The Kelvin temperature scale is based on the properties of absolute zero, the lowest possible temperature in the universe. Absolute zero is defined as the point at which all molecular motion ceases, meaning that there is no thermal energy present. In the Kelvin scale, absolute zero is assigned the value of 0 Kelvin (0 K).
The Celsius scale, on the other hand, is based on the freezing and boiling points of water. In the Celsius scale, the freezing point of water is defined as 0 degrees Celsius, and the boiling point of water is defined as 100 degrees Celsius (under standard atmospheric conditions).
To convert between Celsius and Kelvin, you need to add or subtract 273.15. The value 273.15 was derived by taking the freezing point of water (0 degrees Celsius) and adding 273.15 to obtain the equivalent value in Kelvin.
So, 0 degrees Celsius is equal to 273.15 Kelvin, not exactly 273 Kelvin. This adjustment ensures that absolute zero is represented as 0 Kelvin on the Kelvin scale.
The Kelvin scale is designed to be an absolute temperature scale, where temperature is measured relative to absolute zero. It provides a meaningful way to express temperatures without negative values, as negative temperatures are not possible in the Kelvin scale.
In summary, the Kelvin temperature scale starts at absolute zero (0 Kelvin) to represent the absence of thermal energy, and the Celsius scale is shifted by 273.15 to align its zero point with absolute zero on the Kelvin scale.