The quantum measurement problem is well known and I will not describe it here. I want to concentrate on the 'Many Worlds' solution to it. What is the Many Worlds theory? Briefly, it says that everything exists. We used to think that the natural order of things was for nothing to exist and our problem was to explain why things do in fact exist. But now atomic physicists have shown that everything exists. So the question, now, is why we don't see everything. Why do we see only some of the things that exist? What selects the things of our particular world?
The usual Many Worlds view is of a vast number of parallel realities that do not interact with each other. Technically, these worlds are perpendicular to each other rather than parallel. No matter which way you turn your head, so to speak, the other worlds are at right angles to your line of sight and you do not see them. I like to the think of the Many Worlds as a vast jungle criss-crossed with walking tracks. Each track can be thought of as a world, and it does not interact with the other tracks. If your track crosses some other track you do not notice it because the crossings are always at right angles. [link not yet implemented]
According to the theory, the Many Worlds are equally real and are fully deterministic (i.e., randomness does not exist in any of them - at least, not randomness as a causal agent). We inhabit one of these worlds but there are countless copies of each of us inhabiting some of the other worlds. This sounds rather fanciful, but most physicists agree that that is the reality. I agree with them. The reason we like this formulation, as opposed to the Copenhagen view of things which I outlined earlier, is that the Many Worlds fall naturally out of the mathematics. In the Copenhagen formulation there is an unnatural step which we have to add by hand before a quantum measurement produces a 'real' result. [link not yet implemented - Cliff Price or John Baez]
The Many Worlds are all deterministic. We can think of this as the tracks in the jungle being continuous and having a coherent direction. If they were not deterministic - if randomness had a say in things - we might find that a track suddenly stopped and the hiker was forced to do something of their own accord. Being deterministic also means that the worlds are logical, or internally consistent. Abominable snowpeople, for instance, might or might not exist in some of the worlds. But in none of the worlds would abominable snowpeople simultaneously exist and not exist. That would be illogical. Nor would any of the worlds have married bachelors, square triangles, or other incompatible objects.
I believe that most physicists have a misunderstanding about the Many Worlds. Most of them say that all of the Many Worlds are equally real and since one of them is 100% real - the world we live in - then all of them are 100% real. I disagree with an aspect of this. Although the worlds are equally real and our own world is 100% real, I think our particular world is different from the Many Worlds because it is a selection from them. Selection is a logical operation and the selected world acquires a logical 'tag' indicating it has been selected. In the case of our world, the tag is the word 'our'. It makes our world different from the other worlds. If we wanted to be literal we might say that 'selected world' is not the same as 'world'.
Most people do not agree with me on this point. Their view is that selection does not affect reality. Reality is what it is and is not affected by our selective view of it, they tell us. I detect an element of dogmatism in their view. They want a fixed-point in their worldview so they declare that reality shall fill that role. My own choice for a fixed-point in the world is not reality but logic, i.e., reality is subservient to logic. According to this 'logic first' view, reality has the characteristics that it has because there is a logic dictating to it. Or we could say that there is a logical reason for our world to be the way it is. Even if people disagree with me on this point - and I admit it is a significant departure from conventional thinking - they should not be dogmatic in their opposition. Changing to a 'logic first' scheme has significant explanatory power in areas where the conventional approach has been found wanting.
If we accept that a selected world is different on account of it having been selected, we get a new view of the Many Worlds theory. The view now is that although the Many Worlds are equally real, their degree of reality is actually zero (i.e., they are virtual). The only world which is not virtual is the one we inhabit, and its degree of reality is 100%. This is a much more commonsense interpretation of the Many Worlds formulation. The old idea was that there were countless near-identical copies of you and me existing in parallel worlds and all of these copies were 100% real. That was hard to believe. The new idea is that there is just one real world, and just one real version of 'me'. This is much less fanciful and agrees with what the man in the street has always thought.
However, there is a twist. Although there is just one real world as we have long believed, this real world of ours can be anything we like. It is not as if our world is set by 'reality' and had to be what reality dictated. That was the old scheme. The new scheme is that our world is a selection from a near-infinite range of virtual worlds, and we can choose any one of them we like to apply the tag 'our' to.
