In daily life? Zero degree? It's just that the boundary is artificially set by the freezing temperature of water, just like the numbers we learned. Zero? There are infinitely many in the world. Zero? It must be an infinite negative number. In fact, from a physical point of view, temperature represents the speed of thermal motion of molecules or atoms in an object. Warm water is hotter than cold water, and cold water is hotter than ice. From the molecular microscopic point of view, water molecules in warm water move faster than those in cold water, and water molecules in cold water move faster than ice.
However, according to the observations of astronomers, there is a planetary nebula named: the boomerang Centauri nebula, which is 5000 light years away from the earth. The lowest temperature of the boomerang nebula is -272. 15 degrees Celsius! It is only one degree higher than absolute zero, which is the closest temperature detected by human beings and the lowest temperature detected by human beings in the universe. Microwave background radiation is the afterglow of the Big Bang.
Almost evenly distributed throughout the night sky, all directions are the same. The temperature is about 2.725K, only a little higher than absolute zero. But in 1995, astronomers observed? The boomerang nebula? At that time, they found that the nebula was absorbing microwave background radiation, indicating that its temperature was even lower. The nebula is expanding at a high speed. The high-speed movement of gas and the rapid expansion of volume lead to the extremely low temperature inside the nebula. Moreover, the boomerang nebula is far away from the star and cannot receive heat. The thermal radiation of the universe is blocked by the gas of the boomerang nebula, so the temperature of the boomerang nebula has been in a state of continuous decline, and it is impossible to heat up.