1 Introduction

Michela Massimi’s recent book, Perspectival Realism [1], has been described as ‘philosophically rich and scientifically packed’ ( [2], p. 164) and as ‘likely [to] become a classic text on realism and pluralism in science’ (ibid.). However, this conjunction has been taken to express an underlying tension in her work: ‘… insofar as it’s realist, PR [‘Perspectival Realism’] isn’t perspectival and insofar as it’s perspectival, PR isn’t (necessarily) realist’ [3].

My aim in this paper is to try to defuse this tension in the context of quantum theory by recasting Massimi’s position within the framework of Husserlian phenomenology. I shall begin by presenting the perspectival aspect, as understood in terms of scientific representation, and then indicate how her two complementary forms of perspectivalism are manifested in the distinction between certain so-called ‘-epistemic’ and ‘-ontic’ understandings of quantum mechanics, namely QBism and Relational Quantum Mechanics, respectively. A brief consideration of Dieks’ perspectivism will then lead to a consideration of the much-maligned and typically dismissed role of the observer in the measurement process. This opens the door to a recent resuscitation of London and Bauer’s phenomenological analysis of that role which, in turn, offers the possibility of a form of ‘phenomenological perspectivalism’. I shall conclude with some reflections on how Husserl’s Euro-centric approach might be modified to accommodate Massimi’s idea of ‘interlacing’ scientific perspectives, using the example of Bose-Einstein statistics that arose from a ‘new cosmopolitanism’.

2 The Two Varieties of Perspectival Representation

The core idea of Massimi’s work is that scientific knowledge is ‘… a distinctive kind of social and cooperative knowledge’ ( [1], p. 19) that is shaped by scientific perspectives. These in turn are characterised as ‘the actual—historically and culturally situated—scientific practice of a real scientific community at a given historical time’ ( [1], p.5). Of course, the notion of a ‘scientific practice’ is necessarily rather broad but crudely speaking can be taken to include not only and obviously theoretical and experimental practices but also justificatory practices through which scientific claims are reliably formed. The upshot is ‘[t]he absence of a scientific ‘view from nowhere’…’ which in turn means ‘… there exists no ideal atlas, and no privileged catalogue of ontological units.’ ( [1], p. 20).

This perspectivalist approach is then applied to the issue of scientific representation, about which a great deal has been written recently (for a brief but useful summary, see [4]). Massimi identifies two forms in this context: ‘perspectival1’ according to which the representation is situated, specifically in terms of being from a specific vantage point (of the spectator), so that, broadly, the ‘scene’ is drawn as it appears from there. Consequently, the representation is about the vantage point from which it takes place. With ‘perspectival2’, however, the emphasis is on there being a clear direction, so that the representation is ‘aimed’, as it were, towards a vanishing point. As a result, the point of view is effectively an empty place-holder so this form is not (self-referentially) about the vantage point. To illustrate the distinction between these two variants, which should be understood as complementary, Massimi draws on particular artworks (as is now the time-honoured fashion in the literature on this topic; see [5], Ch. 3). So, Velázquez’s Las Meninas is taken as a paradigmatic example of perspectival1 representation, since it skilfully represents the Infanta Margarita and her entourage from the vantage point, not of the painter, but of the spectators, who in this case are the King of Spain, Philip IV, and his wife Mariana. A clear example of perspectival2 representation, on the other hand, can be seen in van Eyck’s Arnolfini Portrait, in which an Italian merchant and his wife (or betrothed) are portrayed with a convex mirror behind them, creating the illusion of a ‘mirror on reality’ ( [1], pp. 33–37).

This is a useful contrast that Massimi deploys to underpin her overall perspectivalist approach to scientific theorizing. Thus, for example, consider the history of such theorizing about the nature of electric charge. According to Massimi, the likes of Helmholtz, Thomson and Planck, ‘each operated with different perspectival1 representations of what we call the electric charge e in that they availed themselves of a variety of situated scientific practices pertinent to their respective scientific perspectives.’ ( [1], p. 319). However, what makes these representations perspectival in the first sense is not that they represent the relevant property from different points of view; rather, the existence of such a property, and its nature, was what was at stake here. The existence of charge was the endpoint of these investigations and so, in that specific sense, the representations were also of the form perspectival2, since they were directed towards something, namely the establishment of electric charge, thereby opening a ‘window on reality’ for us ( [1], p. 320).

Here I want to proceed along a different avenue and suggest, first, that Massimi’s two forms of perspectivalism can also be seen as manifesting in the distinction between QBism and Relational Quantum Mechanics (RQM) but that, secondly, it is in an older account of quantum mechanics that we can find these two forms brought together along the lines that Massimi suggests.

