Quantum theorem shakes foundations

Post Reply New Topic

Does that mean you do not accept the Everett interpretation?

The Everettian picture as described above, however, has an obvious problem. Namely, if the quantum wavefunction is all that there is, if we only have the quantum formalism, as given by the Schrödinger equation, how can we make sense of the experimental data observed (not just numerically but also ontologically)? More precisely, what is the actual ‘stuff’ in the Everettian picture that is capable of taking us from the very formalism to the empirical (macroscopic) observations? Can the wavefunction just by itself provide that ‘connection’, so to speak? This worry is raised by Tim Maudlin in his chapter ‘Can the World Be Only Wavefunction?’. The answer to the above questions, in Maudlin’s view, is negative. What Everettians face, really, is an epistemic problem, not exclusive of many worlds but common to all so-called ‘monistic’ interpretations of quantum mechanics, such as GRW and other collapse interpretations. Maudlin’s point, more precisely, is that it is not even logically possible for such monistic views to be able to fill in the gap between their theoretical machinery and the empirical phenomena these are supposed to account for. This is because the quantum formalism by itself—be it given by the Schrödinger equation with no further modification, be it a further version of it modified to accommodate collapse (as it is the case of GRW)— does not contain the right ontological ‘stuff’, i.e. actual particles. The quantum formalism, in other words, if taken just on
its own, lacks the capacity to make the connection with the empirical data observed macroscopically. Only Bohmian mechanics can sensibly do that, Maudlin’s argument goes. For it explicitly incorporates extra ontology on the top of the formalism.

By contrast, proponents of many worlds claim that it is decoherence that can do the job. This is the position defended in the three first papers of the book, by David Wallace, Jim Hartle, and Jonathan Halliwell. The appeal to decoherence theory is not free of difficulties, however. On the one hand, decoherence is elusive in some cases and even completely absent in some others (although this seems not to be a serious worry). On the other hand, decoherence theory is put at work in a context of ‘emergence’. In that view, as defended by Wallace, ‘emergent structures’ correspond to the observed macroscopic objects. Again, this seems not enough for Maudlin. For in what sense, he insists, can be said that such structures emerge, if the theory does not contain an underlying fundamental ontology to start with? To this question, defenders of many worlds do not seem to have a good answer.

A pretty good free download book on the merits or lack there of can be found below. For a pretty good critical position see Maudlin's Chapter 4: "Can the World be Only Wavefunction?"

Many Worlds? Everett, Quantum Theory, and Reality
http://bacon.umcs.lublin.pl/~lukasik/wp ... eality.pdf

A brief review of this book can be found below. Some interesting quotes from there:


Many Worlds: Quantum Theory and Reality?
http://fs-morente.filos.ucm.es/docentes ... eality.pdf

Too much concern with philosophical matters will cause Brain Rot.

What has been lost sight of is that physics as a subject of thought is a dynamic interplay between storytelling and equation writing. Neither one stands alone, not even at the end of the day. But which has the more fatherly role? If you ask me, it’s the storytelling. Bryce DeWitt once said, “We use mathematics in physics so that we won’t have to think.” In those cases when we need to think, we have to go back to the plot of the story and ask whether each proposed twist and turn really fits into it. An interpretation is powerful if it gives guidance, and I would say the very best interpretation is the one whose story is so powerful it gives rise to the mathematical formalism itself (the part where nonthinking can take over). The “interpretation” should come first; the mathematics (i.e., the pre-existing, universally recognized thing everyone thought they were talking about before an interpretation) should be secondary.

If a physicist claims to have produced a system with a particular wave function, does this represent directly a physical wave of some kind, or is the wave function merely a summary of knowledge, or information, about the system? A recent no-go theorem shows that models in which the wave function is not physical, but corresponds only to an experimenter's information about a hypothetical real state of the system, must make different predictions from quantum theory when a certain test is carried out. Here we report on an experimental implementation using trapped ions. Within experimental error, the results confirm quantum theory. We analyse which kinds of theories are ruled out...The fundamental question of the interpretation of the wave function of a quantum system was partially resolved. If systems have real states, regardless of an experimenter or measurements performed, then a natural question is whether the quantum state is epistemic, i.e. corresponding merely to knowledge of these underlying real states. In the presented manuscript we tested for this specific possibility and ruled out the most natural class of such models to a high degree of confidence.