Meeting the security requests in transportation is nowadays a must. The intelligent transport systems represent the support for addressing such a challenge, due to their ability to make real-time adaptive decisions. We propose a new variant of the travelling salesman problem integrating security constraints inspired from ITSs. This optimization problem is called the secure TSP and considers a set of security constraints on its integer variables. Similarities with fuzzy logic are presented alongside the mathematical model of the (...) introduced TSP variant. (shrink)

The traveling salesman problem is one of the most important issues in combinatorial optimization problems that are used in many engineering sciences and has attracted the attention of many scientists and researchers. In this issue, a salesman starts to move from a desired node called warehouse and returns to the starting place after meeting n customers provided that each customer is only met once. The aim of this issue is to determine a cycle with a minimum (...) cost for this salesman. One of the major weaknesses of the PSO algorithm in the classical version is that it gets stuck in local optimizations. Therefore, in the proposed algorithm, called MPSO, the best solution in the current iteration is also used in the movement step. In addition, a variety of local search algorithms are provided that are used when better answers are generated than before. Also, a new method for moving the particle towards the best particle is presented, which, in addition to probably increasing the quality of the new answer, prevents the premature convergence of the algorithm due to consideration of the concept of random. The results evaluated with the results of several metaheuristic algorithms in the literature show the efficiency of the MPSO algorithm because it has been able to achieve excellent solutions in most of these instances. (shrink)

This paper investigates the Generalized Traveling Salesman Problem (GTSP), which is an extension of the well-known Traveling Salesman Problem (TSP), and it searches for an optimal tour in a clustered graph, such that every cluster is visited exactly once. In this paper, we describe a novel Memetic Algorithm (MA) for solving efficiently the GTSP. Our proposed MA has at its core a genetic algorithm (GA), completed by a Chromosome Enhancement Procedure (CEP), which is based (...) on a TSP solver and the Shortest Path (SP) algorithm and for improving the convergence characteristics of the GA, a Local Search (LS) operation is applied for the best chromosomes in each generation. We tested our algorithm on a set of well-known instances from the literature and the achieved results prove that our novel memetic algorithm is highly competitive against the existing solution approaches from the specialized literature. (shrink)

The travelling salesman problem (TSP) belongs to the class of NP-hard problems, in which an optimal solution to the problem cannot be obtained within a reasonable computational time for large-sized problems. To address TSP, we propose a hybrid algorithm, called GA-TCTIA-LBSA, in which a genetic algorithm (GA), tour construction and tour improvement algorithms (TCTIAs) and a list-based simulated annealing (LBSA) algorithm are used. The TCTIAs are introduced to generate a first population, and after that, a search is (...) continued with the GA. The problem of premature convergence of the GA to local optimum is tackled by a method called social disaster technique. Afterwards, the LBSA is applied to generate a new population based on one of two proposed operators called packing and judgement day. The proposed algorithm is implemented in the MATLAB environment, and its two variants, called GA-TCTIA-LBSA packing and GA-TCTIA-LBSA judgement day, are tested on symmetric and asymmetric instances from TSPLIB. The overall results demonstrate that the proposed GA-TCTIA-LBSAs offer promising results, particularly for small-sized instances. (shrink)

The travelling salesman problem is one of the most popular problems in combinatorial optimization. It has been frequently used as a benchmark of the performance of evolutionary algorithms. For this reason, nowadays practitioners request new and more difficult instances of this problem. This leads to investigate how to evaluate the intrinsic difficulty of the instances and how to separate ease and difficult instances. By developing methodologies for separating easy- from difficult-to-solve instances, researchers can fairly test the performance (...) of their combinatorial optimizers. In this work, a methodology for evaluating the difficulty of instances of the travelling salesman problem near the optimal solution is proposed. The question is if the fitness landscape near the optimal solution encodes enough information to separate instances in function of their intrinsic difficulty. This methodology is based on the use of a random walk to explore the closeness of the optimal solution. The optimal solution is modified by altering one connection between two cities at each step, at the same time that the fitness of the altered solution is evaluated. This permits evaluating the slope of the fitness landscape. Later, and using the previous information, the difficulty of the instance is evaluated with random forests and artificial neural networks. In this work, this methodology is confronted with a wide set of instances. As a consequence, a methodology to separate the instances of the travelling salesman problem by their degree of difficulty is proposed and evaluated. (shrink)

This paper proposes a Multi-Agent based Particle Swarm Optimization (PSO) Framework for the Traveling salesman problem (MAPSOFT). The framework is a deployment of the recently proposed intelligent multi-agent based PSO model by the authors. MAPSOFT is made up of groups of agents that interact with one another in a coordinated search effort within their environment and the solution space. A discrete version of the original multi-agent model is presented and applied to the Travelling Salesman Problem. (...) Based on the simulation results obtained, it was observed that agents retrospectively decide on their next moves based on consistent better fitness values obtained from present and prospective neighborhoods, and by reflecting back to previous behaviors and sticking to historically better results. These overall attributes help enhance the conventional PSO by providing more intelligence and autonomy within the swarm and thus contributed to the emergence of good results for the studied problem. (shrink)