QBism began life as ‘Quantum Bayesianism’ but with the distinction between Bayesian approaches to probability in general and subjectivist interpretations in particular, the name is now taken as a ‘stand-alone’ label (see [6]; also [7]). Some QBists have gone so far as to insist that ‘[m]any ideas voiced, and even committed to print, during earlier stages of Quantum Bayesianism turn out to be quite fallacious when seen from the vantage point of QBism’ ( [7], p. 1).Footnote 1 Identifying the core features of this position can therefore be contentious, but for the purposes of this essay, it can be broadly understood as ‘an interpretation of quantum mechanics in which the ideas of agent and experience are fundamental’ [9]. Consequently, the QBists maintain, the wave-function should be understood solely in epistemic terms, as representing not some state of a physical system but rather that of the agent with regard to their possible future experiences. It does this by encoding the agent’s coherent degree of belief in each of certain alternative experiences that result from some act they perform, such as the outcomes of a measurement procedure.Footnote 2 These beliefs may then be updated through some mechanism such as, but not necessarily, Bayes’ Theorem, for example (see [11], p. 1).Footnote 3

It is important to recognise that within the QBist framework, the measurement apparatus becomes merely an extension of the agent’s sensory faculties [12] and as a result, ‘[t]he trinary decomposition object + apparatus + agent simply does not exist in QBism. QBism is all about the agent and her external world—the decomposition is a binary one’ ( [13], p. 9). There is then more to say about both the ‘kicks’ from the world, as Fuchs calls them and the nature and role of the agent (for a phenomenological perspective on the latter, see [14]; [15]). However, here I will simply emphasise those features of QBism that place it under Massimi’s ‘perspectival1’: it offers a first-person account; the wave-function is to be understood in epistemic terms; and it encodes an agent’s degree of belief regarding alternative experiences.

Turning now to RQM, Massimi herself presents it as offering a perspectival account ( [1], p. 205). Here the central idea is that ‘… all (contingent) physical variables are relational’ [16], in the sense that the value such variables take should not be simply ascribed to the physical system under consideration but must always be (implicitly or explicitly) indexed to a second system (ibid.). The latter can be any kind of system and so neither measurements nor observers are given any privileged role in this interpretation. Nevertheless, if we take the second system to be an ‘observer’ in some generic sense, then the core idea can be expressed as ‘different observers can give different accounts of the same set of events’ ( [17], p. 1643; see also [18] p. 4), clearly expressing the perspectival character of this interpretation.Footnote 4 Consistency between observer is then achieved via the theory itself: any comparison of observations will involve a physical process that will itself be described in quantum mechanical terms and so the internal self-consistency of the theory guarantees that there will be no discrepancy between different observers (see also [19], pp. 403–404).

In contrast to QBism, then, the focus here is away from the agent and towards the world, conceived of relationally in the sense that it ‘must be described as a net of interacting components, where there is no meaning to ‘the state of an isolated system’, or the value of the variables of an isolated system. The state of a physical system is the net of the relations it entertains with the surrounding systems. The physical structure of the world is identified as this net of relationships’ [16]. In this respect, RQM obviously bears close comparison with structural realism (see [16]). Again, there is more to say, but again I simply want to note that this account can be understood as falling under Massimi’s ‘Perspectival2’: it is world-, rather than agent-, oriented; the wave-function is to be interpreted ontically; and it represents the relational state of the system under consideration.

Now, as noted above, Massimi takes her two perspectival forms to be complementary as embodied in a given scientific representation. Indeed, such a representation can be said to be perspectival1 only insofar as it is also perspectival2. Consider artistic representations for example, in which the vantage point and vanishing points in effect go hand-in-hand:

‘… a representation can be perspectival1 because it is drawn from a particular vantage point … But a representation can also be said to be perspectival2 because it is drawn towards one or more vanishing points. These two ways of thinking about what makes a representation perspectival are two side of the same coin. It is because a representation has one or more vanishing points that it appears to be drawn from a particular point of view’ ( [1] p. 13).

Likewise, in the case of electric charge, the different investigators approached the property from their particular situated ‘vantage points’, but the equivalent of the ‘vanishing point’ was that property of charge, toward which their investigations were drawn of course. However, in the case of QBism and RQM we have a failure to combine the two forms, with the former bringing to the fore the role of the agent and the latter the nature of the world.Footnote 5 In effect what we have are two sides of different coins! And just as Massimi argues that we need both forms acting in a complementary manner in order to understand scientific knowledge, so I shall suggest here that we should draw on an earlier and long disregarded account in order to understand quantum mechanics, one that emphasizes the vantage point of the agent while also acknowledging her engagement with the world.

