Search for Quantum Gravity

A satisfactory theory of quantum gravity maynecessitate a drastic modification of our perception ofspace-time, by giving it a foamy structure at distancescomparable to the Planck length. It is argued in this essay that the experimental detectionof such structures may be a realistic possibility in theforeseeable future. After a brief review of differenttheoretical approaches to quantum gravity and the relationships between them, we discussvarious possible experimental tests of the quantumnature of space-time. Observations of photons fromdistant astrophysical sources such as Gamma-Ray Bursters and laboratory experiments on neutral kaon decays may be sensitive to quantum-gravitational effectsif they are only minimally suppressed. Experimentallimits from the Whipple Observatory and the CPLEAR Collaboration are already probing close to the Planck scale, and significant increases in sensitivityare feasible.