Abstract In this chapter we shall discuss these and related questions. We shall summarize what is well established and what has been clarified in the last several decades concerning these issues, trying to distinguish as clearly as possible different issues which are all called the “measurement problem”, and in each case, making an effort to clarify as sharply as possible the nature of the problem.
Abstract In this chapter we shall discuss these and related questions. We shall summarize what is well established and what has been clarified in the last several decades concerning these issues, trying to distinguish as clearly as possible different issues which are all called the “measurement problem”, and in each case, making an effort to clarify as sharply as possible the nature of the problem.
Abstract Chapter 6 was devoted to argue that the MHI offers a solution to the measurement problem for both ideal and non-ideal measurements, and to show how it provides a distinction between reliable and non-reliable measurements in the non-ideal case. However, in the last decades more complex measurement scenarios have been considered, some as old as the so-called Wigner’s friend experiment, and others recently designed to test the theoretical predictions of quantum mechanics. For this reason, in the present chapter, the measurement problem is revisited from the perspective of the challenges that those scenarios pose to interpretation.
In most textbooks, measurement does not receive the full attention it deserves and sometimes is even not treated at all, apart a brief and cryptic mention of the “reduction of the wave packet.” However, in the last decades, the situation has profoundly changed and it is time to consider measurement a fundamental part of quantum mechanics, even, to a certain extent, an important generalization of the traditional theory (see also Chs. 14–15). This chapter consists of three major parts. In the first block (Secs. 9.1–9.4) we develop the main physical features of the measurement process: the heart of the argument is here represented by the aspects related to the interpretation. In the second part (Secs. 9.5–9.8) we discuss several special (and partly interdependent) topics of measurement: the heart here is represented by experimental aspects. In the third part (Secs. 9.9–9.12) we deal with the measurement process on a more formal plane, making use, in particular, of the generalization represented by the concepts of effect and positive operator valued measure (POVM). As we have said, the measurement problem is one of the most fundamental issues in the conceptual structure of quantum mechanics (as described in Sec. 9.1) and has a long history that will be examined in Sec. 9.2. In this context, the existence of apparently paradoxical quantum states comes about: the so-called Schrödinger cat states (see Sec. 9.3).
The notion of an individual and the related issues on individuation are topics that appear in the philosophical discussion ever since the antiquity. The idea of an individual thing is intuitively clear: an individual is something of a specific kind that is a unity, having its own identity, and being so that it is possible at least in principle to discern it from any other individual, even of similar species. But when we try to leave the intuitive realm and push this idea to a logical analysis, we find a cluster of problems that are difficult to overcome within standard logico-mathematical contexts. In this work, we shall be concerned with some aspects of this intuitive concept of an individual and on some related facts about individuation taken from recent discussions that arose ever since the inception of quantum theory, pushing the discussion to a “logical” view, which in our opinion is still lacking in the usual debates on such issues. In the final part of the paper, we propose a metaphysics where the notion of identity is substituted, for some objects, by a weaker notion of indiscernibility, and we try to justify such a move. In most of the uses of the expression “quantum theory”, we shall not make explicit the distinction between the non-relativistic and the relativistic approaches, although they of course are quite different, for we think that the problems as we shall present them appear in both versions. But, as the text goes, the context will distinguish between them and these questions will become clear to the reader.
Q UANTUM MECHANICS, TOGETHER WITH RELATIVITY, are the basis of most of what we know of the very large, the very small, and the very fast.And in all of these areas our knowledge is extensive.It would be hard to say how good these theories are; arithmetic, one might say, is good mathematics.For all that, there is a problem, a strange and amorphous difficulty: it is the problem of measurement.This problem has become much more interesting, and much more pressing, as a result of some recent developments.Hitherto the difficulty has been so peculiar, and so formless, that physicists have on the whole thought it a matter of philosophy.But that is not quite right (or that is what I shall argue).It is certainly philosophical, but it is also a matter of methodology, a question of what physics is to do; and now the matter has come to seem quite pressing.In this sense the measurement problem has become a problem for physics.But what is the problem of measurement?As a first stab, we can say this: on the basis of quantum mechanics, there is a difficulty in accounting for the
Abstract Spontaneous collapse theories of quantum mechanics turn the usual Schrödinger equation into a stochastic dynamical law. In particular, in this paper I will focus on the GRW theory. Two philosophical issues that can be raised about GRW concern (a) the ontology of the theory, in particular the nature of the wave function and its role within the theory, and (b) the interpretation of the objective probabilities involved in the dynamics of the theory. During the last years, it has been claimed that we can take advantage of dispositional properties in order to develop an ontology for GRW theory, and also in order to ground the objective probabilities which are postulated by it. However, in this paper I will argue that the dispositional interpretations which have been discussed in the literature so far are either flawed or—at best—incomplete. If we want to endorse a dispositional interpretation of GRW theory we thus need an extended account which specifies the precise nature of those properties and which makes also clear how they can correctly ground all the probabilities postulated by the theory. Thus, after having introduced several different kinds of probabilistic dispositions, I will try to fill the gap in the literature by proposing a novel and complete dispositional account of GRW, based on what I call spontaneous weighted multi-track propensities. I claim that such an account can satisfy both of our desiderata.