Introduction. I. The Quantum Essentials. 1. History. 2. The “dualistic” quantum formalism - II. Quantum-Mechanical Conundrums. 1. The transition from the quantum to the classical world. 2. Is Quantum Mechanics a complete theory? 3. Non-locality and non-separability in nature. 4. Individuality in quantum theory - III. Interpretations of Quantum Mechanics. 1. Interpreting interpretations. 2. Operationalism. 3. Quantum Mechanics as a theory of information about nature; 3.1. The Copenhagen interpretation; 3.2. Subtler interpretations. 4. Unitary Quantum Mechanics; 4.1. Bohmian Mechanics; 4.2. Many Worlds; 4.3. Modal interpretations; 5. Modified Quantum Mechanics - IV. Philosophical Implications Writ Large. 1. Downward causation and ontological emergence. 2. Quantum Mechanics and the mind-brain problem. 3. Epistemic issues; 3.1. Bridging the gap with Humanities? 3.2. Is Science just a social construction? - V. Theological considerations. 1. Initial remarks. 2. Divine Action in nature. 3. Are chance and randomness compatible with God? 4. The theological meaning of an open nature - VI. Conclusions.
Together with Relativity Theory, Quantum Mechanics (QM) is currently the accepted-by-all most fundamental and successful scientific theory of nature. Since its first steps at the turn of the 20th century, QM has played a crucial role in our understanding of the universe. Some of its weirdest aspects, e.g., superposition of possibilities, indetermination, and nonlocality, are known to most philosophers of nature and thinkers in general. However, beyond its impressive technical success in explaining the subtlest physical processes of nature, QM remains a source of interpretational conundrums especially about its very formalism. Even though the Copenhagen interpretation of QM remains the standard interpretation, lack of a wholly accepted view has spawned many others. Nevertheless, irrespective of interpretations, QM provides new insights for reflection about a God-created nature.
After briefly introducing the essentials of QM (section I) and its most relevant counterintuitive aspects (section II), this entry will tackle the thorny issue of interpretations of QM because of their mediation role between quantum physics and its philosophical and theological implications (section III). Sections IV and V will be devoted to the philosophical and theological implications of quantum theory, respectively, in a broader sense, i.e. in connection with classical philosophical and theological issues. Indeed, these two last sections deal with an open field of research where special prudence is needed due to the weirdness of QM and the lack of consensus as to how the theory must be interpreted. Nonetheless, despite all these caveats, QM is already a mature scientific theory, whose basic tenets provide relevant material for philosophical and theological investigation.
I. The Quantum Essentials
1. History. The year 1900 is customarily marked as the date of the beginning of quantum physics. The physics of the 19th century knew the problem of adjusting with a suitable theoretical model the radiation spectrum of a black body. German physicist Max Planck gave rise to the old quantum theory with a revolutionary hypothesis: electromagnetic waves carry energy dependent on their frequency. Specifically, Planck’s hypothesis is that the energy of a wave is transported in “energy quanta,” discrete units of energy proportional to the frequency of the wave. Thanks to this hypothesis, the new model was able to accurately predict the blackbody radiation curve. Planck’s hypothesis would be strengthened years later, being crucial for the resolution of other well-known physical problems as the photoelectric effect and the stability of atoms. To wit: Planck proposed his hypothesis only as a mathematical model. Only with Einstein’s explanation of the photoelectric effect and Bohr’s explanation of the atom the quantization was for the first time actually physica.
The old quantum theory provided some rules to establish the levels of energy quantization. But it rather consisted of ad hoc recipes to explain the frequencies of absorption and emission of energy of the atoms of the various elements. In the 1920s, the transformation of the old quantum physics into modern QM took place through an axiomatic formulation and a perfectly defined mathematical apparatus, mainly thanks to Werner Heisenberg’s matrix mechanics and, especially, Erwin Schrödinger’s wave equation, where the main variable—wave function Ψ—is interpreted as an amplitude of probability: Ψ is a complex-valued function whose square modulus quantifies the probability of measuring the system to which the wave function is associated in a determined state. Heisenberg and Schrödinger’s formulations turn out to be equivalent, and equivalent to more sophisticated formalisms as e.g. Feynman’s path integrals, but Schrödinger’s wave function had the upper hand as mainstream formalism. (For standard introductions to QM formalism, see for example Landau and Lifshitz, 1977; Cohen-Tannoudji, 2006.)
2. The “dualistic” quantum formalism. An amplitude of probability as the basic concept for describing a physical system was something new in physics from Newton’s era (Heisenberg, 1958). In classical physics, we are used to having a direct relationship between the measured physical quantities (observables) and the symbols that represent them in the equations. In QM, however, the wave function represents the state of the system without direct reference to observable quantities. Indeed, observables in QM are no longer numbers but operators, whose eigenvalues provide the possible results of measurements. Ψ changes in space and time according to the Schrödinger equation, a linear equation in partial derivatives that accounts for Ψ’s evolution. Once the initial and boundary conditions of the problem are settled, the evolution of the wave function is deterministic, i.e. the value of the wave function in the past completely determines its value at any time in the future. This process is usually christened U in the literature, meaning a “unitary” evolution of Ψ in which no information is lost (Penrose, 2004).
On the other hand, partaking of a linear equation, Ψ can be decomposed into many addends, each of which is also a solution of the Schrödinger equation. New problems do appear because each of these addends represents a possible result of the concrete measurement carried on the system (e.g. a particle’s position) and, overall, QM does not predict which of them will be realized. It simply tells the likelihood of obtaining each of the results according to the Born rule, namely, the probability is proportional to the square module of the relative weight of each addend of Ψ. One is thus faced with a theory of nature that, at its most fundamental level, is probabilistic and not deterministic. Moreover, the results of the measurements cannot be determined before the actual measurement is made. Uncannily, extracting information from the system results in its determination in a specific state, so that the wave function, which initially was a weighted sum of possible results, is “reduced” to one of those possible addends: the one corresponding with the result of the measurement. This is process R (meaning a “reduction” of Ψ).
The ongoing combination of processes U and R lies at the heart of the well-known paradoxes of QM, such as the double-slit experiment or the Schrödinger cat. From a strict physical perspective, this unsolved and vexed question is the so-called “measurement problem:” what is there so special about a measurement conducive to change Ψ’s behavior from U (deterministic) to R (probabilistic)? Do processes U and R exist in the same way out there, or are physicists just using a theoretical construction masking their ignorance of what occurs at nature’s deepest levels? Different interpretations of QM offer different answers to these questions.
