What is absolute zero?

Absolute zero is a temperature 273 degrees Celsius (459 degrees Fahrenheit) below freezing. Nothing can ever be colder than absolute zero, just as it is impossible to have less than no thickness. The colder something is the harder it is to cool it any further. This is the bottom of the scientific temperature scale, or zero degrees Kelvin. This way of measuring temperature is named after Lord William Kelvin who devised the theory behind the unit in the middle of the 19th century.