Quantum Gravity for Dummies
I have been asked to write brief, gentle introduction to the basic idea behind the field of “quantum gravity” in 1500 words or less. Doing so appears to be almost as great a challenge as coming up with a consistent theory of quantum gravity. However, I will try. Disclaimer: The views expressed in this article are my own and do not represent the consensus of the quantum gravity community. 1 Semantics To get some idea of quantum gravity it is helpful to look at the meaning of those two words separately. The word “quantum” refers to the theory of quantum mechanics which was developed in the 20th century and which incorporates various seemingly paradoxical properties of light and matter such as wave-particle duality, the uncertainty principle, and the probabilistic nature of measurements into a coherent theoretical framework. Quantum Mechanics undergirds the basic technological framework of the world we live in. Without quantum mechanics we would not understand how semiconductors work and without semiconductors we would not be able to build the integrated circuits that power most modern electronic devices. Without QM we would not have NMR machines, CT scans, electron microscopes, superconductors or superfluids. Many of the theoretical implications of quantum mechanics have been realized outside the laboratory and are embedded in the many layers of technology that surround us. Many more of its implications - quantum computation and teleportation for e.g. - are still in the laboratory, not yet mature enough to venture out into the real world. The word “gravity” refers not to Newton’s theory of gravitation, but to Einstein’s theory of general relativity which superseded the Newtonian conception of gravity. In the Newtonian framework, gravity was thought of as a force which acted between any two massive bodies in a manner given by the well-known formula: F = Gm1m2/r 2 . By 1905 the Newtonian concept of motion, grounded in the postulates of absolute time and absolute space, had dissolved to give way