Determinism in Current Physics. Is It Possible

Global Philosophy (2024) 34:19 https://doi.org/10.1007/s10516-024-09725-2 ORIGINAL PAPER Determinism in Current Physics. Is It Possible? Daniel Heredia González1 · Marco Gomboso2 Received: 1 December 2023 / Accepted: 17 September 2024 © The Author(s) 2024 Abstract We discuss the possibilities of determinism in reality, taking under consideration both quantum and classical physics. We present this firstly by questioning the supposed nature of quantum physics as non-deterministic, following the proposal of Penrose: the collapse of the wavefunction interpreted as particular measurements which seem to indicate certain contingency does not actually give the full picture of the reality of the former. In addition to what Penrose suggests, we consider this collapse as part of a bigger deterministic picture. Secondly, we analyse the distinction between this microphysical scenario and our macrophysical experience, in the light of determinism as well. We suggest that this experience can be understood as particular “measurements” similar to what happens in quantum mechanics. For instance, the image of a person with certain identity features is a highlight or particularization of all the possibilities the identity of this person experienced, experiences and will experience through time. The “collapse” is thus linked to individuation, not less real, but incomplete of reality. By linking the domain of quantum physics in a deterministic fashion to the phenomenological or macrophysical realm, we aim to show that a non-contingent character of reality is possible when accepting measurements or particular instances of things as forms of comprehension given by the physical world (thus not just mere subjective interventions). We argue that the complete picture (closer to the wavefunction) cannot give distinctive information (understanding this as differentiation of elements, such as particles in the microphysical domain and a certain colour in the macrophysical one). Keywords Determinism · Quantum mechanics · Entropy · Anthropic principle · EPR Extended author information available on the last page of the article 13 19 Page 2 of 26 Global Philosophy (2024) 34:19 1 Introduction Current physics is characterised by the description of natural processes in an indeterministic way. This has been controversial since the origins of quantum mechanics, being the source of numerous debates not only within the physical domain. But also from the historic philosophical one, such as in the case of authors like David Hume, William James, or Baruch Spinoza, to cite some of the many of them who were interested in the topic. The results of quantum mechanics continue to consolidate and reality seems to be stubborn in showing its indeterministic side; this, however, is not an obstacle to the continued existence of defenders of a deterministic nature. One of the greatest representatives of this philosophical perspective is Roger Penrose. In this work we will try to see on what philosophical-physical bases Penrose builds his defence. For this we have divided the work as follows. In Sect. 2 we will make an analysis of various types of determinism, to be able to glimpse which one Penrose’s thought adheres to. In Sect. 3 we will begin to see what physical arguments he brings to elaborate his deterministic position. In this section we will come into contact with the concept of anthropic principle. Section 4 will introduce another physical concept to which Penrose gives importance, that of entropy. It will aim to answer the question that Penrose asks himself about whether the anthropic principle explains entropy. Within Sects. 5 and 6 we will see some arguments in favor of determinism, taking into account fundamental concepts of quantum mechanics. Section 5 will be divided into two subsections, one dealing with the EPR experiment, where we will try to see the role of the entanglement concept, and another that aims to show the scope of the implications of said experiment. Section 6 brings up the concept of the wave function and will also be divided into two subsections: one will expose the importance of this function; the second will explore a rethinking of the famous mental experiment of Schrödinger’s cat that Penrose elaborates. Section 7 will be dedicated to the description of the situation of quantum mechanics and whether it is possible or not to carry out a reform in it of the type that Penrose longs for. Finally, Sect. 8 will contain the conclusions we have reached in this work. 2 Determinism: Characteristics and the Penrosean Vision Determinism is a topic in Penrose’s scheme that is transversal within his thought, but, nevertheless, it is not extensively explained by him. The inevitable consequence of this is that what he intends to expose is understood in an inadequate way, since it is not specifically treated in his work. Before going on to see how our author deals with this issue, we find it convenient to specify what is meant by determinism in a broader sense. Generally, to talk about determinism it is necessary to take into account that this concept is usually divided into two types: the scientific and the philosophical. Scientific determinism is defined by as the “theory according to which the state of the world at any moment determines a single possible future, and knowledge of the position of all objects, as well as the dominant natural forces at each moment, would allow that 13 Global Philosophy (2024) 34:19 Page 3 of 26 19 an intelligent being could predict the future state of the world with absolute precision” (Alonso 2004: 250). This definition closely conforms to the one elaborated by the French mathematician Pierre-Simon de Laplace, hence this type of determinism is also known as Laplacian determinism. On the other hand, philosophical determinism is understood as that theory in which every element depends on some other phenomena, in such a way that it can be foreseen, produced or prevented with certainty, just by knowing, producing or preventing those phenomena1 (Février 1957: 16). Let’s see what are the main similarities and differences between both types of determinism. One of the main aspects we have to face is the importance of causation. In determinism, both scientific and philosophical, once we know with certainty the cause of a phenomenon, we can assure (in an equally certain way) the knowledge of the effect that it will produce. The notion of determinism, therefore, carries within it the condition of necessity2. Nevertheless, there are features that distinguish one determinism from the other. The main divergence is that scientific determinism is more concrete than philosophical. The first, as its own name indicates, is limited to the knowledge of phenomena, that is, to what is capable of being studied by science. Meanwhile, the second also encompasses knowledge in which science has little or nothing to say (Février 1957: 17). However, some thinkers such as the cited Paulette Février see that this difference ends up being superficial. Once scientific determinism runs into certain limits it must abandon science as an underlying principle, thus making itself almost indistinguishable from philosophical determinism: Ainsi l’on se rend compte que même lorsqu’il s’agit du déterminisme strictement scientifique, c’est-à-dire restreint aux phénomènes observables, il est encore question, dans les définitions qu’en donnent les savants eux-mêmes, d’une croyance, d’un principe rationnel, beaucoup plus que d’une constatacion a posteriori assimilable à une donnée expérimentale pure. Et ceci ne vient pas faciliter la distinction nette que nous nous proposions d’etablir entre déterminisme philosophique et scientifique (Février 1955: 5). We think it is important that we dwell on this aspect, because it will help to understand the concept of scientific determinism as we understand it in this work. Février’s analysis of this distinction has, in our opinion, two aspects that are not treated correctly. The first of these is to imply that scientific thought must lack metaphysical foundations in order to continue to be considered scientific. Although science does not support the guarantee of its success on a fully (and not even in a majority) metaphysical basis, no less true is that science from its beginnings until today does not do without metaphysical assumptions. To what extent could we say that we are still talking about scientific determinism if we understand that metaphysical assumptions do not alter 1 Although we handle this conception, it can be said that there are those who think that it is not enough to refer the cause of everything to other phenomena. It is also necessary to take into account that these phenomena have to be intelligible as well because they are based on indubitable philosophical postulates. 2 This can be detected in other expressions of determinism, such as theological determinism and fatalism. 