Can experiment access Planck-scale physics?

Physics on the large scale is based on Einstein's theory of general relativity, which interprets gravity as the curvature of space–time. Despite its tremendous success as an isolated theory of gravity, general relativity has proved problematic in its integration with physics as a whole, and in particular with the physics of the very small, which is governed by quantum mechanics. There can be no unification of physics that does not include both general relativity and quantum mechanics. Superstring theory and its recent extension to the more general theory of branes is a popular candidate for a unified theory, but the links with experiment are very tenuous. The approach known as loop quantum gravity attempts to quantize general relativity without unification, and has so far received no obvious experimental verification. The lack of experimental guidance has made the issue extremely hard to pin down.