(a) A closed timelike curve, in which p2 is a chronology-respecting system, and p1 is a time-traveling system that can jump from point tA to the past point tB through a spacetime wormhole, has the ability to interact with itself in the past. (b) In an open timelike curve (OTC), the system cannot interact with itself in the past. In the new study, physicists have theoretically shown that OTCs can violate Heisenberg’s uncertainty principle, provided p1 is entangled with p2. This proposal could be tested by performing experiments on entangled systems in Earth’s gravitational field. Credit: J. L. Pienaar, et al. ©2013 American Physical Society

Curves in spacetime violate Heisenberg’s uncertainty principle

February 19, 2013 by Lisa Zyga

(Phys.org)—If an object traveling through spacetime can loop back in time in a certain way, then its trajectory can allow a pair of its components to be measured with perfect accuracy, violating Heisenberg’s uncertainty principle. This new finding involves a particular trajectory called an open timelike curve (OTC), which is a special case of a closed timelike curve (CTC), a theoretical concept that has previously provoked controversy because it raises the possibility of traveling backwards in time.

According to Heisenberg’s uncertainty principle, measurements of any pair of variables must have at least a minimum amount of error. The most well-known example of the pair of variables is position and momentum, but the principle applies to any two variables that have a mathematical relationship which makes them conjugate variables. The uncertainty principle is thought to be an inherent property of quantum systems due to their wave-particle duality, rather than any observational limitations. Although previous studies have found that CTC models can theoretically violate the uncertainty principle, nobody knew that this could happen for the special case of an OTC.

Now, physicists Jacques Pienaar, Tim Ralph, and Casey Myers at The University of Queensland in Australia have theoretically shown that OTCs can allow scientists to measure a pair of conjugate variables of a quantum state to an arbitrary degree of accuracy forbidden by the uncertainty principle. The finding could have implications for quantum gravity and change the way that scientists view quantum uncertainty.

“There is some speculation that the Heisenberg uncertainty principle might be different in a future theory of quantum gravity,” Pienaar told Phys.org. “However, most of these studies suggest that quantum gravity will introduce more uncertainty. Our model suggests the complete opposite: that a theory of quantum gravity might actually remove the uncertainty of quantum mechanics.”

Read more: Curves in spacetime violate Heisenberg's uncertainty principle — phys.org.

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