Lorraine,
"we have already assumed that the interconnections in the equation, including the "=" sign, represent causation in physical reality"
Exactly the problem. It is a bad assumption. a(b+c)=ab+bc is a mathematical identity, but not a physical identity. The physical manifestation of one side of the equation requires two multipliers, the other requires only one. The math equation only equates the "result" of the computation, not the computation itself. This is a point that has confused so many physicists, that it has spawned this year's essay contest. That fact that a "result" of a mathematical physics computation may perfectly "equal" an observable measurement, provides *no* evidence whatsoever, that the underlying physical manifestation is even remotely similar to the structures in the mathematical theory. Many physicists have assumed otherwise, which is the source of the unending confusion. All the weirdness in modern physics, including decoherence, are manifestations of this bad assumption.
You are aware of the problem with reconciling a deterministic future, with free-will. And with the problem of having enough hardware to "compute the cosmos", and with the problem that the equations of physics do no distinguish between forward and backward time-travel.
You can kill-off all three of these problematic "birds" with one stone:
The cosmos computes itself, by simply being itself. An electron is employed both as itself, and as a symbol for itself. Hence, predictions of all events, are "physically" equal to, not just "symbolically" equal to the event itself. This "cosmic" computer employs all the available resources. Hence, no other computer is as powerful, since they cannot employ all the resources. But even for this most powerful of all possible computers, the amount of time required to compute/predict a future event, is exactly equal to the amount of time required for the event itself to unfold, precisely because they are one and the same thing. Consequently, even if the laws of physics are entirely deterministic *after the fact*, they can never be used to predict the future, except in cases "devoid of information", which is to say, events that do not depend upon knowing anything other that a tiny subset of the initial conditions required to describe the entire cosmos. Such a tiny subset *Can* be built into a computer, built, in turn, from a tiny subset of the matter in the cosmos. In other words, trivial events, devoid of information, like all those described by physics, may be predictable. But complex events, like living entities, remain unprediatable, even in a universe with fully deterministic laws.
Rob McEachern