Protective measurement, which we have introduced recently, allows one to observe properties of the state of a single quantum system and even the Schrödinger wave itself. These measurements require a protection, sometimes due to an additional procedure and sometimes due to the potential of the system itself The analysis of the protective measurements is presented and it is argued, contrary to recent claims, that they observe the quantum state and not the protective potential. Some other misunderstandings concerning our (...) proposal are also clarified. (shrink)

Do sensory measurements deserve the label of “measurement”? We argue that they do. They fit with an epistemological view of measurement held in current philosophy of science, and they face the same kinds of epistemological challenges as physical measurements do: the problem of coordination and the problem of standardization. These problems are addressed through the process of “epistemic iteration,” for all measurements. We also argue for distinguishing the problem of standardization from the problem of coordination. To exemplify (...) our claims, we draw on olfactory performance tests, especially studies linking olfactory decline to neurodegenerative disorders. (shrink)

We critically evaluate the treatment of the notion of measurement in the Consistent Histories approach to quantum mechanics. We find such a treatment unsatisfactory because it relies, often implicitly, on elements external to those provided by the formalism. In particular, we note that, in order for the formalism to be informative when dealing with measurement scenarios, one needs to assume that the appropriate choice of framework is such that apparatuses are always in states of well defined pointer positions after (...) class='Hi'>measurements. The problem is that there is nothing in the formalism to justify this assumption. We conclude that the Consistent Histories approach, contrary to what is claimed by its proponents, fails to provide a truly satisfactory resolution for the measurement problem in quantum theory. (shrink)

This paper shows that the non-Boolean logic of quantum measurements is more naturally represented by a relatively new 4-operation system of Boolean fractions—conditional events—than by the standard representation using Hilbert Space. After the requirements of quantum mechanics and the properties of conditional event algebra are introduced, the quantum concepts of orthogonality, completeness, simultaneous verifiability, logical operations, and deductions are expressed in terms of conditional events thereby demonstrating the adequacy and efficacy of this formulation. Since conditional event algebra is nearly (...) Boolean and consists merely of ordered pairs of standard events or propositions, quantum events and the so-called “superpositions” of states need not be mysterious, and are here fully explicated. Conditional event algebra nicely explains these non-standard “superpositions” of quantum states as conjunctions or disjunctions of conditional events, Boolean fractions, but does not address the so-called “entanglement phenomena” of quantum mechanics, which remain physically mysterious. Nevertheless, separating the latter phenomena from superposition issues adds clarity to the interpretation of quantum entanglement, the phenomenon of influence propagated at faster than light speeds. With such treacherous possibilities present in all quantum situations, an observer has every reason to be completely explicit about the environmental–instrumental configuration, the conditions present when attempting quantum measurements. Conditional event algebra allows such explication without the physical and algebraic remoteness of Hilbert space. (shrink)

A complete set of mutually unbiased bases for a Hilbert space of dimension N is analogous in some respects to a certain finite geometric structure, namely, an affine plane. Another kind of quantum measurement, known as a symmetric informationally complete positive-operator-valued measure, is, remarkably, also analogous to an affine plane, but with the roles of points and lines interchanged. In this paper I present these analogies and ask whether they shed any light on the existence or non-existence of such symmetric (...) quantum measurements for a general quantum system with a finite-dimensional state space. (shrink)

A large literature has grown up around the proposed use of ‘weak measurements’ to allegedly provide information about hidden ontological features of quantum systems. This paper attempts to clarify the fact that ‘weak measurements’ involve strong measurements on one member of an entangled system. The only thing ‘weak’ about such measurements is that the correlation established via the entanglement does not correspond to eigenstates of the ‘weakly measured observable’ for the remaining component system subject to the (...) weak measurement. All observed statistics are straightforwardly and easily predicted by standard quantum mechanics. Specifically, it is noted that measurement of the pointer steers the remaining degree of freedom into new states with new statistical properties—constituting a non-trivial disturbance. In addition, standard quantum mechanics readily allows us to conditionalize on a final state if we choose, so the ‘post-selection’ that features prominently in time-symmetric formulations is also equipment from standard quantum theory. Assertions in the literature that weak measurements leave a system negligibly disturbed, and/or that standard quantum theory is cumbersome for computing the predicted measurement results, are therefore unsupportable, and ontological claims based on such assertions need to be critically reassessed. (shrink)

