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String Theory

The latest "new thing" in physics is string theory, an effort to explain ... what? Recent reports from the theorists' offices are difficult to follow: "... in a background of five-dimensional anti-de Sitter space times a five-sphere obeys a duality relationship with superconformal field theory in four spacetime dimensions." With origins in the quantum and relativity revolutions of the opening decades of the 20th century, string theory is an effort to reconcile deep consequences of our best descriptions of how the world looks and works, answers to questions about the nature and origins of matter itself.

The fundamental theories of physics contain inherently conflicting pictures of the world. Is the structure of matter particle or wave? Is reality inherently uncertain, or do some absolutes exist? What dimensionality of space and time adequately describes our universe? Different theories can resolve, or at least explain a few of these antinomies, but none has reconciled them all. By viewing everything as vibrations or disturbances along a hypothetical quantum mechanical string, and by greatly expanding the number of dimensions in which these strings quiver, string theory hopes to reconcile these conflicts in a single grand theory. This is as fundamental as a theory can get, and yet ... as far removed from our everyday experience as it is possible to imagine. String theory is, in a way, a post-modernist joke, a stunningly opaque but still significant answer to an essentially human question: Why?

The search for answers marks us as uniquely human. Laughter and humor, the ability to tell and respond to jokes sets us apart from the other animals. As does the simple childhood question, "Why?" We alone among the beasts observe and then insist on an explanation of what we have seen. Why is the moon round? Why does the sun set? Why do rocks fall? Why is the sky blue? These simple but profound questions generated the marvelous enterprise we call science. The answers are our theories of astronomy, gravity, light, and electromagnetism. Scientists from Galileo to Einstein have successfully explained countless observations while telescopes, microscopes, spectrographs and other tools have extended our senses.

The movements of moon, planets, and stars were explained by Isaac Newton's theory of gravitation and his dynamical theory that linked force and movement. By the 19th century, this Newtonian explanation was essentially complete, until an upwardly mobile laboratory assistant named David Faraday, confused by advanced mathematics but unerringly clever in experiment, discovered remarkable connections between electricity and magnetism by observing moving magnets and moving charges. Then, James Clerk Maxwell, skilled at the math Faraday lacked, used these startling observations to create a complete theory of electromagnetism. For many, Maxwell's theory for electromagnetic waves combined with Newton's particle theories completed physics' description of nature. Only a few details of calculation remained to be resolved.

Despite the many "whys" these theories answered, some simple observations remained unexplained. Why did an iron rod, heated in a blacksmith's forge, glow red, then yellow, then blue-white hot? Why did a colorless flame turn yellow when salt was scattered over it? And why, when the flame was examined with one of Newton's prisms, did the yellow appear as a narrow line of color, rather than a smear? As the 19th century ended and the 'modern' 20th began, these everyday questions led to the scientific and philosophical upheaval that eventually gave birth to string theory.

In 1905, an obscure young assistant in a Swiss patent office, rather far outside the academic mainstream, wrote a series of short, simple-sounding papers on theoretical topics. Each answered a "why" question that could be connected to a simple observation. One suggested how even a dim light could cause strong electrons to break away from atoms. Another explained the details of how tiny spores of moss seen in a microscope danced the jitterbug called Brownian motion. And a third, most profound of all, asked and answered a childhood question -- how would a beam of light look if you were yourself riding on a beam of light? The young man's name was Einstein, and 1905, the year he turned physics upside down, became known as his annus mirabilis -- his year of wonders.

In his explanations, wave and particle theories collided. By the time the dust had settled, energy came in fixed lumps called quanta; light, though a wave, interacted with atoms as a particle called a photon; and energy, matter, and motion were connected through a famous, if often misunderstood equation, E = mc2. Time and space were no longer independent; we lived in a physical world of four, not three, intertwined dimensions. The recourse to higher dimensions, a mathematical abstraction, to explain our world had begun.

A burst of experimental and theoretical work followed. The new quantum concept could explain, among other things, the precise colors of light emitted by atoms of neon in neon sign tubes or atoms of mercury in high pressure streetlights. The cost was great, however. The new theory of quantum mechanics replaced crisp cause and effect with a calculus of probabilities, in which solid things -- electrons, protons, and soon, neutrons -- became fuzzy waves. Quantum experiments were more actuarial than actual. Einstein himself so disliked these consequences that he long sought, but failed, to find a more deterministic theory. And while other theorists labored to make a successful quantum mechanics compatible with his theory of special relativity, Einstein quickly turned to another "why" question of his own -- why should someone falling freely in an elevator be completely unaware of gravity and thus of his predicament? He was not, of course, an Otis engineer. He was reconstructing the fundamental laws of physics so that no observer, however they moved, could claim privileged status over any other. Einstein's greatest insight was that nature insists that observers and their frames of reference are relative and not absolute.

By early in World War I, he had his solution -- his General Theory of Relativity, which explained how massive objects, like stars, distorted space-time and influenced the movement of both particles and light. Newton's gravitation became an effect of the curvature of space-time, and Einstein's falling elevator no different from any other laboratory. And as Einstein's quantum and speed of light theories had forced the recognition that classical physics was incomplete, so his general theory made incomplete both standard quantum mechanics and the (special) relativistic quantum mechanics that followed. Little progress was made in resolving these incompatibilities until recent decades. String theory is now seen to have the potential to resolve these questions with a new explanation of larger scope. Unfortunately, as the past one hundred years has demonstrated, it is a theory of more and more unfamiliar assumptions, of increasingly bizarre descriptions of a world we thought was familiar.

Einstein and his contemporaries straddled two worlds, that of the 19th century and its classical certainty, and the 20th with its relativity, ambiguity, and underlying confusion about what is. They moved and thought in that classical world, but their insights conclusively destroyed it. They abandoned the simple theories that easily answer our childhood questions. Similarly, these new string theories straddle the passage from the 20th century to the 21st, but do not answer our own 'whys' or resolve our own observations. Instead, they answer the 'whys' of other physicists, resolve obscure observations it takes hundreds of talented scientists spending hundreds of millions of dollars over many years of time to carry out. The questions are no less profound, and the answers no less important to our understanding of the world, but we have all delegated our understanding. We stand on the sidelines, appreciating analogies and comparisons, but gaining no satisfactory answers to match those given by Newton, Faraday, Maxwell, or even by Einstein. String theory is a post-modern theory for a post-modern world. We hope to be told if and when The Theory of Everything has been established, but we will have to trust the reports, and be satisfied that somewhere, there are those for whom it answers a burning, "why?"

-- Michael Templeton

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