Water can boil and freeze at the same time

Water can boil and freeze at the exact same time. This happens at its triple point, a precise temperature and pressure where solid, liquid, and gas coexist in equilibrium. For water that is 0.01°C and 0.006 atmospheres. In a vacuum chamber, if you hit that point, you see ice forming while bubbles boil off the same sample. It is why the triple point of water was used for decades to define the Kelvin temperature scale. It is a visible reminder that phases are not separate worlds, but balances of energy.