I address the recent debate between Meehan and Vaidman concerning the claim made by the former for a new problem to quantum mechanics. I argue that while Meehan's incompatibility claim does hold in the situation he presents, it does not genuinely involve considerations that can limit quantum state preparation, nor does it introduce new constrains over possible interpretations of quantum theory.

The nondecay probability of an unstable particle at a definite moment of time is investigated provided this particle existed at all earlier observation moments separated with the time interval Δ. Using the usual postulates for quantum measurements it is proved that this probability is described by the exponential function of Δ>0, and it tends to 1 as Δ → 0. An approximate formula is found for the effective decay width Γ(Δ) appearing in the case of multiple measurements. It (...) is shown that Γ(Δ) → 0 as Δ → 0. For Δ → ∞, the width Γ(Δ) → Γ0, with Γ0 being the standard decay with in Weisskopf-Wigner theory. At finite δ's Γ(Δ) may be smaller or greater than Γ0 depending on the parameters of the theory. (shrink)

We prove a Gleason-type theorem for the quantum probability rule using frame functions defined on positive-operator-valued measures, as opposed to the restricted class of orthogonal projection-valued measures used in the original theorem. The advantage of this method is that it works for two-dimensional quantum systems and even for vector spaces over rational fields—settings where the standard theorem fails. Furthermore, unlike the method necessary for proving the original result, the present one is rather elementary. In the case of a qubit, we (...) investigate similar results for frame functions defined upon various restricted classes of POVMs. For the so-called trine measurements, the standard quantum probability rule is again recovered. (shrink)

It will be shown that the Peres–Mermin square admits value-definite noncontextual hidden-variable models if the observables associated with the operators can be measured only sequentially but not simultaneously. Namely, sequential measurements allow for noncontextual models in which hidden states update between consecutive measurements. Two recent experiments realizing the Peres–Mermin square by sequential measurements will also be analyzed along with other hidden-variable models accounting for these experiments.

A large literature has grown up around the proposed use of 'weak measurements' to allegedly provide information about hidden ontological features of quantum systems. This paper attempts to clarify the fact that 'weak measurements' are simply strong measurements on one member of an entangled pair, and that all such measurements thus effect complete disentanglement of the pair. The only thing 'weak' about them is that the correlation established via the entanglement does not correspond to eigenstates of (...) the 'weakly measured observable' for the component system that is subject to the weak measurement. It is observed that complete disentanglement always occurs, whether post-­‐selection is performed before or after the pointer detection. Assertions in the literature that weak measurements leave a system negligibly disturbed are therefore inaccurate, and claims based on those assertions need to be critically reassessed. (shrink)

Well-being measurements are frequently used to support conclusions about a range of philosophically important issues. This is a problem, because we know too little about the intervals of the relevant scales. I argue that it is plausible that well-being measurements are non-linear, and that common beliefs that they are linear are not truth-tracking, so we are not justified in believing that well-being scales are linear. I then argue that this undermines common appeals to both hypothetical and actual well-being (...) measurements; I first focus on the philosophical literature on prioritarianism and then discuss Kahneman’s Peak-End Rule as a systematic bias. Finally, I discuss general implications for research on well-being, and suggest a better way of representing scales. (shrink)

Interaction-free measurements introduced by Elitzur and Vaidman [Found. Phys. 23, 987 (1993)] allow finding infinitely fragile objects without destroying them. Many experiments have been successfully performed showing that indeed, the original scheme and its modifications lead to reduction of the disturbance of the observed systems. However, there is a controversy about the validity of the term “interaction-free” for these experiments. Broad variety of such experiments are reviewed and the meaning of the interaction-free measurements is clarified.

