What is the empiric reason behind the assumption that there is lowest thermodynamic temperature (absolute zero)? And that all other temperatures of bodies in thermodynamic equilibrium are always higher ? I am looking for a reason not using the entropy concept, as the entropy was derived historically with the assumption that there is lowest temperature which ideal gas can have. So the argument using entropy would be circular. Or do you think that entropy is more fundamental than temperature and positive thermodynamic temperature is a just a consequence the properties of entropy ?