Before we go through the conundrums of QM and its philosophical and theological implications, a word must be said regarding the quantum decoherence program initiated by Zeh (1970) and Zurek (1981; 1982), which aims at downplaying quantum oddness in everyday life. The models of decoherence are rooted in the common universal experience of physicists, who know that the quantum regime is extremely sensitive to uncontrolled influences on the system. The noise in the system spoils the subtle interferences of the different addends of Ψ, making QM become a sort of statistical mechanics in practical terms. Allegedly, decoherence tops at explaining how something like a process of reduction R can be reached from a process of pure evolution U, “for all practical purposes” (Bell 1990). Empirically tested though, the decoherence program has been criticized on fundamental grounds (Penrose, 2004, pp. 797-804; Lombardi, Fortín, and Castagnino, 2012); being itself in need of interpretation. Most physicists agree that decoherence helps to explain why we do not observe superpositions of possibilities (just U processes) in nature, but it does not solve the problem of the definite outcomes (Schlosshauer, 2007) and needs additional tenets to account for the emergence of a preferred basis in measurements (Sánchez-Cañizares, 2019).
II. Quantum-Mechanical Conundrums
1. The transition from the quantum to the classical world. The measurement problem is theory’s main interpretative concern, but is also commonly viewed as an instance of the more general problem of the transition from the quantum (U-only world) to the classical world. The question naturally emerges of up to what point QM is adequate to describe the whole reality. From Wigner’s times, the term “Wigner’s friend” was coined in QM to raise the following problem: imagine a physicist (Wigner’s friend) who carries on a measure within a lab and is being observed by Wigner outside the lab. Applying the QM formalism, Wigner’s friend will have to deal with a reduced Ψ after the measurement, but it remains unclear whether Wigner must use a reduced or a non-reduced Ψ including the linear superposition of his friend’s different possible knowledges. In other words, can QM be self-consistently applied to all levels of reality (knowledge included)?
Recently, some gedanken-experiments have been proposed (Frauchiger and Renner, 2018) showing inconsistencies when self-referential usage of the quantum formalism is performed, i.e. if one knows that someone must already know the definite outcome of an experiment and the former tries to implement the assumption of the latter’s knowledge into the quantum description of the problem. Possible ways out of such inconsistencies make recourse to non-representational (Bub, 2018) or strongly relational schemes of QM forbidding simultaneity in definite outcomes (Yang, 2018) on the one hand, or many-world interpretations (see section III.4.2) on the other. But even if one cuts off the quantum outreach at the level of the experimenter’s observational content, the question remains: can QM be applied consistently to arbitrarily complex systems (such as Schrödinger cats and human beings)? If yes, since experimenter’s observation implies actualization of just one among the possible outcomes, what is special about observation in nature? If not, how does the transition from the purely unitary quantum world (process U) to the classical world (mediated by process R) arise?
2. Is Quantum Mechanics a complete theory? The problem of the completeness of QM has a long history. The seminal paper of Einstein, Podolsky and Rosen (1935) (EPR), questioning quantum theory in its ability to describe all the physical reality at play, settled the terms of the argument until the 1960s, when Bell’s inequalities (1964) and Kocher and Specker theorem (1967) entered the scene. Bell derived a theoretical inequality that must be violated by the observables of an experiment when correlations among them cannot be explained through the actual existence of hidden local variables with determined values—allegedly unknown to QM and making the theory incomplete, as Einstein thought. Furthermore, Kocher and Specker theorem proves that if one assumes that all hidden variables corresponding to quantum-mechanical observables have definite values at any given time, such values are not independent of the device used to measure them, i.e. are contextual (not universally-defined).
Violations of Bell’s inequalities have been continually reported to occur since the experiments performed by Alain Aspect in Paris (1982). Possible loopholes in the technical realization of the experiments have been closed in recent experiments (Hansen et al, 2015; Rauch et al, 2018) making increasingly harder the defense of the existence of global hidden variables that, e.g. would influence the upshot of earthly experiments through high-redshift quasars whose light was emitted billions of years ago. Were one not to engage in such “superdeterminism,” Einstein’s dream of a physical theory describing natural processes also when there are no measurements becomes all but impossible. Bohr and Heisenberg end up carrying the day, for “[t]he laws of quantum theory are such that the ‘hidden parameters’, invented ad hoc, can never be observed. The decisive symmetry properties are thus destroyed if we introduce the hidden parameters as a fictitious entity into the interpretation of the theory” (Heisenberg, 1958, p. 120).
Succeeding generalizations and experimental realizations of Bell’s inequalities, in blatant contradiction of local hidden variables, have also been achieved (Greenberger, Horne, and Zeilinger, 1989). Therefore, even if Vanney states that “in order to affirm the determinism or indeterminism of a given scientific theory, it is necessary to move forward to an in-depth study of the kind of reasoning behind scientific theories and this requires adopting a meta-theoretical epistemological perspective” (Vanney, 2015), there seems to be good scientific reasons to conclude the existence of a not purely epistemic, but truly ontological indetermination of nature, at least in its deepest physical levels. A different question is how to relate such scientific conclusion with metaphysical and theological issues (see subsection IV.1 and section V).
3. Non-locality and non-separability in nature.The EPR paradox is also linked with one of the subtlest aspects of QM: the overall impossibility of separating a system in two subsystems, which would allow for an independent treatment of each. If two apparently disentangled systems have been entangled in the past and have unitarily evolved (i.e. only process U has taken place and not process R), a local measurement in one of them will have an instantaneous effect in the other due to process R globally occurring. Obviously, if process R is something physical, such state of things crudely clashes with one of the basic tenets of Relativity Theory, i.e. the rejection of physical action at a distance because of the finite speed of light. Usually one refers to this feature of QM as quantum non-locality, stressing its ontological aspect, or quantum non-separability, underscoring its epistemic dimension.
Quantum non-locality is a linchpin of QM and one of the main obstacles down the road in order to reach a consistent theory of quantum gravity (Penrose, 2004). In its standard version—including process R—, QM is overtly non-Lorentz invariant, privileging the observer’s local viewpoint and choices in the whole formalism describing an experiment. Nevertheless, it cannot be said that QM falsifies Relativity Theory because in the reduction process there is no actual sending of information at a faster-than-light speed. Inasmuch as the R-process remains non-physical (as is the case in many interpretations of QM, see section III), the contradiction stands at the level of interpretation. Defenders of interpretations heavily drawing on physical non-locality, as David Bohm, deem quantum non-locality a manifestation of an implicate order continually unfolding in nature (Bohm, 1980). Be as it may, quantum non-locality is at the base of teleportation phenomena and encryption projects minimizing risks of eavesdropping via secured keycodes.
