IMAGINE driving along a straight road full of potholes. Very likely, you will have to endure swerves and bumps to reach your destination. Something similar could be happening to light travelling through the vacuum of space: it surges ahead in places and takes diversions at others, because the fabric of space-time is thought to be 鈥渇oamy鈥� rather than smooth. Soon, the world鈥檚 largest telescopes could look for this effect, perhaps allowing us to glimpse the very nature of space-time for the first time.
Quantum theory says that at scales below 10-35 metres (known as the Planck scale), space-time is writhing with random fluctuations. Particles are constantly being created and destroyed, making space-time convoluted and foamy. So far detecting any such foaminess, and its effects, has remained well beyond our ability.
聯Particles are constantly being created and destroyed making space-time convoluted and foamy聰
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Now, cosmologists Jack Ng, Wayne Christiansen and Hendrik van Dam at the University of North Carolina in Chapel Hill think they know how to detect the foam鈥檚 effects. 鈥淟ight travelling from a very distant source in the universe, billions of light years away, must pass through space-time foam, if it exists, on its long journey to reach us, and those very tiny effects may gradually accumulate,鈥� says Christiansen. 鈥淭he incoming light should be slightly scattered by these space-time foam fluctuations, so that very distant sources will appear to be spread out into a small, fuzzy halo rather than a point.鈥�
The trio say that new instruments now being built could detect this 鈥� particularly the European Southern Observatory鈥檚 Very Large Telescope Interferometer (VLTI) on Mount Paranal, in Chile, once it is fully operational in a few years (Physical Review Letters, vol 96, p 051301).
The VLTI will work by combining light from two or three massive 8.2-metre telescopes and some smaller telescopes. Analysing the interference patterns created by combining light from two or more telescopes allows astronomers to resolve much finer detail than if they used a single telescope. The North Carolina team says that the instrument should also be able to pick up tiny corrugations in what would otherwise be a flat wavefront of light, caused by the space-time foam (see Graphic). 鈥淭he VLTI is key because it alone has the sensitivity and resolution to detect the tiny space-time fluctuations experienced by light over huge distances,鈥� Ng says.
聯The instrument should also be able to pick up the tiny corrugations caused by space-time foam聰
If the idea works, the VLTI could give physicists an insight into the fundamental structure of space-time and also point them to the correct theory of quantum gravity, which aims to unite quantum mechanics and general relativity to explain gravity at the small scales of the quantum world. So far, the Hubble Space Telescope has failed to see any fuzzy haloes around the images of very distant quasars, ruling out some popular theories of quantum foam. The VLTI鈥檚 increased sensitivity could help clarify this further, the researchers say.
Giovanni Amelino-Camelia, a cosmologist at the University of Rome La Sapienza in Italy and one of the pioneers in the study of quantum foam, has welcomed the research. 鈥淭he paper, of course, must still be digested by the community,鈥� he says. 鈥淏ut it certainly does have the smell of a major step forward for researchers hoping to test space-time foam models using interferometers.鈥�
Other astronomers are more cautious. 鈥淭his is an extremely interesting idea but it still has to be seen if these small effects can be distinguished from similar effects due to the turbulence of the Earth鈥檚 atmosphere,鈥� says Andreas Glindemann, the head of the VLTI. 鈥淗owever, it is intriguing to see that large interferometers are now within reach of tackling even cosmological questions.鈥�
