One very popular interpretation of quantum mechanics is the many worlds interpretation (MWI) This is roughly the idea that if the wave equation describes all possibilities that all possibilities are equally real and we're just in one of those universes. In effect it equates possibility and actuality - in direct contrast to most philosophies. There are numerous reasons MWI is popular. My personal, biased, view is that the main reason it is popular in physics is because it makes the mathematics of quantum mechanics far less mysterious. One treats the wave equation as a true real description of all reality. Certainly if, as is common in physics, one is integrating over possible worlds or have variables that relate to possible worlds (as one does in the Hamiltonian) then why not take it at face value?
Let me briefly explain why I just don't buy MWI.
First off let me 'fess up. Even though I often attack positions in philosophy as more a kind of wish fulfillment I fully admit I'm doing it here. That is I roll my eyes when people reject four dimensionalism because they want a certain kind of free will and openness of the future to be true. Yet here I'm definitely a hypocrite. In large measure I don't accept MWI because I don't want it to be true. (There's an old Larry Niven short story about a guy who thinks about MWI that really captures my feeling) If MWI is true then there is a copy of me out there that does horrible things. That really, really bothers me. The notion of "self," even if it is a problematic notion, is far, far more problematic in MWI.
Going beyond my admited hypocrisy though I have to confess that my number one reason to reject MWI is that it appears to me that what folks call the "collapse of the wave function" appears to be gradual. (This New Scientist article has a nice description) That is quantum events are really quantum processes and the process takes time. I just have a hard time reconciling this to MWI. Sure it isn't an absolute argument. After all if universes bifurcate that would probably take time as well. But the notion of this being a process (even if I think the whole notion of a "collapse" to be somewhat misplaced) just suggests that we're dealing with a single process.
I'll confess that confusing actuality with possibility bothers me as well. Although MWI is actually much more limited in that than say Lewis' realism of possible worlds. (Since what is logically possible is probably larger than what is quantumly possible)
Hi Clark. I agree with you in rejecting the MWI. Part of my feeling on this is just intuition, I guess. One of my deepest intuitions is that possibilities are real in our world, and the work done by measurement interactions in QM to resolve indeterminate states into outcomes fits with this picture. MWI says there are no outcomes.
But there may be an Occam’s razor part of this which might go beyond just competing intuitions.
There wouldn’t be any Quantum Mechanics without measurements, would there? Heck, there really isn’t any science without experimental outcomes. MWI really overthrows the whole edifice. And it does this without providing any improvements to our understanding of the physics as far as I can see. (Matt Leifer had a nice post along this line at his blog Quantum Quandaries).
Best regards, - Steve Esser
I think you are on to something, but what? Those copies of you would not really be you, so what does it matter what they do? Still, it would be mysterious what makes this you you... It could not be being the actual one, if the others are actual (in their worlds). Anyway, I certainly agree with your last reason for rejecting MWI, as I see QM as a theory of what happens in this world, an apparently uncertain world, with an open future (whether I want it to have one or not).
The problem with the appeal to Ockham's Razor is that MWI really doesn't come out much worse than the alternatives and in many cases better. That's because most other theories add in various extra things to make it work. On the other hand our intuitions of how Ockham's Razor ought apply - by multiplying metaphysics beyond our normal world intuitions rather than formally counting suppositions - does make MWI hard to buy.
But I've long thought Ockham's Razor is a bit of a dodge. Fun to apply but rather messy when you get down to the nitty gritty.
I take your point on Ockham. Maybe that wasn't the right label for my discomfort that MWI doesn't fit with the fact that science is based on repeatable experimental outcomes (not "seeming" outcomes).
Entities should not be multiplied beyond necessity applies to MWI almost exactly. MWI multiplies entities (alternate universes) beyond necessity (the other universes offer no explanatory power beyond the standard Copenhagen interpretation of QM).
Occam's Razor is tricky to apply in general, so I agree with Clark there. However, in deciding between competing scientific explanations, it is a nice rule of thumb and very helpful. For me Occam's razor is the deciding factor here. MWI offers no more predictive power than does Copenhagen, so it is rejected. If MWI predicts something that Copenhagen cannot, and it is observer, then Copenhagen should be rejected in favor of MWI. In that case we would need the extra entities.