13 19 Page 4 of 26 Global Philosophy (2024) 34:19 its nature? Here is the difficulty that Février talks about when trying to distinguish scientific from philosophical determinism and where, we think, there is an error of exposition. This second problem arises from understanding scientific determinism as independent from philosophical one. According to us, is convenient to conceive the first as a category (or a subcategory) of the second. Thus, scientific determinism does not cease to be philosophical at any time, because it belongs to it, and just at the moment it hits the limits of science it must return to its philosophical nature, not allowing itself to be, in turn, scientific. In this way we can talk about scientific determinism as a concrete determinism, while when we refer to philosophical determinism we do so about a general determinism. We have seen in this first distinction between philosophical and scientific determinism that without the pertinent clarifications the matter can become problematic. However, not all types of determinism give rise to these types of drawbacks. Some are clearly differentiated and hardly difficult to identify. Examples of these types of determinisms are logical, ontological and causal. Logical determinism is the one that supports the thesis that there is only one possible world (Arana 2013: 3). Assuming any change that you want to introduce, no matter how small, would cause a drastic transformation in the whole. Therefore, logical determinism implies the acceptance of a total determinism, since admitting a partial one would contradict this with its own term. The causal chain in logical determinism is unique and necessary, making the universe an immovable whole. Despite the inflexibility to which this type of determinism submits to the universe, this does not prevent a regional determinism from being recognized within this determinism. Regional determinism allows reality to be divided into entirely independent regions (Arana 2013: 4), but this could never affect the immovable unity of the universe, since it continues to be necessary. In the formal aspect, logical determinism also has its particular feature. After having seen the previous characteristics, it is easy to see that this type of determinism is based on the principle of the excluded middle or, if you like, on that of bivalence (Moya 2017: 64). Some think that the formal level may not be taken into account perfectly, since the discussions on determinism are focused on the concrete. This, however, does not correspond to the reality of the matter3. With respect to ontological determinism, as with logical determinism, the idea of unity persists, trying to find the need for it, although with the characteristic that it does so outside of the entities analyzed. Diverting attention from entities, the framework of ontological determinism appears more open than that of logic. For ontological determinism, for example, the thesis of the only possible world can be a mere possibility. With logical determinism we had a universe doomed to follow a single path, in which entities gave us clues to discover the deterministic nature of the universe. However, ontological determinism contemplates the possibility of opening new paths, which, although they also have the condition of being necessary, the logician’s own unity disappears. But if we cannot admit that the universe is deterministic 3 In the debates about determinism in physics at the beginning of the 20th century, the formal section was extensively discussed. For a comprehensive study on the importance of the formal level in this matter, see for instance Jammer (1974: 2–20). 13 Global Philosophy (2024) 34:19 Page 5 of 26 19 from the entities involved, what does the weight fall on in this type of determinism? Well, in what allows the description of the behavior of the universe, that is, what determines it: the laws of nature. If the universe has an order, it is not due to the necessary behavior of the entities that compose it, but to the order established by the laws of nature. Therefore, the order is intrinsic in nature but extrinsic to the entities that compose it. Finally, we have causal determinism. This type of determinism has normally been the subject of debate. To avoid entering the bogged down terrain that causality brings with it, we have decided to take the definition of Moya (2017), who offers a very panoramic perspective of said concept. His definition of causal determinism is as follows: everything that happens necessarily happens (it cannot not happen) given the previous state of the universe and the laws of nature (Moya 2017: 64). This concrete causal determinism includes the two previous types of determinism, because it focuses both on the entities of the universe and on the laws of nature. To what extent is it conflictive to understand causal determinism in this way? It can become a tricky issue, for example, if we take into account legal determinism, which is -broadly speaking- the one that is sustained solely and exclusively in the laws. The difficulty would reside in the fact that Moya’s definition is very open and he would not be able to clarify how we would be talking about one type of (causal) or another (legal) determinism. But since we will not run into legal determinism throughout this work, the aforementioned problem will not exist. It is clear that identifying the different types of determinism is essential to avoid falling into fruitless debates. And it is not that we are trying to come up with a precise definition of determinism, as that would only further complicate the matter. What we find convenient is to be clear about when one is talking about a concrete determinism and when about a general one. Explanatory scheme of the different types of determinism, being the philosophical the general, and the others the concrete one (differentiated, in turn, between them). Note that causal determinism derives from both logical and ontological determinism. This is because causal determinism is presupposed in both cases: the only possible world of a logical structure involves the assumption that this world is consecuence of a determined chain of causal events; in the case of ontology, all the possible worlds also derive from precedent states that cause their reality. Still, it is true that this way of seeing determinism does not include a more fatalistic or absolutely immediate one. The latter is not discussed in this paper Once this review is done, we will now see how Penrose treats determinism in his work. With this we will reach the end of this section, that is, knowing in a more concrete way what type of determinism the one exposed by him belongs to. It is not a question of classifying Penrose’s determinism, but rather of clarifying an issue that seems not to be sufficiently explicit in his exposition. This aspect is not without appeal, since Penrose does not hesitate to declare himself as a determinist. However, his way of approaching this concept ends up dragging him towards an indisputably controversial position. In the first place, it should be noted that in a part of The Emperor´s New Mind (1991: 199–203), Penrose reviews different scientific theories and classifies them into three categories according to which they are more faithful to reality. The clas- 13 19 Page 6 of 26 Global Philosophy (2024) 34:19 sification differentiates between SUPERB, USEFUL and TENTATIVE theories, in clear hierarchical fashion. The reason for taking such a classification into account is because Penrose places as an argumentative basis (yes, in a very timid way) that the SUPERB theories have in common that all of them keep within themselves a strict determinism: […] Normally, the issue of free will is discussed in relation to determinism in physics. Recall that in most of our SUPERB theories there is a clear-cut determinism, in the sense that if the state of the system is known at anyone time, then it is completely fixed at all later (or indeed earlier) times by the equations of the theory (Penrose 1991: 534). However, Penrose is not rash enough to put the full weight of his position on this point. Actually, it does not even seem like he is using it as an argument for determinism. What does constitute in a more obvious way a key point in his exposition of determinism is the relationship that he establishes between it and the term “computational” (or “algorithmic”). As a general rule, it is usually understood that everything that is likely to be computable must necessarily be deterministic. This makes perfect sense because computability, like deterministic processes, has as one of its main characteristics that what happens does so in a necessary way. Therefore, the equivalence between computability and determinism seems indisputable. However, not every determinism must be computable. Penrose argues that this need not be necessarily so. In line with what he maintains about consciousness (which he tries not to leave aside) he defends that natural processes contain procedures that are not computable. How is it possible that he understands that nature contains non-computable procedures while being, at the same time, deterministic? A crude way of saying it is that even Penrose himself does not know for sure: My own point of view although it is not very well formulated in this respect, would be that some new procedure […] takes over at the quantum-classical borderline which interpolates between U and R (each of which are now regarded as approximations) and that this new procedure4 will contain an essentially non-algorithmic element. This would imply that the future would not be computable from the present, even though it might be determined by it. I have tried to be clear in distinguishing the issue of computability from that of determinism […]. It seems to me to be quite plausible that CQC might be a deterministic but non-computable theory- (Penrose 1991: 535; italics in the original). What Penrose really wants to defend does not contain an insurmountable difficulty. In fact, he explains it with the clarifying example of meteorology. In his con4 As these processes will continue to appear in this paper, we offer a brief explanation of them. Roughly speaking, the process R is what Penrose calls the reduction of the state of a system. We speak about the reduction of the state of a system when the value of the state of that system is determined from among all possible values. This process is indeterministic and is opposed to the U process, which occurs through the deterministic Schrödinger equation. These two processes coexist in current physics, but there is a clear inconsistency between them, being irreconcilable when we try to make quantum measurements, and this, according to Penrose, is something that we should change. 13 Global Philosophy (2024) 34:19 Page 7 of 26 19 ception there is a conflict between what he can account for through science and his inner conviction. According to Penrose, nature is determined, but this cannot be demonstrated because said determination depends on a non-algorithmic process, which, as we see, if it were discovered, could give the last answer. Herce (2014), for example, although he agrees that Penrose conceives nature as deterministic and non-computable, he also understands that the Penrosean system of nature admits a certain type of opening that would not occur in extreme determinism (Herce 2014: 176). About the determinism that Penrose expounds is certainly not extreme5, we completely agree. However, we defend that the underlying idea of determinism that our author intends to adopt can be interpreted in a more closed way than Herce deduces. Posts to categorize, we are inclined to think that the type of determinism carried out by Penrose is scientific. We really do not see how Penrose strays from the scientific determinism of Laplace or Einstein (both of which are not that far from each other either). What mainly happens is that Penrose ends up encountering the problem that Février highlighted with respect to determinism: not being able to distinguish it from philosophical determinism. But, as we said above, this does not have to be a problem if we understand scientific determinism as part of philosophical determinism, so the first one must go back to the second one when scientific explanations do not give more than themselves (this is the situation that science is experiencing today, as denounced by Penrose himself!). Penrose does not deny freedom (at least the appearance of it) as far as the human dimension is concerned. However, he finds it more difficult to understand freedom (not even its appearance) in the realm of the nature of the universe. This idea is manifestly exposed in his conception of natural selection, which he considers could not have occurred arbitrarily or “freely.” 