A neural network is a model of the brain’s cognitive process, with a highly interconnected multiprocessor architecture. The neural network has incredible potential, in the view of these artificial neural networks inherently having good learning capabilities and the ability to learn different input features. Based on this, this paper proposes a new chaotic neuron model and a new chaotic neural network model. It includes a linear matrix, a sine function, and a chaotic neural network composed of three chaotic neurons. One (...) of the chaotic neurons is affected by the sine function. The network has rich chaotic dynamics and can produce multiscroll hidden chaotic attractors. This paper studied its dynamic behaviors, including bifurcation behavior, Lyapunov exponent, Poincaré surface of section, and basins of attraction. In the process of analyzing the bifurcation and the basins of attraction, it was found that the network demonstrated hidden bifurcation phenomena, and the relevant properties of the basins of attraction were obtained. Thereafter, a chaotic neural network was implemented by using FPGA, and the experiment proved that the theoretical analysis results and FPGA implementation were consistent with each other. Finally, an energy function was constructed to optimize the calculation based on the CNN in order to provide a new approach to solve the TSP problem. (shrink)

Ormerod and Chronicle reported that optimal solutions to traveling salesperson problems were judged to be aesthetically more pleasing than poorer solutions and that solutions with more convex hull nodes were rated as better figures. To test these conclusions, solution regularity and the number of potential intersections were held constant, whereas solution optimality, the number of internal nodes, and the number of nearest neighbors in each solution were varied factorially. The results did not support the view that the convex hull (...) is an important determinant of figural attractiveness. Also, in contrast to the findings of Ormerod and Chronicle, there were consistent individual differences. Participants appeared to be divided as to whether the most attractive figure enclosed a given area within a perimeter of minimum or maximum length. It is concluded that future research in this area cannot afford to focus exclusively on group performance measures. (shrink)

This paper shows statistical analyses of the search-space landscape of travelling salesman problems in due consideration of stochastic optimization. It is known from existing works that travelling salesman problems have landscape called “a rugged landscape” and “big valley structure”. This work reveals more detailed structure of the landscape. We deal with the 1000 travelling salesman problems of 6 to 9 cities where the cities are arranged randomly and a travelling salesman problem of 100 cities. It (...) is assumed that the rugged landscape is a combination of the global valleylike structure and the local noiselike structure. Each of them is characterized by the statistical properties of the search-space landscape, that is, the global valleylike structure has linearity with the distance from the optimum, and the variance of the local noiselike structure increase monotonously with the distance from the optimum. On the other side correlation of the tours with the costs close upon the optimum cost is low. For this reason to combine the genetic search with the local search is supported. Even if the number of cities and the definition of the intercity cost value are changed, the structure of the landscape has the same feature. Although the number of the cities of the examined travelling salesman problems is not large, obtained results seem to be universal. It is forecasted that not only travelling salesman problems but also many practical problems have the structure which is characterized with the same measure. These results are useful to compose more effective optimization methods without trial and error. (shrink)

The “wisdom of the crowd” phenomenon refers to the finding that the aggregate of a set of proposed solutions from a group of individuals performs better than the majority of individual solutions. Most often, wisdom of the crowd effects have been investigated for problems that require single numerical estimates. We investigate whether the effect can also be observed for problems where the answer requires the coordination of multiple pieces of information. We focus on combinatorial problems such as the planar Euclidean (...) traveling salesperson problem, minimum spanning tree problem, and a spanning tree memory task. We develop aggregation methods that combine common solution fragments into a global solution and demonstrate that these aggregate solutions outperform the majority of individual solutions. These case studies suggest that the wisdom of the crowd phenomenon might be broadly applicable to problem-solving and decision-making situations that go beyond the estimation of single numbers. (shrink)

In this paper, we propose the c AS, a new ACO algorithm, and evaluate the performance using TSP instances available at TSPLIB. The results show that c AS works well on the test instances and has performance that may be one of the most promising ACO algorithms. We also evaluate c AS when it is combined with LK local search heuristic using larger sized TSP instances. The results also show promising performance. c AS introduced two important schemes. One is to (...) use the colony model divided into units, which has a stronger exploitation feature while maintaining a certain degree of diversity among units. The other is to use a scheme, we call cunning, when constructing new solutions, which can prevent premature stagnation by reducing strong positive feedback to the trail density. (shrink)

