![]() In part two, “The World without Time”, Rovelli puts forward the idea that events (just a word for a given time and location at which something might happen), rather than particles or fields, are the basic constituents of the world. Rather, our understanding peters out at those very small intervals for which we need both quantum mechanics and relativity to explain things. For example, it is far from certain that space-time is quantized, in the sense of space and time being packaged in minimal lengths or periods (the Planck length or time). There are parallels with thermodynamics and Bayesian probability theory, which both rely on the concept of entropy, and might therefore be used to argue that the flow of time is a subjective feature of the Universe, not an objective part of the physical description.īut I quibble with the details of some of Rovelli’s pronouncements. Rovelli gives good descriptions of the classical physics of Newton and Ludwig Boltzmann, and of modern physics through the lenses of Einstein and quantum mechanics. The malleability of space and time mean that two events occurring far apart might even happen in one order when viewed by one observer, and in the opposite order when viewed by another. Einstein showed us that time is just a fourth dimension and that there is nothing special about ‘now’ even ‘past’ and ‘future’ are not always well defined. In the first, “The Crumbling of Time”, Rovelli attempts to show how established physics theories deconstruct our common-sense ideas. ‘Forward in time’ is the direction in which entropy increases, and in which we gain information. This stems from the fact that some equations of quantum gravity (such as the Wheeler–DeWitt equation, which assigns quantum states to the Universe) can be written without any reference to time at all.Īs Rovelli explains, the apparent existence of time - in our perceptions and in physical descriptions, written in the mathematical languages of Newton, Einstein and Erwin Schrödinger - comes not from knowledge, but from ignorance. Nevertheless, its agenda of joining up these two fundamentally differing laws is incredibly ambitious.Īlongside and inspired by his work in quantum gravity, Rovelli puts forward the idea of ‘physics without time’. ![]() In contrast to the better-known string theory, loop quantum gravity does not attempt to be a ‘theory of everything’ out of which we can generate all of particle physics and gravitation. Rovelli is one of the creators and champions of loop quantum gravity theory, one of several ongoing attempts to marry quantum mechanics with general relativity. The whole Universe obeys the laws of quantum mechanics and thermodynamics, out of which time emerges. So what does Rovelli think is really going on? He posits that reality is just a complex network of events onto which we project sequences of past, present and future. Even Albert Einstein’s relativistic space-time - an elastic manifold that contorts so that local times differ depending on one’s relative speed or proximity to a mass - is just an effective simplification. ![]() Indeed, as Rovelli argues in The Order of Time, much more is illusory, including Isaac Newton’s picture of a universally ticking clock. ![]() The Order of Time Carlo Rovelli Allen Lane (2018)Īccording to theoretical physicist Carlo Rovelli, time is an illusion: our naive perception of its flow doesn’t correspond to physical reality.
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