Strung Along

For anyone interested in physics, I highly recommend this article about string theory.

Modern physics has some big problems: there are two different theories of How Things Work, but they don't fit together. Einstein's General Relativity has passed every experimental test we can throw at it, and explains how the universe works on the scale of solar systems, galaxies, and bigger. At the other end of the spectrum, various quantum theories combine into the Standard Model, which has passed every experimental test we can throw at it, and explains how the universe works on the scale of molecules, atoms, and smaller.

In the middle, at human-scale sizes and energies, they both reduce to classical Newtonian physics.

But the two theories are basically incompatible. There is no good explanation of How Things Work in places where both theories could apply, such as extreme gravitational fields packed into supersmall sizes.

The two theories are very different in other ways, too. General Relativity was the brilliant work of one genius--Einstein--who came up with the whole thing based on the logical extension of first principles. General Relativity has remained essentially unchanged since it was created in the first decades of the 20th century, and it may be fair to say that Einstein was at least a century ahead of his time. GR relies on only two parameters, the speed of light and the gravitational constant, and is probably the most elegant scientific theory ever devised.

The Standard Model, on the other hand, has been the work of many physicists and has grown over a century as new experimental evidence gets incorporated into the theoretical framework. Significant refinements continue to be made even to this date (for example, until the 90's the theory held that neutrinos have no mass. We now know that they do). The Standard Model requires a menagerie of fundamental forces and particles, each with its own fundamental parameters, and no good reason for why they are what they are. Compared to GR, the Standard Model is inelegant, arbitrary, and messy.

String theory tries to resolve the conflicts between the two, but doesn't appear to have any experimental evidence.

In many ways, I think the conflict between General Relativity and the Standard Model is similar to the crisis at the end of the 1800's, when (then current) theories of physics failed important experimental tests. The difference is that now we have a situation where there's too many theories and no experiments to guide them, whereas a century ago the problem was the opposite.

The resolution will probably be the same: new physics (probably driven by new experiments) will lead us to a much deeper understanding of the universe. Odds are, the result will be something much weirder and more beautiful than anything anyone has thought of up to now.