What is the common name for the temperature 273 degrees below zero, centigrade (460 degrees below zero, Fahrenheit)?

Temperature is fundamentally a measure of the energy and motion of atoms. The faster particles vibrate, the hotter an object is. As an object cools, its particles slow down. This leads to a logical limit: a temperature so cold that all classical atomic motion ceases. This theoretical point, where particles possess the minimum possible energy, is known as absolute zero. It serves as the starting point for the Kelvin temperature scale (0 K), which is equivalent to -273.15 degrees Celsius or -459.67 degrees Fahrenheit.

While it's the lowest temperature theoretically possible, reaching absolute zero is considered impossible according to the laws of thermodynamics. Even the coldest, emptiest voids of deep space are not at absolute zero; the faint afterglow of the Big Bang keeps the universe at a background temperature of about 2.7 Kelvin. In specialized laboratories, scientists have gotten incredibly close—within a billionth of a degree—creating exotic states of matter and observing strange quantum effects that only appear at these extreme lows.