In addressing the Lucretian symmetry problem, the content-based approach attends to the difference between the contents of the actual life and those of relevant possible lives of a person. According to this approach, the contents of a life with an earlier beginning would substantially differ from, and thus be discontinuous with, the contents of the actual life, whereas the contents of a life with the same beginning but a later death would be continuous with the contents of the (...) actual life. In this paper, I examine two versions of the content-based approach: the identity account and the preference account. The identity account holds that, in the sense of identity which is relevant to the evil of nonexistence, the subject of the actual life, though identical to the person in the life with a later death, is distinct from the subject of the life with an earlier beginning. The preference account maintains that, given one’s attachments to actual particulars, a life with an earlier beginning is not rationally preferable to one’s actual life, whereas a life with a later death is. I argue that each version of the content-based approach is implausible, while discussing some of the complications that face each of them. (shrink)

The heavily discussed (neo-)Lucretian symmetry argument holds that as we are indifferent to nonexistence before birth, we should also be indifferent to nonexistence after death. An important response to this argument insists that prenatal nonexistence differs from posthumous nonexistence because we could not have been born earlier and been the same ‘thick’ psychological self. As a consequence, we can’t properly ask whether it would be better for us to have had radically different lives either. Against this, it’s been (...) claimed we can form preferences as to which ‘thick’ (psychological) self our ‘thin’ (metaphysical) self would be better off ‘associated’ with. I argue that these discussions draw the right distinction, but do so in the wrong place: understanding the ‘thin’ self phenomenally instead of metaphysically allows us to understand how we can rationally form preferences to have been somebody else. (shrink)

In previous work we have defended the deprivation account of death’s badness against worries stemming from the Lucretian point that prenatal and posthumous nonexistence are deprivations of the same sort. In a recent article in this journal, Fred Feldman has offered an insightful critique of our Parfitian strategy for defending the deprivation account of death’s badness. Here we adjust, clarify, and defend our strategy for reply to Lucretian worries on behalf of the deprivation account.

Lucretius famously argued that if we think death is bad because it deprives us of time we could have had by living longer than we do, then when we are born must be bad too, since we could have been born earlier than we were, and so be deprived of that time as well. John Martin Fischer thinks Lucretius’s symmetry argument fails because we have a bias toward the future. I argue that Fischer’s approach does not answer Lucretius. In (...) contrast to Fischer, I think that we can show an objective difference between the time before our birth and the time after our death, which means that we are justified in adopting different attitudes towards them. I revise a point made by Thomas Nagel that while we might live longer than we do, we cannot exist earlier than we did and remain the same people throughout. (shrink)

Here I respond to Anthony Brueckner and John Martin Fischer’s “The Evil of Death: A Reply to Yi.” They developed an influential strategy in defense of the deprivation account of death’s badness against the Lucretian symmetry problem. The core of their argument consists in the claim that it is rational for us to welcome future intrinsic goods while being indifferent to past intrinsic goods. Previously, I argued that their approach is compatible with the evil of late birth insofar (...) as an earlier birth would have generated more goods in the future. In reply, Brueckner and Fischer argue that my critique fails to appreciate an important aspect of their thought experiment, which aims only to show that the deprivation of past goods per se is not bad for us. Thus, purportedly, my critique poses no threat to their view. Here I argue that since the deprivation account explains the evil of death with recourse to how one’s life would have fared had one lived longer, it ought to respond to the symmetry problem with reference to how one’s life would have fared had one been born earlier. However, it is not generally true that the life one would have had with an earlier birth is not preferable to one’s actual life, because in many cases such a life would contain more future goods. (shrink)

