A new theory is expected to unite Einstein’s gravity and quantum mechanics.

This seems like one of the few truly novel approaches to reconciling General Relativity and Quantum Mechanics that we’ve seen in decades.

Professor Jonathan Oppenheim has come up with the radical suggestion which in contrast to previous attempts to quantize spacetime involves modifications to quantum mechanics itself. His “postquantum theory of classical gravity” suggests that spacetime is truly classical thus resulting into arbitrary variation in the mass measured to an accuracy in the order of say 10^-20G heavier or lighter than any universal standard weight. There are now active experiments for determining for whether spacetime is classical or quantum, which are proposed tests which include along with others, the observation of stochastic density variations and gravitationally orchestrated entanglement. It could revolutionise our perception of quantum gravity and spacetime, the results.

In this article, the author explores the manner in which this radical theory avoids the standard quantization of spacetime.

Modern physics relies on two cornerstone theories: traditionally the rules of quantum mechanics that applies on the atomic level, and general relativity which is Alan Einstein’s theory on the gravitational forces. Nonetheless these two theories are diametrically opposed and scientists are still in search of a common theory for over a century.

Classically, people thought that Einstein’s theory has to be “quantised” to recover with quantum mechanics and provide the framework for such modern quantum gravity theories like string theory and loop quantum gravity.

However, there is a new theory by none other than Professor Jonathan Oppenheim who works for UCL Physics & Astronomy that challenges this conventional notion as listed and published on Physical Review X (PRX). As for his “postquantum theory of classical gravity”, spacetime can stay classical, ungoverned by quantum mechanics.

Unlike the concept of altering spacetime this theory amends quantum mechanics which it suggests that spacetime is responsible for inherent unpredictability leading to sizeably farther reaching fluctuations than those proposed by quantum mechanics. Therefore when the force of measurement to objects is taken to very large extent the exact mass associated with an object can also be unpredictable.

In a related paper published in Nature Communications, several of Oppenheim’s former PhD students expound on the theory as well as put forward an experiment that can be employed to determine mass very accurately, or rather, examine for weight changes over time.

For instance, daily at International Bureau of Weights and Measures in France, there is weighing of a 1kg mass which was the standard unit of measurement. If the theory is wrong then the mass fluctuations should be mathematically inadmissible and thus perhaps refute the theory.

This and other experiments will decide if spacetime is quantum or classical – a question on which an expensive wager between University of Sydney Professor Daniel Oppenheim and leading quantum gravity researchers Professor Carlo Rovelli and Dr Geoff Penington rests.

It is this kind of theory that the UCL research team has been conducting a series of studies for approximately five years in order to check its applicability across disciplines.

As Professor Oppenheim noted with edge that “Now that we have a consistent fundamental theory when spacetime remains classical; it’s anyone’s guess how this will play out. ”

Zach Weller-Davies who worked on theory and the experimental proposals during the work on his PhD at UCL mentioned that it challenges our understanding of gravity and opens new ways of studying the quantum nature of gravity.

He said that if spacetime is not quantum then curvature of spacetime fluctuates randomly and that this is testable. Both in quantum and in classical gravity, the spacetime experiences stochastic dynamics, but if spacetime is classical, these dynamics are larger than a specific scale that can be probed in superpositions experiments…

Co-authors of the paper Dr. Carlo Sparaciari and Dr. Barbara Šoda, who provided key analytical and numerical calculations for the experiments, said that these experiments might help to answer if pursuing quantum gravity is the right direction.

The currently working at the Perimeter Institute of Theoretical Physics, Dr. Šoda said that measuring the flow of time in quantam or classica form is as basic as evaluating whether or not a mass’s weight must remain stable or oscillate in a certain way.

Dr. Sparaciari went on to say that even though the basic idea behind the experiment is quite easy there is great precision in determining the mass of the given object at hand. The exciting aspect is proving a clear relationship between two measurable quantities: the size of fluctuation of spacetime and the duration for which objects such as atom or an apple can remain in a state of double existence that is in two places at the same time. These quantities can then be determined experimentally These quantities can then be determined from experiment resulting in accurate measurements and predictions of the micron scale surface topography.

Weller-Davies then went further to explain the rather delicate interplay between quantum parts and the classical curvature by bending spacetime and there exist a trade off between atoms showing wave characteristics and the size of random fluctuations of spacetime.

The intended test to check if spacetime is classical through a fluctuation of mass random to the observer goes well with another test to assert the quantum nature of spacetime through the “gravitationally mediated entanglement. ”

Sougato Bose, who was not among the researchers listed in the latest announcement but proposed the entanglement experiment, came to the defense of such large-scale attempts to come to grips with the fundamental laws of the universe. He hopes that these experiment could provide answers over the period of 20 year’s time.

The same applies also to other aspects of quantum theory in light of the postquantum theory; it also makes the infamous measurement postulate redundant given the fact that quantum superpositions self-localse in interactions with classical spacetime.

The motivation that led Professor Oppenheim to formulate this theory was to solve the black hole information paradox; in traditional quantum mechanics, the object that has gone through a black hole at some point in time should somehow be radiated out at a later time. This seems to violate the principles of general relativity of Einstein which claim that nothing escaping the event horizon of black hole can be known. The new theory permits erasure of information, due to elementary chaos.

Background information About quantum mechanics it is the law that controls all matter in the universe; however, is well observed in atomic and molecular form. They are notorious to obey Heisenberg’s uncertainty principle meaning that the more precisely one measures the position of the particle, the less information is available about its velocity and vice versa. The particles such as electrons exhibit wave like behaviour and can appear at a number of places simultaneously, a condition which is referred to as ‘superposition’.

Quantum mechanics encompasses many fields such as the mechanics of semiconductors in computer chips or lasers and radioactive decay. However, classical systems possess well-defined properties—like a cat being either alive or dead, but not both. The postquantum theory dispenses with the measurement postulate because classical spacetime interferes with quantum systems, forcing them to collapse.

The concepts have developed from Newton to Einstein where now gravity is defined as spacetime curvature by objects such as the sun, thus holding the earth in its place. Spacetime can be broken into three dimensions of space and time as the fourth dimension of space. According to general relativity, black holes and the big bang are supposed to exist, and time is relative, meaning that it can vary in different places, a factor which is important in assessing the coordinates of the GPS used in the smartphone.

Historical Context Sparaciari Oppenheim, in collaboration with Šoda and Weller-Davies, derived the most general consistent form of dynamics of a quantum system coupled to a classical system. This framework uses an approach based on general relativity combined with quantum field theories that have been developed by physicists.

The proposal that gravity could be related to wavefunction collapse was initially suggested by F. Karolyhazy in 1966, L. Diosi in 1987, and R. Penrose in 1996. The idea that spacetime could be classical is as old as I. Sato (1950) and C. Moller (1962), but a fully consistent theory did not exist until recently.

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