Bose–Einstein condensate (BEC) is what happens to a dilute gas when it is made very cold, near absolute zero (0 K which equals −273.15 °C or −459.67 °F). It forms when the particles that make it up have very low energy. Only bosons can make a Bose–Einstein condensate. The gas has extremely low density, about one-hundred-thousandth the density of normal air.