The Copenhagen interpretation is primarily an epistemological reading with a few implications for metaphysics. It isn't, however, a fleshed out metaphysical theory. So I don't think you can first apply Ockham to it and most definitely can't compare it with MWI, Bohmian mechanics, or Von Neumann's notion of a wave function collapse.
To add, one might call the Copenhagen interpretation an anti-realist view. While that's not entirely fair, it really isn't concerned with the ultimate reality that MWI appeals to. Now for many people that's a plus rather than a minus. For Empiricists or Instrumentalists the whole question of realism is a bit beside the point.
The proponents of the Copenhagen interpretation specifically tried to avoid as much metaphysics as possible, so of course it is going to have few implications for metaphysics and will not be a fleshed out metaphysical theory. This is a strength, not a weakness. The whole point of science is to try and get away from metaphysics as much as possible, and to only venture there when absolutely necessary.
It is possible to do metaphysics and science at the same time which is what people like Bohm try to do. The rub is that eventually you have to make some kind of prediction which less metaphysical and simpler theories do not and then be shown to be correct through observation. Unfortunately for people like Bohm, their metaphysical speculation hasn't led anywhere.
But that's the point. How can you compare the metaphysical commitments of two theories if one of them is inherently vague? One can call it a strength of course, but then it makes appealing to Ockham over MWI impossible.
Sorry to get personal, but on many occassions you have told me that my desire for precision was misguided and that I had to accept a certain amount of vagueness, and now suddenly vagueness matters?
In any event Copenhagen goes out of its way to avoid metaphysical committments and to stick to measureable phenomena. That's its metaphysical committment, to only to committ to things measureable and nothing more. You could of course object to the notion of measurement being vague, but you haven't so far...
Don't get me wrong. I like vaguenss. But you'll note I didn't appeal to Ockham for why MWI is bad. If you're going to compare two theories you have to do it on the same grounds. To say one theory is better ala Ockham because it is vague then that's just misuse of Ockham in my view. That's because it is indeterminate what ones commitments are. Put an other way, Copenhagen may have more metaphysical commitments when we move from epistemology to metaphysics. Indeed many defenders of MWI make just that point. You just can't compare epistemology to metaphysics when applying Ockham. It's apples and oranges.
Incidentally, I agree with you both, that MWI does seem to violate the intuitive principle (whatever it is) that makes us accept Occam's razor (when we do). I wonder, would we make up a lot of dark brain, if we discovered (counterfactually) that human brains were not big enough to account for consciousness? Would we not just bite that bullet (if it happened) and accept a strongly dualistic theory of mind? Or would the materialistic majority (in science) really conclude that they had discovered that there was a lot of the brain that was unobservable? I would think, if they did that, that they were being too metaphysical, too unscientific (after all, they accept matter rather than sets of sense-data), but they could easily dismiss me as metaphysical (after all, I would have them discovering the soul, in that scenario). That is, the concept of what is metaphysical seems to be a fuzzy as Occam's razor's edge (?)
"Dark brain" theory - that's a great thought experiment! - Steve
But you'll note I didn't appeal to Ockham for why MWI is bad. No, but you did give half hearted assent when you said, On the other hand our intuitions of how Ockham's Razor ought apply - by multiplying metaphysics beyond our normal world intuitions rather than formally counting suppositions - does make MWI hard to buy.
If you're going to compare two theories you have to do it on the same grounds. To say one theory is better ala Ockham because it is vague then that's just misuse of Ockham in my view. I never claimed that either was vague, they both are clear and precise as to that they assert. It is because of this that one can apply Occam's razor. If either was vague then it could not be applied because you simply cannot analyze vague concepts or theories, they allow for endless interpretation and wiggling.
That's because it is indeterminate what ones commitments are. Then why bother discussing it, it's indeterminate anyway.
You just can't compare epistemology to metaphysics when applying Ockham. I still don't see how I have done that, perhaps you can enlighten me.
It's apples and oranges. Perhaps it is apples and oranges.
Thanks Steve. More seriously, since I need to argue against MWI (as it's a lemma of my forthcoming), so I'm wondering about any other good sites to look up (other than the ones mentioned above, which I have found useful, thanks). The beauty of MWI is that even if I fail to argue against it convincingly, it's an argument against materialism (which I also don't like): since MWI is popular amongst physicists (most of whom are materialists), and is therefore popular amongst naturalists (most of whom are materialists), whereas surely most people would reject MWI (on such reasonable grounds as the above), hence we have that many materialists favour MWI, which is a bit like “many Monotheists favour sex-discrimination” (which materialists seem to see as an argument against Monotheism).
