The Strange Second Life of String Theory

K. C. Cole in Quanta:

String theory strutted onto the scene some 30 years ago as perfection itself, a promise of elegant simplicity that would solve knotty problems in fundamental physics — including the notoriously intractable mismatch between Einstein’s smoothly warped space-time and the inherently jittery, quantized bits of stuff that made up everything in it.

It seemed, to paraphrase Michael Faraday, much too wonderful not to be true: Simply replace infinitely small particles with tiny (but finite) vibrating loops of string. The vibrations would sing out quarks, electrons, gluons and photons, as well as their extended families, producing in harmony every ingredient needed to cook up the knowable world. Avoiding the infinitely small meant avoiding a variety of catastrophes. For one, quantum uncertainty couldn’t rip space-time to shreds. At last, it seemed, here was a workable theory of quantum gravity.

Even more beautiful than the story told in words was the elegance of the math behind it, which had the power to make some physicists ecstatic.

To be sure, the theory came with unsettling implications. The strings were too small to be probed by experiment and lived in as many as 11 dimensions of space. These dimensions were folded in on themselves — or “compactified” — into complex origami shapes. No one knew just how the dimensions were compactified — the possibilities for doing so appeared to be endless — but surely some configuration would turn out to be just what was needed to produce familiar forces and particles.

More here.