Diagnóstico de la problemática

It is not the case that every physicist who considers himself as being a supporter of the Copenhagen views will necessarily agree with the content of Wheeler’s article. In the opinion of many among these

scientists, the Copenhagen views are based on the assertion that the ‘classical’ or ‘macroscopic’ objects and events exist in some absolute sense which is in no need of being defined. Indeed, trying to define it, or even trying to speak about it, would (so they think) be idle talk. Or if it is not, if such a task is not entirely meaningless, at least it is one which, in their opinion, can and should be entirely left to the philosophers. They then claim that we should not try to speak of the quantum objects by themselves and that any valid description of the quantum phenomena must be anchored on the notion of these

obviously existing objects and events (and in particular on the two closely related notions of ‘complete experimental set up’ and of ‘conditions of observation’ so often appearing in Niels Bohr’s works). Such a conception may conveniently be called macro-objectivism; and we may then assert that many theoretical physicists identify the Copenhagen view with a special case of macro-objectivism.

Now, macro-objectivism is a view which works very well in practice but which meets with conceptual difficulties that are actually quite serious. The most conspicuous of these is that it seems unavoidable to consider macroscopic objects as ultimately composed of microscopic, i.e. quantum, ones. And one of the notions which one was trying to discard, namely the notion of quantum objects existing in some absolute sense independently of the conditions of observation, seems thereby to be inescapably creeping back. Closely related with this difficulty is the one that macro-objectivism seems to require a rather sharp distinction to be made between classical and quantum objects (and events), whereas physics proper does not seem really to give us any clue as to how such a distinction could be made objective in any sense that would be in harmony with the basic ideas of, precisely, macro-objectivism. Admittedly irreversibility has—at least as regards events—been considered by many authors as a good candidate for playing the role of a criterion in that respect. But, again, it seems difficult to define irreversibility in a way which would make no reference whatsoever, not even an implicit one, to the

limitations of the abilities of the community of observers. In fact, the proposals that have been made along these lines do not seem to comply with the requisites that, for consistency, a macro-objectivist must have in mind when he considers an ‘objective’ macroscopic event. An alternative possibility, namely the idea that quantum mechanics should only be an approximate theory, remains open. But it is not substantiated by any experimental fact and it would be quite a new thing if a momentous scientific change were initiated neither by new findings nor by new theoretical developments but just by considerations that can well be called philosophical about the nature of reality.

Under these conditions it seems that whoever wants to ‘remain faithful’ to the letter of the Copenhagen conception should preferably not identify the latter with macro-objectivism. Moreover it seems that

he will thus remain closer to the real spirit of the Copenhagen founding fathers. In his book Physics and Philosophy, Heisenberg, for instance, considers that a statement ‘can be made objective’ if we may consistently claim that its content does not depend on the conditions under which it can be verified. And when he then defines several varieties of realism, he dismisses as meaningless any ‘metaphysical realism’ (this is the expression he used) that would not reduce either to what he calls practical realism or to what he calls ‘dogmatic realism’; that is, to a conception asserting that most or, respectively, all of our meaningful statements about the material world can be ‘made objective’, in the sense just specified. Now what is most significant in this standpoint of Heisenberg is not the distinction he makes between practical and dogmatic realisms (although this, of course, is important too). It is the very fact, first, that this author does define what he calls objectivity and realism instead of considering that these are primary concepts and, second, that he defines them by referring to what can actually be done. By choosing to define these terms and to define them in this way, Heisenberg in fact makes verification the primary concept; that is, he chooses as a primary concept in science one which basically refers to the actions of men. This choice has implications which are in fact so momentous that most of the physicists who consider themselves as agreeing with the Copenhagen viewpoint seem somehow not to have dared taking them quite fully into account.

This however is not the case with John Wheeler. In Wheeler’s paper the ultimate referent is ‘meaning’, a concept for which Føllesdal’s definition ‘Meaning is the joint product of all the evidence that is available to those who communicate’ is taken. Another key word of this paper is ‘phenomenon’. However let us not be abused by the fact that in current scientific language the word ‘phenomenon’ is very often understood as just signifying a type of event taking place within a reality whose concept is tacitly understood as being the ultimate referent. Wheeler’s sentence ‘no phenomenon is a

phenomenon until it is an observed phenomenon’ very clearly dismisses this ‘commonsense’ view. Indeed his ‘phenomena’ should be understood in the etymological sense (which is also the one in which Kant used the word); namely, ‘what is observed and about which an agreement gets established amongst the community of all people in their right mind’. It is important to stress that in Wheeler’s paper there is no primary concept other than these two (or just ‘meaning’ if we consider that ‘phenomenon’ refers to ‘meaning’). In particular, we shall not understand this article if we consider that there is another primary concept, namely ‘reality’, tacitly underlying it. The article in question makes no use of such a concept but if it did there is no doubt that reality would be defined relative to one of the aforenamed two concepts or to both—again, just as is the case in Kant’s work. Consequently, Wheeler urges us ‘to abandon for the foundation of existence a physics hardware located “out there”

and to put in instead a “meaning” software located who knows where’.

There is no point in reviewing Wheeler’s article further, except to notice that the qualitative ambiguities and difficulties mentioned above are of course removed by such a drastic approach. In particular it is clear from the whole content of this paper that its author does not give any basic status to the concept of irreversibility. (He does mention the notion of an ‘irreversible act of amplification’ however, but it seems that he considers it as a mere

‘potential’ phenomenon, unless it is ‘put to use’ to make the meaning.) For example, the splitting of a uranium nucleus, though it is called irreversible, could be undone in principle. It then would not count as a phenomenon. Indeed, if we are right, his way of solving the well-known quantum riddle ‘How is it possible that mere information (that is, “software”) should in some cases (e.g. that of the Schrödinger cat) modify the real state of macroscopic things (hardware)?’ is as follows. He answers by just denying to this postulated hardware any existence of its own. This way of solving the problem will be analysed and discussed in the next section.