With only two to five slots of visual working memory (VWM), humans are able to quickly solve complex visual problems to near optimal solutions. To explain the paradox between tightly constrained VWM and impressively complex human visual problem‐solving ability, we propose several principles for dynamic VWM allocation. In particular, we propose that complex visual information is represented in a temporal manner using only a few slots of VWM that include global and local visual chunks. We built a model of (...) human traveling salesman problem solving based on these principles of VWM allocation and tested the model with eye‐movement data. Exactly as the model predicted, human eye movements during traveling salesman problem solving have precise quantitative regularities with regard to both the general statistical pattern of attentional fixations and how they vary across individuals with different VWM capacities. Even though VWM capacity is very limited, eye movements dynamically allocate VWM resources to both local and global information, enabling attention to fine details without loss of the big picture. (shrink)

Ant colony optimization, which is one of the metaheuristics imitating real ant foraging behavior, is an effective method to find a solution for the traveling salesman problem. The rank-based ant system has been proposed as a developed version of the fundamental model AS of ACO. In the ASrank, since only ant agents that have found one of some excellent solutions are let to regulate the pheromone, the pheromone concentrates on a specific route. As a result, although the (...) ASrank can find a relatively good solution in a short time, it has the disadvantage of being prone falling into a local solution because the pheromone concentrates on a specific route. This problem seems to come from the loss of diversity in route selection according to the rapid accumulation of pheromones to the specific routes. Some ACO models, not just the ASrank, also suffer from this problem of loss of diversity in route selection. It can be considered that the diversity of solutions as well as the selection of solutions is an important factor in the solution system by swarm intelligence such as ACO. In this paper, to solve this problem, we introduce the ant system using individual memories aiming to improve the ability to solve TSP while maintaining the diversity of the behavior of each ant. We apply the existing ACO algorithms and ASIM to some TSP benchmarks and compare the ability to solve TSP. (shrink)

In contrast to Constructivist Views, which construe perceptual cognition as an essentially reconstructive process, this article recommends the Deictic View, which grounds perception in perceptual-demonstrative reference and the use of deictic tracking strategies for acquiring and updating knowledge about individuals. The view raises the problem of how sensory-motor tracking connects to epistemic and integrated forms of tracking. To study the strategies used to solve this problem, we report a study of the ability to track distal individuals when only (...) their directions can be perceived and not their locations. We introduce a new experimental paradigm named the 'Modified Traveling Salesman Problem' (MTSP), which requires subjects to visit n invisible targets in a 2D display once each. Surprisingly, subjects are competent at this task for up to 10 targets. We consider two types of tracking strategies that subjects might use: 'location-based' strategies and 'deictic direction-based' strategies. A number of observations suggest that subjects used the latter, at least for larger numbers of targets. We hypothesize that subjects used perceptual-demonstrative reference and deictic strategies (i) to perform the sensory-motor tracking of directional segments, (ii) to bind the segments with their updated status in the task, and (iii) to perform the epistemic tracking of invisible targets by means of perception-based inferences. (shrink)

Theodore Sider has recently produced an argument which he takes to show that three-dimensionalism is incompatible with the possibility of time travel. I wish to argue that there is indeed a problem for the three-dimensionalist who wishes to countenance time travel, but that Sider has misdiagnosed it. I show why his putative challenge fails, and furthermore that if it were to succeed this would be as problematic for a wide class of four-dimensionalist positions, including Sider’s own, as it would (...) be for three-dimensionalism. Finally, I present the problem that the possibility of time travel genuinely poses for the three-dimensionalist. (shrink)

We consider a special case of heuristics, namely numeric heuristic evaluation functions, and their use in artificial intelligence search algorithms. The problems they are applied to fall into three general classes: single-agent path-finding problems, two-player games, and constraint-satisfaction problems. In a single-agent path-finding problem, such as the Fifteen Puzzle or the travelling salesman problem, a single agent searches for a shortest path from an initial state to a goal state. Two-player games, such as chess and checkers, involve (...) an adversarial relationship between two players, each trying to win the game. In a constraint-satisfaction, problem, such as the 8-Queens problem, the task is to find a state that satisfies a set of constraints. All of these problems are computationally intensive, and heuristic evaluation functions are used to reduce the amount of computation required to solve them. In each case we explain the nature of the evaluation functions used, how they are used in search algorithms, and how they can be automatically learned or acquired. (shrink)

