Some brief remarks are made on the relation between the ordering and dimensionality properties of time and the laws of physics. Time is defined as the ordinal of the set of photographs describing the configuration of the Universe associated with each collision of a test particle. This set of pictures is ordered by a parameter which appears in simple physical laws, and it is these laws which determine the ordering. Time is one-dimensional because these snapshots can be ordered with a (...) single parameter. The signature of space-time appears to be related to the measurement process. If there were no time dimension, there would probably be no physical laws, because there would seem to be nothing to predict: while if there were more than one timelike dimension, then the extra dimensions may be unobservable and so physically nonexistent. (shrink)

The meaning of the phrase “the direction of time” and the physical problems involved are considered. These problems are discussed and plausibility arguments are given to show that all clocks run in the same direction (almost always), that the most probable development of the Universe during the early stages of the expansion would result in the introduction of some internal organization, and that the expansion of the Universe and the increase in entropy define time directions that have the same sense. (...) The question of what properties of the laws governing the Universe lead to these results is studied. (shrink)

The term “frame of reference” is defined for both classical physics and quantum mechanics. The definition is the usual one, simply made explicit. It is used in the study of coherent superposition, and in particular the dependence on the observer (frame of reference) of the coherence of superposition of state vectors. This dependence is then used as the basis of an analysis of a criticism of previous work on the nonexistence of superselection rules. We again reach the conclusion that they (...) do not exist. (shrink)