Observing the relationship between temperature and atomic molecular motion, physicists are able to calculate the temperature at which atomic molecular motion comes to a stop. This temperature is known as absolute zero. It is -273 degrees Celsius or -459.67 degrees Fahrenheit. Since temperature is a function of atomic molecular motion and such motion has come to a complete stop, it is impossible to have a temperature that is below absolute zero. For further information see the site below and post questions.