By Marcus Chown QUANTUM theory may be losing its mystery. A physicist has shown how the bizarre behaviour of the quantum world could arise from time warps that are created as particles interact. Myriad strange things happen in the quantum world. For instance, the properties of a subatomic particle, such as its position and momentum, hover in fuzzy superpositions of various states until the moment they are measured, at which point they become certain. But why does a measurement have this effect? Physicists have come up with many speculative ideas, for instance, that the transition from uncertainty to certainty somehow arises out of the interaction of the particle with a measuring instrument, or even with human consciousness itself. Mark Hadley, a physicist at the University of Warwick, claims he has cracked the puzzle by drawing on Einstein’s suggestion that particles might be tiny warps in space. Hadley has developed this idea, treating particles as warps or kinks in space-time called “geons”. Inside a geon, time could loop back on itself, allowing a particle to be influenced by events in its future as well as its past. In earlier work, Hadley has shown how this could lead directly to all quantum weirdness—from the strange indeterminacy of properties like a particle’s position and momentum to the ghostly link between particles that are separated by large distances (“All the world’s a time machine”, New Scientist, 7 March 1998, p 38). Now Hadley says he has shown that the interaction of one geon with another can constitute a quantum measurement. In a forthcoming issue of the International Journal of Theoretical Physics, he points out that such an interaction must involve a change in the shape, or topology, of space-time. For instance, when a particle and its antimatter counterpart come together and annihilate to leave no particles, space-time containing two knots transforms into space-time that is flat. Such changes would create the time loops needed to generate strange quantum effects. Imagine a circle of space-time distorting to become two circles. When this occurs, a timeline inevitably loops back on itself (see Diagram). “Measurement is simply an abrupt change in the topology of space-time,” Hadley concludes. “The peculiar thing that happens to time when particles interact is exactly what is needed to create all quantum weirdness.” “Hadley’s work is quite a nifty way to show how weird and wacky things in quantum measurement theory can be explained in a classical context,” comments Jonas Mureika, a physicist at the University of Toronto. But he urges caution when playing games with time. “My question is: where does one draw the line? If the direction of time can change on a quantum scale, why can’t it change in the large-scale Universe?