When one is using a theory, one naturally pretends that the constructs of the theory are ‘‘real’’ or ‘‘exist’’. If the theory is highly successful (i.e. correctly predicts the sense perceptions of the user of the theory) then the confidence in the theory is built up and its constructs tend to be identified with ‘‘elements of the real physical world’’. This is however a purely psychological matter. No mental construct (and this goes for everyday, prescientific conceptions about the nature of things, objects, etc. as well as elements of formal theories) should ever be regarded as more ‘‘real’’ than any others. We simply have more confidence in some than others.

The constructs of classical physics are just as much fictions of our minds as those of any other theory we simply have a great deal more confidence in them. It must be deemed a mistake, therefore, to attribute any more ‘‘reality’’ here than else- where.

From the viewpoint of the theory, all elements of a super- position (all ‘‘branches’’) are ‘‘actual’’, none any more ‘‘real’’ than another. It is completely unnecessary to suppose that after an observation somehow one element of the final superposition is selected to be awarded with a mysterious quality called ‘‘reality’’ and the others condemned to oblivion. We can be more charitable and allow the others to coex- ist—they won’t cause any trouble anyway because all the separate elements of the superposition (‘‘branches’’) individu- ally obey the wave equation with complete indifference to the presence or absence (‘‘actuality’’ or not) of the other ele- ments.

On the other hand, properties are now intrinsically ‘‘relative’’:
All statements about a subsystem [. . .] become relative statements, i.e. statements about the subsystem relative to a prescribed state for the remainder.

[if we] consider a large number of interacting particles [...], throughout the course of time the position amplitude of any single particle spreads out farther and farther, approaching uniformity over the whole universe, while at the same time, due to the interactions, strong correlations will be built up, so that we might say that the particles have coalesced to form a solid object. That is, even though the position amplitude of any single particle would be ‘‘smeared out’’ over a vast region, if we consider a ‘‘cross section’’ of the total wave function for which one particle has a definite position, then we immediately find all the rest of the particles nearby, forming our solid object.

What we mean by the statement, ‘‘a hydrogen atom has formed in the box’’, is just that this correlation has taken place—a correlation which insures that the relative configura- tion for the electron, for a definite proton position, conforms to the customary ground state configuration.

You also raise the question of what it means to say that a fact or a group of facts is actually realized. Now I realize that this question poses a serious difficulty for the conventional formulation of quantum mechanics, and was the main motives for my reformulation. The difficulty is removed in the new formulation, however, since it is quite unnecessary in this theory ever to say anything like ‘‘Case A is actually realized.’’