Quantization of Gravity

When we are talking about quantization of gravity,one question strikes in our mind is that What is the motivation to quantize the gravity and what are the problems physicists are facing to quantize gravity? What are the attempts to quantize gravity and how much are they successful?

Theory of gravity is the general theory of relativity,we can say that the gravitational field is described by the general theory of relativity. Besides gravitational field there are another fields in nature like electromagnetic field, strong nuclear field and weak nuclear field.These fields are already quantized except gravitational field. To quantize a field or interaction a new subject quantum field theory emerges, which has traditionally been a pursuit of particle physicists. Quantum field theory predicted the anomalous magnetic moment of the electron correctly to six decimal places. It was formulated in early 1950s, many years after quantum mechanics.

The idea of quantizing the field arise from the planck. Quantisation blurs the distinction between particles and fields, point particles become fuzzy and subject to a wave equation and the electromagnetic field, classically represented as a continium, takes on a particle nature. Actually the photons are the quanta of the field which describes the interaction between the particles of matter.

Similarly achievements of Quantum field theory are numerous but quantization of general relativity is beset by great problems. First, there are mathematical ones. Einstien’s field equations are much more complicated than Maxwell’s equations of electromagnetism. In fact Einstien’s equations of general relativity are non linear. There is inconsistency with the superposition principle.

Mathematical expressions of quantum domains require the existence of linear vector space. Second, there are conceptual problems. In Einstein’s theory the gravitational field is manifested as a curvature of space time. In electrodynamics, the field is, as it were, an actor on the space­time stage, whereas in gravity the actor becomes the spacetime stage itself. In some sense, then, we are faced with quantization of space time; what is the meaning of this? Finally, there are practical problems.                                 Quantization of Gravity

Maxwell’s equations predict electromagnetic radiation and this was first observed by Hertz. Quantization of the field results in the possibility of observing individual photons; these were first seen in the photoelectric effect. Similarly Einstein’s equations for the gravitational field predict gravitational radiation, so there should, in principle, be a possibility of observing individual gravitons, quanta of the field. There are many attempts going on, to verify the gravitational waves and LIGO is one of them.

Inspite of these problems, some groups tried to quantize the gravity. String theory and Loop quantum gravity are the main theories. String theory is going to unify theory of all interactions if string modes are detectable. Loop quantum gravity just deals with the quantization of gravity. In short, String theory physicists geometrized the fields while in LQG, geometry of space time is quantized. Still we are in journey of quantizing the gravity and world needs great young minds to understand the theories of nature.                                              Quantization of Gravity

Written by-
Rahul Aggrawal
Ramanujan Shodh Sansthan

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