Physicists have used a laser to cool molecules down to a record low temperature, breaking a barrier that seemed almost impassable, which could shed light on how atoms are bound together in molecules. By firing a laser tuned to a particular frequency at atoms confined in a space by a magnetic field, called a magneto-optical trap, researchers from The Centre for Cold Matter at Imperial College London were able to cool molecules of calcium monofluoride down to temperatures of just 50 trillionths of a kelvin, or 0.00000000005 degrees Celsius above absolute zero — minus 273.15 degrees Celsius. Referred as Doppler cooling, atoms that move into the laser at a given velocity absorb a photo of light, bumping one of its electrons to a new energy level, which then emits a photon in a random direction when it comes back down. The process results in an overall decrease in momentum for the atoms, which slows down leading to cooling. To find out more check out Laser Cooling Molecules.