This study investigates a new experimental paradigm called the Modified Traveling Salesman Problem. This task requires subjects to visit once and only once n invisible targets in a 2D display, using a virtual vehicle controlled by the subject. Subjects can only see the directions of the targets from the current location of the vehicle, displayed by a set of oriented segments that can be viewed inside a circular window surrounding the vehicle. Two conditions were compared. In the (...) “allocentric” condition, subjects see the vehicle move across the screen and change orientation under their command. The “egocentric” condition is similar except for how the information is provided: the position and orientation of the vehicle icon remains fixed at the center of the screen and only target directions, as indicated by the oriented segments, change as the subject “moves” the vehicle. The unexpected finding was that this task can be performed, in either condition, for up to 10 targets. We consider two possible strategies that might be used, a location-based strategy and a segment strategy. The location-based strategy relies on spatial memory and attempts to infer the locations of all the targets. The segment strategy is more local and focuses on the directional segments themselves, keeping track of the ones that represent already-visited targets. A number of observations suggest that the segment strategy was used, at least for larger numbers of targets. According to our hypothesis, keeping track of the segments requires one to use indexical reference for associating the segments with their status in the task - given by current status predicates Visited or Not-visited -, perhaps using visual indexes, deictic pointers, or object files. (shrink)

This article proposes a new problem which is called the Stochastic Travelling Advisor Problem in network optimization, and it is defined for an advisory group who wants to choose a subset of candidate workplaces comprising the most profitable route within the time limit of day working hours. A nonlinear binary mathematical model is formulated and a real application case study in the occupational health and safety field is presented. The problem has a stochastic nature in travelling and (...) advising times since the deterministic models are not appropriate for such real-life problems. The STAP is handled by proposing suitable probability distributions for the time parameters and simulating the problem under such conditions. Many application problems like this one are formulated as nonlinear binary programming models which are hard to be solved using exact algorithms especially in large dimensions. A novel binary version of the recently developed gaining-sharing knowledge-based optimization algorithm to solve binary optimization problems is given. GSK algorithm is based on the concept of how humans acquire and share knowledge during their life span. The binary version of GSK depends mainly on two stages that enable BGSK for exploring and exploitation of the search space efficiently and effectively to solve problems in binary space. The generated simulation runs of the example are solved using the BGSK, and the output histograms and the best-fitted distributions for the total profit and for the route length are obtained. (shrink)

Due to the difficulty in solving combinatorial optimization problems, it is necessary to improve the performance of the algorithms by improving techniques to deal with complex optimizations. This research addresses the metaheuristics of marriage in honey-bees optimization based on the behavior of bees. The current study proposes a technique for solving combinatorial optimization problems within proper computation times. The purpose of this study focuses on the travelling salesperson problem and the application of chaotic methods in important sections of the (...) MBO metaheuristic. Three experiments were conducted to measure the efficiency and quality of the solutions: MBO with chaos to generate initial solutions ; MBO with chaos in the workers ; and MBO with chaos to generate initial solutions and the workers. The application of chaotic functions in MBO was significantly better at solving the travelling salesperson problem. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:270 HISTORY OF PHILOSOPHY The Prophets of Paris. By Frank E. Manuel. (Cambridge: Harvard University Press, 1962.) This perceptive and sophisticated contribution to the history of ideas is organized around the intellectual biographies of Turgot, Condorcet, Saint-Simon, the Saint-Simoniarts, Charles Fourier, and Auguste Comte. Professor Manuel's prophets were all Frenchmen and all, he believes, can be placed in a common tradition marked by their conviction that Paris was the (...) mount from which the new gospel had to be delivered, that love was the key to social organization, and that social and religious relationships were more significant than political forms. He presents them as prophets in the Old Testament sense--as unsparing moral critics, teachers and the "revealers of a divine historical design." They were philosophers of an age of crisis, convinced that theirs was the instant of a great human divide and therefore victims "of the anguish of futurity." The future they so confidently foretold to anyone who cared to listen, and to many who did not, has found many of their prophetic visions to be poor predictions, but for Manuel they cannot be dismissed as utopian cranks or frustrated totalitarians. Many of the issues they raised and problems they sensed have yet to be adequately confronted, and it is this prescience, particularly with regard to the psychological conditions of social existence, that Manuel wishes to emphasize. This treatment, as its author admits, is a "frank attempt at rehabilitation, to right the balance of historical judgement and bestow new worth upon thinkers who have often been treated with superficiality" (pp. 1-10). Manuel's approach to the history of ideas lends itself quite effectively to this purpose. He admits to a "romantic view of history-writing" which entails an effort to establish an intimacy with his subjects through an immersion in their manuscripts, in the "scribbled brouillons, the casual notes, the personal letters," as well as in the identity presented through their published works. His writing of history is romantic not only in this regard but much more profoundly in his historicism, which attempts an immediate empathetic confrontation with the total organic complex of his subject's life, ideas, and environment. Manuel's evident sympathy occasionally tempts him into apologetics, but essentially he is not arguing a brief for the defense but trying to understand what it was that made these men see so far, and yet with such myopic arrogance, and what it was they saw. It seemed to me that his approach is most successful with Fourier, and least so with Turgot. Charles Fourier, the self-taught travelling salesman from Besan~on, is often summarily dismissed as a cosmic crank with easy reference to his fantastic aberrations --his seas of lemonade and the copulation of the planets. Manuel helps us to understand not only the aberrations but the prescient insights by establishing the relationship between Fourier's personality and his ideas, as well as by tracing the connections between apparently contradictory conceptions. He does not misuse this technique of intellectual biography by patronizing or justifying a system of thought with reference to its psychological antecedents, but rather helps to illuminate a philosophy by examining the reasons for its expression. This works particularly well with Fourier, an obsessed and deprived personality, whose great contribution, according to Manuel, was the assimilation into a social doctrine of the fundamental needs and drives of mankind--its "manifold wants, its secret desires, and its obstinate fixations" (p. 203). Both Fourier and the SaintSimonians believe that it was pointless to tinker with the social environment without regard for permanent psychological realities, but the latter hoped to sublimate human passions through a social organization that redefined them, while Fourier wanted a social system that would provide for their total gratification (p. 226). Occasionally Manuel rather triumphantly unearths striking parallels with our present BOOK REVIEWS 271 concerns that do not demonstrate the vision of his seers into the future so much as his discovery of analogues in the past. Fourier's case is not particularly strengthened by the observation that his vision of a climate so benign under the regime of phalansteries as to render tire very poles inhabitable is "no longer as... (shrink)

