Like all of my predecessors have mentioned, I feel a need to point out that absolute zero is in fact -273.15 degrees Celsius, -459.67 degrees Fahrenheit, or zero degrees Kelvin. It is the theoretical temperature which matter ceases to move and all energy is robbed from this particular particle. It is considered the lowest possible temperature, which gives it the name “absolute” zero.
Understandably, such a temperature has never been achieved, and possibly never will be achieved. Consider this case; an object has been converted to zero degrees Kelvin, now we would attempt to measure this object’s temperature to confirm this. But how? Would we put a thermometer in it and measure the temperature? But the heat energy would transfer from the thermometer to the object, and it would no longer be at the temperature of absolute zero. Maybe we should freeze the thermometer to absolute zero before measuring the object? Well, when I say all energy in robbed, I mean absolutely all energy including electrical energy, which runs the thermometer; or if this thermometer is less sophisticated mercury/ (any other possible fluid) thermometer, the fluid on which this thermometer operates would cease motion and thus be rendered useless.
Going into even higher sophistication, maybe a thermal camera, which would not need to even contact the object, might work? Nope. To measure the temperature of an object, that object has to emit black body radiation, and of course, an object at absolute zero has no energy to emit. In fact, we can not even shine a light, or any other energy, at the object because that would add energy to the object and increase its temperature. Of course, that’s after achieving absolute zero, but even to achieve this temperature is an impossibility. Although it is possible to reach temperatures close to it through the use of cryocoolers, and laser cooling can be used to cool temperatures to within a billionth of a degree of absolute zero, it can be shown from the laws of thermodynamics that absolute zero can never be achieved artificially. [Thus, there is no way, to the best of our knowledge, that an object at absolute zero can ever be achieved or ever be measured and confirmed.
So if that’s true, how can we claim that such state of no energy exists, and how is it -273.15 Celsius? As far back as 1702, a physicist by the name of Guillaume Amontons predicted that this “absolute zero” is at -240 degrees Celsius using an air thermometer, which was later improved by Johann Heinrich Lambert to -270 degree. But this had not been commonly accepted at the time, more absurd numbers ranging from -600 degrees all the way to -3000 degrees Celsius was predicted. It was not until Lord Kelvin after whom the Kelvin scale was named that an accurate and acceptable value was reached. Using solely the laws of thermodynamics, he predicted that absolute zero is at -273.15 degrees Celsius.
So what does this all mean? Not much, unless of course if you are a scientist, or anybody particularly interested in this field of science. But it should be noted that absolute zero is a value from which some very important mathematical and scientific theories are derived.