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"It raced so fast the pulse exited a specially-prepared chamber before it even finished entering it."

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For the experiment, the researchers manipulated a vapour of laser-irradiated atoms that boost the speed of light waves causing a pulse that shoots through the vapour about 300 times faster than it would take the pulse to go the same distance in a vacuum.

Light travels slower in any medium more dense than a vacuum, which has no density at all. For example, light travelling through glass slows to two-thirds its speed in a vacuum. If the glass is altered, the light can be slowed even further.

The NEC team produced the opposite effect. Inside a chamber, they changed the state of a vapour in a way that light travelling through it would travel faster than normal.

When the pulse of light travelled through the vapour, the pulse reconfigured as some component waves stretched and others compressed. As the waves approached the end of the chamber, they recombined, forming the original pulse.

The key to the experiment was that the pulse reformed before it could have gotten there by simply travelling through empty space. This means that, when the waves of the light distorted, the pulse traveled forward in time.

The NEC researchers published their results in this week's issue of the journal Nature.

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