The so-called paradoxes of time travel have played a significant role in both the physics and philosophy literatures - but how much force do these alleged paradoxes really have?

Philosophical Investigations, Volume 45, Issue 2, Page 146-160, April 2022.

Good Agricultural Practices are central to sustainability standards and certification programmes in the global cocoa chain. Pruning is one of the practices promoted in extension services associated with these sustainability efforts. Yet concerns exist about the low adoption rate of these GAPs by smallholder cocoa farmers in Ghana. A common approach to addressing this challenge is based on creating enabling conditions and offering appropriate incentives. We use the concepts of inscription and affordance to trace the vertically coordinated travel of recommended (...) pruning from research to extension and farming sites, and to describe how pruning is carried out differently at each site. Our analysis suggests that enactments of pruning at the extension site reduce the number of options and space for interactions, and this constrains making the practice meaningful to farmers’ repertoires. The conventions guiding and legitimising actions at this site, reinforced by sustainability standards, certification schemes and associated inspections and audits, favour standardised recommendations and consequently narrow room for context-specific diagnostics and adaptions. Therefore, we reframe the adoption problem as a matter of fit between different sites in the ‘agricultural research value chain’ embedded in the operational cocoa chain. Our contribution problematises the dominant framing of low adoption and highlights that the movement of pruning and the sequential enactment at different sites constrain the affordances available for rendering the practice meaningful to farmers’ repertoires. Consequently, addressing the low uptake of GAPs requires institutional work towards conventions that can construct a fit between sites along the agricultural research value chain. (shrink)

ABSTRACT In 'An Insoluble Problem', Storrs McCall presents an argument which he takes to reveal the real problem with backwards time travel. McCall asks us to imagine a scenario in which a renowned artist produces his famous works by copying them from reproductions brought back to him by a time-travelling art critic. The novelty of the scenario lies in its introduction of aesthetic constraints on the possibility of time travel, something which sets it apart from other time travel (...) cases. McCall states that 'The puzzle lies... in finding where artistic creativity enters the equation', and that 'Unlike the traditional "paradoxes of time travel", this problem has no solution'. We offer four responses to McCall's puzzle. Whilst we show that the puzzle is not insoluble, we also argue that it reveals something about the proper relationship between copying and creativity, which may not have been apparent without considering time travel. (shrink)

Are there difficulties raised by the idea of backwards time travel—travel to earlier times—that are peculiar to objects? By ‘object’ in this context I mean something that takes up space, that typically prevents other items in the same category from occupying the same space, and for which it is generally thought appropriate to talk in terms of persistence conditions. One such problem is raised in H. G. Wells’ The Time Machine, but highlighted in the philosophical literature only very recently, (...) by William Grey. Consider Tim, who boards his time machine and, at 12 noon precisely, presses the button to send him back into the past. At any moments after noon, both Tim and the machine have ceased to exist. (shrink)

The methodology and theory developed by Koselleck has been successfully spread globally. Less attention has been devoted to reflections on the conditions and possibilities of universalizing his approach beyond the geographical area on the basis of which it was developed. This article proposes to reread Koselleck's three core contributions to the theory of history—the anthropological constants, the contemporaneity of the non-contemporaneous, and the Sattelzeit—from a postcolonial viewpoint. Empirically it is based on the history of the South Asian Muslims, exploring how (...) Koselleck can help raise new questions, but also how the change in the geographical viewpoint may lead to a reconsideration of some of his assumptions. (shrink)