Of course, perspectivalism has been introduced into the philosophy of quantum mechanics previously. Thus, as is well-known, Dieks has also argued that quantum objects should not be characterized by monadic properties ‘but by relations to other systems. Accordingly, physical systems may possess different properties with respect to different “reference systems”’ ( [20], p. 51). As a result, ‘different descriptions, given from different perspectives, are equally objective and all correspond to physical reality’ ( [21], p. 647). However, when it comes to the nature of the agent and specifically that of a conscious observer, Dieks is adamant:

‘The appeal to consciousness … appears to invoke a deus ex machina, devised for the express purpose of reconciling unitary evolution with definite measurement results. More generally, the hypothesis that the definiteness of the physical world only arises as the result of the intervention of (human? ) consciousness does not sit well with the method of physics’ ( [20], p. 53).

Here, of course, he is referring to the so-called ‘measurement problem’, where the theory’s description of a unitarily evolving superposition of states, as described by the wave-function, appears to conflict with the definite outcomes obtained through some measurement. Again, this can be framed in perspectivalist terms:

‘The properties associated with the superposition and the definite outcomes, respectively, would relate to two different perspectives – the idea already suggested by von Neumann and London and Bauer. Of course, we should avoid the earlier problems associated with consciousness and ill-defined transitions. The different perspectives, and different relational states, should therefore be defined in purely physical terms’ ( [20], p. 56).

In what follows, I shall push back on Dieks’ claim that appealing to consciousness invokes a kind of ‘deus ex machina’ that does not mesh with the methodology of physics and in doing so, will suggest an alternative way of bringing together the above perspectival forms, one that renders the core ideas of QBism and RQM as complementary and which, also and crucially, offers a way of reconceiving realism within Massimi’s perspectival framework.

3 Consciousness and Collapse

Between 1961 and 1964 a debate took place within the pages of the journal Philosophy of Science (which also spilled over into the American Journal of Physics) that had a fundamental impact on approaches towards the measurement problem within the philosophy of physics. On one side there were Margenau and Wigner and on the other, Putnam and Shimony but lest anyone portray this as a straightforward bout between physicists and philosophers, it should be born in mind, first, that although Margenau began his scientific career applying quantum mechanics to dipole molecules, he became well-known for his work in the philosophy of physics and the philosophy of science more generally. Secondly, Putnam initially worked on the foundations of probability theory (his PhD thesis was supervised by Reichenbach), and, thirdly, Shimony was not only awarded a PhD in philosophy, supervised by Carnap, also on probability theory, but also obtained another one in physics (on statistical mechanics) with none other than Wigner himself! What actually divided these figures was their understanding of the measurement situation and the role of consciousness in yielding a definite outcome. Although an emphasis on this role is often attributed to ‘the Copenhagen Interpretation’ (a label that only began to be applied in the 1950s and to an inhomogeneous set of views), it was Wigner who adopted and promulgated the view that the intervention of the conscious observer somehow resulted in the superposition ‘collapsing’ leading to a definite measurement outcome (for details about this and the debate, see [22]).

The debate began with Margenau and Wigner responding to a short paper by Putnam on the EPR thought experiment in which he had raised concerns about the treatment of measurement within quantum mechanics [23]. They argued that the concerns were misplaced and set out what they took to be the ‘orthodox’ account of measurement, drawing on von Neumann and, crucially, a ‘little book’ by London and Bauer [24]. Putnam replied, Margenau and Wigner counter-responded, Shimony then weighed in and the debate ended with neither side giving ground (for details see [22], Ch. 3). As far as Margenau and Wigner were concerned, the role of the observer had been clearly and explicitly elaborated in London and Bauer’s work [25], which they took to be a summary of von Neumann’s account. According to this, in the absence of any sharp physical distinction between micro- and macro-scopic domains, any interaction would result in further entanglement between systems, proceeding up the ‘chain’ from the system under examination to the measurement apparatus and the body of the observer. The only way of cutting this chain of correlations would be through the intervention of something non-physical, namely the consciousness of the observer.

Putnam and Shimony’s responses can be summed up in the questions: in virtue of what is consciousness able to affect nature ‘in this peculiar way’? What is the mental process of reducing a superposition? And in the absence of any plausible answer to such questions, the role of consciousness in quantum measurement came to be dismissed, and the door was opened to alternative solutions to the measurement problem, such as Bohm’s and Everett’s.

However, as it turns out, although all parties in this debate cited and explicitly drew upon London and Bauer’s ‘little book’ to either support or deny the role of the observer, neither side really understood it.

4 The Observer Returns

What follows is taken from [22] which itself is an elaboration of [26].

