Zur Einleitung ein paar meiner Lieblingsbeispiele aus Dänemark
When asked about an underlying quantum world, Bohr would answer,
“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.“
(Niels Bohr)
This work suffers from the fundamental misunderstanding which affects all attempts at ‘axiomatizing’ any part of physics. The ‘axiomatizers’ do not realize that every physical theory must necessarily make use of concepts which cannot in principle be further analyzed. […] The fact, emphasized by Everett, that it is actually possible to set-up a wave function for the experimental apparatus and a Hamiltonian for the interaction between system and apparatus is perfectly trivial, but also terribly treacherous; in fact, it did mislead Everett to the conception that it might be possible to describe apparatus + atomic object as a closed system. […] This, however, is an illusion.
(Leon Rosenfeld über Everett)
Letter Everett to Petersen
Letter Rosenfeld to Bergmann
At that juncture, Zeh's senior at Heidelberg, the Nobel Prize winner J. H. D. Jensen decided to ask Rosenfeld's advice on the paper. Rosenfeld's opinion was devastating.
“I have all the reasons in the world to assume that such a concentrate of wildest nonsense [decoherence] is not being distributed around the world with your blessing, and I think to be of service to you by directing your attention to this misfortune.”
(H‐D Zeh, Foundations of Physics, 1, 69–76 (1970). Rosenfeld to Jensen, 14 Feb 1968)
Eine gute Zusammenfassung siehe
Olival Freire Jr.: From the margins to the mainstream: Foundations of quantum mechanics, 1950–1990
Es ist einfach, weitere derartige Zitate bzgl. des Denkverbots aus Kopenhagen zu finden, aber das soll’s erst mal gewesen sein …
… dennoch, Zeilinger (als Beispiel) beruft sich auch heute im Wesentlichen auf diese Ansicht
It is also suggested that the austerity of the Copenhagen interpretation should serve as a guiding principle in a search for deeper understanding.
(Anton Zeilinger)
I have purposely not dealt with questions like: Is there a border between micro- and macro physics? Is a new form of logic necessary for quantum processes? Has one's awareness an active, dynamic influence on the wave function? Such or similar positions were proposed by several physicists, but in my opinion they would all fall victim to Occam's razor: Entia non sunt multiplicanda praeter necessitatem. It is the beauty of the Copenhagen interpretation that it operates with a minimal set of entities and concepts.
(Anton Zeilinger)
Das ist eine explizit instrumentalistische Position “im Geist von Kopenhagen” wenn auch nicht dogmatisch vertreten. Zeilinger weicht letztlich nur insofern ab, als auch makroskopische Objekte der Quantenmechanik gehorchen und durch ihre Gesetze beschrieben werden - falls nicht ein Messprozesses vorliegt. Die o.g. Erklärungslücke, wann genau dies der Fall sein soll, bleibt damit bestehen.
Nachdem wir nun wissen, womit wir es zu tun haben, im Folgenden gegenteilige Ansichten, die „Kopenhagen“ und/oder den Instrumentalismus sowie seine Spielarten explizit ablehnen: Zunächst Einstein sowie einige Philosophen – da wäre auch noch Feyerabend zu nennen, ebenso Quine
The important thing is not to stop questioning. Curiosity has its own reason for existing.
(Albert Einstein)
True ignorance is not the absence of knowledge, but the refusal to acquire it.
(Sir Karl Popper)
It is not intuitive ease I am after, but rather a point of view which is sufficiently definite to clear up some difficulties, and to be criticized in rational terms. (Bohr's complementarity cannot be so criticized, I fear; it can only be accepted or denounced - perhaps as being ad hoc, or as being irrational, or as being hopelessly vague.)
(Sir Karl Popper)
A scientific theory is usually felt to be better than its predecessors not only in the sense that it is a better instrument for discovering and solving puzzles but also because it is somehow a better representation of what nature is really like. One often hears that successive theories grow ever closer to, or approximate more and more closely to, the truth. Apparently, generalizations like that refer not to the puzzle-solutions and the concrete predictions derived from a theory but rather to its ontology, to the match, that is, between the entities with which the theory populates nature and what is “really there.”