3 Determinism, Natural Selection and the Anthropic Principle According to the aforementioned Penrosean classification of scientific theories, that of natural selection is among the so-called SUPERB (that is, it is one of those that guarantee a faithful description of nature). And not only that. As Herce (2014: 67) points out, this is the only one of the SUPERB theories that is not physical, which shows its potential and the importance that Penrose grants it6. Undoubtedly, as with most of Penrose’s thought, the conception of natural selection that he defends is peculiar. According to Penrose, natural selection is somehow closely related to the anthropic principle. Penrose focuses on the two anthropic prin5 For an actual and clear example of extreme determinism, see the brief chapter of the Nobel Prize in Physics, Gerard t’Hooft (2019), who even bets on a super-deterministic position, since he considers that this has not yet been the subject of any objection (t’Hooft 2019: 29). 6 First of all, the specific theory of natural selection that our author is talking about is the one developed by Darwin and Wallace. And, secondly, it is strictly necessary to clarify that, although Penrose recognizes a great scope for this theory, he also does not hesitate to emphasize that, in any case, said scope is very far from any physical theory (Penrose 1991: 199). 7 They are acronyms of Weak Anthropic Principle and Strong Anthropic Principle. 13 19 Page 8 of 26 Global Philosophy (2024) 34:19 ciples highlighted by the Australian physicist Brandon Carter; these are the weak and the strong. The weak tells us that our location in the universe is necessarily privileged to the point of being compatible with our existence as observers (Arana 2012: 332). The strong demands that it be possible for observers to appear in the universe at some stage of its evolution (Arana 2012: 332). Now, how are the two principles different? Juan Arana, following José Manuel Alonso, quotes in this regard: […] The difference between the WAP and the SAP7, in Carter’s formulation, consists in that the former alludes only to our location in this universe, indicating that it is biased […] Instead, the SAP no longer speaks of our location in the universe, but of the universe itself […], which leads Carter to consider a set of universes, while the WAP did not need to consider more than one universe (Alonso, cited by Arana 2012: 332). Penrose understands these principles in exactly the same way. He offers a feature that suggests that the weak anthropic principle, despite his last name, is also an extreme approach. That said aspect is that the exclusivity of the conditions of the world as we know it that makes it possible for things to happen the way they do (Penrose 1991: 537). Regarding the strong anthropic principle, Penrose does not add anything new to what has been seen above. What is worth noting is that he considers that this type of anthropic principle does not fit into his approach. Once the main features of the anthropic principle have been seen, it is appropriate to ask to what extent Penrose relates it to natural selection. He believes that something as sophisticated as consciousness cannot be the product of pure chance. Is he thus acknowledging something like a hidden plan, which had reserved the appearance of the human being and, with it, of consciousness? As we have seen, this would be admitting a weak anthropic principle (carried even to the extreme) and this is not made explicit in any of Penrose’s writings. What is detected in his arguments (Penrose 1991: 516) is that the idea that a directed nature makes more sense than an arbitrary nature. Despite the fact that sometimes he seems to be going to give a more forceful argument about what he wants to defend (in our opinion, an unmitigated Laplacian determinism), the truth is that in the end he always seems to recoil (like all scientific determinism is forced to do). He not only ends up renouncing the possibility of a strong anthropic principle (something he is not really convinced at all), but also skeptical of conceiving a weak anthropic principle as a strong metaphysical argument that can explain the appearance of consciousness (Penrose 1991: 538). It is true that Penrose is forceful in the quote when it comes to renouncing the [weak] anthropic principle as the supporter of natural selection that gave rise to human consciousness. This categoricalness, however, is unimportant, since what he is doing is abandoning an assumption that he himself brought up without any obligation to do so. His mistake is, in our opinion, having resorted in the first place to the anthropic principle (already in whatever form it was). 7 They are acronyms of Weak Anthropic Principle and Strong Anthropic Principle. 13 Global Philosophy (2024) 34:19 Page 9 of 26 19 On the other hand, it is not a gross error on Penrose’s part either. If he puts the anthropic principle on the table to give it some kind of credit to later take it away, it is to show how this principle has its limitations. For our author, one of the most obvious limitations of the anthropic principle is related to the inability to account for the mysteries related to entropy, specifically its behavior according to the second law of thermodynamics. 4 Does the Anthropic Principle Explain Entropy? According to Penrose, it is important to take into account the concept “entropy”. This idea is not only relevant with respect to the study of the universe and its origin, but also in the concrete domain of the life of living beings. Although we are not going to see Penrose’s cosmological perspective in depth here, it will be necessary to understand some aspects of it to fit them with the conception that he has of entropy and the anthropic principle. First of all, a fundamental question must be answered: what is entropy? As we have seen outlined above, this concept owes its development to the field of thermodynamics. As Penrose does in The Road to Reality (henceforth RTR), we will start by looking at what the first law of thermodynamics says in order to have a clearer perspective of what the concept of entropy means. The first law of thermodynamics determines that the total energy of an isolated system is conserved. This law helps us to understand the nature of energy and also to know its value, which remains constant despite the fact that all sorts of complicated processes can take place, so the total energy after the process is equal to energy before the process. Penrose exposes the first law to make manifest the difference between it and the second law of thermodynamics. Although the first speaks of equality, the second does so of inequality. This is where the concept of entropy comes in. In general, entropy is known as the “manifest disorder” within a system. This definition, however, does not do justice to the scope of the concept. Still, this should not be a problem for what we will see about it, since we will see the applicability of this concept, above all, to a very specific feature of nature: the possibility of life for living beings on our planet. Now, what does the second law of thermodynamics tell us specifically? Basically, that in nature entropy tends to increase, that is, that the universe is becoming more and more disordered. Despite the fact that this definition of entropy is neither orthodox nor precise, it will not take us too far away from what Penrose intends to expose about said conception. Actually, the manifest implications of the second law are remarkably intuitive and hold no mystery. Hence, most physicists feel some sympathy for it, to the point of believing that the most reasonable physical theories should satisfy it (Penrose 2006: 937). To make the implications of the second law visible, Penrose develops a concrete assumption (borrowed from Boltzmann, although with additions of his own). The 13 19 Page 10 of 26 Global Philosophy (2024) 34:19 image assumes a phase space8 P in which a physical system x represented at a point in this space behaves in a certain way. The phase space P is composed of subregions, which are called the “coarse-graining” of P (Penrose also calls them “boxes”). In the assumption we have that the system x (at the moment NOW) is located in one of the coarse-graining (V), which has a smaller volume than those that surround it. Once x is set in motion y in a phase space in which there is no special inclination or trend (as this is) its fate is to end up in “coarse- grainings” with more volume (in an overwhelming majority of cases! ). System x is headed for disorder y in a (most likely) irreversible way: […] Once x finds its way into a box with a certain entropy measure, it becomes overwhelmingly unlikely that, in any sensible period of time, it can find itself back in a box of significantly smaller entropy than that. To reach a significantly smaller entropy would mean finding an absurdly tinier volume, and the odds are immensely against it. (Penrose 2006: 937). Everything seems to fit perfectly. But in the expression “irreversible” above is one of the keys to understanding that the implications of the second law are not so definitive. With the conclusion of the assumption exposed by Penrose we must conclude a temporal asymmetry. This is tremendously controversial, since the physics in which the assumption is developed understands temporality in a symmetrical way (Penrose 2006: 938). In what way is the conflict between temporal symmetry and asymmetry translated in relation to the second law and the supposed treatise? Putting