Although Fritz London anticipated certain features of the Dirac-Jordan transformation theory [27] he is perhaps most well-known for his work using the new quantum mechanics to explain various phenomena [28]. Thus, and in brief, together with Heitler he explained the formation of chemical bonds in terms of permutation invariance (and in this context, Margenau worked with him), with his brother, Heinz, he developed the first quantum model of superconductivity and, finally, he further accounted for the superfluid behaviour of liquid helium using Bose-Einstein statistics – a programme that culminated in his classic two-volume work, Superfluids [29]. Clearly, then, London was at the forefront of moves to apply the new quantum mechanics to a wide range of phenomena, including, and in particular, macroscopic phenomena such as superconductivity and superfluidity (and in this regard, his research stood in contrast to the stance adopted by Bohr and his followers [30]). Given that, and despite his early work mentioned above, it might come as a surprise to find that he also co-authored what has come to be regarded as a work of major significance in the philosophical foundations of the theory [25].

It is perhaps worth noting at this point that the ‘little book’ that played such a major role in the above debate was not published in a scientific journal but ‘under the direction’ of Langevin by the Parisian publishing house Hermann & Co. (founded in 1876 by the mathematician Hermann), as part of their series Actualités Scientifiques et Industrielles (‘Scientific and Industrial News’). The series itself was initiated by Hermann’s son-in-law Freymann (who was also the Mexican cultural attaché), prompted by none other than de Broglie, who also introduced him to Einstein and Langevin.Footnote 7 Its aim was to publish the latest developments on a given topic and despite the passage of over a decade since the publication of the foundational works of Heisenberg, Schrödinger et. al., as well as textbooks by the likes of Dirac and Weyl, and popular expositions by Jeans, Thomson and others, not to mention, of course, the more recent magisterial presentation by von Neumann, London and Bauer obviously felt there to be a need for a clear statement on the process of measurement as understood within the framework of quantum theory.

Although the work was based on London’s lectures in Paris, it is perhaps because the series occupied the ‘liminal space’ between a research paper, a textbook and a semi-popular exposition that he felt able to put a particular philosophical ‘spin’ on the technical exposition. For as well as being thoroughly adept in the new quantum physics, London also had a strong philosophical background in Husserlian phenomenology [28]. Indeed, his two interests were more or less intertwined, geographically speaking, for while he was at Munich, studying with Sommerfeld, London met Pfänder, at the time second only to Husserl within the phenomenological movement ( [28], pp. 11–12).Footnote 8 London showed Pfänder his essay on the ‘logical interpretation of deductive theory’ and the latter was evidently so impressed that he urged London to write it up and submit it as a dissertation in philosophy.Footnote 9 Indeed, it was then accepted for publication in the Jarbuch für Philosophie und phaenomenlogische Forschung, which was co-edited by Pfänder, with Husserl as editor-in-chief.

After graduating from Munich, London spent a year as an assistant science teacher before moving to Göttingen to work with Born.Footnote 10 At the time he wanted to work on the philosophy of the new quantum mechanics, but Born was ‘very much opposed to philosophizing’ ( [28], p. 27) and sent him to Sommerfeld to do some ‘real work’.Footnote 11 Sommerfeld in turn persuaded London to do a straightforward calculation regarding the intensity of band lines in atomic spectra and, according to Born, ‘he never became a philosopher again’ (https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4522-3). That is debatable, however, as London maintained his interest in phenomenology and during his time in Paris held extensive discussions with Gurwitsch, a friend who also had an academic background in both physics and philosophy, studying the former with Planck, no less, as well as learning mathematics with Karatheodory and Schur. Within the phenomenological movement, Gurwitsch is renowned for the role he played in establishing the approach in the USAFootnote 12 and went on to develop a ‘constitutive phenomenology’ that combined it with Gestalt theory (see [33] for a useful summary of the extent to which Gurwitsch deviated from the Husserlian framework). Crucially, Gurwitsch advocated a ‘non-egological’ form of phenomenology according to which consciousness has only a constitutive function, consisting in the correlation between a given act and its intended object ( [33], p. 940). As we’ll now see, this bears on how we should understand the London and Bauer manuscript, or so it has been claimed [22, 26].Footnote 13

That this is no run-of-the-mill presentation of the basics of quantum mechanics as it applies to the measurement process is clear from the very beginning, where London and Bauer write:

‘Without intending to set up a theory of knowledge, although they were guided by a rather questionable philosophy, physicists were so to speak trapped in spite of themselves into discovering that the formalism of quantum mechanics already implies a well-defined theory of the relationship between the object and the observer, a relation quite different from that implicit in naïve realism, which had seemed, until then, one of the indispensable foundation stones of every science’ ( [25], p. 220).

