Inspired by a recent conversation in the 'free will' thread, I felt compelled to have a go at refuting the MWI...

From the SEF ( http://plato.stanford.edu/entries/qm-manyworlds/ ):

The Many-Worlds Interpretation (MWI) is an approach to quantum mechanics according to which, in addition to the world we are aware of directly, there are many other similar worlds which exist in parallel at the same space and time. The existence of the other worlds makes it possible to remove randomness and action at a distance from quantum theory and thus from all physics.

... every time a quantum experiment with different outcomes with non-zero probability is performed, all outcomes are obtained, each in a different world, even if we are aware only of the world with the outcome we have seen.

... Firstly, assuming that there are many worlds like this that exist at the same space & time, it should be acknowledged that these worlds cannot be comprised of the same matter, for if one (the same) set of matter exists at one (the same) set of space & time, then we only have one world, not many. That is, the MWI requires that different matter/bodies exist at the same space & time. But, how can more than one body exist at the same space & time? That is illogical. (Problem 1)

Secondly, ignoring the first problem, let us focus upon the claim that "The existence of the other worlds makes it possible to remove randomness and action at a distance from quantum theory and thus from all physics.". No it does not, is my retort. Why? Because if what distinguishes one world from another is the distinct/separate bodies that already exist in each of these worlds, then whichever 'experiment with different outcomes with non-zero probability is performed' the outcome in each of these worlds is still indeterminable. Why? Because one body cannot jump into another world where a pre-existing body of an exact likeness already exists. How do I know this? Because I am yet to see more than one of anything... and if it were the case that mirroring-bodies could jump from one universe to the next, then we would expect to see numerous variants of some bodies such as, say, Stonehenge, all co-existing together. In other words, almost everything would be an observed blur - the consequence of it existing simultaneously with variances of its potential.

... Bodies a; b; c; d; e, etc, already exist in this world. The MWI would have it that different like-bodies of a; b; c, etc, exist in another world. So, whatever happens to those bodies will happen to them in their world. It won't happen to them in this world. Therefore, the MWI does not eradicate randomness from quantum theory. Further, it cannot explain nor eradicate the problem of 'action at a distance', for the same problem arises: even if there are many Stonehenges - what happens to 'it' will happen to it in its own world... since it cannot transcend that world into another. (2nd problem)

Lastly, for now, the MWI is physically dependent. That is, the likelihood of an outcome is assessed from physical potential. However, we all know that the likelihood of events isn't contingent upon physical potentials. I know, for instance, given the evolution of my own life/mind, that the likelihood of me becoming a materialist tomorrow, is zero. I have no doubt about that, given that I've already been there and seen the flaws thereof (not to mention everything else I've 'seen'). Likewise, you all may be sure of some thing or other. Further, for example, though the physical potential exists, the likelihood of tomorrow's papers headlining The Pope as a murderous gay atheist, seems bleak, to say the least. Therefore, are these many worlds constrained by what is physically possible, or by what is sensibly possible? That is, do mental/emotive concerns dictate what worlds are possible, or simply physical potentials? On the face of it, it would seem that the MWI doesn't have any recourse towards mental potential/agency. (3rd problem).

I started this thread because two people informed me that the MWI is not irrational and that any assault upon it was bound to be a consequence of incredulity, on my part. In other words, I started this thread to try and prove why reason can undermine the MWI. I expect to think of further problems with it as the discussion evolves.

... Any serious input is welcome. Btw, I'm supposed to be extremely busy with something else until next Tuesday evening, so pardon me if my responses seem a bit light up until that point. However, my mind has become focused upon this issue and I felt compelled to put it out there. Thankyou.

UndercoverElephant wrote:

Therefore, are these many worlds constrained by what is physically possible, or by what is sensibly possible?

The former. In some branch of an MWI multiverse, somebody is in the Guinness Book of Records for rolling 100,000 consecutive sixes without cheating....

Is MWI sensible? Depends what non-sensible things you are trying to get rid of.

You seem to have overlooked the first two problems, focusing instead upon addressing the 3rd problem, lightly.
When you send me a cheque for £10,000, I will take heed of your response to the 3rd problem.

Zwaarddijk wrote:It's interesting how terrible your arguments are. They don't stand up to any scrutiny. (And I reject MWI just as you do - I just find your arguments to be very worthless.)

Snide criticisms, devoid of reasoning. They certainly don't stand up to any scrutiny and are about as worthless as worthless can be. Keep up the good work.

