About us
During the past year, our institution - Indian Institute of Technology Madras - was identified as one of the Institutes of Eminence (IoE) in India. As an IoE, our institute has instituted several Centres of Excellence (CoE), one of which is Centre for Strings, Gravitation and Cosmology ( https://ioe.iitm.ac.in/project/strings-gravitation-and-cosmology/). The current members of this centre are: Prof. Suresh Govindarajan, Prof. L. Sriramkumar, Prof. Prasanta Kumar Tripathy, Dr. Dawood Kothawala, Dr. Chandra Kant Mishra, Dr. Samir Choudhuri and Dr. Raghuveer Garani.
Broad theme of the Centre
Amongst the four forces of nature (viz. gravitation, electromagnetism, weak and strong), while gravitation and electromagnetism have a long range, the weak and the strong forces operate over considerably shorter distances. The theoretical frameworks used to describe these interactions prominently involve the three fundamental constants of nature: Newton’s gravitational constant G, the speed of light c and Planck’s constant ℏ; see Figure 1. Due to their long range, the influences of gravitation and electromagnetism have been known — through phenomena such as falling apples, rubbed combs lifting pieces of paper or magnets attracting each other — for more than two millennia. However, they were described by concrete mathematical theories only in the seventeenth and the nineteenth centuries. In the early part of the twentieth century, the realization that Maxwell’s theory of electromagnetism is inconsistent with the laws of Galilean and Newtonian dynamics led to the formulation of special relativity by Einstein. The next natural step was to reconsider the non-relativistic law of Newtonian gravitation and arrive at a relativistic formulation of the gravitational force. This effort led to insights far beyond a simple relativistic extension of the law of the gravitational force. It brought to the fore the notion of spacetime as a dynamical entity, with gravitation emerging as a manifestation of spacetime geometry rather than as a force. The first and simplest description of this manifestation is the theory of general relativity, which was conceived single-handedly by Einstein a decade after he had formulated special relativity.
The fact that gravitation and electromagnetism operate over a long range implies that there exist domains where these theories can be described classically. While it was the results from a variety of experiments that led to the development of the theory of electromagnetism, as we mentioned, the general theory of relativity was proposed primarily due to the motivation to bring gravitation within the ambit of relativity. But another major development of the twentieth century, viz. the formulation of quantum mechanics, clearly established that nature is fundamentally quantum mechanical. Nowhere is this more evident than in the characterization of the weak and the strong forces — descriptions which must be inherently quantum since these forces operate over small scales where the quantum effects dominate. Therefore, for a complete characterization of the physical interactions, one must also describe electro-magnetism and gravitation in a quantum framework. As a first step in the process, a quantum theory of electromagnetism was constructed and the lessons learnt from these exercises were applied to understand the weak and the strong forces. These efforts have since led to a unified quantum field theory of the weak and the electromagnetic forces. Though there exist aspects of the strong force that remain to be understood satisfactorily, it would be fair to say that we have a reasonable working knowledge of the strong force. These developments took place during the the latter half of the twentieth century.
As we mentioned, it is the classical relativistic theory of gravitation that is expected to play a pivotal role at the largest scales comparable to the size of the universe. At the smallest lengths — much smaller than those over which the weak and the strong forces operate — it is the quantum theory of gravitation that is expected to become important (see the regions highlighted in figure 1). However, despite half a century of effort, the approaches that have helped us understand the quantum nature of the electro-magnetic, weak and strong forces, have not proved adequate to allow us to construct a viable quantum theory of gravitation. In such a situation, there have been two approaches adopted in the literature which we can broadly refer to as the top-down and the bottom-up approaches. Without a doubt, string theory constitutes the most popular bottom-up approach. It attempts to construct a fundamental description of all interactions in terms of the dynamics of extended objects called strings. In the top-down approach, one essentially attempts to reconstruct an effective description of spacetime, guided by some very generic results that arise when one combines the basic principles of general relativity and quantum field theory. Such an approach is independent of any specific framework of a quantum theory of gravitation, and it is expected to serve as a bridge between any such framework and the large scale, classical description of spacetime. One can then explore observational and experimental implications of such an effective description. With the recent discovery of gravitational waves from merging binary black holes, the classical theory of gravitation is being probed to increasingly higher precision and greater strengths. It is also being simultaneously tested on the largest scales through observations of the distribution of matter in the universe. With improved observational techniques, it is expected that we would be able to probe the very early universe through the imprints of primary as well as secondary gravitational waves. It is hoped that these observations will provide us with some clues to the quantum nature of gravitation. With a plethora of experimental results and theoretical formulations that led to a comprehensive understanding of these results, twentieth century can clearly be labeled as the century of the weak and the strong forces. One fondly hopes that the twenty-first century will see the successful development of a quantum theory of gravitation and be referred to as the century of gravitation.
The key theme of our proposed Centre for Strings, Gravitation and Cosmology will be to explore the fundamental laws of physics from largest scales in the universe down to the smallest of scales dominated by quantum gravity, with the aim of deriving the imprints and possible relics of a quantum spacetime that can be tested using various upcoming observational missions in cosmology and gravitational wave physics.
Gravitation and Cosmology in Chennai
IIT Madras is amongst one of the oldest and leading technical institutes in India, and has been consistently ranked as a top institute in the country. The Department of Physics at IITM is one of the largest in the country, with research spanning a wide range of topics in theoretical and experimental physics. Apart from IITM, Chennai is also home to the Chennai Mathematical Institute (CMI) and the Institute of Mathematical Sciences (IMSc). These institutes have research groups actively working in the areas of gravitation and cosmology, making it an attractive destination for research in these directions. One of the aims of our Centre would be to showcase this fact, and provide an exposure to graduate students and post-doctoral fellows to current issues and recent developments in the areas of Classical and Quantum Gravity, Cosmology, and Gravitational waves.