Desktop cosmos: Small is beautiful for big physics - physics-math - 23 June 2010 - New Scientist

Desktop cosmos: Small is beautiful for big physics - physics-math - 23 June 2010 - New Scientist

IN THE control centre on the Hanford Nuclear Reservation in Washington state, banks of plasma screens await a signal that might never come. Hope springs from two concrete tubes that stretch out at right angles from the control centre and extend 4 kilometres towards the horizon. Inside them, laser beams ping relentlessly back and forth. The site is one of two that make up the Laser Interferometer Gravitational-Wave Observatory, LIGO, the largest experiment so far for spying the ripples in space-time known as gravitational waves.

Off the coast of west Africa, perched on the highest point of the Canary Islands, a gamma-ray telescope called MAGIC - the name stands for the Major Atmospheric Gamma-ray Imaging Cherenkov telescope - scans the heavens for bursts of high-energy photons from far corners of the universe. Every now and again it catches a fleeting glimpse of something. Seconds, perhaps, of activity are followed by silence again.

Back in the US, meanwhile, teams work flat out on plans for a $650 million space probe called the Joint Dark Energy Mission. It is just the latest and most ambitious bid to study how the universe is expanding and tell us what the vast bulk of the cosmos is made of.

These are just three of many experiments that could deliver breakthroughs in our understanding of nature's most enigmatic force, gravity. If so, they will do it in the traditional way of big physics, with large collaborations and hefty bank balances. But that might not be the only way. If ideas being explored by a good few physicists are right, quantum gravity and dark energy could all be laid bare on the bench-top by the strange dances of atoms cooled to within a nudge of absolute zero.

Familiar yet unfathomable, gravity is a perennial tease. Its quiet muscularity binds stars and galaxies together, steadies Earth on its trek around the sun, and keeps our feet firmly on the ground. According to our current theory of gravity, Einstein's general relativity, all this is down to massive objects warping space and time and so making things slide towards them.

There are a few wrinkles to this explanation: for example, the failure of instruments such as LIGO to spot gravitational waves despite general relativity indicating that accelerating cosmic bodies should be producing them. Yet overall the theory seems solid. No experiment has delivered a result in disagreement with general relativity's predictions.

But still many physicists are unsatisfied. For them it is profoundly unsettling that general relativity is not a quantum theory, unlike the theories that describe the other three forces of nature. Add to that the observation that the cosmos seems to be expanding ever faster - something hard to explain if gravity does indeed dominate the universe - and it is clear why we feel we have much still to learn