Absolute zero is not at 0 degrees Celsius because Celsius is a temperature scale that is based on the properties of water. The Celsius scale sets the freezing point of water at 0 degrees and the boiling point at 100 degrees at standard atmospheric pressure. However, the concept of absolute zero is based on the behavior of atoms and molecules.
Absolute zero is defined as the lowest possible temperature that can theoretically be achieved, where the thermal motion of atoms and molecules reaches its minimum. It is the point at which the particles have the least amount of kinetic energy. In the Kelvin temperature scale, absolute zero is designated as 0 Kelvin (0 K).
The Celsius scale and the Kelvin scale are related, and their numerical values differ by a constant offset. To convert between the two scales, you add or subtract 273.15. Therefore, absolute zero on the Celsius scale is -273.15 degrees Celsius. At absolute zero, there is no molecular or atomic motion, and all thermal energy has been removed from a system.
In summary, absolute zero is not at 0 degrees Celsius because the Celsius scale is based on the freezing and boiling points of water, while absolute zero is a theoretical temperature at which molecular and atomic motion ceases.