In principle, nothing that enters a black hole can leave the black hole. This has considerably complicated the study of these mysterious bodies, which generations of physicists have debated since 1916, when their existence was hypothesized as a direct consequence of Einstein's Theory of Relativity. There is, however, some consensus in the scientific community regarding black hole entropy—a measure of the inner disorder of a physical system—because its absence would violate the second law of thermodynamics. In particular, Jacob Bekenstein and Stephen Hawking have suggested that the entropy of a black hole is proportional to its area, rather than its volume, as would be more intuitive. This assumption also gives rise to the "holography" hypothesis of black holes, which (very roughly) suggests that what appears to be three-dimensional might, in fact, be an image projected onto a distant two-dimensional cosmic horizon, just like a hologram, which, despite being a two-dimensional image, appears to be three-dimensional. Since we cannot see beyond the event horizon, how is it possible to calculate this measure? The theoretical approach adopted by Hawking and Bekenstein is semiclassical and introduces the possibility of adopting a quantum gravity approach in these studies in order to obtain a more fundamental comprehension of the physics of black holes. Planck's length is the dimension at which space-time stops being continuous as we see it, and takes on a discrete graininess made up of quanta, the "atoms" of space-time. The universe at this dimension is described by quantum mechanics. Quantum gravity is the field of enquiry that investigates gravity in the framework of quantum mechanics. Gravity has been very well described within classical physics, but it is unclear how it behaves at the Planck scale. Daniele Pranzetti and colleagues, in a new study published in Physical Review Letters, present an important result obtained by applying a second quantization formulation of loop quantum gravity (LQG) formalism. LQG is a theoretical approach within the problem of quantum gravity, and group field theory is the "language" through which the theory is applied in this work. The idea at the basis of their study is that homogenous classical geometries emerge from a condensate of quanta of space introduced in LQG in order to describe quantum geometries. Thus, scientists obtained a description of black hole quantum states, suitable also to describe 'continuum' physics—that is, the physics of space-time as we know it. http://phys.org/news/2016-05-loop-quantum-gravity-theory-glimpse.html Paper: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.211301
