The same goes for ‘hot’ and ‘cold’: there are no ‘hot’ or ‘cold’ things at a microscopic level but, when we put together a large number of microscopic constituents and describe them in terms of averages, then the notion of ‘heat’ appears: a hot body is a body where the average speed of single constituents is raised. We are able to understand the meaning of ‘up’ or ‘hot’ in certain situations: the presence of a nearby mass, or the fact that we are dealing only with average values of many molecules, and so on.
