Monday, June 7, 2010

The Planck Dive - Greg Egan

"The key idea dated back to Sakharov: gravity was nothing but the residue of the imperfect cancellation of other forces; squeeze the quantum vacuum hard enough and Einstein's equations fell out. But since Einstein, every theory of gravity was also a theory of time. Relativity demanded that a free-falling particle's rotating phase agree with every other clock that traveled the same path, and once gravitational time dilation was linked to changes in virtual particle density, every measure of time--from the half-life of a radioisotope's decay (stimulated by vacuum fluctuations) to the vibrational modes of a sliver of quartz (ultimately due to the same phase effects as those giving rise to classical paths)--could be reinterpreted as a count of interactions with virtual particles.

It was this line of reasoning that had led Kumar--a century after Sakharov, building on work by Penrose, Smolin and Rovelli--to devise a model of spacetime as a quantum sum of every possible network of particle world lines, with classical "time" arising from the number of intersections along a given strand of the net. This model had been an unqualified success, surviving theoretical scrutiny and experimental tests for centuries. But it had never been validated at the smallest length scales, accessible only at absurdly high energies, and it made no attempt to explain the basic structure of the nets, or the rules that governed them. Gisela wanted to know where those details came from. She wanted to understand the universe at its deepest level, to touch the beauty and simplicity that lay beneath it all.

That was why she was taking the Planck Dive."

4 out of 5

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