ourselves in the assumed phase space, in which entropy tends to increase, let’s try to see the behavior of the system back in time. Although theoretically the entropy should increase, what happens, however, is that its entropy is less and less (as a consequence of having to come from “coarse-graining” with more volume), which violates the second law if we take into account time symmetry counts! Does this mean that the second law inevitably leads to absurd conclusions on the physical plane? Penrose does not understand it that way, despite the fact that in the specific case of phase space he determines it that way. What our author does expose is that the second law has different dimensions with special characteristics9 and these constitute a mystery to science as far as we know it today. That is why he believes it convenient to examine those cases in which entropy shows special characteristics. Our attention will be focused, as we saw above, in the special case of living beings on our planet. Entropy in living beings is special to the extent that for life to occur it 8 The phase space is an abstract space that is used within quantum mechanics. This type of space is useful to be able to talk about the kinematics and dynamics of particles and has the particularity that it consists of 6 dimensions. Penrose explains that phase space comprises that for a classical system of n particles (without distinctive features), in a 6n-dimensional space P, each point of which represents the complete family of positions and momenta of all n particles (Penrose 2006: 929). This space is a fundamental tool for us to visualize and explain the complex implications of quantum mechanics. 9 These are the ones that occur, for instance, at the origin of the universe, black holes and living beings. We see a deep treatment on this topic in his work Cycles of time: an extraordinary new view of the universe (Penrose 2010). 13 Global Philosophy (2024) 34:19 Page 11 of 26 19 is necessary for entropy to remain at a low level. The role of the Sun in this scenario is essential but, Penrose qualifies, not in the sense in which it is generally believed: […] There is a common misconception that the energy supplied by the Sun is what our survival depends upon. This is misleading. For that energy to be of any use to us at all, it must be provided in a low-entropy form. Had the entire sky been uniformly illuminated, for example, with some uniform temperature—whether that of the Sun or anything else—then there would be no way of making use of this energy (whatever kind of creature we might imagine having evolved to try to cope with it). An energy supply in thermal equilibrium is useless. We, however, are fortunate that the Sun is a hot spot in an otherwise cold background. During the day, energy reaches the Earth from the Sun, but during the course of the day and night it all goes back again into space. The net balance of energy is (on the average) simply that we send back all the energy that we receive (Penrose 2006: 948; italics in the original). That is to say, that life on Earth does not simply depend on the energy coming from the Sun, but on the balance that exists between this and the energy that the Earth sends back into space. The balance is that the Sun sends our planet high-frequency yellow photons that contain more energy; while in the opposite direction (that is, from the Earth to the Sun) low-frequency infrared photons are emitted that contain less energy. This balanced exchange prevents, for instance, the Earth from suffering extreme heating. But not only that, but it also allows living beings such as plants to arise and that these (through photosynthesis) keep their entropy low and that of the beings (among them, of course, humans) that benefit from them, (either by eating them, eating something that eats them, or breathing the oxygen they release) (Penrose 2006: 948). Does it mean, then, that living things contradict the second law? At first it may seem so, especially considering that this is true in practically the entire known universe. Nevertheless, if we conceive living beings as open systems, they can avoid contradicting what the second law postulates (Herce 2014: 112). We then have that the validity of the second law is not in danger and the increase in entropy is a fact that is fulfilled. Now, attending to this aspect and returning to the common thread of this point (determinism), a question arises: is Penrose recognizing that with the undeniable increase in entropy a freedom is given place, which would come face to face with the determinism that he himself defends? He does not really have to understand himself that way. Penrose points out in Fashion, Faith and Fantasy (henceforth FFF) that understanding entropy or the second law in terms of organization is a common mistake that should be avoided: […] In colloquial terms, we could say that the low entropy states, being “less random”, are therefore “more organized”, and therefore the 2nd Law is telling us that the organization in the system is continually becoming reduced. However, from another point of view, we could say that the organization in the highentropy state that the system ends up in is just as organized as was the initial low-entropy state. The reason for this claim is that (with deterministic dynamical equations) the organization is never lost, because the final high-entropy 13 19 Page 12 of 26 Global Philosophy (2024) 34:19 state contains vast numbers of detailed correlations in the particle motions, these being of such a nature that if we were to reverse every motion exactly, then the entire system would work its way back until it reaches the “organized” initial state of low entropy. This is just a feature of dynamical determinism, and it tells us that simply referring to “organization” by itself gains us nothing in our understanding of entropy and the 2nd Law. The key point is that low entropy corresponds to manifest or macroscopic order, and that subtle correlations between the locations or motions of the submicroscopic ingredients (particles or atoms) are not things which contribute to the entropy of the system. This, indeed, is a central issue in the definition of entropy, and without such a term as manifest or macroscopic in the above descriptions of the entropy notion, we would not have been able to make any headway towards an understanding of entropy and of the physical content of the 2nd Law. (Penrose 2017: 313–314; italics in the original). Therefore, according to Penrose, determinism is not affected by entropy, but rather, in a certain sense, is somehow benefited by the implications of this and the second law10. It is easy to see why a concept like entropy serves to defend the Penrosean deterministic position. After all, a concept that includes some kind of trend or purpose generally stands as support for determinism. And if this is so, why is Penrose so reluctant to accept the anthropic principle? The reason why he hesitates in this specific aspect is due, as we saw outlined above, to the fact that in cosmological terms the anthropic principle does not respond adequately to the mysteries that entropy entails. Penrose arrives at this verdict through the analysis of a specific cosmological position, that is, the inflationary11 one. He defines [roughly] this theory12 as follows: [According to the inflationists] our actual universe, almost immediately following its Big Bang origin, in an extremely tiny period between about 10− 36 and 10− 32 seconds just after that momentous event, became subject to an exponential expansion – called inflation – that resembled the effect of the presence of a huge cosmological constant Λinfl which vastly exceeded the presently observed value of Λ by an enormous factor (Penrose 2017: 375; italics in the original). Penrose acknowledges that the inflationary theory has a certainly high degree of acceptance by the scientific community (Penrose 2017: 375). Despite this, he believes that this theory conflicts with principles and laws that are too fundamental to be Insofar as determinism is not involved in any contradiction, even becoming almost indifferent to said law, as can be seen in the previous quote. 10 Here we will not see the inflationary theory, since this would unnecessarily distance us from the matter at hand. In any case, Penrose offers his analysis of this in (Penrose 2006: 1002–1016) and, above all, (Penrose 2017: 374–394). 11 12 For the definition, our author uses the works of Alan Guth and Alexéi Starobinski. 13 Global Philosophy (2024) 34:19 Page 13 of 26 19 accepted outright. In fact, he rejects it for the way in which it precisely contradicts the second law of thermodynamics. The contradiction is easy to spot. If we assume that the universe at its beginning underwent an exponential expansion, it means (very briefly) that it reached the degree of maximum entropy at that time (contradicting the increase in entropy of the second law! ). How does a theory that so flagrantly contradicts the second law gain the credibility of the scientific community? Firstly, the second law, as we have seen, is not so clear to explain certain phenomena of nature (some as fundamental as the life of living beings on our planet). Second, the inflationary theory satisfactorily answers three very perplexing cosmological problems, the so-called horizon, smooth, and flat. For Penrose, on the other hand, the inflationists in the background do not adequately solve any of the three problems. Although he grants them some credit regarding the horizon and flatness problems, in reference to the smoothness problem he understands that it remains unresolved in any way. As we saw above, the second law in principle does not fit as postulated by the inflationary theory either. This, however, is not an obstacle for inflationists, since to respond to the contradiction regarding the second law they frequently appeal to the anthropic principle. And here is the reason why Penrose feels a certain suspicion towards the conception of this principle. His contrary position is based on the fact that he considers that inflationists do not have an adequate conception of the anthropic principle (Penrose 2017: 409), in the sense that they give said principle a greater scope than it belongs to. As we saw in the previous section, the idea of a weak anthropic principle does not displease Penrose (an aspect that remains even in his most current works, such as FFF). Another matter is that the anthropic principle (in whatever form) is conceived as the last response. Undoubtedly, the [weak] anthropic principle and the second law could serve as support for Penrose’s determinism, but he himself knows that the way these ideas are developed today, such support is partially given. There are other physical arguments that are more convincing to him and that he uses with greater development, such as those that we will see in the following sections. 