgan, author of The End of Science, and feisty and provocative as ever, is ready for combat with scientists in the Edge community. "I'd love to get Edgies' reaction to my OpEd piece — "In Defense of Common Sense" — in The New York Times", he writes.

Physicist Leonard Susskind, writing "In Defense of Uncommon Sense", is the first to take up Horgan's challenge (see below). Susskind notes that in "the utter strangeness of a world that the human intellect was not designed for... physicists have had no choice but to rewire themselves. Where intuition and common sense failed, they had to create new forms of intuition, mainly through the use of abstract mathematics." We've gone "out of the range of experience."

— JB

JOHN HORGAN oversees the science writings program at the Stevens Institute of Technology. His books include The End of Science and Rational Mysticism.

John Horgan's Edge bio page

THE REALITY CLUB: Verena Huber-Dyson, Robert Provine, Spencer Reiss, Daniel Gilbert, John McCarthy, Leonard Susskind respond to John Horgan. Horgan replies.


As anyone remotely interested in science knows by now, 100 years ago Einstein wrote six papers that laid the groundwork for quantum mechanics and relativity, arguably the two most successful theories in history. To commemorate Einstein's "annus mirabilis," a coalition of physics groups has designated 2005 the World Year of Physics. The coalition's Web site lists more than 400 celebratory events, including conferences, museum exhibits, concerts, Webcasts, plays, poetry readings, a circus, a pie-eating contest and an Einstein look-alike competition.

In the midst of all this hoopla, I feel compelled to deplore one aspect of Einstein's legacy: the widespread belief that science and common sense are incompatible. In the pre-Einstein era, T. H. Huxley, aka "Darwin's bulldog," could define science as "nothing but trained and organized common sense." But quantum mechanics and relativity shattered our common-sense notions about how the world works. The theories ask us to believe that an electron can exist in more than one place at the same time, and that space and time — the I-beams of reality — are not rigid but rubbery. Impossible! And yet these sense-defying propositions have withstood a century's worth of painstaking experimental tests.

As a result, many scientists came to see common sense as an impediment to progress not only in physics but also in other fields. "What, after all, have we to show for ... common sense," the behaviorist B. F. Skinner asked, "or the insights gained through personal experience?" Elevating this outlook to the status of dogma, the British biologist Lewis Wolpert declared in his influential 1992 book "The Unnatural Nature of Science," "I would almost contend that if something fits in with common sense it almost certainly isn't science." Dr. Wolpert's view is widely shared. When I invoke common sense to defend or — more often — criticize a theory, scientists invariably roll their eyes.

Scientists' contempt for common sense has two unfortunate implications. One is that preposterousness, far from being a problem for a theory, is a measure of its profundity; hence the appeal, perhaps, of dubious propositions like multiple-personality disorders and multiple-universe theories. The other, even more insidious implication is that only scientists are really qualified to judge the work of other scientists. Needless to say, I reject that position, and not only because I'm a science journalist (who majored in English). I have also found common sense — ordinary, nonspecialized knowledge and judgment — to be indispensable for judging scientists' pronouncements, even, or especially, in the most esoteric fields.

For example, Einstein's intellectual heirs have long been obsessed with finding a single "unified" theory that can embrace quantum mechanics, which accounts for electromagnetism and the nuclear forces, and general relativity, which describes gravity. The two theories employ very different mathematical languages and describe very different worlds, one lumpy and random and the other seamless and deterministic.

The leading candidate for a unified theory holds that reality stems from tiny strings, or loops, or membranes, or something wriggling in a hyperspace consisting of 10, or 16 or 1,000 dimensions (the number depends on the variant of the theory, or the day of the week, or the theorist's ZIP code). A related set of "quantum gravity" theories postulates the existence of parallel universes — some perhaps mutant versions of our own, like "Bizarro world" in the old Superman comics — existing beyond the borders of our little cosmos. "Infinite Earths in Parallel Universes Really Exist," the normally sober Scientific American once hyperventilated on its cover.

All these theories are preposterous, but that's not my problem with them. My problem is that no conceivable experiment can confirm the theories, as most proponents reluctantly acknowledge. The strings (or membranes, or whatever) are too small to be discerned by any buildable instrument, and the parallel universes are too distant. Common sense thus persuades me that these avenues of speculation will turn out to be dead ends.

Common sense — and a little historical perspective — makes me equally skeptical of grand unified theories of the human mind. After a half-century of observing myself and my fellow humans — not to mention watching lots of TV and movies — I've concluded that as individuals we're pretty complex, variable, unpredictable creatures, whose personalities can be affected by a vast range of factors. I'm thus leery of hypotheses that trace some important aspect of our behavior to a single cause.

Two examples: The psychologist Frank Sulloway has claimed that birth order has a profound, permanent impact on personality; first-borns tend to be conformists, whereas later-borns are "rebels." And just last year, the geneticist Dean Hamer argued that human spirituality — surely one of the most complicated manifestations of our complicated selves — stems from a specific snippet of DNA. Although common sense biases me against these theories, I am still open to being persuaded on empirical grounds. But the evidence for both Dr. Sulloway's birth-order theory and Dr. Hamer's "God gene" is flimsy.

Over the past century, moreover, mind-science has been as faddish as teenage tastes in music, as one theory has yielded to another. Everything we think and do, scientists have assured us, can be explained by the Oedipal complex, or conditioned reflexes, or evolutionary adaptations, or a gene in the X chromosome, or serotonin deficits in the amygdala. Given this rapid turnover in paradigms, it's only sensible to doubt them all until the evidence for one becomes overwhelming.

Ironically, while many scientists disparage common sense, artificial-intelligence researchers have discovered just how subtle and powerful an attribute it is. Over the past few decades, researchers have programmed computers to perform certain well-defined tasks extremely well; computers can play championship chess, calculate a collision between two galaxies and juggle a million airline reservations. But computers fail miserably at simulating the ordinary, experience-based intelligence that helps ordinary humans get through ordinary days. In other words, computers lack common sense, and that's why even the smartest ones are so dumb.

Yes, common sense alone can lead us astray, and some of science's most profound insights into nature violate it; ultimately, scientific truth must be established on empirical grounds. Einstein himself once denigrated common sense as "the collection of prejudices acquired by age 18," but he retained a few basic prejudices of his own about how reality works. His remark that "God does not play dice with the universe" reflected his stubborn insistence that specific causes yield specific effects; he could never fully accept the bizarre implication of quantum mechanics that at small scales reality dissolves into a cloud of probabilities.

So far, Einstein seems to be wrong about God's aversion to games of chance, but he was right not to abandon his common-sense intuitions about reality. In those many instances when the evidence is tentative, we should not be embarrassed to call on common sense for guidance.