If you want to hear something very quiet, you need to reduce the ambient volume of your surroundings. For quantum physicists, though, that meant creating the world's quietest gas.
That's exactly what a team from the University of California, Berkeley, has done, cooling a gas to a billionth of a degree above absolute zero. It's not the coldest temperature ever recorded, but their setup does result in the lowest entropy ever measured — another way of saying that it's the quietest state ever achieved.
The gas, known as a Bose-Einstein condensate, consists of about a million rubidium atoms that are trapped by a beam of light, isolated in a vacuum and cooled down to their lowest energy state. In turn, that gives rise to the lowest entropy gas ever created. "Temperature generates something like a constant rumble of sound in the gas, and the entropy is like a count of how many sound-wave excitations remain," Dan Stamper-Kurn, one of the researchers, told PhysOrg. "The colder a gas becomes, the less entropy it has and the quieter it is." The research is published in Nature Physics.
Of course, it's not just been made for the sake of it: this ultra-low entropy system will allow scientists to understand how the quantum world works better. In particular, they expect to be able to use it to understand how quantum magnets and high-temperature superconductors work. "When all is quiet and all is still," mused Stamper-Kurn to PhysOrg, "one might discern the subtle music of many-body quantum mechanics."
Picture: Guian Bolisay/Flickr