4. Individuality in quantum theory. One of the less known consequences of the quantum formalism may be the fact that, strictly speaking, extreme non-locality makes individuality of systems a virtual impossibility. The individuation of a subsystem, even a fundamental particle, falls short of being a clear-cut issue and has something of conventional. But the issue acquires a dramatic turn when dealing with identical particles (e.g. electrons, photons) because the Principle of Identity of Indiscernibles (PII) is at risk. In the case of particles following Bose-Einstein statistics (bosons), a new state of matter called Bose-Einstein condensate emerge in which all bosons in their fundamental quantum state form a collective matter state with global properties, wherein reference to single particles makes no sense at all. However, one still may describe the global wave function as a symmetric sum over all possible permutations of individual bosons. With fermions one does not fare much better because, although not forming fermionic condensates because of Pauli Exclusion Principle, one still needs to refer to a global wave function on many occasions, with anti-symmetric properties. In both cases, one can exchange two allegedly different particles without discernible difference in the global system. To wit: one is considering particles that are indiscernible in the system as different. Does the PII still rule?
As a way out of this conundrum, van Fraassen seems to imply that we should get rid of the notion of individual (van Fraassen, 1991). But such statement has been rejected on fundamental grounds by Butterfield (1993), who insists on the applicability of the notion of individual even though PII fails to work. The involved paradox looms even larger in quantum field theories where particle number changes, what seems to strongly go against the very definition of individuals. To sum up, our theory-laden quantum wave functions draw heavily on the initial distinguishability of particles but end up with ontological collective matter states in which the abovementioned presupposition breaks down. Today, the most accepted positions on this topic are French and Krause’s logic without identity (French and Krause 2003) and Muller and Saunders’s weak discernibility (Muller and Saunders 2008).
III. Interpretations of Quantum Mechanics
Every physical theory—described via mathematical symbols and relations among them—needs interpretation. Nevertheless, from its inception, QM asked for interpretation in larger terms due to the extant gap between the wave function and the observables of the theory, in addition to the conundrums described in the previous section.
1. Interpreting interpretations. Each interpretation tries to solve the quantum paradoxes according to their own philosophical commitments. Small wonder if throughout almost one century of history QM interpretations have skyrocketed, with increasing disagreement on what is to be interpreted and what is an acceptable explanation (Felline, 2018; Wallace, 2019). For instance, Wallace claims that quantum theory is a framework in which many theories or instantiations live; it is unclear at what level the problems of interpretation must be addressed. The interested reader may recur to the Stanford Encyclopedia of Philosophy or even Wikipedia in order to get but a glimpse on QM interpretations and different criteria—epistemic and metaphysical—to classify them.
Since reference to mainstream interpretations is unavoidable, I will use in this entry a broad criterion to introduce interpretations, depending on their commitment to an information-theoretic (non-representational) or to a representational view of the description of nature carried on by QM. Overall, these two big fields of interpretations can be equated with antirealist and realist philosophical stances, or with non-unitary (accepting R) and purely unitary (rejecting R) QM defenders, respectively. Non-representational interpretations are deemed to provide sort of “abstract” solutions, suspending judgment on the ontological value of Ψ whereas admitting R as information update. But one still needs further representational language in order to describe the system dynamics. On the contrary, representational schemes pay more heed to the “real physics” (whatever this means) described by Ψ and U, trying to make R redundant; the big question being if they may succeed in reproducing R from more basic processes.
Wallace (2019) sees an irony throughout this situation: “Advocates of hidden-variable or dynamical-collapse theories are normally ardently committed to some form of scientific realism; to compare them to the logical positivists would be a killing insult. But what are the advocates of primitive ontology looking for, if not something like the observation language that the logical positivists sought in vain? And again, the problem with this strategy is not so much that the metaphysical distinction between primitive and non-primitive ontology is ill-defined or unmotivated; it is that we do not know how to make it, for realistic physics, in a way which achieves the task it is supposed to perform.” In their turn, non-representational interpretations have been usually accused of positivism in philosophy of science (Becker, 2018). A further irony, in my own view, is that antirealist QM interpretations allow for non-monist metaphysical commitments whereas realist stances tend to subsume information and knowledge into all-encompassing physical processes: information and knowledge would be just sheer epiphenomena of nature.
2. Operationalism. The simplest solution to the quantum paradoxes in non-representational fashion may lie in an operational interpretation of QM, also dubbed New Pragmatism (Wallace, 2008). A summary of this interpretation could be as follows: QM has by and large shown its extraordinary predictive power. But it is naive to think that, beyond a strict operational protocol, QM provides us with a deeper knowledge of nature as it is. Instead of briefing us on what nature is like, QM simply tells what we must do to predict the results of our measurements. Science should not question what occurs behind the curtain of the experiments. Consequently, it simply makes no sense to ask about the ontology of the wave function and of processes U and R. For instance, Stephen Hawking, in his philosophical debate with Roger Penrose states that “I do not demand that a theory correspond to reality because I do not know what it is. Reality is not a quality you can test with litmus paper. All I’m concerned with is that the theory should predict the results of measurements. Quantum theory does this very successfully. It predicts that the result of an observation is either that the [Schrödinger] cat is alive or that it is dead” (Hawking and Penrose 1996, p. 121).
Operationalism thus builds a strict separation between QM and its interpretation, in the spirit of an empiricist philosophical stance. Nonetheless, one might ask at this point for the rationale of making measurements and whether operationalism ends up isolating science from the general human knowledge enterprise. Why do human beings care about interrogating nature if its answers have little to do with nature itself? It does not seem that operationalism tout court is a philosophically tenable position, but rather a desire not to discuss certain issues. David Mermin illustrates this intellectual silence with a notorious imperative addressed to physicists to summarize how to deal with quantum paradoxes: “Shut up and calculate” (Mermin, 1989). But for how long can that position be kept? It hardly dovetails with the general views of the great precursors of the scientific revolution and it does not seem very useful for those who wish to deepen in the knowledge of “physis,” of that which “is in a certain way.”
3. Quantum Mechanics as a theory of information about nature. Even if not as radical as operationalism, non-representational interpretations of QM share part of its philosophy. They give up the dream of a complete knowledge of nature and focus on the information that can be gained thereof. Undoubtedly, the most famous of such interpretations—and of all interpretations for the time being—is Copenhagen interpretation, albeit subtler interpretations have emerged during the last decades in the same non-representational spirit.
3.1. The Copenhagen interpretation. Copenhagen interpretation (CI) comprises a cluster of shared ideas among some of the founding fathers of QM, namely Niels Bohr, Werner Heisenberg and Max Born (Faye, 2019). For most of the 20th century, it has been considered the standard interpretation of QM. Despite having a large number of critics—who deem it a non-fundamental interpretation for its (alleged) failure in explaining what a measurement is—it still rallies many adherents among the current community of physicists. One can distinguish between particular interpretations of Bohr and Heisenberg, with their own philosophical nuances, but a series of features common to this interpretation can be enumerated. CI has got a certain pragmatist air because it considers the R process as actual and accounting for the results of the experiments. Since we do not directly experience the wave function Ψ—with its superposition of possible results—or its evolution U, R is, in the end, what we can have the greatest certainty about. Ψ and U need not have actual existence for most CI adherents, who consider them (pace Schrödinger) as a kind of “subjective,” but crucial tools for calculation.
