To measure the record hottest temperature, scientists chilled potassium atoms to a few billionths above a set-point called absolute zero. Absolute zero is the theoretical lowest possible temperature and it is normally measured on a temperature scale called the Kelvin scale
(where it is zero on this scale, which is equivalent to −273.15° on the Celsius scale or -459.7° on the Fahrenheit scale).
According to the research note
, through the use of lasers and magnets, the researchers managed to get the atoms to jump to a high-energy state creating an atomic gas in the laboratory. The new creation was extremely hot because of the high energies of the particles.
However, the new temperature registered as a negative on the Kelvin temperature scale. The negative temperature on the Kelvin scale means that particles at high energies outnumber those at low energies. Negative temperature refers to temperatures that are expressed as negative numbers on the more familiar degrees Celsius or Fahrenheit scales
So, paradoxically, the magazine Wired
notes, the hottest temperature ever measured was actually recorded as a ‘negative’ temperature.
Although we tend to think of temperature in terms of something feeling hot or cold, temperature is a measure of the average energy of the particles in a sample. For example, each of the molecules buzzing around in a pot of boiling water has more energy on average than a sluggish water molecule within an ice cube.
To help with this puzzle, Business Insider
has attempted an explanation:
“To comprehend the negative temperatures scientists have now devised, one might think of temperature as existing on a scale that is actually a loop, not linear. Positive temperatures make up one part of the loop, while negative temperatures make up the other part. When temperatures go either below zero or above infinity on the positive region of this scale, they end up in negative territory.”
According to Nature
, scientists hope that the measurement will aid scientific understanding of quantum phenomena and further understanding about the way that energy works. The main focus of the next phase of the research will be with dark energy
, a force that is apparently causing the universe to expand at an accelerating rate.
The study was led by Ulrich Schneider at the Ludwig Maximilians University of Munich. The findings were published
in the journal Science
in January 2013. The reference is:
S. Braun et al. Negative Absolute Temperature for Motional Degrees of Freedom. Science. Vol. 339, January 4, 2013, p. 52