In the mechanical example, to declare that "dx" is not a geometric displacement because it ignores the dynamic relationship between displacement, force, and energy is not correct. Displacement, as a concept in geometry, does not require the concepts of energy and force for its definition, and so one might expect that entropy may not require the concepts of energy and temperature for its definition. The situation is not that simple, however. In classical thermodynamics, which is the study of thermodynamics from a purely empirical, or measurement point of view, thermodynamic entropy can "only" be measured by considering energy and temperature. Clausius' statement "dS= δQ/T", or, equivalently, when all other effective displacements are zero, "dS=dU/T", is the only way to actually measure thermodynamic entropy. It is only with the introduction of statistical mechanics, the viewpoint that a thermodynamic system consists of a collection of particles and which explains classical thermodynamics in terms of probability distributions, that the entropy can be considered separately from temperature and energy. This is expressed in Boltzmann's famous entropy formula "S=kB ln(W)". Here "kB" is Boltzmann's constant, and "W" is the number of equally probable microstates which yield a particular thermodynamic state, or macrostate.