David consider a vague claim that makes only two metaphysical commitments. In the vague but empty part for it to be determinate say there are three choices. A theory with four extra commitments, a theory with five, and an other theory with four. Those are all the logical possibilities.
Now if we look at just the vague part it will appear to just hold to two metaphysical commitments. So we compare it with a more determinate theory that has four total metaphysical commitments. Now if we ignore that vague part it will appear that the vague theory is simply in terms of Ockham. That's because it has only two formal commitments whereas the theory we're comparing it to has four. But this is misleading because once we look at the theory in its possible determinate forms it has six or seven commitments and thus is actually more complex.
So by ignoring the features of vagueness Ockham's razor gives the illusion of simplicity but does this by a subtle dodge.
As to conflating epistemology with metaphysical claims I'd point you to the SEP on Copenhagen. It does an excellent job on this.
Enigman, I admit that I find arguments pro and con physicalism or materialism a bit dodgy simply because I see both as moving targets. However I don't see why MWI is anti-materialistic. If we take materialism as the thesis that all that exists is stuff in space-time then surely MWI is an example of a materialistic theory. Now it makes claims about what space-time is, but that can't make it non-materialistic since it seems that those claims are more fundamental than materialism. That is they are better seen as claims about what materialism consists of rather than claims incompatible with materialism.
I'd assume you disagree so I'm quite curious as to your reasoning.
I wonder if MWI makes all other scientific theories unnecessary. Take Darwinian evolution, for example. It explains the genesis and development of organisms. But if the MWI is correct, then who needs natural selection, etc. If every "possible" event is actual in another world, then there is an arbitrarily large number of worlds in which the particles on this planet happened to come together in the right way to constitute organisms, etc. The same can be said for any complex phenomena. Right?
I don't see how MWI is problem for evolution. Natural selection is the feedback via probability that selects certain individuals. Thus in most universes those aggregates of creatures will be selected. In some universes highly improbable but physically possible situations will occur. Presumably we're in one of the universes near the middle of the bell curve though which is why everything seems normal. But there are universes where highly, highly improbable events happen like sugar spontaneously separating from coffee.
Clark,
I didn't mean to suggest that MWI is a "problem" (i.e., evidence to the contrary) for Darwinian evolution, but that it provides a rival explanation for, say, the emergence of sea otters. The convergence at the right place and time of the requisite particles to spontaneously generate a sea otter is extremely improbable, but presumably it is a quantum possibility. If all such possibilities are actualities in alternative worlds, then there are worlds (a lot of them, in fact) in which sea otters are spontaneously generated. The same can be said for any other species. Indeed, it can be said for any phenomenon whatever.
Right, but I think even buying into MWI one can reject improbable events just as one could in a single world with objective probability.
Maybe I'm reading you wrong, but it seems like you're saying that improbable events happen and thus MWI explains events that would normally require more extensive explanations for the improbable. But I just don't see MWI providing this in its canonical form. That is I just don't see MWI changing how we view probabilities at all in a practical sense. Just in an ontological sense.
(Weird how in a post about how I can't believe MWI I'm spending an awful amount of time defending it)
Clark,
Perhaps I do not sufficiently understand MWI. Tell which premise I'm going astray on:
(1) According to MWI, every possible quantum event is an actual quantum event in an alternate world.
(2) The spontaneous generation of a sea otter is a conjunction of possible quantum events.
(3) The spontaneous generation of a sea otter is a conjunction of actual quantum events in an alternate world (for all we know, this one).
A simpler way to put it: if every possibility is an actuality, then the notion of improbability disappears.
Improbability in MWI would just be the number of universes relative to the whole in which this event transpires. So it really doesn't affect the notion of improbable. So yes, the improbable happens always but that's not really the point.
Yes, that account of improbability for the MWI makes sense. But isn't it the point (at least the one I am attempting to make) that every improbable event happens? According to the MWI, isn't there at least one world in which every complex phenomenon is the result of spontaneity? And for all we know, it could be the world we live in.
By the way, I think such a conclusion is absurd, and amounts to a reductio of the MWI. I'm just trying to follow the MWI out to its conclusion.
Well I don't think it a reductio - or at least not a useful one. But certainly it follows that every possibility happens. But really this is just a sneaky way of saying, I intuitively want to separate out possibility and actuality.
