How Common Sense Turns Our World Upside Down

If there’s one quality that’s sure to get a scientist into trouble, it’s common sense. Over and over again in the history of science, common sense has been exposed as a lousy guide to truth.

Take astronomy, for example. In 1825, the French philosopher Auguste Comte argued that humankind could never find out what stars were made of. And what could be more sensible? Anyone can see that stars are far too remote to analyze in a lab.

Within a century, however, astronomers had learned to read the bright and dark lines in the spectra of starlight for clues not only to the physical makeup of stars, but also to their temperature, age and motion.

Or take biology. Who would have thought that our very bodies were populated with hordes of species of bacteria before Leeuwenhoek came along and looked at saliva through his first crude microscope? Today we know that the vast majority of life forms on Earth and in the oceans make themselves visible only through microscopes; we fuzzy mammals are the lumbering oddballs.

Much more recently, biologists came to the common-sense conclusion that life needed sunlight and oxygen to survive. No sooner had they concluded that than whole colonies of life forms were discovered in the total darkness of the ocean floor, living off sulfurous fumes steaming from boiling hot ocean vents.

Indeed, the common-sense view that life requires oxygen completely distorts the historical record. Free-floating oxygen is a newcomer to our planet, a toxic poison released into the atmosphere by the first green plants.

And contrary to the conventional wisdom that pouring carbon dioxide into the air “pollutes” our planet, it actually serves to bring it back to its natural state. (Humans, of course, are not “natural” to Earth, and would not survive such a dramatic change.)

Even geologists, who study the comparatively sedate Earth and planets, haven’t been immune from the perils of common sense. Only recently did they finally bring themselves to believe the seemingly absurd (but true) notion that the continents drift around, careening into each other like so many bumper cars, setting off earthquakes in the process.

And what about that rock from Mars carrying markings that looked like ancient fossils? Planetary scientists tell us it got chipped off the red planet by a visiting asteroid, then wandered about the solar system for 16 million years before plopping down in an Antarctic ice field. Just a few years ago, researchers didn’t believe that chunks of Mars could get to Earth at all. Today, they estimate that 100 pounds of Mars rains on our planet each year.

The mathematicians have been the worst of all, turning common sense inside out with astonishing regularity.

First, they invented obviously nonsensical negative numbers. (What does it mean to have minus 2 apples?) Then, they discovered irrational numbers like pi, that run on forever. According to legend, the nonsensical idea of irrational numbers was treated much like the nonsensical idea of a spherical Earth that revolved around the sun; scientists were ridiculed, or worse, for promoting such ideas.

Today, mathematicians accept everything from imaginary and transcendental numbers to infinities that are bigger than other infinities, and 20-dimensional geometries. And calculus--initially denounced as an absurdity because it deals with ghost-like “infinitesimal” quantities--is now routinely studied in high school.

The unsettling truth is that nature doesn’t give a hoot what humans think is “common sense,” and great scientists have learned to accept this better than the rest of us.

Isaac Newton said flat out that his own theory of gravity was such a great absurdity that no reasonable person could believe in it because it relied on the notion of invisible influences spreading through empty space. Yet, it was Newton’s laws that enabled NASA to send a spacecraft to Mars (and sent Mars rocks to Antarctica). The moral is: If it works, it’s probably right--sensible or not.

The late physicist Frank Oppenheimer used to get exasperated when people urged him to use his “common sense” and accept the world the way it was--whether the subject was science or social policy. Time and again, he’d remind them: “It’s not the real world. It’s a world we made up.”