# Scientists studied the classical theory of gravity and quantum mechanics

The researchers, through their calculations, found the uncertainty relation induced by the noise of gravitons – hypothetical quantities of gravity and elementary particles that mediate the force of gravitational interaction – taking a step forward towards unifying the classical theory of gravity and quantum mechanics. While classical physics is a set of rules and equations that describe how normal objects behave, quantum physics describes the world of atoms and smaller objects.

Mr. Soham Sen and Prof. Sunandan Gangopadhyay from the Department of Astrophysics (IIA) and High Energy Physics at S.N. Bose National Centre for Basic Sciences are engaged in finding the signatures of quantum gravity in terrestrial systems, which will lead to a better understanding of the full quantum theory of gravity. This is a fundamental problem that has remained unsolved since the time of Albert Einstein.

Quantum gravity (QG) is a field of theoretical physics that describes gravity in accordance with the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored, such as compact astronomical objects like black holes or neutron stars.

It has been shown previously that when the gravitational field is treated quantum mechanically, it generates fluctuations, or noise, in the lengths of the arms of gravitational wave detectors such as LIGO's interferometer. The characteristics of this noise depend on the quantum state of the gravitational field. Detecting this fundamental noise would be direct evidence for the quantization of gravity and for the existence of the graviton, the link between gravity and quantum theory.

Extending such work, Prof. Gangopadhyay and Mr. Soham Sen have investigated the fate of freely falling bodies in a quantum gravitational field. Their calculations have yielded an uncertainty relation between the position and momentum variables induced by gravitational noise. The uncertainty relation indicates a true quantum gravitational effect and the calculations clearly indicate that there is a correct coupling of the degrees of freedom of the particle with the quantized gravitational field. “Our derivation of the generalized uncertainty principle is robust in the sense that the result was obtained by taking into account the quantum nature of gravity,” said Prof. Sunandan Gangopadhyay.