5 Argument in Favour of Determinism within Quantum World I: EPR Experiment 5.1 EPR-Type Experiments and a Fundamental Idea Behind Them: Entaglement One of the most widely used theoretical physics arguments as an attempt to keep determinism on the physics scene after the appearance of quantum mechanics is the EPR experiment. This experiment never came to jeopardise the explanatory power of quantum mechanics. However, those who feel sympathy for a deterministic approach, including Penrose, return to the implications of this experiment. In order to better understand the rest of the section, we believe it is necessary to summarise the article13 13 We have used the original version (Einstein et al. 1935). 13 19 Page 14 of 26 Global Philosophy (2024) 34:19 where the experiment was exposed in order to see the basis of the argument for the need to return to EPR14. The first part of the article15 raises the question of what a scientific theory must fulfil in order to be considered serious. The main feature that a serious theory must have is that its concepts must try to correspond to objective reality (that is, independent of any subject). Once we analyse a theory there are two pertinent questions: (1) Is the theory correct?; (2) Is the description offered by the theory complete? Both questions could only be answered positively if there was agreement between the conclusions of the theory and human experience. In other words, what is considered within physical reality would respond to the results of measurements and experiments (Einstein et al. 1935: 777). With all these elements it is necessary to give a definition of reality. This definition is offered in the article, although it is warned that it should not be taken as categorical. For EPR, reality could be understood as follows: “If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there is an element of physical reality corresponding to this physical quantity” (Einstein et al. 1935: 777). The second part of the article offers a description of quantum mechanics, expressed in terms of Schrödinger´s wave function. In the explanation of quantum mechanics, it is stated that two physical quantities, represented by operators that do not commute, cannot be measured at the same time with a full degree of precision of both. The better we know one, the worse we know the other16. This is basically what Heisenberg’s uncertainty principle tells us, and the article argues that far from being able to offer us a faithful description of reality, the only thing we can infer is that it is an incomplete theory. After this statement, we go on to a third part in which an example is shown that tries to display that a more complete theory can be obtained than those that support quantum mechanics. The example consists of imagining a concrete system, formed by two particles (called I and II), of which we can measure and predict with certainty the momentum of particle I at the same time that we could do it with the momentum of particle II without altering it. This would also be possible with the position. Of course, this example is pertinent if we take into account the definition of reality that was given above, in which, precisely, the conclusions reached through quantum mechanics do not fit. With the example we have that both particles belong to the same physical reality, while with the uncertainty relations this was not possible. The fourth part is the recapitulation of all these ideas to conclude that there may still be a more complete tool that can describe reality (taking the idea of the example as that possibility and not the example itself) and this is not, of course, quantum mechanics. 14 For recent studies of actual experiments on EPR, see Hess (2022). 15 For the structure of the article, we have used the analysis of Jammer (1974) too, since we consider that with it is simpler than with the original. While in the original the article is divided into two parts, Jammer breaks it into four, revealing some more features. 16 In the article it says that when we know one of these quantities, the other (since it is unknown) ceases to have physical reality. 13 Global Philosophy (2024) 34:19 Page 15 of 26 19 For those who do not feel sympathy with the implications (of whatever kind) of quantum mechanics, it is clear that EPR is constituted as a weapon that they can use. Penrose does it and even contemplates other experiments inspired by EPR. One of the most relevant alternatives for the EPR experiment is the one developed by David Bohm (1951). Bohm’s experiment is based on the assumption of the disintegration of a particle with spin zero at a specific point (central) and from this disintegration two particles of spin arise ½, which recede in exactly opposite directions. What is remarkable about this particular case is that once we decide to measure the spin of one of the two particles produced (which Penrose identifies as an electron and one as a positron) in one direction, we find that the other particle has a spin in the opposite direction. This leads to the conclusion that such a choice of the measure of one of the particles seems to have simultaneously fixed (determined) the axis of rotation of the other (Penrose 1991: 357). The conclusion of this experiment is not based on a simple logical inference like the one we have just seen, but we can find it within the formalism of quantum theory17. With this conclusion an important debate is being highlighted, that is, specifying whether the particles behave independently, as classical physics would approach them or if, on the contrary, they do so as dictated by quantum theory, that is, intertwined way. Penrose is unambiguous on this point, defending entanglement and rejecting independence. Penrose points out that the results of the experiments that have been carried out in accordance with what is stated in this experiment seem to tell us that nature behaves in an intertwined way, that is, as quantum theory tells us. But if Penrose accepts all of this, does not that put him on the opposite side of EPR’s statements? To be precise, the answer is a resounding no. Penrose does not intend to abandon quantum theory and return to a physics that complies with the classical guidelines. What he is looking for is to reform quantum physics, finding what does not work in order to develop it in a more adequate way. And entanglement is an idea that should be kept in mind, since it manages to explain that mysterious connection that seems to exist in nature. In fact, Penrose defends that despite the fact that said entanglement clearly exists18, he also recognizes the mystery of proving it19. The way in which Penrose distances himself from the quantum vision faced by the EPR perspective is to opt for an objective realism, that is, a realism in which the role of the observer is almost secondary: […] It seems to me that something of the nature of a “measurement” is always an essential part of the setting up of a quantum experiment, to ensure that the state is uncontaminated by swarms of these unwanted entanglements. In saying this, I do not mean to imply that the experimenter deliberately sets up a “measurement” to achieve this. It is my own view that Nature herself is continually 17 For details of that formalism, see for instance (Penrose 1991: 357–360) (Penrose 2006: 787–789). 18 Thanks to the experiments that have been carried out and not to a personal opinion of him. Specifically, Penrose talks about the double mystery that the demonstration of entanglement has to face: (i) regarding how to interpret the phenomena and (ii) finding the reason why we do not perceive entanglement more frequently (Herce 2014: 96). 19 13 19 Page 16 of 26 Global Philosophy (2024) 34:19 enacting R-process effects, without any deliberate intentions on the part of an experimenter or any intervention by a ‘conscious observer’ (Penrose 2006: 797; italics in the original). These are the philosophical, or metaphysical, reasons on which Penrose is based, but they are not the only ones. In fact, he relies to a greater extent on scientific arguments. The main one is the one with which he rejects the classical Bell inequalities, which, roughly speaking, deny entanglement in favor of independence20. For such rejection, Penrose is based on the results of a specific experiment, that is, the one carried out by Alain Aspect and his colleagues (Aspect & Grangier 1986, Aspect et al. 1982). Aspect’s experiments end up agreeing with EPR and calling into question Bell’s inequalities. In Aspect’s experiments, a certain type of entanglement was observed. These results, however, are not definitive and there are those who reject the abandonment of Bell’s inequalities, pointing out that the development of experimental devices (detectors) does not allow us to reach a conclusive result. However, our author is one of those who do give credit to Aspect’s work: […] To my own way of thinking, it would be exceedingly unlikely that the excellent fit between quantum theory and experiment that is exhibited in the Aspect experiment […] is somehow an artefact -an artefact of the insensitivity of the detectors- and that with more perfect detectors the agreement with theory would somehow go away, to the considerable extent that would be needed in order that the Bell relationships could be recovered (Penrose 2012: 266; italics in the original). Another EPR-type experiment that Penrose brings up is the one proposed by Lucien Hardy (Hardy 1993). This shares with Bohm’s the emission of two particles of spin ½ in opposite directions from a central point. Both particles are directed towards spin detectors located at very distant points (denoted as L – since it is directed to the leftand R –its direction is to the right). The difference from Bohm’s experiment is that the initial state of the central point is not spin 0, but a particular spin 1 state (Penrose 2017: 242). Penrose offers a technical explanation of this EPR-type experiment in RTR (Penrose 2006: 792–794), but in FFF he develops a counterexample that, in our opinion, makes the explanation of what he intends to expose clearer. The aforementioned counterexample consists of trying to see if a classical model can account for the problems, especially those related to entanglement, that EPR-type experiments raise. To do this, he asks us to imagine Hardy’s example, but with the particularity that the 20 Bell illustrates his point with a simple example, which is known as Bertlmann’s socks, which Penrose explains as follows: Bertlmann was a colleague of his who invariably wears socks of different colours. […] if one happened to catch sight of his left sock and noticed that it was green, then one would instantly obtain the knowledge that his right sock was not green. Nevertheless, it would be unreasonable to infer that there was a mysterious influence travelling instantaneously from his left sock to his right sock. […] The effect can be easily arranged merely by Bertlmann determining ahead of time that his socks will differ in colour. Bertlmann’s socks do not violate Bell’s relationships, and there is no long-distance “influence” connecting his socks (Penrose 2012: 265; italics in the original). 