What is the value of absolute zero in kelvin?
This question is asking us to recall a numeric value. But first, let’s recall what absolute zero is conceptually. The lowest possible temperature that any object anywhere in the universe could ever have is absolute zero. This sounds kind of absurd. But to better understand it, remember that an object’s temperature basically measures the average kinetic energy of the atoms and molecules inside it. So, the more kinetic energy, the more atoms and molecules are moving around and bumping into each other, the higher the temperature. But at absolute zero, matter particles are at their lowest possible energy. And because particles at absolute zero can’t have less energy, it would be meaningless to have a temperature scale that measures anything below absolute zero. It’s just not physically possible.
Now, the kelvin temperature scale in particular is considered an absolute temperature scale, meaning it doesn’t have any negative values. This is in contrast to other temperature scales like Celsius and Fahrenheit. For instance, we might recall that absolute zero measures at negative 273 degrees Celsius or negative 459 degrees Fahrenheit. But because kelvin is an absolute temperature scale and thus doesn’t have any negative values, absolute zero is simply expressed as zero kelvin.
Now, remember all three of these ways of expressing absolute zero are valid. But in kelvin, the base SI unit of temperature, absolute zero is zero kelvin.