It would be frightfully cold.

1) "Absolute zero describes a theoretical system that neither emits nor absorbs energy. The Absolute zero temperature is known to be 0 K (–273.15 °C). It is the point at which particles have a minimum energy, determined by quantum mechanical effects, which is called the zero-point energy. By international agreement, absolute zero is defined as precisely 0 K on the Kelvin scale, which is a thermodynamic (absolute) temperature scale, and –273.15 °C on the Celsius scale" "It is not possible to cool any substance to 0 K, but scientists have made great advancements in achieving temperatures close to absolute zero, where matter exhibits odd quantum effects such as superconductivity and superfluidity. In 2003, researchers at MIT achieved a record low of 450 pK (0.45 nK)." "It can be shown from the laws of thermodynamics that absolute zero can never be achieved artificially, though it is possible to reach temperatures close to it through the use of cryocoolers. This is the same principle that ensures no machine can be 100% efficient. At very low temperatures in the vicinity of absolute zero, matter exhibits many unusual properties including superconductivity, superfluidity, and Bose-Einstein condensation. In order to study such phenomena, scientists have worked to obtain ever lower temperatures." Source and further information: http://en.wikipedia.org/wiki/Absolute_zero 2) Temperature of one particular degree of freedom: "As of November 2000, nuclear spin temperatures below 100 pK were reported for an experiment at the Helsinki University of Technology's Low Temperature Lab. However, this was the temperature of one particular degree of freedom — a quantum property called nuclear spin — not the overall average thermodynamic temperature for all possible degrees of freedom" Source: http://en.wikipedia.org/wiki/Absolute_zero 3) Negative absolute temperature: "Certain semi-isolated systems (for example a system of non-interacting spins in a magnetic field) can achieve negative temperatures; however, they are not actually colder than absolute zero. They can be however thought of as "hotter than T=∞", as energy will flow from a negative temperature system to any other system with positive temperature upon contact." Source: http://en.wikipedia.org/wiki/Absolute_zero "a system with a truly negative temperature is not colder than absolute zero; in fact, temperatures colder than absolute zero are impossible. Rather, a system with a negative temperature is hotter than the same system with an infinite temperature." "Negative temperatures can only exist in a system where there are a limited number of energy states (see below). As the temperature is increased on such a system, particles move into higher and higher energy states, and as the temperature becomes infinite, the number of particles in the lower energy states and in the higher energy states becomes equal. (This is a consequence of the definition of temperature in statistical mechanics for systems with limited states.) By injecting energy into these systems in the right fashion, it is possible to create a system in which there are more particles in the higher energy states than in the lower ones. This situation can be characterised as having a negative temperature. A substance with a negative temperature is not colder than absolute zero, but rather it is hotter than infinite temperature. As Kittel and Kroemer (p.462) put it, "The temperature scale from cold to hot runs +0 K, . . . , +300 K, . . . , +∞ K, −∞ K, . . . , −300 K, . . . , −0 K."" Source: http://en.wikipedia.org/wiki/Negative_temperature

Using P1V1/T1 = P2V2/T2, in theory, gases would have zero volume but in reality the above equation is shown to be only an approximation that doesn't hold at low temperatures, where other things come into play (eg the gas turning into a solid for starters)