13 Global Philosophy (2024) 34:19 Page 17 of 26 19 particles are pre-programmed to give certain results when they reach the detectors. In turn, such results will depend on how each of the detectors is oriented. Another characteristic is that the individual components of the mechanism that governs the behavior of each particle send signals to each other once the particles have separated from O (Penrose 2017: 243), which is how the central point denotes. With all this, the particle detectors must be oriented to be able to measure a specific direction (Penrose speaks of the ← direction, because with it we can account for the orthogonality or non-orthogonality of the studied system). The reason for this is that at least some of the particles to result in said direction, obeying the orthogonality and non- orthogonality rules21. However, this case in which only one of them is predisposed in this way, as classical physics may require, ends up breaking one of these rules (specifically the first). This has the consequence that if we want to comply with the rules we cannot do it through devices that obey classical physics. Therefore, the solution is to abandon this model and embrace the idea of entanglement that quantum mechanics supposes. Although this seems hardly refutable, it is no less true that Penrose acknowledges that in reality the intertwining is not as obvious as he himself would like it to be. Entanglement is a [more than] possible property that is still tremendously subtle and requires a very sophisticated vision to be able to intuit it (Penrose 2017: 244). This, however, does not prevent him from considering that the path to follow should be aimed at deciphering entanglement22. 5.2 The “Real” Scope oF EPR Why is it so important for Penrose to prove entanglement between particles? Does not current physics tell us that said entanglement can only be intuited in the way it does? The second question is important within Penrose’s approaches, because, as we have seen on several occasions, what he is precisely looking for is to reform current physics to answer this question, among many others. A reinterpretation of EPR would guarantee a more adequate approach to reality, which can be understood as an answer to the first of the questions. Penrose is convinced that the idea of objective reality defended in EPR has to be real. Moreover, its nature has to be deterministic. The Penrosean interpretation of quantum entanglement is precisely this: if everything is entangled, to what extent is Said [necessary] rules are three and Penrose defines them as follows: (i) that if the spin-measuring detectors at L and R are both set to measure ↓, then sometimes (with a probability of 1/12, in fact) it will indeed be found that both detectors obtain ↓ (i.e. YES, YES). […] (ii) that if one detector is set to measure ↓ and the other to measure ←, then they cannot both find these results (i.e. at least one finds NO). Finally, it tells us (iii) that if both detectors are set to measure ←, then they cannot both find the opposite result →, or, put another way, at least one of the detectors must find ← (i.e. YES) (Penrose 2017: 243; italics in the original). 21 22 In practice, most physicists seem to believe that when performing these experiments, the particles previous entanglements with the outside world can be ignored, or averaged, without influencing the result. Penrose considers that the problem is in the interpretation that is made of the results. Rather than interpreting the U/R formalism, a more complete theory that overcomes the apparent dichotomy should be sought. The paradox of the measurement process continues to be an explanatory challenge with no solution (Herce 2014: 96). 13 19 Page 18 of 26 Global Philosophy (2024) 34:19 it correct to continue to claim that natural processes are indeterministic? This affirmation- interrogation carries with it an idea, to say the least, controversial, that is, to relate indeterminism to the independence between natural events. In fact, we would not have seen the idea of entanglement come to life in physics if it had not been for quantum theory. Now it is true that an idea in which nature is ultimately intertwined, even at the particle level, fits more appropriately, at least roughly, with deterministic ideas than with indeterministic ones23. However, all this is still mysterious. Although this problem is mysterious, Penrose believes that even with what we have in current science it is possible to get a little more to the bottom of the matter. He specifically speaks of another new reinterpretation, but this time on the Schrödinger wave function, thus adopting, again, a position that brings him closer to Einstein (who felt great sympathy for this idea as a deterministic answer). 6 Argument in Favour of Determinism Within the Quantum World II: The Wave Function 6.1 Importance of the Wave Function Penrose refuses to believe that determinism was defeated in the debates at the beginning of the 20th century that we have seen above and for this reason he defends that this current can still be found in quantum physics. For this task, he believes that the proper use of complex numbers is essential, because these numbers are more related to reality than is initially believed. Such a relationship is concretely evident at the quantum level (Penrose 2012: 275), while real numbers are enough for classical physics (Penrose 2012: 276). Complex numbers are the most appropriate because they have the ability to explain the peculiarities of nature at the quantum level, such as superposition, for example. Superposition is a key concept for what the Schrödinger wave function manages to explain, and it is possible to recognize it as something objectively real: […] It is just a fact that we appear to find that the quantum-level world actually behaves in this unfamiliar and mysterious way. The descriptions are perfectly clear cut-and they provide us with a micro-world that evolves according to a description that is indeed mathematically precise and, moreover, completely deterministic! (Penrose 2012: 277; italics in the original). It is common to associate determinism with simplicity, especially if we take into account that classical physics (markedly deterministic) is much simpler than quantum physics. However, Penrose argues that this is a mistaken idea, since we can understand determinism within the framework of quantum theory. A concept that is essential to understand not only Penrose’s proposal, but also quantum theory in general is known as Schrödinger evolution or unitary evolution. 23 Despite, as we have seen, the concept of entanglement is taken into account from quantum studies, which are widely recognized as indeterministic. 13 Global Philosophy (2024) 34:19 Page 19 of 26 19 Unitary evolution is the translation made by the Schrödinger equation (or wave function) of the state of a system, which is altered when a measurement is made on said system. Another concept is the so-called reduction of the state vector or collapse of the wave function. With the reduction of the state vector, the system is aware of when it is being subjected to the measure mentioned above. According to the science that we know, therefore, there is an alternation between the state that describes the unitary unit and the one that describes the reduction of the state vector, depending on whether or not a measurement is being made in the studied system. While the unitary evolution, being the result of the Schrödinger equation, is a deterministic process, the reduction of the state vector is indeterministic. It is convenient to remark that the reduction of the state vector is generally subject to debate, which revolves around determining if it is a fact of physical “reality” or if it is a simple tool of theory (Penrose 2006: 713). Penrose does not enter into such a debate and limits himself to explaining said process as it is used in quantum mechanics. As a last point, it should be said that for later mentions (and as indicated in note 5), that the unitary evolution is henceforth denoted as U, while the collapse of the wave function is denoted as R. The question that arises again is whether U can only account for, due to its deterministic condition, the simple events of nature. And, again, the answer is no. In fact, U contemplates the previously mentioned superposition in an unforced way. Penrose explains it with the example of the behaviour of light particles: Consider a situation in which light impinges on a half-silvered mirror -which is semi-transparent mirror that reflects just half the light falling upon it and transmits the remaining half. Now in quantum theory, light is perceived to be composed of particles called photons. We might well have imagined that for a stream of photons impinging on our half-silvered mirror, half the photons would be reflected and half would be transmitted. Not so! Quantum theory tells us that, instead, each individual photon, as it impinges on the mirror, is separately put into a superposed state of reflection and transmission. If the photon before its encounter with the mirror is in state |A), then afterwards its evolves according to U to become a state that can be written |B) + i|C), where |B) represents the state in which the photon is transmitted through the mirror and |C) the state where the photon is reflected from it (Penrose 2012: 279; italics in the original). In approaching this problem, it is not assuming that each of the photons splits and ends up being two, but rather, thanks to the complex numbers that allow calculations in quantum theory, this coexistence between the alternatives is contemplated (Penrose 2012: 281). This is a situation that was already exposed by Schrödinger himself with his famous mental cat experiment, which we will focus on in the next point. Regarding R, Penrose defends that although it is completely necessary for current physics, it is no less true that with this we cannot aspire to give a faithful description of natural processes, because it is contradictory to U! With R we can measure one of the two superimposed states that are described thanks to U, with the drawback that this measure can only be explained by chance, due to the “jump” it requires. R is very necessary because it translates complex quantum processes into simpler clas- 13 19 Page 20 of 26 Global Philosophy (2024) 34:19 sical physics terms. However, according to Penrose, physics (or, rather, physicists) cannot be satisfied with this description and must continue in search of a more complete, if not definitive, one. Penrose is convinced that R does not have the ability to describe the “reality” of the quantum state it purports to describe. It is a very useful tool, but it has an expiration date. So radical is his position that he defends that one cannot fully believe in quantum mechanics, that is, accepting U and R at the same time. The key is in U and we can see it again with Schrödinger’s cat. 6.2 To the Rescue of Schrödinger’s Cat Physics is misfocused, and a rereading of Schrödinger’s cat experiment might provide us with some clues about that misapproach. To do this, Penrose slightly modifies the original conditions proposed by Schrödinger. The most significant change is to have someone observe the experiment from inside the room, where originally only the cat was. However, this is not the only one. Another of the modifications is to change the quantum event: while in the original this corresponded to the disintegration of a radioactive atom, in Penrose’s it is insisted that this is represented by the firing of a photocell by a photon, which is reflected. in a semi-reflecting mirror (Penrose 1991: 367). The reason why Penrose decides to place someone who observes the experiment is because this, in principle, would be the perspective that corresponds to R, since the observer can see the cat either alive or dead and not in both states at the same time. An observation corresponding to U belongs only to an observer outside the room. With these modifications our author highlights what Schrödinger also wanted to emphasize, that is, the inability we have to explain superposition in the macrophysical realm. But unlike Schrödinger24, Penrose does not go so far as to think that this condition is due to some deficiency of the U process, but rather to R. What consequences or what conclusions does Penrose’s new interpretation of Schrödinger’s experiment lead us to? What he intends to put on the table is that the perspective of current physics is extremely subjective. Obviously, this is not convenient if what we want is to offer a faithful description of nature. However, the only thing that. Penrose can contribute to this problem is his disagreement, appealing to the philosophically legitimate conviction that our conception of experience is very limited: […] I do not see why what we call “experiences” need to be un-superposed. Why should an observer not be able to experience a quantum superposition? It is not what we are used to, of course, but why is it not? It may be argued that we know so little about what actually constitutes a human “experience” that we are certainly entitled to speculate about such matters in one way or another. But we may definitely question why human experiences are to be allowed to un-superpose a given quantum state into two parallel world states, rather than 24 At least in the early stage of his thought, Schrödinger was more in favor of the indeterministic perspective. But, to be fair, the truth is that he never leaned strongly to either of the two doctrines. 13 Global Philosophy (2024) 34:19 Page 21 of 26 19 maintaining just one superposed world state –which is what the U-description actually provides us with (Penrose 2017: 269; italics in the original). Undoubtedly, Penrose’s proposal is very suggestive and would very likely expand the explanatory capacity of science. However, it is also evident that the real possibility of carrying out a change of this caliber seems, to say the least, unlikely. This is precisely the most recurrent criticism that Penrose has to face when he exposes his ideas. On the other hand, this does not prevent him from continuing to defend his position strongly. A cat may be too complex as an object of study for superposition to be reflected. Nonetheless, this should not pose an insurmountable problem for science, because, as Einstein said [again], what is important is the proper construction of the theory. So, let’s rescue the cat. Our author considers that if his proposal represents an abyss with respect to current science, it is because of its situation, which is not conducive to contemplating changes, not only very pronounced ones like the ones he suggests, but also for any type of change. 7 Status Of Quantum Theory According to Penrose, there are several aspects in current physics that do not allow a change of focus. The first of them is related to what we have just seen with Schrödinger’s cat. Quantum theory has the drawback of contemplating all possibilities. On the one hand, this can be positive, but on the other (which is what Penrose defends) it can be negative. For our author it is negative because it does not allow us to determine which calculations are possible and which are impossible, since there is no sharp distinction between the different possibilities (Penrose 1991: 370). But the fact that quantum theory leaves all possibilities open does not mean that anything goes with it. In fact, if there is something that characterises quantum theory, it is its powerful precision in describing natural processes. Penrose’s criticism, however, is entirely reasonable. Another aspect is that quantum theory does not offer an adequate description of the environment of experiments (both mental and empirical). Penrose acknowledges that this is a real problem, but he also takes it upon himself to make it clear that trying to deal with a complete description of the environment is an impossible task (Penrose 1991: 370). After all, we cannot have the attributes of Laplace’s demon. The universe is still tremendously complex and we seem condemned to offer a subjective answer about it. Is it possible to move away from such a perspective? Penrose is hopeful that this will be the case, although he acknowledges the difficulty involved. Where does the solution go? As we have already seen on several occasions, Penrose defends that returning to the deterministic perspective would help us to achieve a different approach, which is what is really necessary according to the current situation of physics. Our author’s proposal is not, far from it, easy to carry out. In fact, Penrose himself acknowledges the difficulty of leaving everything in the hands of determinism: 13 19 Page 22 of 26 Global Philosophy (2024) 34:19 One might try to take the line that the actual evolution is the deterministic U, but probabilities arise from the uncertainties involved in knowing what the quantum state of the combined system really is. This would be taking a very “classical” view about the origin of the probabilities that they all arise from uncertainties in the initial state. One might imagine that tiny differences in the initial state could give rise to enormous differences in the evolution, like the “chaos” that can occur with classical systems […]. However, such “chaos” effects simply cannot occur with U by itself, since it is linear: unwanted linear superpositions simply persist forever under U! To resolve such a superposition into one alternative or the other something non-linear would be needed, so U itself will not do (Penrose 1991: 371; italics in the original). It is necessary to find a non-linear procedure that allows the desired change of focus. This, for Penrose, is a problem and it is perfectly perceptible through the problem of consciousness. If consciousness cannot be adequately explained in such a way that we can determine that it is not computable, it is precisely because current physics does not allow it. Penrose does not have the arrogance and audacity necessary to believe that he is the only one who has raised this type of problem from the perspective in which he does. That is why he recognizes the works of Von Neumann, Wheeler or Wigner, despite the fact that none of them fully convinces him. A little more credit is given to Everett’s many universes or multiple universes theory (Everett 1957). While it is true that he does not fully subscribe to this particular approach, this does not prevent him from feeling a certain sympathy for some of his fundamental ideas. The one that convinces him the most is the renunciation of the indeterministic process R by Everett’s theory25, despite the fact that he does not fully share the idea: […] Claims have been made that the “illusion” of R can, in some sense, be effectively deduced in this picture, but I do not think that these claims hold up. At the very least, one needs further ingredients to make the scheme work. It seems to me that the many-worlds view introduces a multitude of problems of its own without really touching upon the real puzzles of quantum measurement. (Penrose 1991: 373). 