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We all make decisions, sometimes dozens in the course of a day. This paper is about what is involved in this activity. It's my contention that the ability to deliberate, to weigh different courses of action, and then to decide on one of them, is a distinctively human activity, or at least an activity which sets man and the higher animals apart from other creatures. It is as much decisio as ratio that constitutes the distinguishing mark of human beings. Homo may not always be rationalis, but he is always decidens.
The paper is about practical decision, although there is also another important kind of decision that I won't discuss, namely cognitive decision. The difference is roughly that which distinguishes the function of a jury from that of a judge, at least in jury trials. The jury's job is to arrive at an answer to the question: guilty or not guilty? This is a cognitive decision, a decision that, on the basis of the evidence, such-and-such is the case. The judge, apprized of the jury's cognitive decision, makes the practical decision to sentence the guilty party to 20 years. On some other occasion, I hope to be able to say something about cognitive decision, as well as about a third kind of decision named value decision.
Paul Davies's principal thesis is that although nothing rules out the possibility of life having originated on some other planet, the oldest forms of life on Earth consist of bacteria and other micro-organisms which eat unappetizing substances like sulphur and hydrogen sulphide and live in scalding volcanic jets four kilometres down at the bottom of the sea. Davies's overall thesis is that the division between living and non-living beings coincides with the introduction of informational software in the form of the genetic code. The hardware is the DNA and RNA molecules; the software is the encoded message they convey to the protein-making factories, which assemble proteins out of amino acid components. A difference between DNA-based information, and the analog information suggested in this chapter to be underlying development, is that the former, based on nucleotide sequences, is one-dimensional, whereas the latter can be three-dimensional or four-dimensional.
What fourth dimension of a four-dimensional space-time continuum. I propose to develop some of the commonly held implications of this view, and to show that they involve a contradiction. Hence whatever time is, it cannot be the thing corresponding to this particular theory.
A stranger runs out of a bank while I am sitting at the wheel of my car waiting for the lights to change; he jumps in beside me, points a gun at me, and says, “Drive me to St. Bruno.” This is Andre Gombay's example, from his excellent paper on duress. The question that interests Gombay and me is: Could I refrain from doing what the gunman asks?
Combining quantum mechanics with special relativity requires (i) that a spacetime representation of quantum states be found; (ii) that such states, represented as extended along equal-time hyperplanes, be invariant when transformed from one frame to another; and (iii) that collapses of states be instantaneous in every frame. These requirements are met using branching spacetime, in which probabilities of outcomes are represented by the numerical proportions of branches on which the outcomes occur. Quantum states of systems are then identified with the probability values, built into spacetime along spacelike hypersurfaces, of all possible outcomes of all possible tests to which the systems can be subjected.
Does time flow? It will be shown in this chapter that if the spacetime structure of the world has a certain branched dynamic form, then time flows. In addition to the flow and direction of time, two issues in quantum mechanics, those of non-locality and the definition of ‘measurement’, are shown to be illuminated by the hypothesis that the world has the spatio-temporal form described. I call the form the branched model, and the interpretation of quantum mechanics to which it gives rise I call the branched interpretation.
Objective time flow
The branched model is a four-dimensional spacetime model in the shape of a tree, each branch of which is a complete Minkowski manifold in which are located objects and events. The trunk represents the past, the first branch point is the present, and the branches constitute the set of all physically possible futures. The scheme is shown in figure 1.
Of the many possible futures which split off at the first branch point, one and only one is selected to become part of the past. The unselected branches vanish, so that the first branch point moves up the tree in a stochastic manner and the tree ‘grows’ by losing branches. This progressive branch attrition is what in the model constitutes the flow of time.
Suppose for example that 1000 lottery tickets have been sold to 1000 different purchasers. Then at the time of the draw, assuming the procedure is completely fair, there will be at least 1000 different kinds of branch at the first branch point: branches on which A wins, branches on which B wins, etc.
A theory of temporal passage is put forward which is “objective” in the sense that time flow characterizes the universe independently of the existence of conscious beings. The theory differs from Grünbaum's “mind-dependence” theory, and is designed to avoid Grünbaum's criticisms of an earlier theory of Reichenbach's. The representation of temporal becoming is accomplished by the introduction of indeterministic universe-models; each model representing the universe at a time. The models depict the past as a single four-dimensional manifold, and the future as a branched structure of such manifolds. Time flow is relativistic in that it manifests itself in a frame-dependent (but not observer-dependent) way. The indeterministic character of the universe-models is mirrored in a “temporal” theory of truth which rejects the principle of bivalence, and suitable semantics are provided for this theory. Finally, an account of physical law is given which defines it in terms of physical possibility, rather than vice versa.