The Vehicle Routing Problem (VRP) has been extensively studied by different researchers from all over the world in recent years. Multiple solutions have been proposed for different variations of the problem, such as Capacitive Vehicle Routing Problem (CVRP), Vehicle Routing Problem with Time Windows (VRP-TW), Vehicle Routing Problem with Pickup and Delivery (VRPPD), among others, all of them with deterministic times. In the last years, researchers have been interested in including in their different models the (...) variations that travel times may experience when exposed to all kind of phenomena, mainly vehicle traffic. This article addresses the VRP from this perspective, proposing the design and implementation of a genetic algorithm based on neutrosophic theory for calculating the fitness function of each route, considering the variability and uncertainty present in travel times. A deterministic genetic algorithm is also implemented with the average travel times to compare it with the neutrosophic algorithm using simulation. As conclusion, a deterministic algorithm does not necessarily generate the best solution in the real world, full of uncertainty. Also, the quantification of uncertainty using neutrosophic theory can be used in route planning, opening a broad and interesting field of research for future investigations. (shrink)

Michael Dummett and Storrs McCall have claimed that time travel scenarios in which an artist copies an artwork from a reproduction of it that has been sent from the future introduce a causal loop of a new kind: one involving artistic value. They have suggested that this poses a hitherto unacknowledged challenge to time travel theories. I argue that their conclusion depends on some unstated essentialist assumptions about metaphysics of art and the status of representations. By relaxing these assumptions, I (...) show that Dummett and McCall’s scenarios contain no causal loop involving artistic value, and thus pose no new problem for time travel theories. (shrink)

ABSTRACT In their contribution to the first part of this special issue Craig Bourn and Emily Caddick Bourne claim to have solved a puzzle I put forward in my ‘An Insoluble Problem’. Here I argue that their attempt fails.

Space and time are the most fundamental features of our experience of the world, and yet they are also the most perplexing. Does time really flow, or is that simply an illusion? Did time have a beginning? What does it mean to say that time has a direction? Does space have boundaries, or is it infinite? Is change really possible? Could space and time exist in the absence of any objects or events? What, in the end, are space and time? (...) Do they really exist, or are they simply the constructions of our minds? Robin Le Poidevin provides a clear, witty, and stimulating introduction to these deep questions and many other mind-boggling puzzles and paradoxes. He gives a vivid sense of the difficulties raised by our ordinary ideas about space and time, but he also gives us the basis to think about these problems independently, avoiding large amounts of jargon and technicality. His book is an invitation to think philosophically rather than a sustained argument for particular conclusions, but Le Poidevin does advance and defend a number of controversial views. He argues, for example, that time does not actually flow, that it is possible for space and time to be both finite and yet be without boundaries, and that causation is the key to an understanding of one of the deepest mysteries of time: its direction. Drawing on a variety of vivid examples from science, history, and literature, Travels in Four Dimensions brings to life some of the most profound questions imaginable. (shrink)

Talk about time travel is puzzling even if it isn't obviously contradictory. Philosophers however are divided about whether time travel involves empirical paradox or some deeper metaphysical incoherence. It is suggested that time travel requires a Parmenidean four-dimensionalist metaphysical conception of the world in time. The possibility of time travel is addressed (mainly) from within a Parmenidean metaphysical framework, which is accepted by David Lewis in his defence of the coherence of time travel. It is argued that time travel raises (...) formidable difficulties which are not satisfactorily resolved by Lewis's ingenious defence of time travel. Objections to time travel considered include: (1) travel to other times is impossible because there is nowhere (or “nowhen”) to go to; (2) the problem that upon setting out on a journey to the past a time machine will collide with itself; (3) time travel generates a mysterious temporal dualism between experiential time and physical time; (4) travel to the past permits reverse causation, raising the possibility of causal loops and attendant problems arising, for example, from the prospect of empirical contradiction and the possibility of someone being one of their ancestors. (shrink)

Current models of autobiographical memory suggest that self-identity guides autobiographical memory retrieval. Further, the capacity to recall the past and imagine one’s self in the future can influence social problem solving. We examined whether manipulating self-identity, through an induction task in which students were led to believe they possessed high or low self-efficacy, impacted episodic specificity and content of retrieved and imagined events, as well as social problem solving. Compared to individuals in the low self efficacy group, individuals (...) in the high self efficacy group generated past and future events with greater specificity, positive words, and self-efficacious statements, and also performed better on social problem solving indices. A lack of episodic detail for future events predicted poorer performance on social problem solving tasks. Strategies that increase perceived self-efficacy may help individuals to selectively construct a past and future that aids in negotiating social problems. (shrink)

This paper focuses on problems for time travel that specifically concern continuous time-travel to the past, problems to do with potential collisions with past obstacles such as former time-slices of the time traveler herself. These problems have not been discussed nearly as much as other questions about time travel, such as the Grandfather Paradox. Here I focus on discussions by Bernstein, Dowe, Grey and Le Poidevin. After examination, I conclude that only the problems of turning around in time have any (...) merit and present a new proposal of my own for turning around in time without collisions. I assume a Lewisian framework throughout. (shrink)

