The Force of Gravity

Theoretical advances suggest that gravity may not be one of the fundamental forces of the universe.

I have emphasised… that the behaviour of bulk spacetime is similar to the behaviour of a macroscopic body of, say, gas and can be usefully described through thermodynamic concepts”: Thanu Padmanabhan, Professor and Dean at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune.

In the same way that pressure exerted by moving molecules of a gas can exert a force on the lid of a container even though it makes no sense to talk of the pressure of each individual molecule, recent papers by T Padmanabhan at IUCAA, Pune, and Erik Verlinde at the Institute for Theoretical Physics have suggested gravity is a property that emerges out of thermodynamic principles acting on the very stuff of the universe.  This would go a long way in explaining the puzzle of gravity, which has stood in the way of a unified theory of physics that would reconcile Quantum Mechanics and the General Theory of Relativity.

For much of the past century, attempts to reconcile the two have ended in failure, but scientists were content to live with the incompatibility because the General Theory deals with the very large where effects of gravity count, while Quantum Mechanics deals with the very small where the effects of gravity are negligible. There is, however, one place where the two theories converge, at the heart of a black hole, and in fact recent theoretical advances have come from the study of black holes.

Think of information in the conventional sense as something stored in a book or computer hard disk. The maximum amount of information in a given space would require the densest amount of matter—that is a black hole. It turns out this maximum is proportional to the surface area of the black hole rather than its volume. Naively, this can be understood to mean that information in any 3-dimensional space can be presented on a 2-dimensional surface, much like a hologram.

The new work starts with such a holographic principle and uses this to derive both Newtonian and Einsteinian laws from thermodynamics under appropriate conditions. In particular, this suggests that the search for the graviton, a fundamental particle believed to mediate the force of gravity, is futile.

forcesgravityQuantum Mechanics