Science News - May 7, 2011

some of the largest detectors in the world: the gravitational wave detectors of the LIGO project, built to search for gentle ripples in spacetime thought to be produced by (among other cosmic events) colliding black holes.

Chasing ever greater sensitivities, these researchers use lasers to still the vibrations of their detectors’ giant mirrors — the behemoths of the optomechanical world, weighing in at more than 10 kilograms. Despite their immense size, these mirrors have now been cooled to 234 quanta, MIT quantum physicist Nergis Mavalvala and LIGO colleagues reported in 2009 in the New Journal of Physics. “Our challenges are really the same as everyone else’s, but we need to somehow cool our gram and kilo-gram-sized objects to nanokelvins,” says Mavalvala.

Working on another gravitational wave detector called AURIGA, researchers in Italy set the record for largest object effectively cooled via optomechanics. An aluminum bar weighing more than 1 ton reached a mere 4,000 quanta, the team reported in Physical Review Letters in 2008.

Whether such large mirrors and bars could ever demonstrate quantum effects, though, is an open question. In principle, some physicists say, quantum mechanics should hold for objects of any size. “We don’t know of any fundamental limit,” Harris says.

Practical considerations may ultimately limit the size of quantum objects, though. Any observation, be it by a pair of eyes or a stray, colliding air molecule, can destroy a quantum state. The larger an object is, the harder it is to keep isolated. But that isn’t stopping researchers with bigger objects from lining up behind Cleland and the NIST team to stretch the bounds on quantum effects.

“If we can prove that quantum mechanics holds for larger and larger objects, that would be quite spectacular,” says Dirk Bouwmeester of UC Santa Barbara. “But it would also be spectacular if we can prove that it doesn’t. New theo-ries would be needed.”

1619 Johannes kepler suggests that the pressure of sunlight explains why comets’ tails (above) always appear to point away from the sun.

suggesting that the mill spins because of the pressure of light. scientists now understand that the heat transferred by light is responsible for the mill’s spinning.

Early pushes interest in the pressure exerted by light goes back centuries.

1746 leonhard euler shows theoreti cally that the motion of a longitudinal wave might produce pressure in the direction it is propagating.

1873 James clerk Maxwell (above) uses electromagnetic theory to show that light reflecting off a surface or absorbing into it would create pres sure. bright sunlight, he calculates, would press on the earth with a force of about 4 pounds per square mile.

1873 that same year, sir william crookes invents the radiometer, or light mill (above), incorrectly

1876 adolfo bartoli, unaware of Maxwell’s work, infers radiation pressure’s existence from the second law of thermodynamics.

1900 russian physicist pyotr lebedev announces at a meeting in paris that he had measured the pressure of light on a solid body.

1903 ernest fox nichols and gordon ferrie hull measure the pres sure to an accuracy within less than 1 percent, publishing the work in the Astrophysical Journal.

One of the slowest tortoises in the race, Bouwmeester’s pace is deliberate. His mirrors, tens of micrometers across, vibrate a mere 10,000 or so times per second and promise an extended quantum lifetime. This durability, he says, is needed to test a controversial idea that gravity and quantum weirdness can’t coexist for long at everyday scales.

More than three-quarters of a century
of research has made scientists more
comfortable with quantum mechanics
at small scales, but supersizing it can
seem as bizarre today as it did to Erwin
Schrödinger. In 1935, he poked fun at the
idea in his famous thought experiment:
a cat in a box that could be both alive
and dead at the same time, as long as no
one peeked inside the box and forced a
choice, killing with curiosity.