The first desktop model of the Big Bang reportedly showed why time travel doesn’t work. But a new look suggests time travel may be possible after all, at least on the lab bench.

In April, electrical engineers Igor Smolyaninov and Yu-Ju Hung of the University of Maryland announced that their model Big Bang, made from metamaterials that moved light just as particles move through mathematical representations of space and time, suggested time travel’s impossibility.

Light couldn’t be steered in a circle, they said. Therefore particles couldn’t loop back to the space-time point where they began. So much for time travel.

But physicist Ulf Leonhardt of the University of St Andrews in Scotland disagrees. “They considered the wrong polarization,” he said. “Making a loop in space is perfectly possible in their model. Therefore, for this model, time travel is possible.”

The discrepancy comes down to the direction in which the light waves wiggle. Light can be broken into two fields, electric and magnetic. These lie at right angles to each other and to the direction in which light is traveling. In the model Big Bang, the electric field has to point upwards from the plane of the metamaterial, or the analogy to space-time falls apart.

According to Leonhardt, the equations used by Smolyaninov are valid when the magnetic field — not the electric field — points upwards. Make the necessary correction, and the barrier to creating time-like loops in the metamaterial disappears.

“That doesn’t mean that real time travel is possible,” he said. “But for this analog model, it is so.”

Smolyaninov stands by his original conclusion, noting that only certain kinds of light can propagate through the model Big Bang in the first place.

“You could create a different physical system, maybe [time travel] would be possible in another model,” he said. “But not in this one.”

Image: Igor Smolyaninov

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