This statement of intent can be directly related to Massimi’s concerns. Note, first of all, the rejection of ‘naïve realism’, previously regarded as ‘one of the indispensable foundation stones of every science’. In its place we have ‘a well-defined theory of the relationship between the object and the observer’ in virtue of which quantum mechanics must be seen not simply as a theory of physical systems (both micro- and macro-scopic, as far as London was concerned) but as a theory of knowledge. As such it is inherently perspectival since the observer herself falls under the remit of the theory; that is, consciousness is not introduced as an extraneous element, as Margenau and Wigner, on one side of the above debate, and Putnam and Shimony, on the other, all thought, but rather is incorporated as an integral part of the process, as described by the theory. How this is accomplished can be seen as follows.

After presenting what is now recognized as the standard formalism of the theory, London and Bauer turn to the measurement process and set out the ‘chain’ of correlations as each interaction is effectively swallowed up by the superposition (it is perhaps because of this argument that they have repeatedly been taken to be simply following von Neumann). However, they then state,

… it is not a mysterious interaction between the apparatus and the object that produces a new ψ for the system during the measurement. It is only the consciousness of an “I” who can separate himself from the former function Ψ(x, y, z) and, by virtue of his observation, set up [in the original French: ‘constituer’] a new objectivity in attributing to the object henceforward a new function ψ(x) = uk(x).’ ( [25], p. 252)

In other words, there is no intervention of consciousness which somehow, mysteriously, causes the superposition to collapse and a definite outcome to be obtained. Instead, on their view, the chain extends all the way to the observer’s consciousness which is also then included in the superposition. However, what distinguishes that consciousness, the ‘I’, from the other elements in the chain, such as the measurement apparatus and the body of the observer, is that it is able to separate itself from those other elements and constitute a ‘new objectivity’ by attributing to the system in question a new state function in virtue of the observation which yields a definite outcome (see [22], Ch. 6).

This separation is effected through

‘… a characteristic and quite familiar faculty which we can call the “faculty of

introspection.” [The observer] can keep track from moment to moment of his own

state. By virtue of this “immanent knowledge” he attributes to himself the right to

create his own objectivity - that is, to cut the chain of statistical correlations …’.

( [25], p. 252)

It is important to bear in mind that the ‘I’ or, in phenomenological terms, the ‘Ego’ is not present as a substantive entity, prior to this separation and the cutting of the chain of correlations. As Husserl emphasized, the Ego is that which is required by the ‘reflective regard’, which is exercised when we introspect, but beyond its ‘modes of relation’, it is empty [34]. In such statements (and it has to be acknowledged that there is considerable debate over the nature and changing role of the ‘Ego’ in Husserl’s works), Husserl seems to adopt a relational or more broadly struturalist conception of the Ego, according to which it is nothing but an empty node or placeholder in the relationship between consciousness and the world. As London’s friend Gurwitsch wrote,

‘As long as we do not adopt the attitude of reflection, the ego does not appear. On the level of non-reflection there is no ego at all. A conscious act, inasmuch as it is free from reflection, does not deal with the ego and is not related to it in any way whatever’ ( [35], p. 329)

There is more to be said (and some of it is said in [22]) but the core idea here is that, according to London and Bauer, the transition from a superposition to a determinate state of the system with a corresponding definite measurement outcome should not be conceived of as some sort of consciousness induced collapse but rather as the mutual separation of what is, in phenomenological terms, the Ego-pole and the Object-pole of the correlative relationship between the observer and the world. As Beck put it, ‘[c]onsciousness and world … stand in a correlative, i.e. mutually dependent, context of being …’ ( [36]; in [37], p. 114). And as far as London and Bauer were concerned, the nature of this correlative relationship is precisely what is captured by quantum mechanics, understood, as they emphasized, as a theory of knowledge.

5 Return to Perspectivalism

We recall Dieks’ assertion that ‘[t]he appeal to consciousness … appears to invoke a deus ex machina …’; that is, it may be thought of as an ad hoc mechanism brought in specifically to resolve a particular issue, in this case, the measurement problem. Clearly, however, within London and Baer’s framework, consciousness does not play the role of a mere plot device, motivated as it is by the phenomenological underpinnings sketched above. Indeed, if we are using literary terms in this context, its introduction may be usefully seen as a form of ‘anagnorisis’, or a critical moment of discovery or realisation regarding the true nature of the situation: what quantum mechanics reveals, in the context of physics, is precisely what phenomenology has been emphasising, namely the existence of that fundamental correlative relationship between us and the world. As Pauli wrote to Bohr (in 1955), quantum mechanics involves the ‘… abandonment of the idea of the isolation (detachment) of the observer from the course of physical events outside himself’ (in [38], p. 564).

