Before we, as philosophers, take a look at string theory I want to mention that more than one person has suggested to me that it is still too early for philosophical and foundational studies of string theory. Indeed, the suggestion emphasizes, since string theory is still in the process of development, and its physical and mathematical principles are not completely formulated, there is, in a sense, no theory for the philosopher to analyze. And I must admit that I think there is something to this suggestion. In a sense I hope I will make clear, there does not yet exist a precise mathematical formulation for string theory as there is Hilbert space for (elementary) quantum theory, and Riemann spacetime for general relativity. Because these latter formulations exist, we can ask precise questions, and prove precise theorems about their interpretation.

Ever since Hilary Putnam claimed that a realist philosophy is “the only philosophy that doesn’t make the success of science a miracle,” explanations for the success of science have proliferated in the philosophical literature (Putnam 1975, p. 73). Realists argue that the success of science, as exhibited by our ability to accurately predict and explain a wide range of phenomena, indicates that our theories have identified some of the underlying causal structures of the world (e.g., Boyd 1985, Ellis 1985, McMullin 1984, Salmon 1984). Nonrealists counter that success cannot provide a warrant for belief in the truth of scientific theories because there have been successful theories in the past that are now believed to be false (Laudan 1981b). Instead, they offer a naturalized account whereby our theories are designed to be successful predictors and only those which fulfill this goal survive (Laudan 1987, van Fraassen, 1980).

In this talk, I'd like to explain a little bit about what string theory is, why theoretical physicists are so excited about it, and why I think that it will have a rather profound impact on some of our ideas about the structure of the physical world.

Let me begin by reviewing the way we think about quantum mechanical particles in a relativistic setting. The classical dynamics of the theory is specified by assuming that the action for a given particle trajectory is proportional to the relativistic interval traversed by the particle. If one sets up a canonical formalism with the variable parametrizing the particle trajectory playing the role of time, then one finds that the four-momentum of the particle is constrained, with the constraint just being the relativistic relation between the mass, energy, and three-momentum of a particle. The particle thus lives on a subspace of the full phase space, and one finds that on this subspace, the Hamiltonian for the system vanishes.

1. 1. Here is a well known theorem. Consider the homogeneous Maxwell equations

   

   (where E and H are functions of x, y, z, and t, and ).

   Use the coordinate substitutions

   

   and the following substitutions for the field variables

   

   Then, if terms depending on second and higher powers of (v/c) are dropped, the resulting equations have the same form as the original homogeneous Maxwell equations, i.e.,

   

Recent discussions about the argument from design have taken into account developments in cosmological theories, most especially the so-called anthropic principle associated with the “Wheeler”- and “Carter”-universes. Part of these discussions can perhaps be summarized as briefly as can be in the following opposition:

1. 1. The world is very unusual, so it must have been made by an intelligent creator.

2. 2. The world is very unusual, but unusual things do occur by chance.

   The phrase “the world is very unusual” is short-hand for something like:

3. 3. It is extremely improbable that a random concatenation of the forces, energies, particles, fields of the universe (or whatever we think the building blocks are) should, in a single trial, form into anything orderly, let alone anything that supports our form of intelligent life.

In this paper I will present conceptions of state reduction and particle and/or system localization which render these subjects fully compatible with the general requirements of a relativistic, i.e. Lorentz invariant, quantum theory. In the case of state reduction, the concept presented has, in it's main features, been advanced by several investigators in recent years, (Giovannini 1983), (Aharonov and Albert 1984), (Malin 1984), (Dieks 1985). My own contribution to this topic has been to elaborate the concept in question and examine, in some detail, the often counterintuitive but never causally anomalous or internally inconsistent consequences that emerge from taking the concept seriously (Fleming 1985,1986). In the case of particle and system localization, the concepts are more nearly my own and have been pursued by me for some time (Fleming 1964, 1965, 1966) as a way of freeing the subject of localization in relativistic quantum systems from the conceptual problems pointed out by Newton and Wigner (1949) myself (Fleming 1965) and extensively studied by Hegerfeldt et. al. (1974, 1980) and Ruijsenaars (1981).

This note will consist of a single rather elementary remark about the overall Quantum state of the world.

Let me say something at the outset about what this remark is supposed to be good for. It will not support and it will also not raise any doubts about any particular cosmological model. The problems which this remark will turn out to have a bearing on are problems which those models aren't intended to address, problems (about which, however, there has lately been a good deal of speculation) connected with the ‘ultimate beginnings’ of the world; and the remark will merely suggest that those problems need not be worried about; that perhaps, after, there simply aren't genuine problems like that.

