A new theory is rocking the foundations of modern physics, rapidly overturning cherished but obsolete notions about our universe and replacing them with new mathematics of breathtaking beauty and elegance. Although there are still some unresolved questions concerning this theory, the excitement among physicists is palpable; throughout the world, leading physicists are proclaiming that we are witnessing the genesis of a new physics.
This theory is called superstrings, and a series of astonishing breakthroughs in physics within the last decade have culminated in its development, indicating that perhaps we are finally closing in on the unified field theory: a comprehensive, mathematical framework that would unite all known forces of the universe.
Advocates of superstrings even claim that the theory could be the ultimate theory of the universe.
Although physicists are usually cautious in their approach to new ideas, Princeton physicist Edward Witten has claimed that the superstring theory will dominate the world of physics for the next fifty years. Superstring theory is a miracle, through and through, he said recently. At one physics conference, he astonished his audience by declaring that we may be witnessing a revolution in physics as great as the birth of the quantum theory. He added, It’s probablygoing to lead to a new understanding of what space and time really are, the most dramatic [understanding]since general relativity. 1
Even Science magazine, always careful not to exaggerate the claims of scientists, compared the birth of the superstring theory to the discovery of the Holy Grail. This revolution, Science magazine claimed, may be no less profound than the transition from real numbers to complex numbers in mathematics.2
Two of the theory’s creators, John Schwarz of the California Institute of Technology and Michael Green of Queen Mary College in London, call ita bit puckishlya Theory of Everything (TOE).3
At the heart of this excitement is the realization that superstrings may provide a comprehensive theory that can explain all known physical phenomenaeverything from the motion of galaxies down to the dynamics within the nucleus of the atom. The theory even makes startling predictions concerning the origin of the universe, the beginning of time, and the existence of multidimensional universes.
To a physicist, it is an intoxicating notion that the vast storehouse of information of our physical universe, painfully accumulated over several thousand years of careful investigation, can be summarized in one theory.
For example, German physicists have compiled an encyclopedia, the Handbuch der Physik, an exhaustive work that summarized the world’s knowledge of physics. The Handbuch, which physically occupies an entire bookshelf of a library, represented the pinnacle of scientific learning. If the superstring theory is correct, then all the information contained in this encyclopedia can be derived (in principle) from a single equation.
Physicists are particularly excited about the superstring theory because it forces us to revise our understanding of the nature of matter. Since the time of the Greeks, scientists have assumed that the building blocks of the universe were tiny point particles. Democritus coined the word atomos to describe these ultimate, indestructible units of matter.
The superstring theory, however, assumes that the ultimate building blocks of nature consist of tiny vibrating strings. If correct, this means that the protons and neutrons in all matter, everything from our bodies to the farthest star, are ultimately made up of strings. Nobody has seen these strings because they are much too small to beobserved. (They are about 100 billion billion times smaller than a proton.) According to the superstring theory, our world only appears to be made of point particles, because our measuring devices are too crude to see these tiny strings.
At first it seems strange that such a simple conceptreplacing point particles with stringscan explain the rich diversity of particles and forces (which are created by the exchange of particles) in nature. The superstring theory, however, is so elegant and comprehensive that it is able to explain simply why there can be billions upon billions of different types of particles and substances in the universe, each with astonishingly diverse characteristics.
The superstring theory can produce a coherent and all-inclusive picture of nature similar to the way a violin string can be used to unite all the musical tones and rules of harmony. Historically, the laws of music were formulated only after thousands of years of trial-and-error investigation of different musical sounds. Today, these diverse rules can be derived easily from a single picturethat is, a string that can resonate with different frequencies, each one creating a separate tone of the musical scale. The tones created by the vibrating string, such as C or B flat, are not in themselves any more fundamental than any other tone. What is fundamental, however, is the fact that a single concept, vibrating strings, can explain the laws of harmony.
Knowing the physics of a violin string, therefore, gives us a comprehensive theory of musical tones and allows us to predict new harmonies and chords. Similarly, in the superstring theory, the fundamental forces and various particles found in nature are nothing more than different modes of vibrating strings. The gravitational interaction, for example, is caused by the lowest vibratory mode of a circular string (a loop). Higher excitations of the string create different forms of matter. From the point of view of the superstring theory, no force or particle is more fundamental than any other. All particles are just different vibratory resonances of vibrating strings. Thus, a single frameworkthe superstring theorycan in principle explain why the universe is populated with such a rich diversity of particles and atoms.
The answer to the ancient question What is matter? is simply that matter consists of particles that are different modes of vibrationof the string, such as the note G or F. The music created by the string is matter itself.
But the fundamental reason why the world’s physicists are so excited by this new theory is that it appears to solve perhaps the most important scientific problem of the century: namely, how to unite the four forces of nature into one comprehensive theory. At the center of this upheaval is the realization that the four fundamental forces governing our universe are actually different manifestations of a single unifying force, governed by the superstring,