In addressing the Lucretian symmetry problem, the temporal bias approach claims that death is bad because it deprives us of something about which it is rational to care (e.g., future pleasures), whereas prenatal nonexistence is not bad because it only deprives us of something about which it is rational to remain indifferent (e.g., past pleasures). In a recent contribution to the debate on this approach, Miguel and Santos argue that a late beginning can deprive us of a future (...) pleasure. Their argument is based on the claim that for birth or death to deprive a person of any value in life, the historically closest counterfactual situation that contains the value is such that the person begins to exist earlier or dies later. This is what they call the Historical Condition. However, the Historical Condition is untenable for several reasons. First, this condition substantially weakens the explanatory capacity of the deprivation account because it implies that most ordinary sorts of pleasures are not deprived by death. In addition, the Historical Condition is vulnerable to counterexamples. In particular, what they offer as a standard case of the deprivation of future pleasure due to a late beginning (what they call Seeing The Beatles), or some of its variants, can be used to falsify this condition. Finally, the Historical Condition is theoretically indefensible because it is based on a faulty analysis of deprivation. (shrink)

In previous work we have presented a reply to the Lucretian Symmetry, which has it that it is rational to have symmetric attitudes toward prenatal and posthumous nonexistence. Our reply relies on Parfit-style thought-experiments. Here we reply to a critique of our approach by Huiyuhl Yi, which appears in this journal: Brueckner and Fischer on the evil of death. We argue that this critique fails to attend to the specific nature of the thought-experiments (and our associated argument). More (...) specifically, the thought-experiments seek to elicit attitudes about (say) past pleasures per se, and not insofar as such pleasures are connected to more pleasures in the future or a greater total amount of pleasures in one’s life overall. (shrink)

Death can be bad for an individual who has died, according to the “deprivation approach,” by depriving that individual of goods. One worry for this account of death’s badness is the Lucretian symmetry argument: since we do not regret having been born later than we could have been born, and since posthumous nonexistence is the mirror image of prenatal nonexistence, we should not regret dying earlier than we could have died. Anthony Brueckner and John Martin Fischer have developed (...) a response to the Lucretian challenge by arguing that it is rational to have asymmetric attitudes toward posthumous and prenatal nonexistence. Recently, Jens Johansson has criticized the Brueckner/Fischer position, claiming that it is irrelevant whether it is actually rational to care about future pleasures but not past pleasures. What matters, according to Johansson, is whether it would be rational for us to care about past pleasures had we come into existence earlier. In this paper, I add to the conversation between Johansson and Brueckner/Fischer by suggesting a way to defend the latter side’s position in a way that has not yet been suggested. I do this by considering a suggestion of Johansson’s for interpreting the Brueckner/Fischer position and by arguing that Johansson’s worry for the position I consider is actually incoherent. (shrink)

In this paper, we develop a novel version of the so-called Lucretian symmetry argument against the badness of death. Our argument has two features that make it particularly effective. First, it focuses on the preferences of rational agents. We believe the focus on preferences eliminates needless complications and emphasizes the urgency to respond to the argument. Second, our argument utilizes a principle that states that a rational agent's preferences should not vary in arbitrary ways. We argue that this (...) principle underlies our judgments of cognitive biases. We should therefore endorse the principle insofar as we think a cognitively biased agent fails to be rational. In the second half of the paper we survey potential ways to resist the new symmetry argument. We show that they all fail to meet the dialectical burden of our argument or involve highly controversial assumptions about the metaphysics of time or the limits of rational preferences. (shrink)

According to the “deprivation approach,” a person’s death is bad for her to the extent that it deprives her of goods. This approach faces the Lucretian problem that prenatal non-existence deprives us of goods just as much as death does, but does not seem bad at all. The two most prominent responses to this challenge—one of which is provided by Frederik Kaufman (inspired by Thomas Nagel) and the other by Anthony Brueckner and John Martin Fischer—claim that prenatal non-existence is (...) relevantly different from death. This paper criticizes these responses. (shrink)

This book is a concise, clearly written, and rigorously argued discussion of the main question regarding the metaphysics of death. In defending the view that death can harm the person who dies, Jack Li refutes Epicurean and Lucretian arguments that death cannot harm us and that it is irrational to fear death. Epicurus held that a person can be harmed only when he exists. Because death is the end of a person’s existence, death cannot harm him. Therefore, death should (...) be “nothing to us”. Lucretius offered the following symmetry argument. No one is harmed by, and no one fears, prenatal non-existence. Postmortem non-existence is symmetrical to prenatal non-existence. Therefore, no one can be harmed by postmortem non-existence, and it is irrational to fear this state.To show that the Epicurean and Lucretian arguments are flawed, Li examines three different theories proposed by such philosophers as Thomas Nagel, Joel Feinberg, Jeff McMahan, and Fred Feldman. The first is the “desire thwarting” theory, which says that death can harm us because it thwarts our unconditional desire to continue living. The second is the “deprivation” theory, which says that death can harm us because it deprives us of the goods we would have enjoyed had we …. (shrink)