Is time-travel possible? Like most intriguing problems that lie within the shared locus of physics, metaphysics and logic, this question admits of many interpretations, each of which engenders a different line of research. At its most anemic, the issue can be just: Is it possible to tell a story about travel into the past that contains no explicit contradictions? Under the stimulation of physical concerns it may develop into a more challenging problem: Do the laws of physics, as best (...) we understand them, admit of solutions that contain closed time-like curves? And next: Would it be physically possible for a massive object to travel along one of those curves into its own local past? Then: Are the known facts about our universe consistent with it being such a world? And finally: Is time-travel in our universe technologically possible? When prodded in this direction our original question arrives at last on the drawing boards of the engineers, having passed successively through the precincts of the theoretical physicists, the mathematicians, and the astronomers. (shrink)

The possibility of continuous backwards time travel—time travel for which the traveler follows a continuous path through space between departure and arrival—gives rise to the double-occupancy problem. The trouble is that the time traveler seems bound to have to travel through his or her younger self as the trip begins. Dowe and Le Poidevin agree that this problem is solved by putting the traveler in motion for a gradual trip to the past. Le Poidevin goes on to argue, (...) however, that the gradual trip gives rise to the Cheshire cat problem, a concern about whether the traveler survives the gradual trip. We address the Cheshire cat problem by proposing and considering new continuity constraints on identity over time. Along the way, we come upon an endurantist conception of temporal parts. (shrink)

The paper first tries to explain how the possibility of "time travel" arises in the Godel universe. It then goes on to discuss a technical problem conerning minimal acceleration requirements for time travel. A theorem is stated and a conjecture posed. If the latter is correct, time travel can be ruled out as a practical possibility in the Godel universe.

Brit J Aesthetics DOI:_ 10.1093/aesthj/ayz041 _.

According to Chomsky, creativity is a critical property of human language, particularly the aspect of ?the creative use of language? concerning the appropriateness to a situation. How language can be creative but appropriate to a situation is an unsolvable mystery from the Chomskyan point of view. We propose that language appropriateness can be explained by considering the role of the human capacity for Mental Time Travel at its foundation, together with social and ecological intelligences within a triadic language-grounding system. Our (...) proposal is based on the change of perspective from the analysis of individual sentences to the flux of speech in which the temporal dimension of language is much more relevant. (shrink)

H. G. Wells’ Time Traveller inhabits uniform Newtonian time. Where relativistic/quantum travelers into the past follow spacetime curvatures, past-bound Wellsians must reverse their direction of travel relative to absolute time. William Grey and Robin Le Poidevin claim reversing Wellsians must overlap with themselves or fade away piecemeal like the Cheshire Cat. Self-overlap is physically impossible but ‘Cheshire Cat’ fades destroy Wellsians’ causal continuity and breed bizarre fusions of traveler-stages with opposed time-directions. However, Wellsians who rotate in higher-dimensional space can reverse (...) temporal direction without self-overlap, Cheshire Cats or mereological monstrosities. Alas, hyper-rotation in Newtonian space poses dynamic and biological problems,. Controllable and survivable Wellsian travel needs topologically-variable spaces. Newtonian space, not Newtonian time, is Wellsians’ real enemy. (shrink)

This paper suggests that time travelling scenarios commonly depicted in science fiction introduce problems and dangers for the time traveller. If time travel takes time, then time travellers risk collision with past objects, relocation to distant parts of the universe, and time travel-specific injuries. I propose several models of time travel that avoid the dangers and risks of time travel taking time, and that introduce new questions about the relationship between time travel and spatial location.

THE PURPOSE OF THIS ARTICLE IS TO SHOW HOW HUME’S SCEPTICISM ABOUT MIRACLES GENERATES "EPISTEMOLOGICAL" SCEPTICISM ABOUT TIME TRAVEL. SO THE PRIMARY QUESTION RAISED HERE IS "CAN ONE KNOW THAT TIME TRAVEL HAS OCCURED?" RATHER THAN "CAN TIME TRAVEL OCCUR?" I ARGUE THAT ATTEMPTS TO SHOW THE EXISTENCE OF TIME TRAVEL WOULD FACE THE SAME METHODOLOGICAL PROBLEMS AS THE ONES CONFRONTING ATTEMPTS TO DEMONSTRATE THE EXISTENCE OF PARANORMAL EVENTS. SINCE HUMEAN SCEPTICISM EXTENDS TO THE STUDY OF PARANORMAL EVENTS (PARAPSYCHOLOGY), HUMEANS (...) ARE COMMITTED TO SCEPTICISM ABOUT THE STUDY OF TIME TRAVEL ("PARAHISTORY"). (shrink)