The standard interpretation states that our description of nature must be essentially probabilistic, without defining itself about the ontology of the wave function. Now, while according to Heisenberg this probabilistic description would stem from an underlying experimental indetermination—every experiment ends up altering the results of the measurements, introducing minimal uncontrollable errors—, according to Bohr nature’s indetermination should be understood in a somewhat different fashion: there is a fundamental complementarity between the various scientific descriptions that we can make of the physical systems, so that none of the descriptions can obtain a complete understanding of nature. Hence, one cannot measure at once with unlimited precision some (conjugated) physical quantities—such as position and velocity—that are complementary to each other. (This is Heisenberg Uncertainty Principle.) In addition, according to CI, QM needs the language of classical physics to describe measuring devices, which must be considered in this sense “classical.” Thus, QM necessarily demands a classic counterpart, so that the former cannot be used in isolation for the description of the quantum world.
3.2. Subtler interpretations. From a more abstract viewpoint, one may consider QM as a theory about how much information nature sets out to deliver. Both Relational Quantum Mechanics (RQM) and Bayesian Quantum Mechanics (BQM) consider the wave function as a mathematical tool that merely encodes the observer’s information of a quantum system, R being an update of information based on outcome.
RQM discards the notions of absolute state of a system, absolute value of its physical quantities, or absolute event, claiming that all physical quantities refer to the interaction between systems. The physical world is seen as a net of interacting components, where there is no meaning to the state of an isolated system. Albeit partly sharing the spirit of many-worlds interpretations (see III.4.4.2), RQM does not multiply ontologies. RQM downplays Ψ’s ontology assuming the observed values as the actual, relational, elements of reality, which occur relatively to other systems, e.g. an observer. Consistency between different observers is reached thanks to the internal self-consistency of the quantum formalism, i.e. comparison among accounts is itself a physical process that must be understood in the context of QM (Laudisa and Rovelli, 2013). Measurements imply specific correlations displaying ontological value, whereas non-relational physical quantities become meaningless. Information gaining always implies correlation, being consequently relative. No wonder that if RQM is true, the universal validity of physics becomes compromised. RQM abandons Einsteinian criteria of reality and gets on well with Bohr’s complementarity, inasmuch as expresses intrinsic limits of science because of intrinsic limits on the information our knowledge may gather.
On its turn, Quantum Bayesianism (or QBism in its most recent version) holds that, rather than directly or indirectly representing a physical system, a quantum state represents the epistemic state of the one who assigns it concerning that agent’s possible future experiences. Unlike CI, QBism maintains a subjective Bayesian or personalist view of quantum probabilities, regarding Ψ as equally subjective: a convenient representation of the observer’s overall belief before carrying out an experiment (Healey, 2017). Once the experiment outcome is obtained, the observer’s information is updated (R-procedure). Whereas QBism would sort out most of QM’s conundrums, it has been criticized because of its pragmatist flavor.
4. Unitary Quantum Mechanics. Under this section I accrue interpretations of QM considering that Ψ and U have ontological reality, but R does not, being instead a dispensable epistemic approximation possibly explained away within strictly unitary quantum formalism. All these interpretations partake of some strong form of scientific realism, eventually including knowledge itself. Obviously, their communal challenge will be how to work out the problem of definite outcomes.
4.1. Bohmian Mechanics. Originally discovered by Louis de Broglie in 1927 and rediscovered by David Bohm in 1952, Bohmian Mechanics (BM) offers one of the simplest examples of a (non-local) “hidden variables” interpretation of QM: a system of particles is described in part by its Ψ, evolving according to U. However, the wave function provides only a partial description of the system. This description is completed by the specification of the actual positions of the particles, which evolve according to a “guiding equation” expressing the velocities of the particles in terms of Ψ (Goldstein, 2017). Probability assignments arise from ignorance of the initial conditions and the usual outcomes of QM can be obtained in a deterministic scheme, without the need of invoking a special status for measurements and R-processes.
However, this interpretation faces a huge number of critics from both scientific and philosophical quarters. Determinism in BM has a high price to pay, namely, blatant non-locality of nature due to the instantaneous influence of other particles’ positions in a particle’s dynamics. As a matter of fact, BM is not Lorentz invariant in its simplest formulation and raises serious doubts on whether it might come to be. In addition, BM reduces each observation to position observation, which is a highly controversial tenet, as well as how to work out decoherence in such scheme (Bacciagaluppi, 2016). On top of that, from a more philosophical stance, BM maintains a double ontology of particles and wave function with an asymmetric role between them. The ontology of Ψ remains in a halo of mystery even though it must have physical effects—the so-called quantum potentials—on particles. Perhaps not surprisingly some scholars deem BM as providing “little more than verbal window dressing of the basic paradox” (Leggett, 2005, quoted by Goldstein, 2017).
4.2. Many Worlds. Despite not coining the name, Hugh Everett III is credited as the founder of the many-worlds interpretation (MWI) of QM. According to Everett’s initial interpretation, a local vector state is always relative (is entangled) with some other relative vector states of coupled systems—in general, the environment (Everett III, 1956). The relative state interpretation draws upon quantum non-locality to offer a relative interpretation of local states, immersed in the universe’s global wave function. The laws of physics govern the universe incorporating all the worlds and this is why, when limiting ourselves to a single world, we may run into a paradox. Not surprisingly, the most popular developments of the relative-state interpretation were dubbed MWI (DeWitt and Graham, 1973; Barrett, 2018) when directly touching upon the ontology of local states. MWI holds that there are many worlds which exist in parallel at the same space and time as our own. Every time a quantum experiment with different possible outcomes is performed, all outcomes are obtained, each in a different world, even if we are only aware of the world with the outcome we have seen. MWI is also popular among supporters of the multiverse and string theorists (Vaidman, 2018). Rejecting the R process whenever a measurement is performed avoids the reference to an external observer and implies the branching of the initial universe into as many worlds as necessary. MWI can turn into many-minds interpretation (Albert and Loewer, 1988) if one assumes that different observations, correlated with different physical states of the observer, can be entangled with their correspondent branches as defined with the help of decoherence. Therefore, such observations would ultimately identify and label the different branches of the universal wave-function.