The remark is that if any linear Quantum-Mechanical equations of motion happen to be the true and universal equations of motion of the world, then it is consistent with everything we observe, and it is consistent with everything we are even likely to observe, to suppose that the present (and past and future) state of the physical world is the vacuum state.

In this paper I formalize the notion of minimal disturbance, as this seems to be required by usual interpretations of the theory of quantum mechanics, and construct a quantum logical (lattice) model of the type of situation that seems to be at the root of the problem of the interpretation of Luders’ projection rule as a criterion of minimal disturbance for individual state transformations. What is particularly interesting in the situation to be depicted here is that, on the basis of a simple model, which depends only on some very general features of the lattice structure of the theory (and its semantical interpretation), usual interpretive assumptions on minimal disturbance appear to be wanting.

If we restrict our attention to the statistics of measurement results, Luders’ rule can, easily be interpreted as a formula describing ‘minimal change’ for statistical states.

Philosophical debate on the measurement problem of quantum mechanics has, for the most part, been confined to the non-relativistic version of the theory. Quantizing quantum field theory, or making quantum mechanics relativistic, yields a conceptual framework capable of dealing with the creation and annihilation of an indefinite number of particles in interaction with fields, i.e. quantum systems with an infinite number of degrees of freedom. I want to show that a solution to the standard measurement problem is available if we exploit the properties of the infinite quantum models available in this broader conceptual framework.

There is a qualitative difference between quantum systems with an infinite number of degrees of freedom and quantum systems with a finite number of degrees of freedom. In the infinite case, there exist many unitarily inequivalent irreducible Hilbert space representations of the algebra of observables of the system. In the finite case, there is only one such representation.

Writing the history of elementary particle physics has all the problems common to writing the history of any other subject “in the making”. There is, however, an additional characteristic, unique to this branch of physics. The development of particle physics, unlike the situation in other branches of physics, reveals a continuously changing picture of what its object of investigation is, of what, in other words, the things we call particles are and how elementary they should be considered. The history of elementary particle physics is, in a way, the history of the continuous reinterpretation of both the ontological and methodological status of the notion of elementarity. Hence, examining the history of elementary particle physics is also an attempt to explicate this changing collective consciousness of the scientific community about the elementarity of particles. In studying, therefore, (practically any aspect of) the history of elementary particle physics, one has to be sensitive about a number of philosophical, and primarily methodological issues which have acquired an added significance due to the relatively recent and mainly theoretical developments.

The optical revolution, that is, the replacement of corpuscular optics by wave optics at the beginning of the nineteenth century, has attracted the attention of philosophers of science for a long time. For a long period the cause of the optical revolution was attributed to “crucial experiments” such as Foucault’s experiment on the velocity of light (Sabra 1954, pp.149-51). Later Frankel argued that social and political factors were necessary for the victory of the wave theory (Frankel 1976, p.142). These accounts, however, were severely criticized by recent theorists of scientific change, especially Lakatos and Laudan. Lakatos calls the opinion that accounted for the optical revolution solely by “crucial experiments” naive “instant rationality” (Lakatos 1978, p.68 & 72n). Laudan also regards the attempt to explain scientific revolution mainly by social and political elements as “jumping to a premature conclusion” (Laudan 1977, p.4).

The Neglect of Experiment: that is the title of Alan Franklin's (1986). He did not mean to imply that scientists were neglecting experiments, spinning well financed cobwebs of theories while laboratories decayed for lack of funds. He meant that historians and philosophers neglected the experimental side of science. That was true, and is no longer so. Although his title was fine when he was writing, the times have passed it by.

A decade before there had been almost no reflective philosophy of experiment. What little had been published was not seen as writing about experiment—that was not something to write about—but as discussion of the theory/observation distinction, or the impossibility of eliminating a theory by crucial experiment, etc. The even-handed Dictionary of Scientific Biography discreetly cut articles on experimenters and expanded those on theorists. Thaddeus Trenn's (1977) on the experimental discovery of isotopes was poorly received.

Historians and philosophers of science have, of late, found a new common ground. During the 1960s the two fields worked together to answer the general question: “how does one theory supersede another?” — followed immediately by a second query: “Is the process rational?” Historians provided examples from the chronicles of science, and philosophers tested these cases against universal models of change. Together the two helped ground an important avenue of inquiry, and today the best of that work — by Feyerabend, Kuhn, Lakatos, Popper, and others — forms a staple of the philosophy of science.

