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On the way to a theory of everything.  Published by Weidenfeld & Nicolson 2000.

On the way to a theory of everything. Published by Weidenfeld & Nicolson 2000.

Possibly one of the most contentious subjects in science today is the quest for a theory to unify two main areas of physics – Einstein’s theory of general relativity which explains things on the very large scale of stars and galaxies, and quantum mechanics which deals with the very small level of atoms and fundamental particles.  And, at least so far, such a great unification has not been achieved.

In his 2000 book Three Roads to Quantum Gravity, the theoretical physicist Lee Smolin described the main approaches at the time.  In his usual clear style, and in what he admits was a personal view, he outlined the route from quantum theory giving rise to string theory, and the road from relativity, modified by quantum phenomena, leading to what is called loop quantum gravity (to which he was himself one of the main contributors).  Both try to describe space and time on the extremely small scale, and one of the aspects on which he focused in the book was the search for what is meant by the temperature and entropy of a black hole, which could be seen as a feature of both paths.

But there could be another approach, with a whole new conceptual framework.  And, whilst Professor Smolin saw some aspects of convergence on a theory that might eventually explain everything, he recognised that there was still some way to go.  At the time, he anticipated that by now physicists would have developed “the basic framework of a quantum theory of gravity”, and he believed that the ideas he had discussed would “turn out to be part of the picture”.  Unfortunately, that picture itself remains elusive to this day.

But, in Black Holes, Wormholes and the Secrets of Quantum Spacetime (Scientific American, November 2016), Juan Maldacena of the Institute for Advanced Study in Princeton takes us down a promising route.  He outlines how quantum entanglement – one of the fundamental (and deeply puzzling) aspects of quantum physics – may be equivalent to the descriptions of the geometry of spacetime which allow for the existence of wormholes, connecting black holes located at vast distances from one another.  And he argues that this might lead eventually to a description of quantum spacetime, and thus the long-sought goal of a theory of everything.

Wormholes have often been seen as a method of allowing instantaneous movement across immense distances in space.  In a previous webpost – Like A Wheel Within A Wheel – I talked about the theory that a rotating black hole might permit the creation of an Einstein-Rosen bridge which allows such access to remote regions.  The idea has turned up in science fiction from time to time.

In the 2014 film Interstellar, a wormhole which has unexpectedly opened up in the outer Solar System offers the chance for humanity to escape from the mess it has made of Earth and transfer to a habitable planet in another star system (and, quite probably, go on to mess that up too).  Though in the 1997 film Event Horizon, the idea is to create an artificial black hole in order to establish a wormhole to another region of the Galaxy.  As becomes all too clear, the location to which it actually ends up going is somewhere far more unpleasant.

But Professor Maldacena points out that current wormhole theory has a distinct downside from the point of view of interstellar travel – wormholes of the science-fictional variety would violate the known laws of physics.  They may well exist provided they are consistent with the laws of general relativity, but that won’t permit a faster-than-light transport system.

So perhaps we are truly heading towards a grand unifying theory of everything, but sadly one of the favoured quick routes to the stars won’t be available.  Well, we can’t really have everything.

Richard Hayes, Assistant Editor (Odyssey)

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