Reports that researchers elicited a temperature “lower than absolute zero” might make one question the meaning of the word absolute. On Built on Facts, Matt Springer writes “temperature is a relationship between energy and entropy, and you can do some weird things to entropy and energy and get the formal definition of temperature to come out negative.” Usually collisions between atoms ensure that less than 50% of atoms in a sample are excited, no matter how much heat you add. But Springer analogizes “What if I start with a huge pile of ground-state atoms, and one by one I whack them with a hammer to get them excited and then throw my collection of excited atoms into a jar?” In this case, as more than 50% of the atoms are excited, physical equations yield a negative temperature. Chad Orzel explains that the smallest negative temperature (i.e. -.01 K) reflects the highest concentration of excited atoms, while larger negative temperatures (i.e. -100K) actually approach lukewarm. In his latest post, Chad Orzel breaks down the highly technical details of the researchers’ accomplishment.
Researchers at the Weizmann Institute of Science have fostered chemical reactions at “one hundredth of a degree above absolute zero,” analogous to conditions in interstellar space. By merging two parallel beams of ultra-cold atoms, scientists kept them sedated enough for quantum behavior. Chemical reactions “took place in peaks, at specific energies – a demonstration of the tunneling that occurs when quantum particles act as waves.” While quantum chemistry is new, physicists have been chilling individual atoms for years—thanks in part to the work of new Nobel laureate Dave Wineland. On Uncertain Principles, Chad Orzel explains that Wineland pioneered the use of lasers to reduce the kinetic energy of trapped ions. Orzel writes, “every time an atom or ion absorbs a photon of light, it gets a kick in the direction the laser was headed.” By only kicking ions when they are headed in the opposite direction, a laser can bring them close to a standstill. And a tip to the balding on Life Lines (with winter just around the corner): the sparse hair of elephants might “keep the animals cool as opposed to keeping them warm as it does for other mammals.” Research showed that with a little wind, elephant hairs “could improve heat loss by 5-20%.”