See below.
Explanation:
The history of temperature measurement helps answer this. The Fahrenheit scale was developed first when a glassblower developed a technique for making uniform glass tubing, a requirement for a reliable thermometer. His discovery allowed him to take the lead in defing temperature. In an attempt to devise a system that would allow others in the world to calibrate their thermometers, he set the 0 point to ice water to whuich salt was added. It was the coldest and reliable method to allow scientist in Norway to set their thermometer to the same temperature as those in Japa, for example. He set the 100 F mark to the temperature of his armpit, again, based on the assumption that people (with armpits) could set their temperature to the same point. At the time, it was unknown just how low a temperature could go, so it was satisfactory to report - F temperatures, relative to salted ice water. Celsius was devloped based on using the freezing and boiling point of water, a more accurate method of calibration. [History note: Celsius originally set boiling to zero and freezing to 100, an odd choice that was soon overturned by the rest of the world.] Still, it was unknown just how low a temperature could go. So the concepture of zero as a measure of heat really wasn't scientifically coreect. There is still plenty of enegy at 0C. As technology improved, the idea, and point, at which a sytem has no heat as labelled "Absoute Zero." That turned out to be -273.15 C. It is cosidered the point at which atoms/molecules have the minimum allowed energy.
A new scale was devloped, Kelvin, that sets it's zero as absolute zero, -273.15C. This scale more accurately reflects the true temperature relationships. For example, if one raided the room temperature from 10 C to 20 C, is that doubling the enegy? No, it is only adding the additional fraction of the energy that was already present at 0 C. One can use the Kelvin scale to see the true increase: The temperature goes from 283.15 K to 293.15 K, which is clearly not a doubling. This is a serious barrier when trying to describe the behavior of materials such as gases. The gas laws relate temperature to pressure, volume, and number of moles. Charle's Law states that at constant pressure that the ratio of volume over the temperature remains a constant, k. V/T = k. Raise the temperature by 2X, and the volume will increase by 2X. This would make no sense on a temperature scale such as C or F, that rely on negative numbers or zero. (V/0) = undefined. (V/-50) also present a problem. The absolute nature of the Kelvin scale eliminates these problems. Although 0 is still allowed (absolute zero), it represents a boundary condition, not a nonsensical blip in the middle of a curve.
