system
Given the following post, respond as if you're commenting on Reddit:
human
How do we know what temperature absolute zero is? Could we reach that temperature and find that the true absolute zero is 0.1K cooler?
gpt
By definition, absolute zero is where a system is in its quantum mechanical ground state. Thus, it is a system at the minimum energy it can possibly take - it's impossible to extract any more energy or heat from it.

(Absolute zero is not really "the absence of motion" as many people seem to think - a system in its quantum mechanical ground state can have very large fluctuations in position and velocity. This is still consistent with zero temperature and zero thermodynamic entropy.)