Even though MWI’s defenders invoke the parsimony principle in ridding of R—the most problematic of the physical laws (Vaidman, 2018)—, they have habitually clashed with two main difficulties: (1) Accounting for probabilities—as provided by Born rule—without falling into circularity (“put probabilities in to get probabilities out”)—what is the meaning of probabilities if every possible outcome does occur? (2) Providing an explanation about when splitting is to be expected (the most general measurement problem) and under which clothes it is to be outfitted (the preferred basis). On the one hand, the only possible meaning for probability in a deterministic QM interpretation as MWI is a subjective probability, but there is no relevant information that an observer who is going to perform a quantum experiment is ignorant about unless one surreptitiously assumes a God-like perspective. On the other hand, the following dilemma inevitably arises: if the splitting of the universal Ψ in keeping with the preferred basis is produced by observations, there is little hope to explain minds with QM; on the contrary, if the splitting is produced just via decoherence, the correspondence between the physically chosen preferred basis and the content of observations needs further explanation (Zurek, 2002; Sánchez-Cañizares, 2019). We will encounter again this problem in subsection IV.2.
4.3. Modal interpretations. Initially developed by van Fraassen, modal interpretations (MI) cover a bunch of QM interpretations breaking the eigenvalue-eigenvector link—in the spirit of denying ontological value to R. Typically, MI distinguish between the “dynamical state”, determining which properties the system may have now and at later times, and the “value state”, representing the well-defined system’s properties at present. However, MI substitute the R process for different actualization rules once we obtain information from observables in an experiment (Lombardi and Dieks, 2017). By so doing, this schema tries to attribute ontological physical values to the system, while complying with no-go theorems forbidding classes of hidden variables and with Born rule.
Actualization rules rely upon preferred partitions of system and environment in the universe and, in some degree, introduce relativeness in the properties possessed by the system—inasmuch as they are witnessed by another system or the environment. By generally dealing with large physical systems and not necessarily with observers and observations, MI aim to ward off the threat of subjectivism, since the relational states should unambiguously follow from the quantum formalism and the physics of the situation. Despite denying the collapse, indeterminacy is a feature of our world for MI because the future is not simply unknown but it is potential or not yet decided. Moreover, the modal distinction between “dynamical state” and “value state” admits a parallelism with the cherished-by-Aristotelians notions of potency and act (Vanney, 2015). Yet it remains highly controversial for a number of reasons if MI provide a satisfactory account of the quantum-to-classical transition and, in particular, of the measurement problem: (1) According to van Fraassen’s interpretation, decoherence must first work out a superposition of possibilities that only then can be attributed ontological value. But remember that decoherence is an ontologically ill-defined procedure, badly in need of interpretation itself. (2) If the dynamical and the value state possess different ontological value, one has to add further fundamental cognitive prescriptions in order to explain the connection between both levels of reality, something which is in itself in need of explanation or interpretation.
5. Modified Quantum Mechanics. A more radical view to tackle the problem of how to consistently link U and R consists in going for a modified quantum theory, implicitly or explicitly assuming incompleteness of QM. Within current QM, if experimenters do possess free will, the free will theorem (Kochen and Specker, 1967; Conway and Kochen, 2006) implies that R cannot be physically determined, i.e. no physical process can be expected to account for R. Were R truly real we could not know its mechanism. Consequently, one last resort is looking for a modified QM by introducing new terms in the Schrödinger equation. Linearity of the U process is lost in exchange for (allegedly) coming to terms with R through a new physical process. Such process would be in itself fundamental—remaining at the axiomatic level of the formulation for the time being. One of the most famous proposals encompasses the dynamic reduction programs initiated by Ghirardi, Rimini, and Weber in the 1980s. In a spontaneous and stochastic way, the wave function would become localized or determined in its main components, thus allowing definite outcomes and the appearance of the macroscopic world familiar to us. However, it is much more unclear what basic components of Ψ must be localized and determined since bare QM does not confer preference to any variable over another.
On a more physical note, Diósi (1989) and Penrose (2004) claim that gravity—an essentially non-quantizable interaction—must ultimately be held responsible for the collapse of the wave function and for the introduction of effective non-linear terms in the Schrödinger equation. Since every system has a certain spatio-temporal distribution of its mass, its wave function will consist of a superposition of all possible mass distributions that are solutions to the Schrödinger equation. Now, general relativity states that this will give rise to several, superimposed, geometries of space-time, which differ in the energy that each of them possesses. When this energy difference multiplied by the duration of the superposition exceeds the order of magnitude of the Planck constant h, Ψ is reduced or determined to only one of the possibilities, in keeping with Heisenberg Uncertainty Principle. Although a not full-fledged theory, Diósi and Penrose’s proposal has the potential to provide criteria for when and how often Ψ’s objective reduction takes place. (We will encounter this theory again in section IV.2; see Bassi et al, 2013 for an overall review of the state of the art.)
IV. Philosophical Implications Writ Large
The relationship between QM and philosophy is bidirectional. If one may agree with Vanney and Polkinghorne’s claim that the multiplicity of coexisting interpretations of QM highlights the need for a meta-scientific perspective to assess them (Vanney, 2015; see Quantum Mechanics)—so that QM can benefit from philosophy—, it is not less true that philosophy of nature can also benefit from the raw materials offered by QM for mature and serene discussion. We will focus on this thread of thought in the current section.
1. Downward causation and ontological emergence. Beyond the problem of interpretations, QM sounds the alarm regarding physicalism and the alleged exclusive existence of mere bottom-up causation in nature. Both compatibilist and epiphenomenalist accounts of nature thus sail on troubled waters. These must face not only the practical impossibility of a logically consistent transition between levels of abstraction in our scientific theories—our current set of theories describing nature smacks of a patchy work—, but the inescapable need of adding further cognitive prescriptions when dealing with a specific system: e.g., define boundary conditions and specify how to perform the coarse graining of the (most basic?) degrees of freedom to make heads or tails of a problem. There are many possible coarse grainings from a fundamental theory (Gell-Mann and Hartle, 2007), but we must usually pick out only one of them serving our explanatory purposes.
In the last decades, the literature on complex dynamical systems has raised the issue of downward causation in nature, namely the system’s realization, as a whole, of top-down influences on its constituent parts. Somehow, complex systems build themselves up and downward causation needs to be invoked in order to explain their permanence (Juarrero, 2000; Auletta, Ellis, and Jaeger, 2008; Ellis, 2016); complex systems are autopoietic. Nevertheless, how to interpret such kind of causality—whether truly causal or ultimately reducible to the non-trivial sum of bottom-up causes—remains highly controversial. The interesting issue introduced by QM itself via its measurement paradox concerns the inability, for principled reasons, of a would-be reduction of top-down to bottom-up causation. Such inability “is consistent with a multilevel view of reality and the emergence of new kinds of events at a higher level of organization” (Barbour, 2000, p. 89). It thus seems undeniable that contemporary physics proposes an ontological pluralism (Sánchez-Cañizares, 2016). Could this pluralism be signaled by an intrinsically limited access to reality through physics? (Vanney, 2015).
