Sitting on a bench at the University of Maryland is the first-ever desktop model of the Big Bang.

Don't worry, the 20-micrometre-wide device simulates how light behaved and time flowed at the universe's spark, not the explosion itself. It could someday help explain why time marches in only one direction.

"What we have done, with simple experimental geometry, is reconstruct the way that space-time expands," said  Igor Smolyaninov, who describes the model in a paper submitted to Physical Review Letters.

Smolyaninov and Yu-Ju Hung, both electrical engineers at the University of Maryland, made their Big Bang simulation from exotic substances called metamaterials, which use alternating slices of different materials to twist light in unusual ways.

Researchers have suggested using metamaterials as  invisibility cloaks that bend light around objects, to disguise one object as another and to build a perfect lens. A few years ago, physicists realised that metamaterials can also mimic astronomical events: a planet orbiting a star, light being trapped in  black holes.

Building a toy cosmos in the lab lets physicists run otherwise impossible experiments on the nature of space and time. With Smolyaninov and Hung's setup, researchers could study the thermodynamic arrow of time, a long-standing problem in physics.

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