SubscribeAt first, the notion that information, like energy, cannot be destroyed seems like a dubious pronouncement. Tear out a page from a book and drop it into a fire and the information seems to vanish. After all, the second law of thermodynamics says that an orderly system (like a page arrayed with words and numbers) will inevitably become more and more disordered, increasing in entropy, until it eventually becomes a meaningless mess. In principle, however, information doesn't truly disappear. The markings of ink on the page are preserved in the way the flame flickers and the smoke curls, in the ripples of heat radiating through the air and the pattern of the ashes delicately falling to the ground. The practical difficulties of retrieving this subtle data and restoring the original order give the second law its vaunted power. But in theory one could reconstruct every paragraph. The information is supposed to be out there in the universe somewhere.Rothko's question, and the answers, all suggest that Hawking radiation is random, which doesn't resolve well with the idea that writing on a burned piece of paper can be reconstructed.
Current astronomical data suggests that the universe is "open", i.e. there is insufficient gravitational pull inward to overcome the outward motion of the outermost galaxies. Most (but not all) galaxies show red-shifted spectra and hence an ever-outward motion. If these trends continue indefinitely the universe will ultimately "die", all particles infinitely spaced apart and at temperature zero. Moreover, there is no apparent mechanism available for reversing the expansion trend. So-called "dark energy" is thought to be its cause, but no one knows the nature of this energy. Still, an open universe would violate many basic concepts of theoretical astronomy. Hence, observation and theory disagree on this effect. Many theoreticians (e.g., [13]) feel that there must be a mechanism for reversing the expansion. We agree with them, based upon the following indirect, but knowledge-based, reasoning as in [1] and [10].Paraphrase: Observation and theory disagree. But theory must ultimately be correct; therefore I have a simply enormous willy!
An unbounded expansion of the universe would rule out cyclical repetition of its states, causing the current state of the universe to exist but once. This would confer a "special" status upon the current state. However, since Copernicus, astronomy has regarded any current state as "typical" and not special (the "Copernican principle"). Also, occurring but once, the state would be extremely rare, so rare as to have vanishing probability of occurrence. How could we then exist?
Given these contradictions, the universe must eventually reverse its expansion and collapse, subsequently expanding and contracting endlessly. How can this transpire?
The success of the EPI approach in constructing physics suggests that natural law really is knowledge-based. Therefore, man - the ultimate seeker and amasser of knowledge - must have a key role to play in the evolution of the universe. That is, knowledge really is power, and hence knowledge must eventually give rise to an effective force.
My expertise is in the philosophy and history of science, which is, in fact, the context for the argument about "determinism", really. As the physicist ozmatli says [here], "Also, I would like to state that determinism means different things to different people.", which is obviously true; but the thing is that in the context of the larger philosophical debate in the history of western science "determinism" has a specific meaning. That meaning specifically is that classical mechanics completely describes the universe and, as such, every event in the universe, large or small, is completely determined by the universe's history back to its origin. This is clearly not true in the context of QM.Rothko writes:
"Our inability to predict the future does not mean the universe we live in isn't deterministic, it just means there are limits to our predictive abilities and knowledge."...which is necessarily true as a literal statement. However, this isn't the claim I, or anyone, was making. My claim is that our "inability to predict the future" is a result of the nature of the universe itself, that no one, within this universe could, even theoretically, "predict the future [of the universe in all its detail]" because of the implications of QM. Rothko's assertion clearly implies a deterministic universe that exists but is outside our intellectual grasp; QM itself, as it stands, describes a universe where that determinism doesn't exist, even hypothetically. Yes, there are/were physicists, Einstein chief among them, who want/wanted a physics beyond QM that described the deterministic universe that classical mechanics showed us. There are various ways in which such a conception could be—one of them is Everett's "many-worlds interpretation" which describes a "mutiverse" where the waveform doesn't collapse and thus is deterministic and it is only our consciousness[es], making its way along a specific-to-a-universe path through this multiverse which is indeterminate. Another is simply asserting what Einstein asserted: that there is a physics we haven't yet discovered which "corrects" this flaw in QM. And others. I don't think String Theory is determinist; but it remains opaque to me, as it is to pretty much everyone. :)
"If the universe is not deterministic, it would not otherwise be chugging along to its inevitable heat death."Well, no, in a variety of ways. One is best described by quoting "Sam", of MetaChat, the aforementioned physicist Gyan pointed us to. This was in an email to me, but I'll take a risk and assume he won't mind me quoting him:
"the fact that the universe is headed inexorably toward a known, given state, and the fact that it currently exists in some given state DO NOT together constitute proof that it is a deterministic system. the classic proof by contradiction is the coffee cup full of hot coffee: we know when i pour it that it's at 212F. and we know it ends up at room temperature. but it's a chaotic system in-between -- it's much easier for us to say what temperature the cup will be at in ten hours than in ten seconds. the small fluctuations that occur in the interim have huge effects on subsequent evolution, and although there is an attractor in the phase space, the coffee can take a weird path to get there."Another is pointing out that, until very recently, this inevitable heat death Rothko speaks of wasn't inevitable: it wasn't known if the universe, in terms of GR, was closed or open and thus whether it was headed to a heat death or a "big crunch". (We only recently—within the last ten years—know that the universe is either perfectly flat or slightly open.)