2. Quantum Mechanics and the mind-brain problem. Unsurprisingly, QM has also been linked to the mind-brain problem from its inception. Thanks to its apparently non-reductive framework, could QM ultimately shed light on the hard problem of consciousness (Chalmers, 1995), i.e. how the physical activity of neurons becomes the phenomenal conscious experience and the subjective feelings that we live? Throughout almost a century, one may find different attempts to make the abovementioned link more explicit (London and Bauer, 1939; Lucas, 1961; Wigner, 1967; and, more recently, Penrose, 1989; 1994; 2004; Stapp, 2017). Even if non-reductive in spirit, QM approaches to the mind-brain problem can still be classified as bottom-up or top-down depending on their grounding assumptions (Sánchez-Cañizares, 2014).
In the wake of the beginning of 21st century, an influential paper by Max Tegmark provided some estimates for decoherence times in the brain according to different theoretical models. Its conclusions set about to downplay the relevance of QM for the physics of consciousness. Decoherence times were deemed too short—ranging from 10-13 to 10-20 s.—in comparison with consciousness typical times—of the order of 10-1 to 10-2 s. (Tegmark 2000). Moreover, QM was expected not to play a significant role in such a crowded, noisy and high temperature environment as the brain. However, Tegmark’s paper was criticized for a few shortcomings. More importantly, the exploding field of quantum biology—providing several instances of QM relevance in living beings—seems to be changing the mainstream view among scientists. Nowadays, the most famous (and controversial) model of a quantum brain is that of Hameroff and Penrose, who propose that the phenomenon of consciousness would have to do with the orchestrated objective reduction of Ψ due to gravity in the brains and, more specifically, inside microtubules of neurons (Hameroff and Penrose, 2014). The model still lacks of sound theoretical and experimental support but deserves credit for explicitly stating a connection that must exist.
3. Epistemic issues. Despite all its conundrums and interpretative travails, QM has had the virtue of bringing sciences and humanities closer. It fosters rethinking the value of methodologies and opens up new conceptual and epistemic possibilities for the goal of the unity of knowledge. Frequently, risks and opportunities go together and it might be only too soon to separate the wheat for the chaff in this field.
3.1. Bridging the gap with Humanities? Beyond the knack of QM to resolve the mind-brain problem or the specific role that consciousness might play in the R process, quantum epistemology opens the door to a more fruitful relationship between the objective and subjective poles of reality. From the very beginning, the founding fathers of QM acknowledged that, to a certain degree, subjectivity played a role in our scientific knowledge: “Certainly quantum theory does not contain genuine subjective features, it does not introduce the mind of the physicist as a part of the atomic event. But it starts from the division of the world into the ‘object’ and the rest of the world, and from the fact that at least for the rest of the world we use the classical concepts in our description. This division is arbitrary and historically a direct consequence of our scientific method; the use of the classical concepts is finally a consequence of the general human way of thinking. But this is already a reference to ourselves and in so far our description is not completely objective” (Heisenberg, 1958, p. 55). As Heisenberg himself notes, quoting Weizsäcker, “Nature is earlier than man, but man is earlier than natural science” (ibidem, p. 56). Therefore, one should not forget that our best scientific theories are the way they are because human subjects observe nature the way they observe. The circularity between the subjective and the objective pole in human knowledge is inescapable.
Such view mollifies the vexed question of incompatibility between natural sciences and humanities—as notoriously stressed by C.P. Snow (1959)—making room for a milder version of complementarity. Actually, inspired by his Complementarity Principle, Bohr himself suggested the idea of extending complementarity to other phenomena, such as the organic models in biology, dialectic argumentations in sociology, and the behavioral and introspective models in psychology (Bohr, 1937; 1950; Vanney, 2015). As a matter of fact, one can contemplate at present the flourishing of new “quantum” disciplines with different targets and scopes. Whereas some of them are striving to earn a well-deserved reputation—think about quantum biology or quantum psychology—others may benefit from the quantum adjective to sneak pseudoscientific ideas in. To wit: complementarity should be used warily, since only too often it involves alternatives that do not stand at the same epistemic level; e.g. it would be misguided to straightforwardly apply complementarity to the field of science and religion. But of course, on the other hand, one has occasionally to take some risks if the epistemic gap between sciences and humanities is to be filled in.
3.2. Is Science just a social construction? The delicate equilibrium between the objective and subjective poles of reality may destabilize due to loss of any of the two parts. Should one unduly press the case of one of the poles over the other, we could obtain either dereliction of humanities or transformation of science in a social construct. Current philosophy of science stands not so far from both when occasionally embracing extreme realist or antirealist stances. Vanney distinguishes different kinds of scientific realisms—metaphysical, semantic and epistemic—and antirealisms—instrumentalists, skeptics, Kantians, pragmatists, methodological, historicists, constructive empiricists—, herself endorsing an instance of critical realism (Vanney, 2015). Whereas realist approaches tend to support with different nuances that scientific theories endeavor to represent and explain the world existing beyond the human mind, anti-realist stances bring to the fore the conceptual limitations of human knowledge, reducing to a minimum beliefs in accepting a theory. For example, van Fraassen’s constructive empiricism (van Fraassen, 1980) only adheres to observational adequacy and assumes that interpretations are necessary, but need not be unique or better than others.
Even if the controversy between realism and antirealism in philosophy of science outreaches the quantum realm, QM’s tormented relationship with realism has funneled antirealist positions and, on a more negative note, fed with new arguments the defenders of non-objectivity of the scientific enterprise. Despite QM’s success in making predictions about what we observe ‘out there’, it is always possible, from a purely logical viewpoint, to invalidate the realist’s arguments by sticking to the goal of just explaining observations. Indeed, concrete observations are crucially mediated by non-scientific, social factors. Small wonder if some forms of antirealism combine with forms of social constructivism (Chakravartty, 2017). Nevertheless, extreme forms of antirealism do suffer from logical inconsistencies, falling into the trap of the hermeneutic circle (Monton and Mohler, 2017). Albeit QM warns against naïve metaphysical realisms, it also provides evidence against interpretations and philosophies closing in themselves. The quantum theory inserts more naturally in the long lasting tradition of thought which deems science a non-isolated province of human knowledge about reality. Some realist position is required should one wish to avoid severing the ties among nature, science, and the human being.
V. Theological considerations
Our last considerations about an overall realist philosophical position are relevant if one wishes to ascertain what QM offers to the science and religion dialogue. Here, the philosophical mediation seems absolutely necessary (Artigas, 2000, p. 12) because of the apparently weak epistemic intersection of physics and theology in the arch of scientific disciplines.