Wodak (2019) persuasively argues that we are not justified in believing that well-being measurements are linear. From this, he infers grave consequences for both political philosophy thought experiments and empirical psychological research. Here I argue that these consequences do not follow. Wodak’s challenges to the status of well-being measurements do not affect thought experiments, and well-being empirical researchers may be justified in making average comparisons even if their measurements are not linear.

Despite their important applications in metrology and in spite of numerous experimental demonstrations, weak measurements are still confusing for part of the community. This sometimes leads to unjustified criticism. Recent papers have experimentally clarified the meaning and practical significance of weak measurements, yet in Kastner, Kastner seems to take us many years backwards in the the debate, casting doubt on the very term “weak value” and the meaning of weak measurements. Kastner appears to ignore both the basics (...) and frontiers of weak measurements and misinterprets the weak measurement process and its outcomes. In addition, she accuses the authors of Aharonov et al. in statements completely opposite to the ones they have actually made. There are many points of disagreement between Kastner and us, but in this short reply I will leave aside the ontology and focus mainly on the injustice in her criticism. I shall add some general comments regarding the broader theory of weak measurements and the two-state-vector formalism, as well as supporting experimental results. Finally, I will point out some recent promising results, which can be proven by projective measurements, without the need of employing weak measurements. (shrink)

Estimating whether the Earth’s biota is in the middle of a crisis relies heavily on comparisons between present and past data about biodiversity or biodiversity surrogates. Although the past is a crucial source of information to assess the severity of the current biodiversity crisis, substantive conceptual and methodological questions remain about how paleodiversity and biodiversity are to be properly compared. I argue that to justify claims of a current biodiversity crisis is harder than it appears. More precisely, I claim that (...) paleodiversity measurements are incommensurable with contemporary measurements, given the different ways that biodiversity is conceptualized and operationalized. I conclude by proposing three possible ways of overcoming this incommensurability problem. (shrink)

The process of turning a myth into a fairy tale, its internal and external causes, patterns, consequences... It may be difficult to find a more traditional way of exploring a fairy tale than this one. We will not avoid it either, because whatever aspect of the fairy tale analysis we choose, it is impossible to bypass this side of its genesis. And the choice of the method of explication of this problem largely predetermines both the angle of her vision and (...) the means of solution. The same traditions have already been given peculiar power lines that urge more and more researchers to move in the area of ​​these lines and to cover more and more varieties of the same dimensions of the object: demythologization and desacralization of the hero, his actions, his environment; giving the myth an exoteric character, with the elements of fiction and irony that are inconceivable as a result; the shrinking of the scale of the hero's actions, and hence the replacement of the mystery of myth with mysteriousness, intrigue in the fairy tale, the decline of the mythological worldview. The topics of branching of the subjects through the myth to the fairy tale, finding and researching common for both phenomena of binary oppositions, etc., are densely addressed. (shrink)

The article addresses the debate about the empirical status of particles versus wave functions in Bohmian quantum mechanics. It thereby clarifies questions and misconceptions about the role of the...

After an outline of the macrorealistic solutions to the difficulties of the measurement theory, a new paradox is proposed and then discussed in the light of three different interpretations of quantum mechanics.

It is shown that Uffink's attempt to protect the interpretation of the wave function against protective measurements fails due to several errors in his arguments.

Noncommuting quantum observables, if considered asunsharp observables, are simultaneously measurable. This fact is exemplified for complementary observables in two-dimensional state spaces. Two proposals of experimentally feasible joint measurements are presented for pairs of photon or neutron polarization observables and for path and interference observables in a photon split-beam experiment. A recent experiment proposed and performed by Mittelstaedt, Prieur, and Schieder in Cologne is interpreted as a partial version of the latter example.