In a recent article, I criticized Anthony L. Brueckner and John Martin Fischer’s influential argument—appealing to the rationality of our asymmetric attitudes towards past and future pleasures—against the Lucretian claim that death and prenatal non-existence are relevantly similar. Brueckner and Fischer have replied, however, that my critique involves an unjustified shift in temporal perspectives. In this paper, I respond to this charge and also argue that even if it were correct, it would fail to defend Brueckner and Fischer’s proposal (...) against my critique. (shrink)

Metaphysicians speak of laws of nature in terms of necessity and universality; scientists, in terms of symmetry and invariance. In this book van Fraassen argues that no metaphysical account of laws can succeed. He analyzes and rejects the arguments that there are laws of nature, or that we must believe there are, and argues that we should disregard the idea of law as an adequate clue to science. After exploring what this means for general epistemology, the author develops the (...) empiricist view of science as a construction of models to represent the phenomena. (shrink)

Extra destinatum -- The philologist and the Epicurean -- Homer atomized -- The pervasive influence.

Cognitive tests show that identity and symmetry reflect intellect. 'Guess of other guess' creates various symmetries, while only one is right: 'absolute symmetry', which can be outvoted by the majority. Prejudices result from differences between ME (my identity) and others. Unbiased judgement is symmetrical, always in the middle: neither in favor, nor against ME. Intelligence reduces prejudices, but the lack of opportunities can counterbalance it. That's why type of bias differs in various groups: people from war zones, people (...) in therapy, artists, etc.. "The law of values' equity" is a symmetrical principle redefining utility in economics, when people equate all their values. E.g. 2 children averagely rich, is better than one child rich and another poor. If 'a' is an average richness, and 'x' is a difference in richness, and Utility multiplies all values, then: a * a > (a - x) * (a + x), which is: a² > a² - x². It does not however imply egalitarianism, as it is still better to have both children rich than both average or poor. (shrink)

In this paper, we defend Lucretian Presentism. Although the view faces many objections and has proven unpopular with presentists, we rehabilitate Lucretianism and argue that none of the objections stick.

Proceedings of the 11th Interdisciplinary Symmetry Congress-Festival of the International Society for the Interdisciplinary Study of Symmetry. Special Theme: “Tradition and Innovation in Symmetry - Katachi”.

the symmetry of our evidential situation. If our confidence is best modeled by a standard probability function this means that we are to distribute our subjective probability or credence sharply and evenly over possibilities among which our evidence does not discriminate. Once thought to be the central principle of probabilistic reasoning by great..

Lucretius wrote: “Look back at the eternity that passed before we were born, and mark how utterly it counts to us as nothing. This is a mirror that Nature holds up to us, in which we may see the time that shall be after we are dead. Is there anything terrifying in the sight – anything depressing – anything that is not more restful than the soundest sleep?”1 The argument is repeated, a couple of millennia later, by Vladimir Nabokov, who (...) opens his memoir with the observation that “our existence is but a brief crack of light between two eternities of darkness. Although the two are identical twins, man, as a rule, views the prenatal abyss with more calm than the one he is heading for (at some forty-five hundred heartbeats an hour).”. (shrink)

Fearful Symmetry brings the incredible discoveries of contemporary physics within everyone's grasp. A. Zee, a distinguished physicist and skillful expositor, tells the exciting story of how today's theoretical physicists are following Einstein in their search for the beauty and simplicity of Nature. Animated by a sense of reverence and whimsy, the book describes the majestic sweep and accomplishments of twentieth-century physics. In the end, we stand in awe before the grand vision of modern physics--one of the greatest chapters in (...) the intellectual history of humankind. (shrink)

