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In this paper I argue that the concept of time-reversal invariance in physics suffers from metaphysical underdetermination, that is, that the concept may be understood differently depending on one’s metaphysics about time, laws, and a theory’s basic properties. This metaphysical under-determinacy also affects subsidiary debates in philosophy of physics that rely on the concept of time-reversal invariance, paradigmatically the problem of the arrow of time. I bring up three cases that, I believe, fairly illustrate my point. I conclude, on the one hand, that any formal representation of time reversal should be explicit about the metaphysical assumptions of the concept that it intends to represent; on the other, that philosophical arguments that rely on time reversal to argue against a direction of time require additional premises.

Mi objetivo en este artículo es desarrollar un mapa metafísico de las posibles actitudes metafísicas que los filósofos pueden adoptar con respecto a las simetrías en física. Aunque es usual distinguir entre realismo y anti-realismo, en este artículo muestro que el panorama metafísico es un poco más complejo que eso. Para ello, distingo al menos nueve posiciones diferentes que han sido adoptadas, o podrían ser adoptadas, en relación al lugar que las simetrías pueden ocupar en la ontología que uno conciba. My main aim in this paper is to lay out a metaphysical map of the possible metaphysical attitudes that philosophers may hold with respect to physical symmetries. Even though it is customary to distinguish between realism vs. anti-realism, I show that the metaphysical landscape looks a bit more complex. To show this, I differentiate at least nine different views that have been held, or might be held, concerning which place physical symmetries occupy in one’s ontology.

A widespread view in physics holds that the implementation of time reversal in standard quantum mechanics must be given by an anti-unitary operator. In foundations and philosophy of physics, however, there has been some discussion about the conceptual grounds of this orthodoxy, largely relying on either its obviousness or its mathematical-physical virtues. My aim in this paper is to substantively change the traditional structure of the debate by highlighting the philosophical commitments underlying the orthodoxy. I argue that the persuasive force of the orthodoxy can benefit from a relational metaphysics of time and a by-stipulation view on symmetries. Within such philosophical background, I submit, the orthodoxy of time reversal in standard quantum mechanics could find a fertile terrain to lay the groundwork for a more thorough conceptual justification.

Symmetry-based inferences have permeated many discussions in philosophy of physics and metaphysics of science. It is claimed that symmetries in our physical theories would allow us to draw metaphysical conclusions about the world, a view that I call ‘symmetry inferentialism’. This paper is critical to this view. I claim that (a) it assumes a philosophically questionable characterization of the relevant validity domain of physical symmetries, and (b) it overlooks a distinction between two opposing ways through which relevant physical symmetries become established. My conclusion is that symmetry inferentialism loses persuasive force when these two points are taken into consideration.

In the debate about the direction of time in physics, the concept of time reversal has been central. Tradition has it that time-reversal invariant laws are sufficient to state that the direction of time is non-fundamental or emergent. In this paper, we review some of the debates that have gravitated around the concept of time reversal and its relation to the direction of time. We also clarify some of the central concepts involved, showing that the very concept of time reversal is more complex than frequently thought.

It is a common view that Popper’s defense of the open society has been a defense of Western, liberal democracies. This seems to imply that by fostering democratic institutions we are ipso facto fostering open societies. I criticize this view by arguing that in-built incentives in democratic mechanisms move us away from (or hamper) the open society. Democracy promotes voters’ ignorance, indulges voters’ irrationality, and allows voters to externalize costs. This is contrary to well-informed, rational decisions and personal responsibility that lie at the fundamentals of the open society. I suggest that it has been free-market capitalism, or free-market societies, which has moved us closer to the ideal of the open society and which best realizes open society’s values.

