Absolute Zero- The absolute floor in terms of temperature. Temperature is in some sense a measure of energy of a system. Because particles are always moving, and vibrating, they always have some energy. At Absolute Zero, the particles or objects would be completely devoid of energy. According to the Third Law of Thermodynamics, it is not possible to achieve absolute zero. In America, we predominantly measure temperatures using Farenheight, and the rest of the world using Celsius. Absolute Zero is accepted to be -459-67 Farenheight and -273.15 Celsius. There are two analog scales, Rydberg for Farenheight and Kelvin for Celsius, which keep the same gradation of degrees, such as 1 degree Farenheight is the same as 1 degree Rydberg, and 1 degree Kelvin is the same as 1 Degree Celsius. However, Rydberg and Kelvin both set their 0s to align with Absolute Zero, whereas 0 Celsius is aligned with the freezing point of water, and 0 Farenheight is aligned with absolutely nothing. (It's actually based on some really convoluted mixtures of ice water, brine, and other chemicals. I'm not sure what they were thinking)
Recently it has been proposed that some scientists have managed to create a temperature colder than absolute zero. The idea is that if you heat something up to an infinite temperature, it "swings around" and becomes a negative temperature. In doing so they have managed to come to a temperature lower than absolute zero. However, absolute zero at the time of this writing has as of yet been unachieved.
