(Continued from my last post)
PQ: Quantum mechanics gives answers that are a set of probabilities all existing at the same time…
Probabilities are not things that exist at some time, any more than they are things that exist at some place. Probabilities are assigned to possibilities, such as the possibility that a given event happens at a given time at a given place. This does not mean that the probability of this event is located at the given place or exists at the given time. (Nor does it mean that the possibility of this event exists now, or that the event itself exists now as a possibility.)
Quantum-mechanical probabilities, in particular, are assigned to the possible outcomes of measurements, and implicit in every quantum-mechanical probability assignment is the assumption that a particular measurement is successfully made at a particular time. It would be silly to imagine that apart from the objective world of actual events and the subjective world of remembered, perceived, or anticipated events there exists, at any given instant, a domain containing the probabilities of all possible outcomes of all possible measurements that are in the future relative to this instant, and it would be sillier still to call this the future.
PQ: We already have a very good nontechnical word for a mixture of possibilities coexisting at the same time — we call it the future.
Our successive experience of the world’s temporal aspect makes it natural for us to hold that only the present is real. The future exists not yet, the past no longer. Again, our self-experience as agents in a successively experienced world makes it natural for us to hold that the past, being known or knowable in principle, is “fixed and settled,” while the unknown and apparently unknowable future is “open.” (According to PQ, a mixture of possibilities exists now, one for each instant of future time.) The origin of these notions is purely psychological. They tell us something about the way we experience the world. They tell us nothing about the world itself.
Because there simply is no objective way to characterize the present, the experiential now has no counterpart in the physical world. And because past and future are defined relative to the present, they too cannot be defined in objective terms. The temporal modes past, present, and future can be characterized only by how they relate to us as conscious subjects: through memory, through the present-tense immediacy of qualia, or through anticipation. In the physical world we may qualify events or states of affairs as past, present, or future relative to other events or states of affairs, but we cannot speak of the past, the present, or the future. The proper view of physical reality is not only what Thomas Nagel has called “the view from nowhere” — the physical world lacks a preferred position corresponding to the location whence I survey it — but also what How Price has called “the view from nowhen” — the physical world lacks a preferred time corresponding to the present in which I experience it. The idea that some things exist not yet and others exist no longer is as true (psychologically speaking) and as false (physically speaking) as the idea that a ripe tomato is red.
To philosophers, the perplexities and absurdities entailed by the notion of an advancing objective present or a flowing objective time are well-known. (Click here or here for extensive discussions of philosophical issues pertaining to time.) To physicists, the objective unreality of our subjective distinctions between past, present, and future was brought home by the discovery of the relativity of simultaneity. For any two events A, B there exist two reference frames FA and FB and a third event C such that C is simultaneous with A in FA and simultaneous with B in FB. This “simultaneity by proxy” of A with B implies that all parts of the spatiotemporal whole are coexistent and equally real. (It also follows from the relativity of simultaneity that this coexistence is not a simultaneous existence but an atemporal coexistence.)
PQ: Unless we believe that all events are predetermined, which would be a very dismal view of the world, this is what the future must be like.
It is a non sequitur to think that the atemporal coexistence of the parts of spacetime rules out free will. An objective event may very well happen because of a decision freely made at an earlier time.
PQ: Of course, there is now a new big question of how one of the possibilities in the future is selected to form what we see as the present and what becomes the past…
Saying in common language “there is a possibility that…” is the same as saying “it is possible that…” It would be silly to take the “there is” in “there is a possibility” as a lesser kind of existence — a matrix of potentialities that transform into the genuine article (either existence proper or nonexistence proper) by way of a measurement.
PQ: Quantum mechanics means that there is a kind of instant awareness between everything. This is quite true, but… by introducing quantum mechanics in the way that we have, the “awareness” is of a very limited kind…
Limited or unlimited, this uncanny “awareness” — e.g. Bell’s theorem (see here and here or here) or the experiment of Greenberger, Horne, and Zeilinger (here, here, and here or here and here) — is a mystery if ever there was one. It’s not just that it’s impossible to explain it; the phenomenon itself seems impossible. Even understanding the mere possibility of it calls for a radical revision of our concepts of matter and space. Mermin quotes a distinguished Princeton physicist as saying that “anybody who’s not bothered by Bell’s theorem has to have rocks in his head.” Quincey appears not to be bothered…
PQ: One of the benefits of viewing the quantum world as not fundamentally different from the classical world is that we can imagine how one changes into the other…
Quincey compares a world in which Planck’s constant is zero with a world in which it has a non-zero value. Contrary to what he claims, these are fundamentally different worlds. One allows us to define natural units by setting Planck’s constant equal to 1, the other does not. One allows us to define natural length scales (Planck scale, Compton wavelength, Bohr radius), the other does not.
What is more serious, however, is that Quincey now contradicts himself. Earlier he made Planck’s constant part of classical physics. Now physics is classical only if Planck’s constant is 0.
The bottom line: Quincey’s assertion that quantum physics “is just classical physics constrained by a simple mechanism” is plain tommyrot.