Likewise, we can now appreciate how off-base the participants in the above debate were in their use of London and Bauer’s ‘little book’, whether as a means of advocating a role for consciousness, as in the case of Margenau and Wigner, or as an entry-point for criticizing and dismissing that role. Shimony, at least, did eventually come to realise the error of his ways: in a footnote to a paper, co-authored with his graduate students on whether the idea of wave-function collapse through the intervention of consciousness could be used to explain so-called telepathic phenomena (spoiler alert: it can’t!), he wrote, ‘… [i]n view of London’s philosophical training as a student of Husserl. . We now are inclined to believe … that the passage quoted should be given a phenomenological interpretation’ ( [39], p. 761 fn. 7). Later, in an interview, he acknowledged that ‘… there were some residues of phenomenology in the little booklet of London and Bauer’ [40]. In particular, the questions that emerged from this debate and which were regarded as fatally undermining any role for consciousness in measurement, can now be seen to be beside the point. To require details of the mechanism by which the Ego ‘causes’ the wave-function to collapse is to precisely demand that phenomenology conform to a framework that it eschews, since the correlative relationship between consciousness and the world is most definitely not to be conceived of as a causal one.

As for the claim that ‘… the hypothesis that the definiteness of the physical world only arises as the result of the intervention of (human? ) consciousness does not sit well with the method of physics’, it should not be assumed that any account of this ‘method’ must incorporate the kind of mind-independence of the world that underpins naïve realism. The latter is exactly what London and Bauer reject, as indicated above, and more generally, from their viewpoint, the ‘method’ of physics, and indeed of all science, must itself be phenomenologically grounded. Indeed, this is one of the central themes of Husserl’s last and perhaps most influential work [41]. There he argued that modern science is in crisis due to the loss of its ‘meaning for life’, where this loss is embodied in the manner in which science is understood to abstract ‘from everything subjective’ and offer an understanding of ‘objectivity’ as ‘exclusively a matter of establishing what the world … is in fact’ ( [41], p. 6).

This crisis can thus only be resolved through revealing the ‘universe of the subjective’ (Husserl 1970 p. 146) but of course, according to London and Bauer quantum mechanics provides just such a revelation and so Husserl’s ‘crisis’ is resolved (see [22], Ch. 7). More generally, but at the most fundamental level, phenomenology represents a shift in interest ‘toward the universe of the subjective, in which the world … comes to have its straightforward existence for us’ ( [41], p. 146). Such a shift would then yield the ‘creation of a science of the ultimate grounds which supply the true force of all objective grounding, the force arising from its ultimate bestowal of meaning.’ ( [41], pp. 146–147). Again, London and Bauer’s work demonstrates that such a science had already been created.

Returning now to Massimi’s perspectivalism, we recall how her two forms, ‘perspectival1’ and ‘perspectival2’ could be understood in this context in terms of the distinction between QBism and RQM. The former’s first-person stance has already encouraged attempts to incorporate it within the phenomenological framework (see [42]), although concerns have been raised as to the ’fit’ in this regard and further, how what Fuchs calls the ‘kicks from the world’ can then be accommodated (see [22], Ch. 8). In particular, since QBism eschews the notions of entanglement and superposition as representing physical features of the world, there is no counterpart to the correlative aspect emphasized in the above understanding of phenomenology. RQM, on the other hand, obviously can accommodate this aspect but with the insistence on the relations holding between any kind of system, shuts the door on the subjective side of things.

London and Bauer’s account, I suggest, effectively brings together Massimi’s ‘perspectival1’ with its emphasis on the first person, and her ‘perspectival2’ with its idea of there being a window on reality. The former, as noted above, incorporates a certain situatedness, in that the perspective is from a specific vantage point, namely that of the observer. In the quantum context, the system is described as measured from that vantage point. With regard to the latter, we have a clear direction, towards the system as the object. In this case the point of view amounts to being an empty placeholder and we can understand this phenomenologically in terms of the absence of the Ego qua substantival entity. Just as Massimi’s two forms are intended to be complementary, so London and Bauer’s phenomenological understanding of quantum mechanics is about both the observer and the world.

In that sense it can be situated between the ψ-epistemic & ψ-ontic accounts. These are typically presented as dichotomous alternatives but this hinges on the assumption that the wave-function Ψ(x, y, z) in general either represents the state of the object in a (again typically, naïve) realist sense and so is ‘ontic’, or it represents the state of the observer and is correspondingly epistemic. However, there is nothing in principle that prevents it from representing both ‘simultaneously’ [43]. And of course, this is precisely how London and Bauer regard it, with their view of quantum mechanics as a theory of knowledge; that is, as much about us, as it has to be phenomenologically speaking, as it is about the world. That we can use that word ‘about’ with regard to its relationship to both us and the world is because of the introspective, ‘post-regard’ separation that London and Bauer identify, from which the system, on the one hand, and the observer, on the other, emerge as ‘poles’ of the relationship ( [22], Ch. 6). As a result, we can talk of the ‘ontic’ state of the system and the ‘epistemic’ state of the observer. Phenomenologically, then, Ψ(x, y, z) is neither ‘ontic’ nor ‘epistemic’ insofar as it expresses the fundamental correlative relationship that sits at the heart of the phenomenological stance and which is captured by the slogan: ‘[N]o object without a subject and no subject without an object’ ( [37], p. 102).

