An interesting sidenote about this is that -273° C being absolute zero is a “coincidence” of using the freezing (0° C) and boiling point (100° C) of water.
Kelvins set absolute zero to 0 K, and uses the same increment scale as Celsius, so 273 K is the freezing point of water. Absolute zero in Fahrenheit is -459° F.
We could have easily created another scale like Celcius slided so freezing is “a trillion”, so absolute zero would be about negative “a trillion”. This makes the desparity seem less extreme between high and low temperatures. That scale just would be far less useful to our everyday lives.
Edit: Added ° symbol for C/F (Kelvin doesn’t use it)
While most answers so far here have been correct (at absolute zero, i.e. 0 K or roughly -273 C, a system has the minimum possible amount of energy in its molecules’ movement), there actually is a negative temperature (less than 0 K) in thermodynamics. This comes up when you define temperature not as the average energy of the particles of a body, but as the required heat (i.e. energy) transfer into a system to change its entropy. It is possible to have systems where the entropy decreases if you add any more energy, which means you have a negative absolute temperature. These systems contain _more_ energy than systems with a positive temperature, so in that sense a system with negative absolute temperature is _hotter_ than a system with positive temperature.
https://en.wikipedia.org/wiki/Negative_temperature
In order to reduce the temperature you have to remove heat, there is no such things as coldness in physics, only heat.
Quantum Physics is the answer to why there is such a limit to how cold an object can be. When you get closer to -273 K the movement of molecules reduce drastically. BUT, when you get bellow -272 K you can only reduce their movement so much, because every atom has a fundamental quantum vibration. Without that quantum vibration there would be no such thing as Hidrogen, Helium etc. The identity of these atoms is there thanks to their fundamental quantum vibration. Think of it as a color, you cannot tell that something which is red, is actually red unless they have that proprety. Therefore if you remove the color from that object you wouldnt identify its color. (I really hope I explained it decently well)
Therefore, not being able to completely cancel their vibration, there will always be some heat left.
Short answer: QUANTUM PHYSICS.
If the question is asking why there isn’t an even number of degrees between the lowest negative degree and the highest positive degree, I think the answer is humans.
First of all, the measurement of “degrees” is made by humans. So, the measurements are relative to humans. We “randomly” decided what degrees would measure, (frozen and boiling water), put 100 degrees between those two points (for Celsius anyway) and used that to compare to everything else.
Absolute zero happens to be closer to the range of degrees humans live in (the one measured by frozen and boiling water) so we can only go to -273. If we had a highest possible temperature (which I don’t know if we do… that’s a question for someone else), it would be entirely possible to make a measurement scale that had an even number of positive and negative degrees between absolute zero and the highest temperature. The only problem is the range of numbers would be completely different from the ones we customarily use. We would be in the negatives all the time I imagine.
Celsius was invented for describing standard conditions on earth for humans. Because it’s an *ad hoc* system based on the freezing and boiling points of water (0 and 100 degrees C) it will give odd sounding results when used for scientific purposes – same way Kelvin (which is scientific temperature where 0 really means 0) looks weird next to F and C readouts of the same temperature.
-273C is more just a way of understanding just how cold absolute zero is, same way describing the distance to mars in miles would show just how far it is, but light minutes and AU are better for understanding it.
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