But despite the best of intentions, in the 1970s the two fields began to pull apart centrifugally. On one side, the philosophers found their concerns concentrated ever more on fundamental issues about meaning and reference, and these seemed to demand idealized histories with simpler structures.

It is not well known that Moritz Schlick, whose name is inseparable from the development of logical positivism, was extremely critical of positivism prior to the 1920’s. The positivism Schlick found fault with was associated with the physicist Ernst Mach. Schlick went to considerable lengths to criticize Machian positivism on both epistemological and ontological grounds. He also objected to the positivist claim to be able to account for relativity theory within its framework.

Schlick’s views before his move to Vienna in 1922 have been labeled a “critical empiricist realism” (see Feigl 1938, p. xx) or a “structural realism” (Friedman 1983, p. 501). His exposure to the work of Ludwig Wittgenstein is generally held up as the crucial factor in turning him away from his early realist views towards positivism. There is general acknowledgment of a major change in Schlick’s philosophical thinking in the early 20’s; disagreement exists, however, over both the extent of the change and whether it was a positive or negative one.

Scientific realism is a doctrine about the relationship of our ideas on the nature of things to the nature of things itself. Part of the doctrine is that there is a nature of things itself. With regard to the rest, Jarrett Leplin has said, “Like the Equal Rights Movement, scientific realism is a majority position whose advocates are so divided as to appear a minority” (Leplin 1984, p. 1). Still, it can be said that what realists would like is that the account of the nature of things provided by science be true and that those things really exist.

Characterized in this way, realism would seem to be a majority position indeed. As Ernst Mach has said of the doctrine,

In the nineteen-sixties, plate tectonics became the accepted theoretical framework in the earth sciences. This framework revived the idea of continental drift that had been first proposed in 1912 by Alfred Wegener (1966). This paper offers an analysis of the arguments of Wegener and his opponents. We shall show that from Wegener’s perspective his hypotheses possessed a high degree of explanatory coherence, while from the opponents’ perspective his theory was incoherent with much that was generally known.

Our analysis uses a new theory of explanatory coherence that has already been applied to several important cases in the history of science: Lavoisier’s argument for his oxygen theory against the phlogiston theory, Darwin’s argument for the theory of evolution by natural selection, and current disputes about why dinosaurs became extinct (Thagard 1988b). This theory is implemented in a connectionist computer program called ECHO that takes statements of explanatory relations as input and creates a network of units, crudely analogous to neurons, with excitatory and inhibitory links among them.

It was once fashionable to treat realism as an explanatory theory of science. This realism treats the sentences of science, both observational and theoretical, literally: such sentences are true or false as the case may be in some correspondence sense of truth. To this was added the epistemological claims that it was in principle possible to discover whether any given sentence was in fact true or false and that science has been progressive. In view of the fact that theories seemed to have a bad track-record - from the point of view of truth they all seem sooner or later come unstuck - the realist offered a more modest goal for science; producing more approximately true theories. The strategy for defending realism was explanatory. The realist claimed that inference to the best explanation (hereafter cited as IBE) was a standard epistemic tool of the scientist and ought to be available to the philosopher.

In this essay I will discuss and appraise two conflicting answers to the question of whether there was a crisis in Ptolemaic astronomy prior to the Copernican revolution. I will begin by giving a brief account of why anybody should be interested in this question. I will discuss the two conflicting answers of Kuhn (1962, 1970), who claims to present evidence which shows that Ptolemaic astronomy was anomaly-ridden at the time of Copernicus, and of Gingerich (1975), who claims that the supposed anomalies, which have been passed down in the historical literature due to poor scholarship, are fictitious. Finally I will appraise Gingerich’s criticism of Kuhn, giving my own evaluation of Gingerich’s arguments. I conclude that Gingerich’s arguments against the existence of a technical crisis in Ptolemaic astronomy prior to Copernicus appear to be, either arguments against the efficacy of the Copernican system, or arguments based on definitions of complexity which are not directly attributable to Kuhn.

In a recent paper1 I argued that observation can be thought of as the result of a properly composed and functioning observation system. In brief, such a system must be composed of a source object and one or more devices which interact with a receptor. If we think of observation as the result of interaction among components are differing functions, we can approach the problem of describing human sense perception as that of describing one type of observation, differentiated from other types by the organic and species specific nature of the receptor devices. Receptor devices are typed by their specific range of sensitivity, which is best thought of as a limit on the type of devices with which the receiver can interact. One consequence of this view is that observation can be achieved in all sorts of ways by all sorts of organic and non-organic systems as long as they satisfy functional conditions.