fevereiro 16, 2012

Falácia de Projecção Mental

Alfred North Whitehead no seu livro Process and Reality de 1929 apresentou o que ficou conhecido como The Fallacy of Misplaced Concreteness:
neglecting the degree of abstraction involved when an actual entity is considered merely so far as it exemplifies certain categories of thought (pg.11).
Este é um aviso sobre o erro de confundir o abstracto com o concreto. Esta ideia possui várias denominações. Talvez a mais conhecida seja a de Alfred Korzybski, 'O mapa não é o território'.

A este mesmo problema E.T. Jaynes designou por Falácia de Projecção Mental. No texto seguinte Jaynes usa-o para discutir as interpretações da teoria quântica e como a confusão entre estes dois níveis -- entre ontologia e epistemologia -- pode ter estado na origem do célebre desacordo de que deus não joga aos dados entre Einstein e Bohr:

The failure of quantum theorists to distinguish in calculations between several quite different meanings of 'probability', between expectation values and actual values, makes us do things that don't need to be done; and to fail to do things that do need to be done. We fail to distinguish in our verbiage between prediction and measurement. For example, the famous vague phrases: 'It is impossible to specify...'; or 'It is impossible to define...' can be interpreted equally well as statements about prediction or statements about measurement. Thus the demonstrably correct statement that the present formalism cannot predict something becomes perverted into the logically unjustified (and almost certainly false) claim that the experimentalist cannot measure it!

We routinely commit the Mind Projection Fallacy: supposing that creations of our own imagination are real properties of Nature, or that our own ignorance signifies some indecision on the part of Nature. It is then impossible to agree on the proper place of information in physics. This muddying up of the distinction between reality and our knowledge of reality is carried to the point where we find some otherwise rational physicists, on the basis of the Bell inequality experiments, asserting the objective reality of probabilities, while denying the objective reality of atoms! These sloppy habits of language have tricked us into mystical, pre-scientific standards of logic, and leave the meaning of any QM result ambiguous. Yet from decades of trial-and-error we have managed to learn how to calculate with enough art and tact so that we come out with the right numbers!

The main suggestion we wish to make is that how we look at basic probability theory has deep implications for the Bohr-Einstein positions. Only since 1988 has it appeared to the writer that we might be able finally to resolve these matters in the happiest way imaginable: a reconciliation of the views of Bohr and Einstein in which we can see that they were both right in the essentials, but just thinking on different levels.

Einstein's thinking is always on the ontological level traditional in physics; trying to describe the realities of Nature. Bohr's thinking is always on the epistemological level, describing not reality but only our information about reality. The peculiar flavor of his language arises from the absence of all words with any ontological import. J. C. Polkinghorne (1989, pp. 78,79) came independently to this same conclusion about the reason why physicists have such difficulty in reading Bohr. He quotes Bohr as saying:
"There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature."
[...] Bohr would chide both Wigner and Oppenheimer for asking ontological questions, which he held to be illegitimate. Those who, like Einstein (and, up until recently, the present writer) tried to read ontological meaning into Bohr's statements, were quite unable to comprehend his message. This applies not only to his critics but equally to his disciples, who undoubtedly embarrassed Bohr considerably by offering such ontological explanations as "Instantaneous quantum jumps are real physical events." or "The variable is created by the act of measurement.", or the remark of Pauli quoted above, which might be rendered loosely as "Not only are you and I ignorant of x and p; Nature herself does not know what they are."

We disagree strongly with one aspect of Bohr's quoted statement above; in our view, the existence of a real world that was not created in our imagination, and which continues to go about its business according to its own laws, independently of what humans think or do, is the primary experimental fact of all, without which there would be no point to physics or any other science.

The whole purpose of science is learn what that reality is and what its laws are. On the other hand, we can see in Bohr's statement a very important fact, not sufficiently appreciated by scientists today as a necessary part of that program to learn about reality. Any theory about reality can have no consequences testable by us unless it can also describe what humans can see and know. For example, special relativity theory implies that it is fundamentally impossible for us to have knowledge of any event that lies outside our past light cone. Although our ultimate goal is ontological, the process of achieving that goal necessarily involves the acquisition and processing of human information. This information processing aspect of science has not, in our view, been sufficiently stressed by scientists (including Einstein himself, although we do not think that he would have rejected the idea).

Although Bohr's whole way of thinking was very different from Einstein's, it does not follow that either was wrong. In the writer's present view, all of Einstein's thinking (in particular the EPR argument) remains valid today, when we take into account its ontological purpose and character. But today, when we are beginning to consider the role of information for science in general, it may be useful to note that we are finally taking a step in the epistemological direction that Bohr was trying to point out sixty years ago.

But our present QM formalism is not purely epistemological; it is a peculiar mixture describing in part realities of Nature, in part incomplete human information about Nature - all scrambled up by Heisenberg and Bohr into an omelette that nobody has seen how to unscramble. Yet we think that the unscrambling is a prerequisite for any further advance in basic physical theory. For, if we cannot separate the subjective and objective aspects of the formalism, we cannot know what we are talking about; it is just that simple. E.T. Jaynes, Probability in Quantum Theory (1996).

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