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Quantum gravity

Physics from geometry

Nature Physics volume 2, pages 725–726 (2006)Cite this article

Two recent developments suggest how familiar properties of gravity and matter may emerge from the quantum geometry that underlies loop quantum gravity.

General relativity is the best theory of space–time structure available today. Its basic premise is that geometry is not an inert arena. Rather, it is a physical entity that acts on and can be acted upon by matter. It then stands to reason that, like matter, geometry may have a quantum nature, and it is widely expected that this is so at the Planck scale, ℓP ∼ 10−33 cm. By contrast, the standard perturbative methods of quantum field theory assume a classical space–time continuum at all scales. When applied to quantum gravity, then, they are fraught with difficulties.

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Figure 1: Is space loopy? In loop quantum gravity, space is fundamentally discrete and continuum is only an approximation.

TERESA IARIA 2004; PIO MONTI GALLERY, ROME

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  1. the Department of Physics, Institute for Gravitational Physics and Geometry, Penn State, University Park, Pennsylvania, 16802-6300, USA

    Abhay Ashtekar

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  1. Abhay Ashtekar
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Ashtekar, A. Physics from geometry. Nature Phys 2, 725–726 (2006). https://doi.org/10.1038/nphys447

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