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鈥檚 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鈥檚 a problem: Einstein鈥檚 wormholes are notoriously unstable, and they don鈥檛 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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Quantum mechanics tells us that the vacuum of space-time is teeming with random quantum fluctuations, which create waves of energy. Now imagine two metal plates sitting parallel in this vacuum. Some energy waves are too big to fit between the plates, so the amount of energy between them is less than that surrounding them. In other words, space-time between the plates has negative energy.
Slow collapse
Theoretical attempts to use such plates to keep wormholes open have so far proved untenable. Now at the University of Cambridge may have found a solution.
鈥淲hat if the wormhole itself could take the place of the plates?鈥� he says. In other words, under the right circumstances, could the tube-like shape of the wormhole itself generate Casimir energy? His calculations show that if the wormhole鈥檚 throat is orders of magnitude longer then the width of its mouth, it does indeed create Casimir energy at its centre.
鈥淯nfortunately, this energy isn鈥檛 enough to keep the wormhole stable. It will collapse,鈥� says Butcher. 鈥淏ut the existence of negative energy does allow the wormhole to collapse very slowly.鈥� Further rough calculations show that the wormhole鈥檚 centre might remain open long enough to allow a pulse of light to get through.
A wormhole is a shortcut through space-time, so sending a light pulse through one could allow faster-than-light communication. And as the two mouths of a wormhole can exist at different points in time, in theory a message could be sent through time.
Butcher cautions that a lot more work is needed to confirm that other parts of the wormhole besides the centre remain open long enough for light to make it all the way through. He also needs to work out whether a pulse large enough to transmit meaningful information could sneak through the slowly collapsing throat. And, of course, we are a long way off translating the theoretical equations into a physical object.
鈥淒oes this mean we have the technology for building a wormhole?鈥� asks Matt Visser at the Victoria University of Wellington in New Zealand. 鈥淭he answer is still no.鈥� Still, he is intrigued by Butcher鈥檚 work. 鈥淔rom a physics perspective, it may revitalise interest in wormholes.鈥�
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