Absolute Zero Is Unreachable

Absolute zero (−273.15°C or 0 Kelvin) is the lowest possible temperature, the point where a system has as little thermal energy as it can. But reaching it is impossible because of quantum mechanics—there’s always some energy left, even in the coldest systems. One of the coldest temperatures ever achieved in a lab is 38 trillionths of a degree above absolute zero, inside a cloud of ultra-cooled atoms. At that temperature, matter starts behaving in strange, almost wave-like ways.