Robert Boyle pioneered the idea of an absolute zero. The zero point of any thermodynamic temperature scale, such as Kelvin or Rankine, is set at absolute zero. By international agreement, absolute zero is defined as 0K on the Kelvin scale and as −273.15° on the Celsius scale. This equates to 0 R on the Rankine scale. Scientists have achieved temperatures very close to absolute zero, where matter exhibits quantum effects such as superconductivity and superfluidity.
When an object is heated, its atoms can move with different levels of energy, from low to high. With positive temperatures (blue), atoms more likely occupy low-energy states than high-energy states, while the opposite is true for negative temperatures (red).