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Issue 1, Volume 3
October 2009

Irreconcilable Differences? Maybe Not
High Energy and Condensed Matter Physicists Find Common Ground

If high energy physics is your “thing”, then you know that SPIRES (Stanford Physics Information Retrieval System) is a database that monitors research papers and their bibliographic information. This system offers a quick glance at what’s “hot” in high energy physics at any given time because it ranks papers according to the number of times each one has been cited by other researchers

Professor Petr Hořava of the Berkeley Center for Theoretical Physics has found himself at the top of the 2009 rankings because his most recent papers have caused such interest. “Membranes at Quantum Criticality,” published in December ’08 has been cited over 100 times; “Quantum Gravity at a Lifshitz Point,” published in January ’09 has been cited over 150 times; and “Spectral Dimension of the Universe in Quantum Gravity at a Lifshitz Point,” published in February ’09 in Physical Review Letters has been cited over 50 times.

What do these rankings indicate? Quite simply, they indicate that Hořava just might be on to something. As a string theorist with an open-mind, Hořava is actively seeking alternatives to string theory, which despite its inherent beauty and popularity is sometimes criticized for being too baroque and too intricate. He and others wonder if there might be something simpler a quantum theory of gravity, perhaps—that brings together the large and the small, galaxies and atoms, to explain the Universe.

And so, Hořava is looking to condensed matter physics, the study of particles at very low energies and at moderate distances, for certain keys to the mysteries of gravity and the Universe. He combines the concepts of quantum gravity with spacetime anisotropy common in condensed matter. In a seemingly unrelated development, European scientists Jan Ambjørn, Renate Loll and Jerzy Jurkiewicz, have developed a discretized computer model of quantum gravity on a lattice, which appears for the first time to yield a smooth 3+1 dimensional spacetime at long distances. Their simulations have also revealed an interesting feature: an apparent dimensional reduction of spacetime to two dimensions at short distances! Surprisingly, Hořava’s approach to quantum gravity predicts the very same effective reduction, as a result of the anisotropy of spacetime at short distances, in “Spectral Dimension of the Universe in Quantum Gravity at a Lifshitz Point.”

This exchange between theoretical high energy physicists and condensed matter physicists goes both ways. The work of string theorists is no longer too exotic for condensed matter systems. It turns out that quantum gravity is a new tool that can help solve difficult problems of condensed matter theory itself!

Maybe, just maybe, what we’ll learn from this is that gravity and non-relativistic quantum theory are not quite as irreconcilable as we once assumed and that the researchers who study them have more in common and more reason to interact than ever before.

Hořava is the organizer of an upcoming conference, “Gravity at the Lifshitz Point,” at the Perimeter Institute in Ontario, Canada on November 8-9, 2009. For more information:



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