Paul Almond wrote:

jamest wrote:... Firstly, assuming that there are many worlds like this that exist at the same space & time, it should be acknowledged that these worlds cannot be comprised of the same matter, for if one (the same) set of matter exists at one (the same) set of space & time, then we only have one world, not many. That is, the MWI requires that different matter/bodies exist at the same space & time. But, how can more than one body exist at the same space & time? That is illogical. (Problem 1)

MWI does not propose that that "more than one body exists at the same time" in any fundamental way. To put it simply, it proposes that the basis for "reality as we know it" is the quantum wave function, and that this has real existence. Parts of the quantum wave function become "decoherent" from other parts, meaning that they cease to interact in any way worth talking about. This gives the appearance of separate worlds, with separate objects. Suppose a ball exists in my world, and I can interact with it. Another ball exists in someone else's world, and I can't interact with that. The two balls don't interact with each other - even though that might be in the same space. The underlying explanation of this isn't that "two bodies occupy the same space". It is that a single wave function occupies the same space, and parts of it don't interact with other parts - and yes, the two parts can overlap. However, the idea that waves can overlap is hardly radical.

A (very crude and open to misuse) analogy might be radio transmissions. Someone might ask how radio transmissions of two separate radio shows can pass through the same space at the same time. Doesn't this require two things to occupy the same space? This is dealt with when we see that nothing really passes through the space except radio waves - and a single description can be made of the radio waves passing through the system. Likewise, you could step back from the many-worlds of MWI and describe everything in terms of just "one world" with the wave function - and parts of that wave function ceasing to interact with other parts explain the appearance of separate worlds. The different worlds in MWI aren't really separate in any ontologically "profound" way but merely by lack of interaction and limited human perception due to our status as observers embedded in the system.

In a way, the concept of matter as we know it is no longer fundamental in MWI anyway. It makes little sense to object to a ball in one world being "the same matter" as the ball in another world. Looked at closely enough it is all just waves anyway.

Even thinking of this in terms of "bodies" existing in different worlds suggests a problem to me, so I have doubts about whether it is worthwhile getting into the other questions right now. I will say that MWI makes no claim that the results of quantum mechanics experiments should be predictable by humans.

Okay, thanks for the explanation. It appears that I've taken this 'many worlds' conception too literally. Anyway, if there are problems with the MWI I need to rethink them.

Paul Almond wrote:

jamest wrote:Okay, thanks for the explanation. It appears that I've taken this 'many worlds' conception too literally. Anyway, if there are problems with the MWI I need to rethink them.

It depends what you mean by "too literally". What is important is that the "splitting" doesn't happen in any kind of (I don't even know what vocabulary I should use here) "ontologically profound" way. However, the theory does propose that these worlds do exist as far as we are concerned. If MWI is true, there will indeed be worlds in which the Nazis won World War II and a statue of Adolf Hitler is standing in London: the proportion of such worlds might be large or small depending on how lucky or not you think you Britain was during World War II. However, the only thing that makes these "other worlds" is the lack of interaction. To some being able to take a "Godseye" view of this, there would just be the wave function. This is the sense in which MWI is supposed to get rid of randomness. Randomness is still apparent to the inhabitants of a single world, but from the "Godseye" perspective, there is just the wave function, developing deterministically over time. To you, the randomness comes from having multiple futures at any time and continually being split as an observer.

Incidentally, a test for MWI was proposed, but I don't advise doing it.

You cannot arouse my curiousity like that and say nothing. What's the test?!

Paul Almond wrote:In any event, I am not suggesting that anyone should do this.

I might be persuaded to do the experiment with just a coin.

I don't see how any of what you said proves anything about MWI. Even within just this world, if I were to flip a coin countless times then eventually I'll a hit a prolongued run of heads or tails. Such possibilities are expected even within the realm of a singular reality. Apparently, it's even possible for a monkey to type the complete works of Shakespeare, even within just this world. Too furry or not too furry, that is not the question. Sorry, I appear to have stepped into the world where I've become mad.

The point you made about not being able to observe one's demise - because one is dead - seems daft to me. MWI is contingent upon statistics, not observation. I mean, after all, there must be many worlds in which I'm already dead, so that the existence of these worlds is not contingent upon my observation of them. Therefore, any analysis of MWI which seeks to prove the theory upon the basis of observation, seems like a dead duck, imo. Though perhaps the duck is alive elsewhere.