(Thomas Kuhn)
There’s nothing particularly quantum-mechanical about instrumentalism. It has a long and rather sorry philosophical history: most contemporary philosophers of science regard it as fairly conclusively refuted. But I think it’s easier to see what’s wrong with it just by noticing that real science just isn’t like this. According to instrumentalism, paleontologists talk about dinosaurs so they can understand fossils […] and particle physicists talk about the Higgs Boson so they can understand the LHC. In each case, it’s quite clear that instrumentalism is the wrong way around. Science is not “about” experiments; science is about the world, and experiments are part of its toolkit.
(David Wallace, einer der führenden Philosophen zur Quantentheorie, mit exzellenter Ausbildung als Physiker)
A physical theory should clearly and forthrightly address two fundamental questions: what there is, and what it does. The answer to the first question is provided by the ontology of the theory, and the answer to the second by its dynamics. The ontology should have a sharp mathematical description, and the dynamics should be implemented by precise equations describing how the ontology will, or might, evolve […]
There is little agreement about just what this approach to quantum theory postulates to actually exist or how the dynamics can be unambiguously formulated. Nowadays, the term is often used as shorthand for a general instrumentalism that treats the mathematical apparatus of the theory as merely a predictive device, uncommitted to any ontology or dynamics at all […] Such an attitude rejects the aspiration to provide a physical theory, as defined above, at all. Hence it is not even in the running for a description of the physical world and what it does.
(Tim Maudelin, ebenfalls einer der führenden Philosophen zur Quantentheorie; s.u.a. Maudlin-Trilemma)
Damit sollte klar sein, dass maßgebliche Positionen gegen den Instrumentalismus existieren - auch wenn sich das nicht überall herumgesprochen hat.
Zur Einstein-Bohr-Debatte
The mid-twentieth century “Bohr-Einstein debate” about quantum theory is often misinterpreted as a personal clash between wizards. So counter-intuitive are quantum theory’s predictions that, under the leadership of one of its pioneers, Neils Bohr, a myth grew that there is no underlying reality that explains them. Particles get from A to B without passing through the intervening space, where they have insufficient energy to exist; they briefly “borrow” the energy, because we are “uncertain” about what their energy is. Information gets from A to B without anything passing in between – what Einstein called “spooky action at a distance.” […] So, while most accounts say that Bohr won the debate, my view is that Einstein, as usual, was seeking an explanation of reality, while his rivals were advocating nonsense.
(David Deutsch)
Der Punkt ist, dass Bohrs Ansicht natürlich funktioniert – was seitens Einstein letztlich nicht in Zweifel gezogen wurde. Einsteins Frage zielte tiefer, aber auf diese Argumentation geht Bohr nicht ein.
Deutsch ist hier nicht der einzige Physiker, der Bohr et al. für diese Haltung kritisiert, bzw. feststellt, dass beide (u.v.a.m) letztlich aneinander vorbeigeredet haben.
Daraus folgen zwei Erkenntnisse: Bohr hatte recht bzgl. des Formalismus und der Vorhersagen der Theorie. Daraus folgt jedoch nichts (!) bzgl. der tieferen Fragen von Einstein. Das wird bis heute oft falsch verstanden, und man findet diverse Zitate namhafter Physiker, die den Unterschied nicht sehen.
Letztlich geht es um die fundamentale Frage nach dem Gegenstand physikalischer Forschung.
Sehr interessant ist John Bells Meinung. Er war wohl für den Nobelpreis nominiert, als er recht früh und unerwartet verstarb.
The Copenhagen interpretation is a very ambiguous term. Some people use it just to mean the sort of practical quantum mechanics that you can do — like you can ride a bicycle without really knowing what you're doing. It's the rules for using quantum mechanics and the experience that we have in using it. […] Then there's another side to the Copenhagen interpretation, which is a philosophy of the whole thing. It tries to be very deep and tell you that these ambiguities, which you worry about, are somehow irreducible. It says that ambiguities are in the nature of things. We, the observers, are also part of nature. It's impossible for us to have any sharp conception of what is going on because we, the observers, are involved. And so there is this philosophy, which was designed to reconcile people to the muddle; You shouldn't strive for clarity— that's naive.
(John Stewart Bell)
Andere sagen es direkter:
Niels Bohr brain-washed a whole generation of physicists into believing that the problem [interpreting quantum theory] had been solved fifty years ago.
(Murray Gell-Mann; The Nature of the Physical Universe, the 1976 Nobel Conference)
Die Kritik richtet sich nicht gegen Details der Theorie, sondern gegen den Diskurs.