In the first argumentative section of Book 1, Lucretius establishes the existence of matter and void , and in the second identifies matter as the atoms and defines their properties . In the third section, following Epicurean tradition, he attempts to refute a representative selection of Presocratic philosophers – Heraclitus , Empedocles and Anaxagoras – whose explanations of basic matter are potential rivals to the atomist theory which he has just outlined. The climax to this section is reached in Lucretius' (...) triumphant personal claim to be an original poet and health-bringing purveyor of truth . His foregoing criticism of the Presocratics as writers and thinkers is deeply coloured by the values he openly professes here. The introductory passages to each philosopher, in particular, are highly revealing of Lucretius' personal inclinations as a poet and exhibit a virtuoso command of several styles and techniques. (shrink)

Highlighting main issues and controversies, this book brings together current philosophical discussions of symmetry in physics to provide an introduction to the subject for physicists and philosophers. The contributors cover all the fundamental symmetries of modern physics, such as CPT and permutation symmetry, as well as discussing symmetry-breaking and general interpretational issues. Classic texts are followed by new review articles and shorter commentaries for each topic. Suitable for courses on the foundations of physics, philosophy of physics and (...) philosophy of science, the volume is a valuable reference for students and researchers. (shrink)

Given its importance in modern physics, philosophers of science have paid surprisingly little attention to the subject of symmetries and invariances, and they have largely neglected the subtopic of symmetry breaking. I illustrate how the topic of laws and symmetries brings into fruitful interaction technical issues in physics and mathematics with both methodological issues in philosophy of science, such as the status of laws of physics, and metaphysical issues, such as the nature of objectivity.

The paper considers the symmetries of a bit of information corresponding to one, two or three qubits of quantum information and identifiable as the three basic symmetries of the Standard model, U(1), SU(2), and SU(3) accordingly. They refer to “empty qubits” (or the free variable of quantum information), i.e. those in which no point is chosen (recorded). The choice of a certain point violates those symmetries. It can be represented furthermore as the choice of a privileged reference frame (e.g. that (...) of the Big Bang), which can be described exhaustively by means of 16 numbers (4 for position, 4 for velocity, and 8 for acceleration) independently of time, but in space-time continuum, and still one, 17th number is necessary for the mass of rest of the observer in it. The same 17 numbers describing exhaustively a privileged reference frame thus granted to be “zero”, respectively a certain violation of all the three symmetries of the Standard model or the “record” in a qubit in general, can be represented as 17 elementary wave functions (or classes of wave functions) after the bijection of natural and transfinite natural (ordinal) numbers in Hilbert arithmetic and further identified as those corresponding to the 17 elementary of particles of the Standard model. Two generalizations of the relevant concepts of general relativity are introduced: (1) “discrete reference frame” to the class of all arbitrarily accelerated reference frame constituting a smooth manifold; (2) a still more general principle of relativity to the general principle of relativity, and meaning the conservation of quantum information as to all discrete reference frames as to the smooth manifold of all reference frames of general relativity. Then, the bijective transition from an accelerated reference frame to the 17 elementary wave functions of the Standard model can be interpreted by the still more general principle of relativity as the equivalent redescription of a privileged reference frame: smooth into a discrete one. The conservation of quantum information related to the generalization of the concept of reference frame can be interpreted as restoring the concept of the ether, an absolutely immovable medium and reference frame in Newtonian mechanics, to which the relative motion can be interpreted as an absolute one, or logically: the relations, as properties. The new ether is to consist of qubits (or quantum information). One can track the conceptual pathway of the “ether” from Newtonian mechanics via special relativity, via general relativity, via quantum mechanics to the theory of quantum information (or “quantum mechanics and information”). The identification of entanglement and gravity can be considered also as a ‘byproduct” implied by the transition from the smooth “ether of special and general relativity’ to the “flat” ether of quantum mechanics and information. The qubit ether is out of the “temporal screen” in general and is depicted on it as both matter and energy, both dark and visible. (shrink)

