Theorists Bridge Space-Time Rips Framework Offers Starting Point to Explaining How Particles Cope with Fluctuations in Gravity

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PHYSICS Theorists bridge space-time rips Framework offers starting point to explaining how particles cope with fluctuations in gravity.

BY EUGENIE SAMUEL REICH University in New York. “It’s inspiring how far Al Shapere at the University of Kentucky in they can go with no fancy machinery.” Lexington, a co-author on the paper, adding ould an analysis based on relatively Wilczek and his co-authors set up a hypo- that, like a magician’s rings, the transforma- simple calculations point the way to thetical system with a single quantum particle tion is impossible to visualize, but does make reconciling the two most successful — moving along a wire that abruptly splits into mathematical sense. Cand stubbornly distinct — branches of modern two. The stripped-down scenario is effectively The desire to escape the mathematical head- theoretical physics? Frank Wilczek and his the one-dimensional version of an encounter aches caused by such transformations is one collaborators hope so. motivation for string theory, which allows The task of aligning quantum mechanics, smooth changes in the topology of space-time, which deals with the behaviour of fundamen- says Greene. He suggests that the approach tal particles, with Einstein’s general theory of developed by Wilczek, Shapere and MIT relativity, which describes gravity in terms of undergraduate student Zhaoxi Xiong could curved space-time, has proved an enormous be applied within string theory too. challenge. One of the difficulties is that neither Although Wilczek originally believed that J. HERRERO/EPA/CORBIS is adequate to describe what happens to parti- the result was new, a 1995 paper by Aiyalam cles when the space-time they occupy under- Balachandran of Syracuse University in New goes drastic changes — such as those thought York proposed a similar strategy for describ- to occur at the birth of a black hole. But in a ing changes in topology in quantum mechan- paper posted to the arXiv preprint server on ics (A. P. Balachandran et al. Nucl. Phys. B 446, 15 October (A. D. Shapere et al. http://arxiv.org/ 299–314; 1995). Balachandran acknowledges abs/1210.3545; 2012), three theoretical physi- that his work hasn’t hit the mainstream and cists present a straightforward way for quantum says that he hopes Wilczek’s paper will prompt particles to move smoothly from one kind of others to take a closer look. “Conventional ‘topological space’ to a very different one. approaches to this problem don’t get very far,” The analysis does not model gravity explic- he says. “This opens up a new technique.” itly, and so is not an attempt to formulate a The framework might also provide inspi- theory of ‘quantum gravity’ that brings general ration for experimentalists working on con- relativity and quantum mechanics under one densed matter. Rob Myers, a string theorist at umbrella. Instead, the authors, including Nobel the Perimeter Institute for Theoretical Phys- laureate Frank Wilczek of the Massachusetts ics in Waterloo, Canada, says that he expects Institute of Technology (MIT) in Cambridge, it to be relevant to an area called quantum suggest that their work might provide a simpli- Frank Wilczek studies how fundamental particles quenches, in which quantum systems evolve fied framework for understanding the effects of respond to drastic changes in space-time. in isolation from the environment and are then gravity on quantum particles, as well as describ- kicked out of equilibrium by an action of the ing other situations in which the spaces that with ripped space-time, which occurs when experimentalist. Condensed-matter physicists quantum particles move in can radically alter, the topology of a space changes radically. The have developed several quantum systems — such as in condensed-matter-physics experi- theorists concentrate on what happens at the including cold-atom traps and superconduct- ments. “I’m pretty excited,” says Wilczek, “We endpoints of the wire — setting the ‘boundary ing circuits — that can be used to test this idea. have to see how far we can push it.” conditions’ for the before and after states of Although the authors lay out their solution The idea is attracting attention not only the quantum wave associated with the parti- in only one dimension, Myers expects that the because of the scope of its possible applica- cle. They then show that the wave can evolve approach will readily generalize to describe real tions, but because it is based on undergrad- continuously without facing any disruptions experiments in three dimensions. But he cau- uate-level mathematics. “Their paper starts as the boundary conditions shift from one tions that the paper represents only a first step. with the most elementary framework,” says geometry to the other, incompatible one. “To really see the impact of this work, that will Brian Greene, a string theorist at Columbia “You can smoothly follow this process,” says take a while,” he says. ■

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