Zeroth Law of Thermodynamics

The zeroth law of thermodynamics describes the fundamental behavior of the temperature of systems in thermal equilibrium [72]. If two given systems $ \mathcal{S}_1$ and $ \mathcal{S}_2$ are in thermal equilibrium with a third system $ \mathcal{S}_3$ , then, the system $ \mathcal{S}_1$ has also to be in thermal equilibrium with the system $ \mathcal{S}_2$ :

$\displaystyle \displaystyle{\left(\frac{\partial{{\sigma}}_1}{\partial{{U}}_1}\...
...\sigma}}_2}{\partial{{U}}_2}\right)}_{\stackrel{\scriptstyle{{N}}_2}{{{V}}_2}}.$ (2.26)

Thus, the zeroth law of thermodynamics describes the transitivity and the symmetry [60] of the equilibrium relationship [73]. According to the definition of the temperature $ \tau$ from (2.22), this law can be also expressed by their fundamental temperatures $ \tau_i$

$\displaystyle \tau_1 = \tau_3 \quad \wedge \quad \tau_2 = \tau_3 \quad\Rightarrow\quad \tau_1 = \tau_2,$ (2.27)

where $ \tau_i$ is proportional to $ T_i$ according to (2.23).

Stefan Holzer 2007-11-19