Many important explanations in physics are based on ideas and assumptions about symmetries, but little has been said about the nature of such explanations. This chapter aims to fill this lacuna, arguing that various symmetry explanations can be naturally captured in the spirit of the counterfactual-dependence account of Woodward, liberalized from its causal trappings. From the perspective of this account symmetries explain by providing modal information about an explanatory dependence, by showing how the explanandum would have been different, had (...) the facts about an explanatory symmetry been different. Furthermore, the authors argue that such explanatory dependencies need not be causal. (shrink)

Symmetry, intended as invariance with respect to a transformation (more precisely, with respect to a transformation group), has acquired more and more importance in modern physics. This Chapter explores in 8 Sections the meaning, application and interpretation of symmetry in classical physics. This is done both in general, and with attention to specific topics. The general topics include illustration of the distinctions between symmetries of objects and of laws, and between symmetry principles and symmetry arguments (such (...) as Curie's principle), and reviewing the meaning and various types of symmetry that may be found in classical physics, along with different interpretative strategies that may be adopted. Specific topics discussed include the historical path by which group theory entered classical physics, transformation theory in classical mechanics, the relativity principle in Einstein's Special Theory of Relativity, general covariance in his General Theory of Relativity, and Noether's theorems. In bringing these diverse materials together in a single Chapter, we display the pervasive and powerful influence of symmetry in classical physics, and offer a possible framework for the further philosophical investigation of this topic. (shrink)

In the fourth line of her first speech in Book 1, to Ilioneus and the Trojan castaways, Dido quotes the first word of the first line of Lucretius’ De rerum natura, and in the fourth line of her second speech, to Aeneas, she quotes the first words of the second line of the De rerum natura. This is not a coincidence but a signal of the importance of Lucretius and Epicureanism for the characterization of Dido in the Aeneid.

This paper is concerned with the relation between two notions: that of two solutions or models of a theory being related by a symmetry of the theory and that of solutions or models being physically equivalent. A number of authors have recently discussed this relation, some taking an optimistic view, on which there is a suitable concept of the symmetry of a theory relative to which these two notions coincide, others taking a pessimistic view, on which there is (...) no such concept. The present paper arrives at a cautiously pessimistic conclusion. (shrink)

Symmetries in physics are a guide to reality. That much is well known. But what is less well known is why symmetry is a guide to reality. What justifies inferences that draw conclusions about reality from premises about symmetries? I argue that answering this question reveals that symmetry is an epistemic notion twice over. First, these inferences must proceed via epistemic lemmas: premises about symmetries in the first instance justify epistemic lemmas about our powers of detection, and only (...) from those epistemic lemmas can we draw conclusions about reality. Second, in order to justify those epistemic lemmas, the notion of symmetry must be defined partly in epistemic terms. 1 Symmetry-to-Reality Reasoning1.1 A rough introduction to symmetry1.2 The symmetry-to-reality inference1.3 Two questions1.4 Two answers1.5 Preliminary clarifications2 Against Redundancy2.1 Redundancy2.2 Is absolute velocity redundant?2.3 Some redundancies3 Against Objectivity4 From Symmetry to Detection4.1 The epistemic approach4.2 The Occamist norm4.3 From symmetry to detection5 The Meaning of ‘Symmetry’5.1 A framework5.2 Formal definitions5.3 Ontic definitions6 Epistemic Definitions6.1 Taking observation seriously6.2 How things look6.3 Observation sentences6.4 Observational equivalence7 Symmetry as an Epistemic Notion 7.1 Observational equivalence and metaphysics7.2 The Occamist norm revisted7.3 Consequences8 Conclusion. (shrink)

The dominance of string theory in the research landscape of quantum gravity physics (despite any direct experimental evidence) can, I think, be justified in a variety of ways. Here I focus on an argument from mathematical fertility, broadly similar to Hilary Putnam’s ‘no miracles argument’ that, I argue, many string theorists in fact espouse in some form or other. String theory has generated many surprising, useful, and well-confirmed mathematical ‘predictions’—here I focus on mirror symmetry and the mirror theorem. These (...) predictions were made on the basis of general physical principles entering into string theory. The success of the mathematical predictions are then seen as evidence for the framework that generated them. I shall attempt to defend this argument, but there are nonetheless some serious objections to be faced. These objections can only be evaded at a considerably high (philosophical) price. (shrink)