What this amounts to, in the context of Massimi’s work, is a radical form of perspectivalism according to which the traditional notion of the ‘state’ of a system, as non-relational, intrinsic or, more generally, mind-independent must be abandoned. Bluntly, ‘systems’ do not possess states in and of themselves independently of observers. That notion must be regarded as situated and dependent on a particular ‘vantage point’ but this is not to say that it ‘floats free’ somehow, as the system remains as the ‘vanishing point’ or ‘Object-pole’ of the correlative relationship. Massimi’s overall claim is that it is in these terms that we should understand scientific knowledge in general and London and Bauer’s position can be taken as insisting that this is how we should understand quantum mechanics in particular, understood as itself a theory of knowledge. This obviously runs contrary to standard, or ‘naïve’ realism, as already indicated, and so the tension identified by Panagiotatou and Psillos dissolves.Footnote 14

Having acknowledged that, however, there is a further issue to be dealt with.

5.1 Escaping One’s Perspective and Securing Intersubjectivity

In a recent paper Adlam has argued that those interpretations of quantum mechanics that deny that states of systems are observer-independent challenge our usual presumption of intersubjectivity regarding measurement outcomes [44]. Specifically, she claims that such observers are ‘…unable to escape their own perspective in order to learn anything about the perspectives of other observers’ (ibid., p. 3) and, as a result, would be unable to confirm the theory; hence, such interpretations cannot be rationally entertained. Now, the manner in which intersubjectivity may be secured is a major issue within phenomenology and London and Bauer were certainly aware of it. Indeed, they acknowledge that, following their account, ‘… it would appear that in quantum mechanics the concept of scientific objectivity has been strongly shaken’ ( [25], p. 258), and that quantum mechanics has driven us towards a kind of solipsism. However, they insist, this is only ‘at first sight’ and, in fact, ‘[n]o physicist has retired into a solipsistic isolation’ (ibid.) because of quantum mechanics. Furthermore, there remains a ‘community of scientific perception’ in the sense of agreement as to what constitutes the object of the investigation.

The question then is, how is such agreement achieved and this ‘community’ established? Their answer hinges on the apparently blunt claim that ‘… one always has the right to neglect the effect on the apparatus of the “scrutiny” of the observer’ [25, p. 258]. The original French text is rather more revealing here as the word ‘scrutiny’ is actually a translation of ‘<< regard>>’, where the placing of this phenomenological term between << >> indicates its significance. It is through the reflective regard-to that the Ego emerges as one pole of the relationship with the object and insofar as this regard is an act, conceived of as an essential phenomenological device, it cannot of course be described in quantum terms, since these properly belong to the ‘natural attitude’ which, of course, is what is under phenomenological scrutiny. When the regard is directed to a physical object, that object is ‘seized upon’ but this is not so for mental processes whose very existence is guaranteed by the regard. It is because the existence of physical objects is not guaranteed in this way that the effect of the observer’s ‘scrutiny’ can be neglected. However, this turning of the ‘mind’s eye’ onto something must not be confused with an act of perception, such as an observation.

The upshot, then, is that the regard or ‘scrutiny’ does not change or affect the apparatus, which must be considered to be a part of what Husserl called ‘the lifeworld’, which is the world of lived experience in which all knowledge is grounded:

‘In this world we are objects among objects in the sense of the lifeworld, namely, as being here and there, in the plain certainty of experience, before anything that is established scientifically … On the other hand, we are subjects for this world, namely, as the ego-subjects experiencing it, contemplating it, valuing it, related to it purposefully; for us this surrounding world has only its ontic meaning given to it by our experiencings …etc.’ ( [41], pp.104–105)

Husserl goes on to insist that this world,

‘… exists not only for isolated men [sic] but for the community of men; and this is due to the fact that even what is straightforwardly perceptual is communalized.’ (ibid., p. 163).

This communalization is achieved by ‘abstracting away’ from the individual, and by virtue of this, London and Bauer maintain, a collective ‘scientific perception’ can be created in which a second observer, looking at the same apparatus, will make the same observations (see [22], Ch. 6 and Ch. 7).Footnote 15 This is also something that Massimi emphasizes as a crucial feature of her perspectivalism, namely that scientific knowledge is cooperative knowledge. However, a further question arises: who is this ‘we’ that Husserl refers to in the above quote?