If our world is a selection from the Many Worlds, what does the selecting? There is only one candidate: logic. Logic is the only candidate for the selecting role because it is the only thing that exists outside the Many Worlds. To select something, the selecting agent logically has to be outside the objects that it scans for possible selection. Logic has that characteristic. Logic can be conceived as lying outside the Many Worlds that it controls, ruling out contradictions such as square triangles and married bachelors, for instance. Effectively, logic scrutinises the worlds from the outside and denies existence to any that are not logically consistent. [link not yet implemented]
It is one thing to identify logic as the selecting agent (the only possible candidate), but it is another to say how it operates. I will offer a suggestion later, but mainly it is a job for science to discover. The important thing for the moment is that we have moved away from the dogmatic assertion that reality comes before all else, and that we are absolutely subservient to it. This has been replaced by the idea that logic comes before all else, and reality is the one that is subservient.
What does it mean to have logic in charge in this way? It means, in particular, that something is real if and only if it contributes to the logic of the world. A thing is not real if all it does is exist 'in itself'. An object with no properties other than self-existence makes no contribution to our world's logic, and can hardly be said to be real. It might contribute to its own world's logic, but that is not relevant to our world. A thing has to have something more than self-existence, some 'impact' on our world, before it can be considered to contribute to the logic of our world and become accepted as real. For instance, some people are fond of telling us that God, angels, and other supernatural beings are real entities in our world, and that we should take them seriously. But these people produce no evidence for the existence of the entities. In the absence of evidence - i.e., in the absence of any impact on the world's logic - the scientific world does not accept that these would-be entities are real. Scientists are not so hard-nosed as to require the entities to be visible to people's eyes, but they do require them to have some logical effect on the world. Until a logical effect is demonstrated, the scientific view is that the entities are not real. Under the old scheme of things, reality was defined as a thing existing in itself, and it was hard to deny that angels or abominable snowpeople might exist in themselves, albeit unseen by most of us. The new scheme is more satisfactory because it does away with defining reality in terms of self existence. So even God, if he exists in himself, is not real. To be real he needs to contribute to the logic of our world. Self-existence simply is not sufficient. So far, there is no scientific evidence that God contributes to the logic of our world.
This view of things make reality 'relative to a world', rather than absolute. This is a respectable philosophical position (which might even be the majority position among philosophers). Philosophers have long entertained multiple semantic worlds, and even accepted the reality of such worlds, because each of them is internally consistent (i.e., cannot be ruled out). [link not yet implemented - David Chalmers?]
To solve the quantum measurement problem, let us briefly consider the Copenhagen view, wherein a quantum measurement is not complete until the experimenter views the dial pointer that gives the result of the measurement. If the experimenter does not look at the dial but takes a photograph of it, the measurement is not completed until the experimenter views the photograph, perhaps a week later. The mathematician John Von Neumann proved exhaustively (though with flaws, apparently) that the measurement makes no contribution to reality - i.e., is not complete - until the experimenter views the result. His proof consisted in showing that the camera that interacts with the experimental apparatus before the experimenter views the result is effectively part of the apparatus. It is only when the person 'checks the apparatus' - now including the camera - that the apparatus can be said to produce a result.
To explain this behaviour in the light of the discussion on this page, we need to recall that something is real if and only if it contributes to the logic of the world. In the quantum measurement, there is no change to the logic of the world until the person views the result, therefore we should not expect a 'real' result until that happens. The intermediate camera might take a photo of the dial pointer, but the logic of the world does not change on that account. It is only when a person views the photograph that the measured result enters the logic of the world and the rest of reality is required to take notice of it. There is nothing mystical about man's observation. It is just a matter of what an experiment is. An experiment is when we set up some apparatus to produce a result that we did not know beforehand and which alters our attitude, if ever so slightly, to the rest of the world. (i.e., has some logical impact on the world.) If we delete the person and pretend that a camera can take his or her place, we are being illogical in insisting that it is still an experiment.
As required by the Copenhagen view, a special role for people does exist in the determination of our world. I will this explain later. It hinges on the word 'our' in 'our world'. If our world is defined by 'our', it is inevitable that the components of the 'our' will be special.
In the next page I will use these ideas - particularly the notion that reality consists in contributing to the logic of the world - to explain some more scientific puzzles, beginning with Schrodinger's Cat. Next page - Page 4
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