The Celsius and Fahrenheit temperature scales were established before the concept of absolute zero was fully understood. Let's explore the historical context and reasons why absolute zero is not used as the zero point for these scales:
Celsius Scale: The Celsius scale was developed by Anders Celsius in the early 18th century. Initially, Celsius used a reversed version of the scale, where 0 represented the boiling point of water and 100 represented the freezing point. Later, the scale was inverted to its current form, with 0 representing the freezing point and 100 representing the boiling point. This modification was made to align the Celsius scale with the newly introduced centigrade scale, which had 100 degrees between the freezing and boiling points of water.
Fahrenheit Scale: The Fahrenheit scale was invented by Daniel Gabriel Fahrenheit in the early 18th century. Fahrenheit originally used a zero point based on a mixture of ice, water, and salt, which was later revised to a zero point based on the freezing point of a brine solution. The scale was then calibrated using fixed reference points such as the freezing and boiling points of water.
At the time these scales were established, the concept of absolute zero as the lowest possible temperature was not yet known or fully understood. It was only in the 19th century that scientists began to investigate the behavior of gases at extremely low temperatures, eventually leading to the discovery of absolute zero as -273.15 degrees Celsius (0 Kelvin).
The Celsius and Fahrenheit scales were already widely used and established by the time the concept of absolute zero was defined. Changing the zero point of these scales to absolute zero would have required significant adjustments to temperature measurements across a range of disciplines and would have caused confusion and practical difficulties. Therefore, the decision was made to maintain the existing zero points on these scales. The Kelvin scale, on the other hand, directly uses absolute zero as its zero point, making it the appropriate scale for scientific applications involving extremely low temperatures.