Book Reviewed: Gravity: How the Weakest Force in the Universe Shaped Our Lives by Brian Clegg

A historical account of spacetime warping This book offers a historical account of gravity, one of the four fundamental forces of nature, and how it eludes our understanding. This is a concise narrative that is engaging without any equations or too much physics. It is explained in a very simple language. But some of the recent and relevant discussions have not been included here. The Newtonian physics describes the behavior of matter and energy in space and time. According to Isaac Newton, time flows equably without relation to anything external, and absolute space is also its own thing, always similar and immovable. Events of physical reality performed independently on a neutral stage where actors strutted and fretted without influencing the rest of the theater. This pretty much explains physical reality we see and experience in our daily life. But Albert Einstein’s theory of general relativity turned Newton’s absolute space and time into a relativistic mash-up. According to him, spacetime is completely amalgamated into a malleable fabric and the two do not exist independently as Newton predicted. This is a new arena in which the players altered the space of the playing field. It was a physics game changer. Einstein also showed in his general theory of relativity that matter and energy warped the spacetime surrounding it. In fact, that is called gravity, which Newton thought was a force. Newton’s apparent force of attraction became a sort of illusion perpetrated by spacetime geometry. The shape of spacetime dictated the motion of massive bodies, and in turn massive bodies determined spacetime’s shape. With our understanding of quantum physics where matter at the most fundamental state is known to have wave-particle duality, that is it exists as both particle and a wave simultaneously. If that is the case, then how does matter exert gravity when it is in a wave-state? Quantum physicists suggested that spacetime at the most fundamental state also exists in discrete quanta, that in bits and pieces, qubits. In fact, the treatment of gravity with quantum physics has led to thorny issues that is largely derived from the black hole physics where spacetime is curved to an extreme extent. To understand the quantum properties of space and time, it is realized that information plays an important role in quantum reality, because it gives the observer a role who becomes an integral part of the physical reality. Recent advances in quantum Information have shown that information naturally describe evolution of quantum geometry. There seems to be a deep connection between information and the nature of space and time, and space and time are losing their role as grounds for an objective physical reality. The observer or the consciousness is an integral part. It may also mean that gravity may be an emergent phenomenon in quantum physics, or gravity and quantum physics are different approximations of a more fundamental theory that is still out there but not yet discovered.