Since 1949, the year that Kurt Gödel presented his solutions to Einstein’s field equations, there has been much discussion of time travel within the philosophical literature. Whereas theorizing about time travel had theretofore been relegated to the realm of science fiction, the imprimatur of Gödel’s work elevated the legitimacy of such discussion. It finally appeared that travel into the past might be a physical—if not yet technological—possibility. For the past few decades, philosophical inquiry into backward time travel and the closely (...) related topic of backward causation has centered on the logical possibility and conceptual coherence of these phenomena. In this paper, various conceptual problems associated with time travel concerning the nature of agency and nomological structure will be explored. However, the existence of such conceptual difficulties does not threaten the logical or physical possibility of time travel. Ultimately, the most rational stance to take regarding time travel may ultimately be one of epistemic humility, by which is meant a stance involving the admission that conceptual analysis may not constitute a very fruitful methodology for understanding the physical nature of our world. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Philosophy, Psychiatry, & Psychology 10.3 (2003) 225-226 [Access article in PDF] Travelers in the Land of Sickness Eric J. Cassell THE PROBLEM OF knowing another person and the world in which that person lives, particularly someone with major mental illness, is addressed in this interesting and rich essay. The number of different metaphors and concepts Potter employs to describe the task of crossing into and then understanding the (...) thoughts, emotions, symptoms, constraints, context, and perspectives of another testifies to the difficulties involved.Yet, as I read the essay, it was not clear what the clinician world traveler, moral tourist, empathizer (and other categories) is supposed to do on the journey to another person. Why do we reach out to the sick person? What is it that we want to know or do that makes this trip necessary? Potter is primarily concerned with mental illness—the examples she cites are patients with schizophrenia—while my experience has in the main been with persons with physical illness, but for the moment, the differences are less important than the central lesson. The illness that the patient presents—the experience of the symptoms, the impairments, disability, and disruptions of the emotional and social existence that happen because of the disease result from an amalgam of the disease process with the specific nature of the sick person. There is no disease in pure form; there is no disease in abstract for clinicians. There is only this sick person. She correctly quotes me, because of all this, as pointing out the importance of integrating knowledge of this particular patient with the abstract knowledge of disease to understand the illness as it is expressed in this person. All to form a basis for the treatment of the patient and especially to help relieve suffering because suffering is always personal, particular, and individual. (It is important in thinking about this topic to remember that most serious diseases, psychiatric and otherwise, are chronic and take place over significant lived time. The acute schizophrenic symptoms or the acute infectious diseases, as dramatic as they are, distract attention from the importance of the place of the sick person.)In physical disease, our long (and continuing) history of separating human beings from nature and the body, and the importance medicine places on objectivity and the objective, have made the inevitable personalization of the disease and symptoms virtually invisible. After ages of explaining psychiatric diseases as the alienation of the person, and a long psychoanalytic period of finding their origins in the person, in the last 30 years these diseases have become increasingly objectified. The place of the person has been diminished as psychiatry has entered the DSM, neurotransmitter, and effective psychotropic drug era. For both physical and mental disease, however, and whatever the current ideology, the nature of person is crucial in determining the onset, diagnosis, course, treatment, and outcome of each illness. It is in order to have an impact on these crucial aspects of sickness that clinicians must come to know their patients to the degree possible. [End Page 225]But there is something more. Nancy Potter quotes a woman with schizophrenia as saying, "All that was my former self has crumbled and fallen together and a creature has emerged of whom I know nothing. She is a stranger to me... She is not real—she is not I... She is I—and because I still have myself on my hands, even if I am a maniac, I must deal with me somehow." (Potter, 2003, p. 215)Must she deal with this crazy self alone? Is that not what her doctors and caregivers are for? But how can they take care of her, protect her, keep what is left intact, and sustain her until she is (hopefully) better without knowing who she is? She makes clear in those few phrases that inside her there is a person with a past, a family, a world, a culture, a role(s) in life, relationships, a body, dreams for the future, things she does, and all the other things that make up a person. It is in... (shrink)

In _Couplets_, Brian Massumi presents twenty-four essays that represent the full spectrum of his work during the past thirty years. Conceived as a companion volume to _Parables for the Virtual_, _Couplets_ addresses the key concepts of _Parables_ from different angles and contextualizes them, allowing their stakes to be more fully felt. Rather than organizing the essays chronologically or by topic, Massumi pairs them into couplets to encourage readers to make connections across conventional subject matter categories, to encounter disjunctions, and to (...) link different phases in the evolution of his work. In his analyses of topics ranging from art, affect, and architecture to media theory, political theory, and the philosophy of experience, Massumi charts a field on which a family of conceptual problems plays out in ways that bear on the potentials for acting and perceiving the world. As an essential guide to Massumi's oeuvre, _Couplets_ is both a primer for his new readers and a supplemental resource for those already engaged with his thought. (shrink)