For the first time, physicists have made light appear to move simultaneously forward and backward in time. The new technique could help scientists improve quantum computing and understand quantum gravity.
By splitting a photon, or packet of light, using a special optical crystal, two independent teams of physicists have achieved what they describe as a 'quantum time flip', in which a photon exists in both forward and backward time states.
The effect results from the convergence of two strange principles of quantum mechanics, the counterintuitive rules that govern the behavior of the very small. The first principle, quantum superposition, enables minuscule particles to exist in many different states, or different versions of themselves, at once, until they are observed. The second — charge, parity and time-reversal (CPT) symmetry — states that any system containing particles will obey the same physical laws even if the particles' charges, spatial coordinates and movements through time are flipped as if through a mirror.
By combining these two principles, the physicists produced a photon that appeared to simultaneously travel along and against the arrow of time. They published the results of their twin experiments Oct. 31 andNov. 2 on the preprint server arXiv, meaning the findings have yet to be peer-reviewed.
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