Yes. That is my polemical reply to the titular question in Travis Norsens self-styled polemical response to Howard Wisemans recent paper. Less polemically, I am pleased to see that on two of my positions --- that Bells 1964 theorem is different from
Bells 1976 theorem, and that the former does not include Bells one-paragraph heuristic presentation of the EPR argument --- Norsen has made significant concessions. In his response, Norsen admits that Bells recapitulation of the EPR argument in [the relevant] paragraph leaves something to be desired, that it disappoints and is problematic. Moreover, Norsen makes other statements that imply, on the face of it, that he should have no objections to the title of my recent paper (The Two Bells Theorems of John Bell). My principle aim in writing that paper was to try to bridge the gap between two interpretational camps, whom I call operationalists and realists, by pointing out that they use the phrase Bells theorem to mean different things: his 1964 theorem (assuming locality and determinism) and his 1976 theorem (assuming local causality), respectively. Thus, it is heartening that at least one person from one side has taken one step on my bridge. That said, there are several issues of contention with Norsen, which we (the two authors) address after discussing the extent of our agreement with Norsen. The most significant issues are: the indefiniteness of the word locality prior to 1964; and the assumptions Einstein made in the paper quoted by Bell in 1964 and their relation to Bells theorem.
Bells theorem can refer to two different theorems that John Bell proved, the first in 1964 and the second in 1976. His 1964 theorem is the incompatibility of quantum phenomena with the joint assumptions of Locality and Predetermination. His 1976 theo
rem is their incompatibility with the single property of Local Causality. This is contrary to Bells own later assertions, that his 1964 theorem began with the assumption of Local Causality, even if not by that name. Although the two Bells theorems are logically equivalent, their assumptions are not. Hence, the earlier and later theorems suggest quite different conclusions, embraced by operationalists and realists, respectively. The key issue is whether Locality or Local Causality is the appropriate notion emanating from Relativistic Causality, and this rests on ones basic notion of causation. For operationalists the appropriate notion is what is here called the Principle of Agent-Causation, while for realists it is Reichenbachs Principle of common cause. By breaking down the latter into even more basic Postulates, it is possible to obtain a version of Bells theorem in which each camp could reject one assumption, happy that the remaining assumptions reflect its weltanschauung. Formulating Bells theorem in terms of causation is fruitful not just for attempting to reconcile the two camps, but also for better describing the ontology of different quantum interpretations and for more deeply understanding the implications of Bells marvellous work.
Many of the heated arguments about the meaning of Bells theorem arise because this phrase can refer to two different theorems that John Bell proved, the first in 1964 and the second in 1976. His 1964 theorem is the incompatibility of quantum phenomen
a with the dual assumptions of locality and determinism. His 1976 theorem is the incompatibility of quantum phenomena with the unitary property of local causality. This is contrary to Bells own later assertions, that his 1964 theorem began with that single, and indivisible, assumption of local causality (even if not by that name). While there are other forms of Bells theorems --- which I present to explain the relation between Jarrett-completeness, fragile locality, and EPR-completeness --- I maintain that Bells t
By rigorously formalizing the Einstein-Podolsky-Rosen (EPR) argument, and Bohrs reply, one can appreciate that both arguments were technically correct. Their opposed conclusions about the completeness of quantum mechanics hinged upon an explicit diff
erence in their criteria for when a measurement on Alices system can be regarded as not disturbing Bobs system. The EPR criteria allow their conclusion (incompletness) to be reached by establishing the physical reality of just a single observable $q$ (not a conjugate pair $q$ and $p$), but I show that Bohrs definition of disturbance prevents the EPR chain of reasoning from establishing even this. Moreover, I show that Bohrs definition is intimately related to the asymmetric concept of quantum discord from quantum information theory: if and only if the joint state has no Alice-discord, she can measure any observable without disturbing (in Bohrs sense) Bobs system. Discord can be present even when systems are unentangled, and this has implications for our understanding of the historical development of notions of quantum nonlocality.
Dynamical quantum jumps were initially conceived by Bohr as objective events associated with the emission of a light quantum by an atom. Since the early 1990s they have come to be understood as being associated rather with the detection of a photon b
y a measurement device, and that different detection schemes result in different types of jumps (or diffusion). Here we propose experimental tests to rigorously prove the detector-dependence of the stochastic evolution of an individual atom. The tests involve no special preparation of the atom or field, and the required efficiency can be as low as eta ~58%.
Since the first derivation of non-Markovian stochastic Schrodinger equations, their interpretation has been contentious. In a recent Letter [Phys. Rev. Lett. 100, 080401 (2008)], Diosi claimed to prove that they generate true single system trajectori
es [conditioned on] continuous measurement. In this Letter we show that his proof is fundamentally flawed: the solution to his non-Markovian stochastic Schrodinger equation at any particular time can be interpreted as a conditioned state, but joining up these solutions as a trajectory creates a fiction.
