Kelvin is an absolute measurement of temperature meaning it starts at absolute zero, the lowest possible temperature in our universe. Absolute zero is 0 Kelvin(K) or -273.15 degrees Celsius(°C). The Kelvin scale is based on the average kinetic energy of particles in a substance. You cannot have a negative Kelvin value because at 0K there is no kinetic energy in the particles and are at their lowest possible state of motion. It is impossible for a system to have less energy than zero. Negative Kelvin would imply that a system has a negative thermal energy which breaks the principles of thermodynamics. It is important to remember that negative temperatures exist in other temperature scales such as the Celsius and Fahrenheit.