There is a very strong sense in which entropy is observer independent. For most evolving physical systems where it’s worth talking about entropy at all, observers that have bounded precision in their observations eventually agree on the entropy of the system “in equilibrium”. Those that have greater precision in their ability to observe just agree later.
Thermometers are generally extremely poor observers from this point of view, and so will tend to agree very quickly in theory. In practice this doesn’t even matter since they are subject to all sorts of sources of error and so don’t quite measure what temperature “really is”, but some approximation to it.
Thanks, the point about observers eventually agreeing makes sense. To make entropy really observer independent we’d have to have a notion of how precise we can be with measurements in principle. Maybe it’s less of a problem in quantum mechanics?
The phrase “in equilibrium” seems to be doing a lot of work here. This would make sense to me if there were general theorems saying that systems evolve towards equilibrium—there probably are?
There is a very strong sense in which entropy is observer independent. For most evolving physical systems where it’s worth talking about entropy at all, observers that have bounded precision in their observations eventually agree on the entropy of the system “in equilibrium”. Those that have greater precision in their ability to observe just agree later.
Thermometers are generally extremely poor observers from this point of view, and so will tend to agree very quickly in theory. In practice this doesn’t even matter since they are subject to all sorts of sources of error and so don’t quite measure what temperature “really is”, but some approximation to it.
Thanks, the point about observers eventually agreeing makes sense. To make entropy really observer independent we’d have to have a notion of how precise we can be with measurements in principle. Maybe it’s less of a problem in quantum mechanics?
The phrase “in equilibrium” seems to be doing a lot of work here. This would make sense to me if there were general theorems saying that systems evolve towards equilibrium—there probably are?