The aim of this paper is to apply the methodology of minimal ontological commitments to moral and political philosophy. As minimal metaphysics in the philosophy of science endorses scientific realism, so we subscribe to moral realism, arguing that the presumption of liberty is the fundamental assumption defining a person. What needs to be justified then are restrictions to liberty and, in particular, the application of coercion upon persons. In examining knowledge claims about normative facts going beyond the presumption of liberty, such as, for instance, facts about a common good, we show that an ontological commitment to such normative facts is at odds with minimal metaphysics. We thus show how minimal metaphysics vindicates a Kantian deontological stance in moral and political philosophy: moral realism is limited to the obligations that follow from extending the presumption of liberty to all human beings in virtue of them being rational animals, hence to respect every person as an end in itself.

In this paper, we put forward an alternative interpretation of time-reversal symmetry in philosophy of physics: Humean time-reversal symmetry. According to it, time-reversal symmetry is understood as a heuristic, epistemic virtue of the best system, not as a property of the Humean mosaic. One of the consequences of this view is that one of the main arguments against a primitive direction of time is rendered harmless, which paves the way for primitivism about the direction of time.

Main conclusion During their domestication process, the species of the genus Opuntia lose their ability to survive in the wild. Presence and concentration of secondary metabolites which play a role in the interaction with their surroundings are modified but without an identifiable pattern. A domestication gradient based on morphological characteristics has been previously described for the species in the Opuntia genus. Secondary metabolites are a diverse group of bioactive compounds that relate to a species evolution, both in their natural and artificial (domestication process) selection environments. In addition, these compounds are associated with plant resistance to stress when growing in the wild. A comprehensive characterization of secondary metabolite profiles in the Opuntia genus that accounts for the genotypic differences related to the degree of domestication has not previously been conducted. This study evaluated the phytochemical composition of young cladodes from fifteen variants, of O. ficus-indica , O. albicarpa Sheinvar, and O. megacantha Salm-Dyck, identified as species with a highly advanced, advanced and intermediate degree of domestication, respectively, and O. hyptiacantha A. Web, and O. streptacantha Lem. identified as wild-intermediate and wild species. Analyses were carried out using a HPLC-diode array detection technique. Out of the 13 identified and quantified phenolic molecules and terpenoids, only the caffeic, ferulic and syringic acids, and the terpenoid β- amyrin were present in all variants. The flavonoid luteolin was absent in all five species. Gallic, vallinic, p -hydroxybenzoic, chlorogenic and p -coumaric acids were only present in 53–87% of variants; flavonoids quercetin, isorhamnetin, rutin and apigenin in 47–87% of the variants. Both, oleanolic acid and peniocerol, were present only in 60% of variants. Isorhamnetin was absent in O. hyptiacantha and quercetin in O. streptacntha . Differences and similarities in the secondary metabolites content showed no recognizable trend relating to the degree of domestication across the species in this genus.

While reasonable knowledge of multidecadal Arctic freshwater storage variability exists, we have little knowledge of Arctic freshwater exports on similar time scales. A hydrographic time series from the Labrador Shelf, spanning seven decades at annual resolution, is here used to quantify Arctic Ocean freshwater export variability west of Greenland. Output from a high-resolution coupled ice–ocean model is used to establish the representativeness of those hydrographic sections. Clear annual to decadal variability emerges, with high freshwater transports during the 1950s and 1970s–80s, and low transports in the 1960s and from the mid-1990s to 2016, with typical amplitudes of 30 mSv (1 Sv = 10⁶ m³ s−1). The variability in both the transports and cumulative volumes correlates well both with Arctic and North Atlantic freshwater storage changes on the same time scale. We refer to the “inshore branch” of the Labrador Current as the Labrador Coastal Current, because it is a dynamically and geographically distinct feature. It originates as the Hudson Bay outflow, and preserves variability from river runoff into the Hudson Bay catchment. We find a need for parallel, long-term freshwater transport measurements from Fram and Davis Straits to better understand Arctic freshwater export control mechanisms and partitioning of variability between routes west and east of Greenland, and a need for better knowledge and understanding of year-round (solid and liquid) freshwater fluxes on the Labrador shelf. Our results have implications for wider, coherent atmospheric control on freshwater fluxes and content across the Arctic Ocean and northern North Atlantic Ocean.