Ipse:
It is not true that MWI says any phenomenon is possible. It is still constrained by the initial conditions of the universe. Thus it may be the case that the initial conditions of the universe are such that the time evolution of the Schroedinger equation never allows for the spontaneous generation of a sea otter. Probably there are some initial conditions for which such a spontaneous generation would occur, though.
Doesn't MWI have implications for how we view the initial conditions of the universe though? That is, why assume a single beginning instead of all the possible ways in which an equation could evolve that happen to have our universe's starting point.
Clark, what are the implications for MWI in Mormon Theology? Is it possible to shoehorn MWI into Mormon Theology? Or are they exclusive?
It seems to me (at least offhand, without protracted thought) that MWI is incompatible with Mormon Theology. Would each world/universe have its own God? If not, is God truly omnipotent, or only within his universe? (depending, of course, on how you define omnipotence and interpret the statements on omnipotence in scripture) How would an ultimate judgement deal with multiple versions of the same person? or are they different people?
Of course, it might be possible to address all this using Joseph Smith's teachings of truths having their own "sphere" where they are true. If each world/universe is its own "sphere" would that make MWI and Mormon Theology compatible?
I suspect this will demand more thought than I can afford to give it!
I can't see judgment or the like making much sense in MWI. So while MWI might be popular for physicists I can't see it being theologically viable for Mormons.
Clark,
Lot of comments and forgive me if I'm repeating something. But I think the MMI and modal realism are pretty distinct positions. Modal realism seems pretty comitted to maintaining the "Evil Clark". And equally bad for me, there is a counterfactual universe where AG is one of the first presidency! Or even worse, there is a universe where I am swayed by an argument from FAIR and become active in church again.
But keep in mind, the reality of logical possible space would be different than the nomically possible space that MMI falls under. So for instance, taking the zombie argument, there wouldn't be a MMI necessarily where all is dark on the inside.
I think the "evil clark" in MMI wouldn't be "you", it's just a great replica. Also keep in mind, that even if God is Satan and Satan is God in another universe, you are still going to go to hell in this universe if you keep proliferating your apostate interpretations of the gospel.
That was sort of my point. Modal realism entails that everything logically possible is real. MWI just says all possible solutions of the initial wave equation are real. Which is much, much smaller than what modal realism is committed to. Sorry if that wasn't clear. The issue of an "evil Clark" though is that such scenarios would appear to be part of a wave equation in most forms of physicalism. Of course if one demands a robust consciousness that denies physicalism (as most Libertarians do) then MWI is simply false on its face anyway.
I'm hazy on MWI, but if what makes your MWI copies (or counterparts) your copies is that each shares some of his past with you, then they could only do things that it was physically possible for you to do. So, if you are OK with it being possible that you would do something, you could be OK with it being done by your other selves, who are after all no longer identical to you (that I find absurd, so I'll post about that on my blog). Of course, you might have a problem with all physical possibilities being actually possible, but then you have a problem with materialism in general, rather than MWI in particular. (I suppose that you might reject MWI on the grounds of its pointlessness if materialism is false.)
It is counter-intuitive that a future MWI copy of you (who is now simply you) could be evil, but I suspect that much of the unattractiveness of that (aside from it being materialistic) comes from your present intent not to be evil, to make such a person nonexistent; and that the unattractiveness of it might therefore lessen when you recall that such a copy would also (just as you will) recall wanting to be good. Insofar as it is now possible for your attempt to be good to fail, you must accept that you yourself might end up being that person, so why reject its MWI existence?
Furthermore, stuff that you might consider physically possible (e.g. torturing infants for fun) might not really be physically possible for you (or at least no more probable than the spontaneous appearance of a sea otter), given materialism, because your ethics would on that hypothesis be physical dispositions of your brain. So again, insofar as you have a problem with materialism saying that such stuff, whilst being very unlikely (given the way your brain is), is actually slightly possible, that is a problem with materialism rather than MWI. And surely MWI copies who are not longer you doing such stuff is actually less problematic than what it logically requires, i.e. the real possibility that you yourself will be doing it?
(Re comment #16, that was my reasoning, sadly—that many materialists see nothing wrong with MWI, just as many monotheists see nothing wrong with sexism, and that such propositions make the respective ism look worse, and so give it a greater burden of proof)
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