In the first argumentative section of Book 1, Lucretius establishes the existence of matter and void, and in the second identifies matter as the atoms and defines their properties. In the third section, following Epicurean tradition, he attempts to refute a representative selection of Presocratic philosophers – Heraclitus, Empedocles and Anaxagoras – whose explanations of basic matter are potential rivals to the atomist theory which he has just outlined. The climax to this section is reached in Lucretius' triumphant personal claim (...) to be an original poet and health-bringing purveyor of truth. His foregoing criticism of the Presocratics as writers and thinkers is deeply coloured by the values he openly professes here. The introductory passages to each philosopher, in particular, are highly revealing of Lucretius' personal inclinations as a poet and exhibit a virtuoso command of several styles and techniques. (shrink)

I examine the link between extensionality principles of classical mereology and the anti‐symmetry of parthood. Varzi's most recent defence of extensionality depends crucially on assuming anti‐symmetry. I examine the notions of proper parthood, weak supplementation and non‐well‐foundedness. By rejecting anti‐symmetry, the anti‐extensionalist has a unified, independently grounded response to Varzi's arguments. I give a formal construction of a non‐extensional mereology in which anti‐symmetry fails. If the notion of ‘mereological equivalence’ is made explicit, this non‐anti‐symmetric mereology recaptures (...) all of the structure of classical mereology. (shrink)

James Henry Collin recently developed a new symmetry breaker favouring the ontological argument’s possibility premiss over that of the reverse ontological argument. The symmetry breaker amounts to an undercutting defeater for the reverse possibility premiss based on Kripkean cases of a posteriori necessity. I argue, however, that symmetry re-arises in two forms. First, I challenge the purported asymmetry in epistemic entitlements to the original and reverse possibility premisses. Second, relevantly similar Kripkean cases equally undercut the original possibility (...) premiss. (shrink)

It seems that people typically prefer dying later to dying earlier. It also seems that people typically do not prefer having been created earlier to having been created later. Lucretius’ Puzzle is the question whether anything typically rationally recommends having a preference for dying later to dying earlier over having a preference for having been created earlier to having been created later. In this paper, I distinguish among three ways in which Lucretius’ Puzzle can be understood and say how I (...) think they ought to be answered. (shrink)

We propose an operator constraint equation for the wavefunction of the Universe that admits genuine evolution. While the corresponding classical theory is equivalent to the canonical decomposition of General Relativity, the quantum theory contains an evolution equation distinct from standard Wheeler–DeWitt cosmology. Furthermore, the local symmetry principle—and corresponding observables—of the theory have a direct interpretation in terms of a conventional gauge theory, where the gauge symmetry group is that of spatial conformal diffeomorphisms (that preserve the spatial volume of (...) the Universe). The global evolution is in terms of an arbitrary parameter that serves only as an unobservable label for successive states of the Universe. Our proposal follows unambiguously from a suggestion of York whereby the independently specifiable initial data in the action principle of General Relativity is given by a conformal geometry and the spatial average of the York time on the spacelike hypersurfaces that bound the variation. Remarkably, such a variational principle uniquely selects the form of the constraints of the theory so that we can establish a precise notion of both symmetry and evolution in quantum gravity. (shrink)

Many have thought that symmetries of a Lagrangian explain the standard laws of energy, momentum, and angular momentum conservation in a rather straightforward way. In this paper, I argue that the explanation of conservation laws via symmetries of Lagrangians involves complications that have not been adequately noted in the philosophical literature and some of the physics literature on the subject. In fact, such complications show that the principles that are commonly appealed to to drive explanations of conservation laws are not (...) generally correct without caveats. I hope here to give a clearer picture of the relationship between symmetries and conservation laws in Lagrangian mechanics via an examination of the bearing that results in the inverse problem in the calculus of variations have on this topic. (shrink)

