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Quantum gravity for dummies
By Dr. Deepak Vaid
Dr. Deepak Vaid is an assistant professor in the Physics department at NITK. He completed his PhD from Pennsylvania State University in 2012. Dr. Vaid tries to do research when not teaching B. Tech. students things that they
don’t care about and will never use in their lives. He enjoys long walks, ice-cream and long naps.
Abstract
I have been asked to write a 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.
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
numerous layers of technology that surround us. Many more of its
implications - quantum computation and teleportation for example
- 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but to Einstein’s theory of general relativity which superseded the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/r2. By 1905 the Newtonian concept of motion,
grounded in the postulates of absolute time and absolute space,
had dissolved to give way to the relativistic approach developed by
Einstein. This new framework was called the theory of “Special
Relativity”. The word “Special” here stands for the fact that this
theory is restricted to describing the behaviour of bodies in inertial
frames of reference - i.e. those that are non-accelerating. Lifting
this restriction, involves a generalization of the theoretical framework to allow a descripti