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The ins and outs of black holes and a new way of thinking about general relativity


By Hamish Johnston

While at the Convergence conference at the Perimeter Institute (PI), Physics World’s Louise Mayor and I had dinner with Sean Gryb. He did his PhD at the PI and is now doing a postdoc at Radboud University Nijmegen in the Netherlands. In the above video he shares some of his highlights of the conference.

Gryb is working on “shape dynamics”, which is a new idea for re-evaluating Albert Einstein’s general theory of relativity (GR). The idea was initiated by Julian Barbour and Gryb became involved in the development of shape dynamics while he was at PI. He now belongs to a small international band of physicists who are developing the concept. While shape dynamics is an alternative treatment of GR, the ultimate goal of their work seems to be the creation of a new framework for a theory of quantum gravity – an important goal of theoretical physics.

What I find most fascinating about Gryb’s work is that he only has a handful of colleagues to bounce ideas off, which must make the development of a new interpretation of a 100-year-old (and much loved) theory a very daunting task.

Indeed, just a few hours after we spoke to Gryb, the lecture theatre at the PI was packed with physicists and non-physicists alike who were there to hear Jürgen Renn explain how Einstein developed his theory. Renn is at the Max Planck Institute for the History of Science in Berlin and he explained how ongoing tensions between the physical realism of the emerging theory and its mathematical soundness led Einstein to his groundbreaking conclusions in 1915. It is interesting that a century later Gryb and colleagues are facing new physical/mathematical tensions in their re-evaluation of GR.

For more technically minded readers, Gryb and colleagues outline their ideas in a paper called “Einstein gravity as a 3D conformally invariant theory”.

And stay tuned to our video channel for more about Einstein from Jürgen Renn.

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  1. MJBridger

    Good luck to Sean Gryb and co with this work. It looks very interesting and could have vast implications re cosmology and our understanding of the nature of reality.
    The paper refers to ‘absolute instantaneity’ and this is useful for an agreement with quantum physics.
    It underlines the significance of entanglement and helps to dispose of the ‘block universe’ interpretation of relativity which has it that the past present and future all equally exist/are determined (so you might travel to them). I think in quantum physics the future does not yet exist or hasn’t been determined; it awaits the collapsing of the wave function.

    • Bruce

      Perhaps it has been predetermined, yet , not comprehended.

      • MJBridger

        Pretty sure that the future is not there to travel to. Though many times one will read the same cliché; “There is nothing in the laws of physics against time travel”.
        No nothing… except of course the most basic physical laws of conservation of momentum. That’s physicists being too clever (academic/impractical) to spot the simple truths.


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