Imagine that we are on a train playing with some mechanical systems. Why can’t we detect any differences in their behavior when the train is parked versus when it is moving uniformly? The standard answer is that boosts are symmetries of Newtonian systems. In this paper, I use the case of a spring to argue that this answer is problematic because symmetries are neither sufficient nor necessary for preserving its behavior. I also develop a new answer according to which boosts (...) preserve the relational properties on which the behavior of a system depends, even when they are not symmetries. (shrink)

Although symmetry has been discussed in terms of a major law of perceptual organization since the early conceptual efforts of the Gestalt school (Wertheimer, Metzger, Koffka and others), the first quantitative measurements testing for effects of symmetry on processes of Gestalt formation have seen the day only recently. In this study, a psychophysical rating study and a “foreground”-“background” choice response time experiment were run with human observers to test for effects of bilateral symmetry on the perceived strength (...) of figure-ground in triangular Kanizsa configurations. Displays with and without bilateral symmetry, identical physically-specified-to-total contour ratio, and constant local contrast intensity within and across conditions, but variable local contrast polarity and variable orientation in the plane, were presented in a random order to human observers. Configurations with bilateral symmetry produced significantly stronger figure-ground percepts reflected by greater subjective magnitudes and consistently higher percentages of “foreground” judgments accompanied by significantly shorter response times. These effects of symmetry depend neither on the orientation of the axis of symmetry, nor on the contrast polarity of the physical inducers. It is concluded that bilateral symmetry, irrespective of orientation, significantly contributes to the, largely sign-invariant, visual mechanisms of figure-ground segregation that determine the salience of figure-ground in perceptually ambiguous configurations. (shrink)

It is often said in physics that if two models of a theory are related by a symmetry, then the two models provide (or could provide) two different representations of the very same situation, alike the case of two maps of different color for the very same city. It is also said that the situations represented by two models of a theory are indiscernible in some ways when the models in question are related by a symmetry of the (...) theory, just like the situation in the interior of the cabin of a train when the train is at rest in the station is empirically indiscernible from the situation in the interior when the train is moving uniformly (in classical mechanics, these two situations are represented by two models related by a boost). In recent years, philosophers of physics have focused a lot of attention in developing various principles that aim to elucidate these and similar remarks on symmetries, models, physical equivalence, and representation that are widespread in physics practice. The goal of the current article is to provide a critical review of these principles, and suggest a new framework for thinking about these kinds of questions. One important upshot of the paper is that questions of indiscernibility, and questions of the representational capacity of models, must be distinguished from one another. (shrink)

Several forms of symmetry in degrees of evidential support areconsidered. Some of these symmetries are shown not to hold in general. This has implications for the adequacy of many measures of degree ofevidential support that have been proposed and defended in the philosophical literature.

The classical field theories that underlie the quantum treatments of the electromagnetic, weak, and strong forces share a peculiar feature: specifying the initial state of the field determines the evolution of some degrees of freedom of the theory while leaving the evolution of some others wholly arbitrary. This strongly suggests that some of the variables of the standard state space lack physical content-intuitively, the space of states of such a theory is of higher dimension than the corresponding space of genuine (...) physical possibilities. The structure of such theories can helpfully be characterized in terms of the action of symmetry groups on their space of states; and the conceptual problems surrounding their strange behavior can be sharpened in light of the observation that it is usually possible to eliminate the redundant variables associated with these symmetries-which turn out to be precisely those variables whose evolution is unconstrained by the dynamical laws of the theory. This paper discusses this approach, uses it to frame questions about the interpretation of classical gauge theories, and to reflect (pessimistically) on our prospects of reaching satisfactory answers to these questions. (shrink)

While empirical symmetries relate situations, theoretical symmetries relate models of a theory we use to represent them. An empirical symmetry is perfect if and only if any two situations it relates share all intrinsic properties. Sometimes one can use a theory to explain an empirical symmetry by showing how it follows from a corresponding theoretical symmetry. The theory then reveals a perfect symmetry. I say what this involves and why it matters, beginning with a puzzle that (...) is resolved by the subsequent analysis. I conclude by pointing to applications and implications of the ideas developed earlier in the paper. (shrink)