“I am a physicist and would be glad to answer some questions about Quantum Mechanics. Also, I would like to state that determinism means different things to different people. Personally I see the Universe as determinstic in the sense that for every effect there is a cause.”—ozomatli, this threadAs I said before, determinism in this context has a specific meaning. It is, in my own words:
Determinisn asserts that every event in the universe, large or small, is completely determined by the universe's history back to its origin. It is like an immense and intricate clockwork, ticking away.Quantum Mechanics denies this view. That this is the case is why there are countless pages written on this topic and why Einstein said:
“Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. Quantum theory says a lot, but does not really bring us any closer to the secret of the Old One. I, at any rate, am convinced that He (God) does not throw dice.”—Albert Einstein, A letter to Max Born, December 12, 1926 cited in Einstein: The Life and Times, p. 414The previously referenced Stanford Encyclopedia of Philosophy, in its entry on causal determinism, provides a "loose and (nearly) all-encompassing definition as follows":
“Determinism: The world is governed by (or is under the sway of) determinism if and only if, given a specified way things are at a time t, the way things go thereafter is fixed as a matter of natural law.”—Hoefer, Carl, "Causal Determinism", The Stanford Encyclopedia of Philosophy (Summer 2005 Edition), Edward N. Zalta (ed.)...about which it clarifies:
“The roots of the notion of determinism surely lie in a very common philosophical idea: the idea that everything can, in principle, be explained, or that everything that is, has a sufficient reason for being and being as it is, and not otherwise. In other words, the roots of determinism lie in what Leibniz named the Principle of Sufficient Reason. But since precise physical theories began to be formulated with apparently deterministic character, the notion has become separable from these roots. Philosophers of science are frequently interested in the determinism or indeterminism of various theories, without necessarily starting from a view about Leibniz’ Principle.”Implicit is the historical context, but I think I should be more explicit.
“...according to QM the fullest description possible of a radium atom (or a chunk of radium, for that matter), does not suffice to determine when a given atom will decay, nor how many atoms in the chunk will have decayed at any given time. The theory gives only the probabilities for a decay (or a number of decays) to happen within a given span of time. Einstein and others perhaps thought that this was a defect of the theory that should eventually be removed, by a supplemental hidden variable theory that restores determinism; but subsequent work showed that no such hidden variables account could exist.”The entry goes on to attempt to repudiate this, arguing in favor of Bohmian Mechanics, a theory that, as mentioned in the other thread, is interesting but certainly not orthodox. A more credible source for a defense of Bohmian Mechanics is found in "What is Bohmian Mechanics?", V. Allori and N. Zanghi, quant-ph/0112008. The standard objections to this theory are covered in that paper, as well as in the Stanford encyclopedia. But, again, this is nevertheless an unorthodox theory. Orthodox quantum mechanics is decidedly indeterministic.
Now that I have looked into it a bit more I think I understand the problem. I think information in the quantum mechanical sense isn't actually information at all, more like complexity. I think the entire discussion about the burned paper is a completely false analogy. I wonder where the notion originated, and I kind of doubt that it comes from a physicist at all.The notion of the burned paper is definitely brought up by the physicists discussing the theory (sometimes the notion is throwing an encyclopedia into a black hole)... I'm not convinced it is meant literally though, as the wikipedia entry on physical information makes obvious, the word 'information' can mean a lot of different things.
The most puzzling aspect of the two-slit experiment is perhaps the following: If, by any means whatsoever, one is able to determine through which slit the particle passes, the interference pattern will be destroyed. This dramatic effect of observation is, in fact, a simple consequence of Bohmian mechanics. To see this one need only carefully consider what determining the slit through which the particle passes should mean. In particular, one must recognize that this must involve interaction with another system that must also be included in the Bohmian mechanical analysis. This destruction of interference is related, naturally enough, to the Bohmian mechanical analysis of quantum measurement (Bohm 1952), and it occurs via the mechanism that leads, in Bohmian mechanics, to the "collapse of the wave function."But it seems to me that this doesn't even attempt to address the source of the deterministic/probabilistic disagreement, the uncertainty principal. I quoted from the stanford article in the other thread (here):
For any quantum experiment we merely take as the relevant Bohmian system the combined system that includes the system upon which the experiment is performed as well as all the measuring instruments and other devices used in performing the experiment (together with all other systems with which these have significant interaction over the course of the experiment). The "hidden variables" model is then obtained by regarding the initial configuration of this big system as random in the usual quantum mechanical way, with distribution given by |ψ|2. The initial configuration is then transformed, via the guiding equation for the big system, into the final configuration at the conclusion of the experiment. It then follows that this final configuration of the big system, including in particular the orientation of instrument pointers, will also be distributed in the quantum mechanical way, so that this deterministic Bohmian model yields the usual quantum predictions for the results of the experiment.So the uncertainty principal still guides particles going into the Bohmian mechanical system and Bohmian mechanics doesn't claim to be able to do anything that the uncertainty principal says you can't do. Of course I could be completely full of shit, that is usually the case.
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posted by MetaMonkey at 6:47 PM on December 3, 2005