weemba@brahms.BERKELEY.EDU (Matthew P. Wiener) (03/24/86)
This comes from a debate in net.philosophy about whether existence is the same thing as following physical law. To make the debate a little more interesting, I shall pursue one standard view of modern physics a la John Archibald Wheeler. In particular, I shall suggest that following physical law, as it is now understood, implies that either physical things do not exist or that a non-physical thing does. Those who've seen this sort of stuff before know I am referring to the EPR (Einstein-Podolsky-Rosen) paradox, Bell's theorem, and the experiments of Aspect et al. I will not give any summary of this circle of ideas, merely state one rather common view of the implications. As Pais once said about Einstein: We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I believed the moon exists only when I look at it. Why did Einstein ask this question? Do you find the question too trivial? In quantum mechanics this question is rather profound. Observation is what collapses wave-functions. What machinery is behind this? None: "Every attempt, theoretical or observational, to [find] such a [mechanism] has been struck down." As J A Wheeler wonders in his magnif- icent essay "Law without Law": Why not simply say of the route it actually takes, Allah willed it? And willed the outcome of every other individual quantum process? To strike down a proposal of this kind, it has been pointed out more than once, is beyond the power of logic. One has to appeal instead to pragmatism. And as J A Wheeler asks in "Law without Law": How does quantum mechanics today differ from what Bishop George Berkely told us two centuries ago, "Esse est percipi," to be is to be perceived? Does the tree not exist in the forest unless there is someone there to see it? Do Bohr's conclusions about the role of the observer differ from those of Berkeley? Yes, and in an important way. Bohr deals with the individual quantum process. Berkeley--like all of us under everyday circumstances--deals with multiple quantum processes. It is these multiple quantum processes that are at the heart of this new opposition to the naive view of reality. It is now known that one cannot pretend that different quantum events act independently. One can construct a giant Hilbert space, with different directions corresponding to distinct objects, but the quantum collapse occurs universally. Wait, you say, the moon is way out there, and runs independently of us. The earth rotates, and the moon sets, only in allusion. It hasn't disappeared. Maybe some ancient and ignorant myths thought so, but we know better, right? Wrong. The moon is as subject to quantum law as photons. And the reach of quantum law is the entire universe: one can observe a quasar billions of light-years away split in two by gravitational lensing and then run a delayed choice experiment on the double images. Quantum mechanics has a very long reach indeed. As J A Wheeler describes the entire universe: From "nothingness ruled out as meaningless," to the line of distinction that rules it out; from this dividing line to "phenomena"; from one phenomenon to many; from the statistics of many to regularity and structure; these considerations lead us at the end to ask if the universe is not best conceived as a self-excited circuit: Beginning with the big bang, the universe expands and cools. After eons of dynamic development it gives rise to observership. Acts of observer-participancy--via the mechanism of the delayed-choice experiment--in turn give tangible "reality" to the universe not only now but back to the beginning. To speak of the universe as a self-excited circuit is to imply once more a participatory universe. Now this is interesting! Metaphysical questions about which came first abound. If you want to reject this time loop, you must then follow Bishop G Berkeley's argument and conclude that there is an Observer that gives existence to the Universe: no Observer, no wave-function collapse. Wheeler says this Observer is all of us. Rather fortunate then, that we came into existence, so as to give existence to the rest of the Universe. Before this century, quasars did not exist, since no one observed them. Taken literally, this is roughly the view that Creationists take about quasars: God created the Universe 10000 years ago, with light from the quasars also on the way. But how can we talk about quasars existing NOW? The light we see from them is billions of years old. The quasars no longer exist, probably. The expert sees where I'm leading. The notion of time is yet another observer created illusion, based on a choice of coordinate frame. "Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows." There is no time loop, and so there is no problem? My conclusion: we don't really know what "exist" means anymore. Or more accurately, we don't know what the pre-conditions for existence are. We do know that one of them is to be observed. And identifying the observer that gives us and our universe existence is a mystery. Us? We learned what tables and chairs and water and light are composed of, we have lost ourselves on the more basic notion of existence! It used to be so easy: Look at it and see if it's there. The problem now is what happens when you don't look at it. If you refuse to look at the moon, does quantum mechanics force you to conclude it does not exist? To those experts who have been laughing up to now, and know that it is just a bunch of formulae that work out every time, then we agree that physical reality is contingent on mathematical reality. But the latter? It keeps me awake at nights, if I think about it. If I don't think about it, it works OK. In other words, mathematical reality makes more sense when NOT observed, as opposed to physical reality. As J A Wheeler concluded, so will I: Today we demand of physics some understanding of existence itself. ucbvax!brahms!weemba Matthew P Wiener/UCB Math Dept/Berkeley CA 94720
torek@umich.UUCP (Paul V. Torek ) (03/26/86)
For a less mystifying view, see N. Maxwell, ``Are Probabilism and Special Relativity Incompatible?'', _Philosophy of Science_ 198[4?]. He suggests that wave-packet collapse occurs whenever the difference in rest-energy between the possible collapsed states exceeds a certain value. His account reproduces all the empirical successes of orthodox QM but gives different predictions for certain as-yet-untested circumstances. More detailed references available upon request. Warning: I have directed followups to net.philosophy and net.physics only. --Paul Torek torek@umich
ellis@spar.UUCP (Michael Ellis) (03/28/86)
>Metaphysical questions about which came first abound. If you want to reject >this time loop, you must then follow Bishop G Berkeley's argument and >conclude that there is an Observer that gives existence to the Universe: no >Observer, no wave-function collapse. Wheeler says this Observer is all of >us. Rather fortunate then, that we came into existence, so as to give >existence to the rest of the Universe. Before this century, quasars did not >exist, since no one observed them. Taken literally, this is roughly the >view that Creationists take about quasars: God created the Universe 10000 >years ago, with light from the quasars also on the way. Those who prefer to believe in an objective, independently existing, 10-15 billion year old Rosenesque universe have another option -- to postulate a Cosmic Observer who has been there since the beginning of time, to assure the existence of everything during those periods of our not-looking. -michael Spinoza should be credited with a certain wisdom worthy of imitation. Attributing the name "God" to independent reality strongly marks the difference between that reality and the purely phenomenal reality, and this is quite in agreement, as we saw, with the teaching of modern physics... Spinoza's use of the word God to denote Being.. is the most direct procedure for comprehensibly expressing the idea that Being is not blind mechanics. - Bernard d'Espagnat (In Search of Reality, Springer-Verlag, 1983)