1. Initial remarks. Surely enough, the feature of indeterminism appears as the quantum feature more propitious to a non-reductionist view of nature, in stark contrast with old-fashioned naturalistic views relying on a deterministic universe. According to determinism, the natural laws together with the state of the universe at any one time uniquely entail the state of the universe at any other time. On the contrary, quantum indeterminism seems to make room for divine action in the world, for the causal power of free will or, at least, for going beyond sheer materialistic causation. Promising as it can be, though, Vanney warns against drawing too simplistic conclusions regarding potential theological implications of quantum indeterminism and the pertinence of a theological discussion stemming from the different quantum conundrums. The existence of determination might be compatible with design, and the existence of indeterminacy might also be compatible with a non-interventionist divine action (Vanney, 2015).
Despite such cautions, one may as well wonder that if everything is determined and can be explained away with natural laws, what arguments remain in favor of a personal Creator? (Thomas Aquinas, Summa theologiae, I, q. 2, a. 3). Aquinas recurs to the distinction between primary and secondary causation to affirm that necesse est ea quae a natura fiunt, etiam in Deum reducere, sicut in primam causam (ibidem). However, could one find out specific traces in the workings of nature—as QM makes it known—pointing towards the primary-secondary (divine-natural) structure in causality? Does QM reveal an intrinsically contingent nature of physical processes, making room for an autonomous self-determination of nature itself? If the deterministic paradigm to understand nature is superseded by the image of an open and creative nature, what is the theological message to be gained? The quantum framework might be telling about the behavior of free agents in conformity with physical laws; it may constrain the ways such beings could be manifested and the sorts of actions a human observer could in principle detect (Clayton 2001, p. 212). Needless to say, these are not only opportunities for risky theologians (Tracy, 2001) but important challenges to the relations between QM and theology (McMullin, 2001, pp. 55-56). All in all, theology also shares the contingent nature of human knowledge and should not be afraid of confronting well-established scientific views.
2. Divine Action in nature. Starting with William Pollard (1959), who suggested that God might act in the world by determining the outcomes of quantum events, the most renowned program tackling the issue of God’s action in nature is called “Scientific Perspectives on Divine Action” (Russell, Stoeger, and Murphy, 2008). Theologians have participated in this project with different models of God’s action, none of which is wholly satisfactory at present. Within the contemporary debate, it is customary to distinguish between general divine action (GDA) and special divine action (SDA): the former accounts for creation and conservation of the universe and the latter accounts for those particular actions that happen hic et nunc, promoting God’s goals for the universe and humanity (Silva, 2014, p. 285).
The articulation of God’s action as GDA and SDA, even if pacifically held in the theological field, is in itself controversial. Of course, one may well wonder if there is actually something in the universe going beyond God’s creation and conservation. But, worst of it, the distinction naturally leads to specific divine actions in the world which amount to some degree of intervention. The problem with an interventionist God is to make of Him a capricious or whimsical Being—dealing with the world in two different manners, as McMullin puts it—or, even worse, a working God through sloppy works. In either case, there would be a permanent gap between God and human intelligence only too resembling the infamous nominalist gap between God’s potentia absoluta (his absolutely free and unlimited power) and potentia ordinata (the contingent order of his actual creation). According to Philip Clayton, (1997, p. 195, p. 203, p. 206 ) is very difficult to come up with an idea of divine action in the world in which such action would not constitute breaking natural law or breaking physical law. Thus, rather unsurprisingly, theologians set out to describe SDA in non-interventionist fashion, with QM being an outstanding candidate thanks to the halo of mystery involving the R process. In particular, Robert Russell has claimed that QM provides a good framework to propose an “objectively special non-interventionist divine action” (Russell et al, 2001).
Nevertheless, not all theologians feel uncomfortable with an interventionist account of SDA. Alvin Plantinga (2008, pp. 375-378) denies that God’s intervention violates the causal closure of the universe inasmuch as the universe is, in his own words, an “open system.” For him, the problem is the Laplacean view, not Newtonian physics—making somehow redundant the theological recourse to QM. Plantinga also endeavors to tackle the problem of miracles, affirming God’s freedom in (apparently) breaking, going contrary to, abrogating, or suspending a natural law (ibidem, p. 376). Yet his discussion turns out scarcely helpful inasmuch as our conceptualization of miracles is contingent upon a concept of nature mediated by current science. Here, a broader picture seems badly necessary.
Assuming without further clarifications that SDA finds its place within the quantum worldview meets other shortcomings. On the one hand, since the quantum picture is partly deterministic (process U) and partly probabilistic (process R), SDA becomes episodic (Polkinghorne, 1995, pp. 152-153) and approaches the unwanted features of a whimsical God. On the other hand, even though fulfilment of Born rule reassures a minimum of steadfastness and predictability in nature, at least in its upper levels, allowing for occasional unpredictable divine interventions, it might as well introduce a limitation in SDA. The very meaning of Born rule is controversial because of dealing with probabilities that can have objective or subjective connotations. Yet, it seems to impose some overall constraint on God’s actions.
Recently, Silva (2014) has provided a better articulation of GDA and SDA within the Thomistic tradition. One should rather speak of different aspects or dimensions of God’s unique creative action (ibidem, p. 284). SDA makes explicit what is implicit in GDA or, even better, in God’s creation. Silva thus makes explicit the epistemic dimension in our conceptualization of divine action in nature—the quoad nos—without compromising its metaphysical power. Within his schema, Silva does not deem ontological indetermination in nature a necessary condition for SDA. However, if ontological indetermination does occur, it opens up new possibilities in order to understand the radical contingency of being in the universe and an autonomy of nature consistent with a personal God (see section V.4).
Since we may never have a workable model of God’s action in nature, it is by no means clear what one should understand by divine action, not to mention the relationship between GDA and SDA. Contemporary research on divine action sails between the Scylla of the god of the gaps—approached by interventionist accounts—and the Charybdis of making God redundant if the primary cause becomes undetectable in natural processes. That being said, we must add that QM might offer an incomplete knowledge of reality while providing new explanatory logics in the science and religion field. QM’s epistemic limits as a theory could be revelatory of true ontological emergence as a pre-scientific proviso for scientific systematization.
3. Are chance and randomness compatible with God? The last considerations usher in the question of the compatibility of a random determination of nature—as apparently required by process R in the standard interpretation of QM—with divine intelligence. If quantum indetermination is truly ontological, sheer randomness does not seem an appropriate feature for God’s intelligent governance of nature. At this level, some epistemological considerations are worthwhile.
