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The Man Behind the Curtain

Physics is not always the seamless subject that it pretends to be

Tony Rothman

“I want to get down to the basics. I want to learn the fundamentals. I want to understand the laws that govern the behavior of the universe.” Thousands of admissions officers and physics department chairs have smiled over such words set down by aspiring physicists in their college-application essays, and that is hardly surprising, for every future physicist writes that essay, articulating the sentiments of all of us who choose physics as a career: to touch the fundamentals, to learn how the universe operates.

2011-05MacroRothmanFA.jpgClick to Enlarge ImageIt is also the view the field holds of itself and the way physics is taught: Physics is the most fundamental of the natural sciences; it explains Nature at its deepest level; the edifice it strives to construct is all-encompassing, free of internal contradictions, conceptually compelling and—above all—beautiful. The range of phenomena physics has explained is more than impressive; it underlies the whole of modern civilization. Nevertheless, as a physicist travels along his (in this case) career, the hairline cracks in the edifice become more apparent, as does the dirt swept under the rug, the fudges and the wholesale swindles, with the disconcerting result that the totality occasionally appears more like Bruegel’s Tower of Babel as dreamt by a modern slumlord, a ramshackle structure of compartmentalized models soldered together into a skewed heap of explanations as the whole jury-rigged monstrosity tumbles skyward.

Of course many grand issues remain unresolved at the frontiers of physics: What is the origin of inertia? Are there extra dimensions? Can a Theory of Everything exist? But even at the undergraduate level, far back from the front lines, deep holes exist; yet the subject is presented as one of completeness while the holes—let us say abysses—are planked over in order to camouflage the danger. It seems to me that such an approach is both intellectually dishonest and fails to stimulate the habits of inquiry and skepticism that science is meant to engender.

In the first week or two of any freshman physics course, students are exposed to the force of friction. They learn that friction impedes the motion of objects and that it is caused by the microscope interaction of the two surfaces sliding past one another. It all seems quite plausible, even obvious, yet regardless of any high falutin’ modeling, with molecular mountain ranges resisting each other’s passage or running-shoe soles binding to tracks, friction produces heat and hence an increase in entropy. It thus distinguishes past from future. The increase in entropy—the second law of thermodynamics—is the only law of Nature that makes this fundamental distinction. Newton’s laws, those of electrodynamics, relativity … all are reversible: None care whether the universal clock runs forward or backward. If Newton’s laws are at the bottom of everything, then one should be able to derive the second law of thermodynamics from Newtonian mechanics, but this has never been satisfactorily accomplished and the incompatibility of the irreversible second law with the other fundamental theories remains perhaps the greatest paradox in all physics. It is blatantly dropped into the first days of a freshman course and the textbook authors bat not an eyelash.

To a physicist, moreover, the material world is divided into billiard balls and springs. An ideal spring oscillates forever, but anyone who has ever watched a real-world spring knows that forever usually lasts just a few seconds. We account for this mathematically by inserting a frictional term into the spring equation and the fix accords well with observations. But the insertion is completely ad hoc, adjustable by hand, and to claim that such a fudge somehow explains the behavior of springs is simple vanity.

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