In the Beginning was Information

For some laws of nature the direction does not play any role (e. g.energy), but for others the process is unidirectional like a one-waystreet. In the latter case one can clearly distinguish between pastand future. In all cases where friction is involved, the processes areirreversible; they proceed in one direction only. Examples of suchlaws are the law of entropy (see the Appendix), the chemicalprinciple of Le Chatelier (Henry Le Chatelier, French chemist,1850 – 1936; see Q20 pp. 128-130), and the law of mass action.Impossibility theorems: Most laws of nature can be expressed inthe form: “It is impossible that ...” The energy law for example, canbe stated as follows: “It is impossible that energy can come intoexistence by itself.” R. Clausius formulated the second law of thermodynamicsas an impossibility: “Heat cannot of itself pass from acolder to a hotter body” The impossibility theorems are very useful,because they effectively distinguish between possible and impossibleevents. This type of scientific formulation will be encounteredfrequently when we come to the information theorems.Geometrical impossibilities can also be devised. Three differentgeometric representations appear in Figure 6, but such bodies arejust as impossible to construct as it is to expect results that are precludedby laws of nature.Laws which describe processes: If the future (prognosis) or thepast (retrognosis) states of a system can be described when the valuesof the relevant variables are known for at least one moment intime, such a formulation is known as a process law. A typical physicalexample is the description of radio-active decay.Co-existence laws: These describe the simultaneous existence ofthe properties of a system. The formula describing the statechanges of an ideal gas, p x v = R x T, is a typical physical coexistencelaw. The values of the three quantities, pressure p, specificvolume v, and absolute temperature T, comprise a completedescription of the “state” of an ideal gas. This means that it doesnot depend on the previous history of the gas, and neither doesit depend on the way the present pressure or the present volumehas been obtained. Quantities of this type are known as state variables.38