First, it must be noted that talk of randomness in the scientific speech always connotes some sort of ignorance regarding the relevant degrees of freedom of a problem. For instance: one may assume an initial random distribution of variables that, after careful insight, shows hidden biases or subtle correlations; or one may obtain a random distribution of outcomes in a measurement, related to the initially assumed relevant degrees of freedom. In this sense, the purpose of human insight always seeks for overcoming sheer randomness (see the initial chapters of Lonergan, 2005). From a purely logical viewpoint, getting to know if a general, potentially infinite sequence of number is actually random is a non-algorithmic procedure (Chaitin, 1975; Sols, 2014), which chimes with the overall contextuality of QM but also warns against a too quick statement of ontological randomness in nature. In fact, some sort of superdeterminism in nature can always be coherently maintained as a metaphysical position, even though, according to recent experiments, correlations among degrees of freedom should spread over more than 7,8 × 109 light years (Rauch et al. 2018).
Second, quantum indetermination does not mean or imply sheer randomness. Even if we do not and cannot know how the R process comes about, nature usually stabilizes itself at upper, coarse-grained levels of description. Quantum decoherence plays a crucial role in achieving this, although its theoretical bases are not well understood yet. Since bare quantum formalism does not privilege any particular configuration, the regularity of patterns in nature’s upper levels demands especial cosmological boundary conditions, effectively local interactions (Tegmark, 2015), and, very likely, downward causal interactions (Ellis, 2016; Sánchez-Cañizares, 2016, see section IV.1). To sum up, QM indetermination does not metaphysically preclude the existence of an orderly determination in nature.
Third, there are compelling reasons to think that God’s action in nature cannot be pigeonholed in clear-cut epistemic categories. Moreover, inasmuch as scientific knowledge and reality are not made straightforwardly equivalent and epistemic limits of scientific theories are acknowledged, one may argue that chance and randomness become more congruent with finality and the theological account of God’s relationship to the world. Chance and randomness are intended features of creation, lying within the purposes and providence of God (Bartholomew, 2008, p. ix, p. 1, p. 99). Random outcomes of experiments in nature seem to make room for divine causality in processes that might be both contingent and guided because “the causality of God, Who is the first agent, extends to all being, not only as to constituent principles of species, but also as to the individualizing principles (…). It necessarily follows that all things, inasmuch as they participate in existence, must likewise be subject to divine providence” (Thomas Aquinas, Summa theologiae, I, q. 22, a. 2; International Theological Commission, Communion and Stewardship: Human Persons Created in the Image of God, 2004, n. 69).
4. The theological meaning of an open nature. In the last decades, theological discussions have taken up afresh the problem of how to blend an omniscient God and human freedom. An interventionist and transcendent God acting in the world from without clashes with the autonomy of natural processes, but a God in detailed charge of every single thing does seem to clash too. Ontological indetermination of QM, however, paves the way for a new theology of nature in which God’s eternity grounds creatural time shunning any kind of predetermination. Unreachable in his ineffable mystery, God is always experienced by creation as its future source of determination (Pannenberg, 2004). In a similar vein, open theism holds that a future that God leaves open can be known only as open possibility without specific foreknowledge. This theological current—mainly in the evangelical camp but not restricted to it—endeavors to attain a new synthesis of Greek philosophy, contemporary science and Christian theology.
Should one not wholly embrace the controversial tenets of open theism, the quantum feature of entanglement may still inspire a more holistic and ecological view of creation. Albeit in different manners and degrees, we dwell in a non-local universe in which everything is interconnected, everything is interrelated (Francis, Encyclical Letter Laudato si’, 2015, nn. 70, 92, 120, 142). Extreme sensitivity to boundary conditions is a hallmark of our universe, allowing for the emergence of complex structures. Such remarkable features could ultimately stem from quantum entanglement, decoherence and top-down determination. In addition, if God interacts with the universe at the upmost level of totality, then he could be causatively effective in a top- down manner without abrogating the laws and regularities that operate at the myriad sub-levels of existence that constitute that world (Peacocke, 1993, p. 159; Vanney, 2015). One might think of God as providing the ultimate top-down causation for the ultimate determination of nature. Obviously, more metaphysical refinement is needed for this conceptualization of God’ causality in nature in order to avoid the “god-of-the-gaps” trap. But such perspective sounds promising inasmuch as it rules out God’s causality as physically traceable while keeping it at a grounding level with physical effects.
QM thus permits us to contemplate the universe as a place in which openness, flexibility and even freedom could naturally emerge (Peacocke, 1995, p. 281; Vanney, 2015). But is this not what one should expect of a creation from a personal Creator? With all its difficulties and paradoxes, QM is leading towards a more mature view of nature, superseding stifling, old-fashioned scientific, philosophical and theological perspectives. The limits of our scientific knowledge—as shown by QM—might be aiming at acknowledging its ontological foundations as necessary presuppositions of scientific endeavor itself. “[I]f the logos of all being, the being that upholds and encompasses everything, is consciousness, freedom, and love, then it follows automatically that the supreme factor in the world is not cosmic necessity but freedom (…). [T]his means that together with freedom the incalculability implicit in it is an essential part of the world. Incalculability is an implication of freedom; the world can never—if this is the position—be completely reduced to mathematical logic (…). A world created and willed on the risk of freedom and love is no longer just mathematics” (Ratzinger, 2010, p. 128). On a more existential note, QM might also help to reevaluate the relationship between man’s cognitive capabilities and God. In a certain sense, the alleged impossibility to build a human representation of what happens at some micro-levels in nature seems a sign of human finitude. Human knowledge withdraws and makes room for acknowledgment of divine presence in creation.
The philosophical and theological implications of Quantum Mechanics remain as an active field of research. Difficulties in interpreting the epistemic and ontological value of the quantum formalism—wave function Ψ, processes U and R—spread over wider regions of human knowledge, affecting our concepts about the universe and even our deep understanding of nature and the human being. One may say that QM touches upon the very articulation between being and knowledge, making it impossible a neat separation of these dimensions of reality as actually accessed by human beings.
Despite its lack of sounder foundations, Quantum Mechanics is here to stay. In between the extremisms of either an absolute reality or an absolute ideality of the quantum world, there is a broad spectrum of positions recognizing true—if partial—knowledge of reality and construction—if objective—of scientific knowledge of reality via Quantum Mechanics. Moreover—as stated by Ratzinger—, “[w]hy should we not be able to understand afresh, on this basis, that in the question of God we must not look, in the Aristotelian fashion, for an ultimate concept encompassing the whole (…)? We meet here the hidden interplay of faith and modern thought. That present-day physicists are stepping outside the structure of Aristotelian logic and thinking in this way is surely an effect already of the new dimension that Christian theology has opened up, of its need to think in ‘complementarities’ (2010, pp. 140-141)”. Because of it, Quantum Mechanics will ever abide as fertile ground for profound reflection on the relationships between science and religion.
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