Famously, he maintained that Europe was both the birthplace and the only home of philosophical reason which gives it a kind of ethical supremacy over all non-European ‘forms of life’. In particular, it is in Europe and only in Europe, and specifically in Greece, that the ‘theoretical attitude’ developed that gave us science:

‘… one must not allow the merely morphologically general features to hide the intentional depths so that one becomes blind to the most essential differences of principle. Before everything else the very attitudes of the two sorts of “philosophers” … are fundamentally different. … only in the Greeks do we have a universal (“cosmological”) life-interest in the essentially new form of a purely “theoretical” attitude …’ ( [41], p. 280)

Thus, although he accepted that the life-world has a “universal structure”, which is equally experienced by all persons, irrespective of their sociocultural situationFootnote 16, for Husserl the otherness, or ‘alterity’, of other cultural groups was an obstacle to be surmounted.Footnote 17

This amounts to a sweeping form of epistemic injustice that Massimi labels ‘epistemic severing’ ( [1] pp. 349–356), through which the contributions of particular communities, including across culturally diverse perspectives, are surgically excised. And as one might expect, there is a considerable literature on how phenomenology might liberate itself from this objectionable attitude. So, Waldenfels, for example, who broadly speaking equated interculturality with inter-subjectivity, argued that just as there are no absolutely separated and independent subjects (which Husserl accepted), so there are no ‘pure’ cultures, delineated in the manner presented by Husserl. For Waldenfels ‘our’ lifeworld, which we see as the homeworld, is essentially and inextricably intertwined with the ‘alienworld’ and is therefore full of otherness, or alterity. As a result, the primary form of interculturality is to be found in the “borderline-play” [Grenzspiel] taking place in the Zwischenwelt [intermediate world] that emerges between cultures [47].

There is a great deal more to say on this, and, in particular, how this intertwining of the homeworld and alienworld(s) then relates to the Husserlian understanding of the nature of scientific knowledge.Footnote 18 Here, however, I just want to note that Waldenfels’ notion bears close comparison with Massimi’s idea of different perspectives, including scientific forms, ‘interlacing’ with one another, not least in that both should be seen as historical features:

‘Historically and culturally situated scientific perspectives have been able to travel, trade and thrive or … ‘interlace’ with one another, not only in the absence of but in fact thanks to the absence of a lingua franca.’ ( [1], p. 339)

According to Eze, the outcome of such ‘interlacing’ is a ‘new cosmopolitanism’ that is marked by a kind of ‘creative interactionism; of human communities in confluence relation with one another’ ( [48]; cited in [1], p. 366). One might think that such a cosmopolitanism would be hard to discern within the history of quantum mechanics, with its near-homogeneous cultural context. However, an illuminating example can be found in the work of Bose, which formed the foundation of one of the two fundamental forms of quantum statistics (and hence of kinds of particles) and which in turn was then used by London to explain the phenomena of superfluidity. The story is well-known, at least when it comes to the physics: determined to present the new quantum theory to his students, Bose realised, as others such as Ehrenfest and Einstein had before him, that the basis for Planck’s derivation of his famous radiation formula was obscure, to say the least. He therefore effectively retro-engineered an appropriate grounding for this formula in terms of the distribution of photons over energy states and wrote it up in a paper that he submitted by the UK based journal Philosophical Magazine. After it was rejected (for reasons unknown), Bose sent it to Einstein, asking for his help in getting the work published in Zeitschrift für Physik. Einstein agreed and the rest, as they say, is history.

What this brief summary leaves out of the picture is the relevant cultural context. This was, of course, shaped by the colonial situation in which Bose lived and worked. However, Banerjee has argued that although this left Bose and his colleagues scientifically impoverished, in terms of resources, it also meant that he was free from the scientific prejudices of the British physics establishment [49]. As a result, he was independently minded in a way that allowed him to ‘creatively interact’ with Einstein’s light quantum hypothesis.Footnote 19 Indeed, Bannerjee suggests, we can identify Bose-Einstein statistics as the product of a form of ‘cosmopolitan nationalism’ [49] that can be regarded as arising from the historical interlacing of European physics with Indian culture and tradition.

6 Conclusion

In their misappropriated and misunderstood ‘little book’ on the measurement process, London and Bauer offered a new phenomenological vision of quantum mechanics as a theory of knowledge, insofar as the entanglement that is a central feature of the theory can be regarded as a physical expression of the mind-world correlation inherent in this philosophical stance. What came to be known as the measurement ‘problem’ is then solved through the separation of the Ego and the object following an act of reflection or ‘regard’. My claim here is that this vision is by its very nature perspectival but in a way that is distinct from Dieks’ version and is closer to Massimi’s. Her work offers an approach to scientific knowledge that centres the situated nature of science and the restoration of the subject at both the quantum and cultural levels not only allows her account to be related to the phenomenological stance but also thereby affords a robust defence against the criticism with which this essay began.