25 In quantum mechanics there is a fundamental problem, that is, the reconciliation between superposition (the ability of quantum particles to be present in several places at the same time) and the determination of what happens in the plane of experience (since it is impossible for us to observe anything like superposition in the macroscopic world). Everett’s theory can, somehow, handle this problem. Sticking to the formal plane, what this theory says (broadly speaking, of course), is that superposition states “are just states of the world in which more than one macroscopically definite thing is happening at once” (Wallace 2010: 5) not in an indeterminate way (as quantum mechanics tells us), but by multiplying these states. In other words, if it is not possible for us to observe something like superposition in experience, it is because the different states unfold and reproduce themselves in different worlds; that is why in this theory it is not necessary to introduce the reduction of the state (that is, the R process), since all the possibilities are contemplated with said multiplication of worlds. Of course, there are many problems within this theory, such as the fact that these worlds do not interact with each other; or how uneconomical the approach of multiplying worlds is. But in this work, we will not stop to analyze the details of this theory since it would distance us from the matter that concerns us. 13 Global Philosophy (2024) 34:19 Page 23 of 26 19 The problem with quantum mechanics is that, although it is ideal for describing processes and solving problems that are impossible to address for classical physics, it is no less true that its capacity is not so infallible at the macroscopic level. In general, classical physics is more practical and more faithful to the macroscopic realm than quantum theory. In Penrose’s view, this is a factor that should not be neglected when judging the need for a reform in current physics. The indeterministic and subjective R process cannot be the definitive solution! However, Penrose recognizes that R can offer us an objective description of the behaviour of a particle, as long as several of them are not involved (Penrose 1991: 374). The knowledge that R provides us, therefore, is inevitably limited and that is why we need to find new alternatives, always taking advantage of what we already have. Penrose is not giving up, and in each new work he does, he returns to the same idea: current physics is insufficient to continue answering certain questions about nature and it needs to be reformed. For us is pertinent to keep asking, it is possible? 8 Conclusions We began our article by pointing out a discussion that, although not a new one, keeps posing certain doubts regarding the nature of reality: the question of determinism. Since our current physics focuses mainly in probabilistic and absolute-uncertain results, we consider the position of Roger Penrose on the subject, who advocates for a reform in physics so determinism takes place not only in classical physics but in quantum theory as well. Determinism seems not implausible under his view, mainly because the collapse of the wavefunction giving certain particular information is not seen anymore as a result of the “manipulation” of the observer, but as a feature of objective reality in itself. If this is the case then any measurement can be considered now not as a probable and non- determined aspect of reality, but as one of the many already settled elements of it. In the article we show how determinism is not incompatible with the principle of entropy and, moreover, that absolute arbitrariness is not necessarily deduced from other principles (such as the anthropic ones). We also discuss how entanglement in quantum physicis works in favour of determinism rather than in its detriment. Afterwards and more importantly, we then go ahead with the understanding of the measurement problem as a non-linear still determined reality: every particularization of a physical state is no arbitrary result but a certain state of a broader picture of possibilities which are “actualized” by the action of measurement. But we add that in our direct everyday experience and in the realm of the phenomenological world things also work this way: every instance of macrophysical acknowledgement is a particular, given and “settled” aspect of a broad world of other intertwined physical elements, that in itself constitutes the totality of the real. This itself is decomposed in relations, particulars related by those relations and existing probabilities, which can happen to be superposed but distinctly identified. For instance, our state of being happy is the identification of something distinct, still full of a not identified superposition of the same elements concerning unhappy feelings, anxiety, etc. Or the identification of something as blue is just a part of a whole reality where this object 13 19 Page 24 of 26 Global Philosophy (2024) 34:19 is presented in other colours, “hidden” by lack of identification. The advantage of quantum mechanics in this respect is that it makes this identification of particular states to be in a paradoxical fashion (thus unveiling somehow that there’s a reality behind, or beyond that particular), unlike our direct experience, where identifications are taken for granted as ultimately real. Now, how do we get to this conclusion? The main aspect to bear in mind is that although nondeterministic in appearance, one cannot say that measurements in quantum physics are “out of the blue” or sui generis. They are “encapsulated” in probabilities and these have been proven quite certain. The fact that the access to particular physical states is partial is not an indicator of absolute indeterminacy. Moreover, this view would make the distinction between microphysics and macrophysics not a full qualitative one (still distinct of course because of the emergence of features that are not intuitively present in the former, such as consciousness, as Penrose says), but showing a single world for them, a deterministic world that may behave superposed and non-linear. Still, it is certainly a question to make how and why the process of particularization occurs. But this is possibly a question that goes beyond the realm of physics. Acknowledgements This study was funded by Next Generation EU, with a Margarita Salas contract (posdoctoral for young researchers) and by Portuguese Foundation of Science and Technology (FCT) (doctoral program). We want to thank Daniele Molinini and two anonymous referees for their useful comments. Authors’ Contributions The authors contributed to the study conception and design. Material preparation, data colletion and analysis were perform by Daniel Heredia González. The first draft of the manuscript was written by Daniel Heredia González and the authors commented on previous versions of the manuscript. The authors read and approved the final manuscript. Conceptualization: Daniel Heredia González, Marco Gomboso; Methodology: Daniel Heredia González; Formal analysis and investigation: Daniel Heredia González, Marco Gomboso; Writing-original and final draft preparation: Daniel Heredia González, Marco Gomboso; Funding adquisition: Next Genetarion EU and Portuguese Foundation of Science and Technology (FCT). Funding Funding for open access publishing: Universidad de Sevilla/CBUA. Declarations Conflict of interest The authors declare that they have no conflict of interest to disclose. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/ licenses/by/4.0/. 13 Global Philosophy (2024) 34:19 Page 25 of 26 19 References Alonso (2004) DiccionarioDekal de Filosofía, Pord. por H. MaYraud y E. Ediciones Akal, Madrid Arana J (2012) Los sótanos Del universo: La determinación natural y sus mecanismos ocultos. Biblioteca Nueva, Madrid Arana J (2013) Los múltiples rostros del determinismo, belong to: Conferencia inaugural de la primera semana de Investigación Interdisciplinar: Determinismo E Indeterminismo. De la Física a la, Filosofía, Buenos Aires Aspect A, Grangier P (1986) Experiments on Einstein-Podolsky-Rosen-type correlations with pairs of visible photons. In: Penrose R, Isham CJ (eds) Quantum concepts in space and time. Oxford University Press Aspect A, Grangier P, Roger G (1982) Experimental realization of Einstein-Podolsky-Rosen-Bohm Gedankenexperiment: a new violation of Bell’s inequalities. Phys Rev Lett 48:91–94 D. Bohm (1951) The paradox of Einstein, Rosen, and Podolsky, in Quantum Theory, 22, 15–19, 611–23, Englewood Cliffs, NJ: Prentice-Hall, (Reprinted in Wheeler and Zurek [1983, 356–68]) Einstein A, Podolsky B, Rosen N (1935) Can Quantum-Mechanical description of physical reality be considered completed? Phys Rev 47:777–780 Everett H (1957) Relative state formulation of quantum mechanics. Rev Mod Phys 29:454–462 (Reprinted in Wheeler and Zurek [1983 Février P (1955) Detérminisme et Indetérminisme. Paris Presses Universitaires de France Février P (1957) Determinismo e Indeterminismo, trans. by R. Gortari, México D.F., Universidad Nacional Autónoma de México Hardy L (1993) Nonlocality for two particles without inequalities for almost all entangled states. Phys Rev Lett 71:1665 Herce R (2014) De La Física A La Mente: El Proyecto filosófico De Roger Penrose. Biblioteca Nueva, Madrid Hess K (2022) A Critical Review of Works Pertinent to the Einstein-Bohr Debate and Bell’s Theorem, in Symmetry, 14, 163 Jammer M (1974) The philosophy of Quantum mechanics: the interpretations of QM in historical perspective. John Willey & Sons, New York Moya C (2017) El libre albedrío: un estudio filosófico, Madrid, Cátedra Penrose R (1991) La nueva mente del emperador, trans. by J. García Sanz, Barcelona, Grijalbo, Mondadori Penrose R (2006) El camino a la realidad, trans. by J. García Sanz, Barcelona, Random House Mondadori, S.A. (Debate) Penrose R (2010) Cycles of time: an extraordinary new view of the universe. Vintage Books, New York Penrose R (2012) Las sombras de la mente, trans. by J. García Sanz, Barcelona, Crítica Penrose R (2017) Moda, Fe y Fantasía en la nueva física del universo, trans. by M. Pérez Sánchez, Barcelona, Penguin Random House Grupo Editorial (Debate) t´Hooft G (2019) Free Will in the theory of everything. In: Scardigli F, t´Hooft G, Severino E, Coda P (eds) Determinism and Free Will: New insights from Physics, Philosophy, and Theology. Springer, Cham, pp 21–48 Wallace D (2010) The Everett Interpretation. Oxford University Press, Oxford Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Authors and Affiliations Daniel Heredia González1 · Marco Gomboso2 Daniel Heredia González [email protected] Marco Gomboso 13 19 Page 26 of 26 Global Philosophy (2024) 34:19 [email protected] 1 Department of Philosophy and Logic and Philosophy of Science (US), University of Seville (US), Seville, Spain 2 Department of Natural Sciences (CFCUL), Center of Philosophy of Science of University of Lisbon (CFCUL), Lisbon, Portugal 13