Like some bizarre form of optical fibre, a long, thin wormhole might let you send messages through time using pulses of light.
Predicted by Einstein's general theory of relativity, wormholes
are tunnels connecting two points in space-time. If something could traverse one, it would open up intriguing possibilities, such as time travel and instant communications.
But there's a problem: Einstein's wormholes are notoriously unstable, and they don't stay open long enough for anything to get through. In 1988, Kip Thorne at the California Institute of Technology and his colleagues speculated that wormholes could be kept open using a form of negative energy called Casimir energy.
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