Ever wonder why the constants of physics, that parade of Greek symbols in science textbooks, have the values they do? A more vexing version of that question continues to plague some of science’s brightest minds. They are struggling to come up with a Theory of Everything that could provide some answers.

“They are beginning to ask, not how the world is, but why the world is and in seminars mostly attended by physicists, not philosophers,” said Dr. Leonard Susskind, a Stanford University string theorist, at a Strings 2005 public lecture on string theory.

For a long time, the elegance of Newton’s equations, which described the motion of objects such as the apple that was said have struck him, held sway. Then, in 1905, Albert Einstein began laying out the foundation of two powerful, yet inconsistent, theories: general relativity, for objects that are big and massive, and quantum mechanics, for the microscopic world of atoms.

Things massive and microscopic don’t often coexist, but there are rare situations when they do meet. Matter falling into black holes-objects so massive and small that not even light can escape their gravitational pull-and events such as the beginning of the universe are two examples where the theories clash, to produce nonsensical results.

A century after Einstein’s groundbreaking work, theorists are still struggling to sort out this mess. But, as University of Amsterdam physicist Robbert Dijkgraff explained, string theory provided a spark of lightning between the two conceptual clouds.

Born in the early 70s, string theory replaces the notion of point particles or events happening at a single point in space-time with the concept of the one-dimensional extended object called a string.

Strings are supposed to exist at scales smaller than the Planck length. This distance is so small that if one expanded an atom to the size of the known universe, the Planck length would be about the size of a tree. Most string theories, since there are more than one, assume six dimensions in addition to our present four (best thought of as length, width, height, and time), twisted up into unimaginable shapes at microscopic length scales.

String theory, though far from complete, may also answer the greatest questions of existence. Ever wonder why the attractive force between an electron and a proton is unimaginably larger than the gravitational force? The relative strength of these forces is important, because minute changes in their values would have produced a universe inhospitable to life.

“The world seems to be full of vast numbers of conspiracies and coincidences,” said Susskind. Gravity is a prime example. If the force of gravity were ten times smaller, it would produce galaxies whose few stars would be unable to catch the elements of life seeded by supernovas. A force ten times greater would result in stars burning too quickly, producing too many black holes.

The greatest insight of string theory may yet be its ability to explain why the universe gives the illusion of intelligent design-a universe whose constants are just right for life to arise.