Previous research has reported that ethical values of business students are lower than those of their peers in other majors. The purpose of this study was to investigate whether a self-selection bias with respect to ethical values exists among students enrolled as business majors when compared with students planning to enter the engineering profession. Engineering students are exposed to a similar technical orientation in academic curricula and also supply the market for managers.A survey instrument was administered to 195 students enrolled (...) in undergraduate business and engineering programs and a graduate business program. The research instrument measured how business and engineering students perceive their own ethical beliefs and actions and how they perceived the ethical beliefs and actions of their peers. (shrink)

O artigo traz resultados de uma investigação de mestrado que teve por objetivo pesquisar as concepções de um grupo de professores a respeito das funções que os mesmos exercem frente à sociedade contemporânea. Partiu-se da premissa de que suas concepções guardam relação com suas práticas educativas e pedagógicas. Trata-se de uma pesquisa desenvolvida na perspectiva qualitativa, com cinquenta e um professores que atuam em seis escolas estaduais da cidade de Ponta Grossa-PR. Elegeu-se como aporte teórico autores que tratam da formação (...) de professores e da profissão docente, como Freire, Imbernón, Ens e Behrens, Tozetto, Sacristán e Tedesco. Os dados foram coletados por meio de questionários, categorizados e analisados seguindo os pressupostos na Análise de Conteúdo. Três categorias foram configuradas a partir de significantes presentes nas respostas dos professores participantes: Categoria I – Professor como um sujeito transformador: educação em uma forma ampla, Categoria II – Professor como profissional do conhecimento, e Categoria III – Professor enquanto sujeito que desempenha vários papéis sociais. Essas categorias nos possibilitaram inferir que as concepções dos professores em relação ao seu papel na sociedade contemporânea vão além da função social da escola, pois centram-se primeiramente na figura de um profissional transformador do mundo; seguida da noção de profissional do conhecimento e, por fim, da ideia de um profissional que desempenha vários papéis sociais. A pesquisa também apontou uma necessária redefinição da profissão docente para que os professores assumam novas competências profissionais na contemporaneidade. Palavras-chave: Profissão docente. Função dos professores. Sociedade contemporânea. Concepções. (shrink)

The clock hypothesis of relativity theory equates the proper time experienced by a point particle along a timelike curve with the length of that curve as determined by the metric. Is it possible to prove that particular types of clocks satisfy the clock hypothesis, thus genuinely measure proper time, at least approximately? Because most real clocks would be enormously complicated to study in this connection, focusing attention on an idealized light clock is attractive. The present paper extends and (...) generalized partial results along these lines with a theorem showing that, for any timelike curve in any spacetime, there is a light clock that measures the curve’s length as accurately and regularly as one wishes. (shrink)

Daylight is the primary cue used by circadian clocks to entrain to the day/night cycle so as to synchronize physiological processes with periodic environmental changes induced by Earth rotation.However, the temporal daylight pattern is not the same every day due to erratic weather fluctuations or regular seasonal changes. Then, how do circadian clocks operate properly in varying weather and seasons? In this paper, we discuss the strategy unveiled by recent studies of the circadian clock of Ostreococcus tauri, the (...) smallest free‐living eukaryotic organism. It combines mechanisms controlling light inputs and clock sensitivity, shaping both the dynamics of the core circadian oscillator and its forcing by light so as to ensure stable and precise synchronization in all weather and seasons.Editor's suggested further reading in BioEssays: Another place, another timer: Marine species and the rhythms of life Abstract. (shrink)

This paper aims at tracking down, by looking at late medieval and early modern discussions over the ontological status of artifacts, the main steps of the process through which nature became theorized on a mechanistic model in the early 17th century. The adopted methodology consists in examining how inventions such as mechanical clocks and automata forced philosophers to modify traditional criteria based on an intrinsic principle of motion and rest for defining natural beings. The paper studies different strategies designed (...) in the transitional period 1300–1600 for making these inventions compatible with classical definitions of nature and artifacts. In the first part of the paper, it is shown that, even if virtually all medieval philosophers acknowledged an ontological distinction between artifacts and natural beings, these different strategies demonstrate a growing concern about the consistency of the art/nature distinction. The next part of the paper studies how mechanical clocks, even before the Scientific Revolution, served as theoretical models for applying mechanistic views to different objects (be they cosmological, physical or biological). The epistemological function of clocks appears to stem from different factors (like the specific manufacturing of late medieval clocks as well as the evolution of 16th-century mechanics) that are listed in this second part of the paper. These factors, combined with the definitional issues raised by automata, explain that clocks became the symbol of a new approach to natural philosophy, characterized by the collapse of the art/nature distinction and the “mechanization of nature”. (shrink)

Cellular circadian clocks represent ancient anticipatory systems which co‐evolved with the first cells to safeguard their survival. Cyanobacteria represent one of the most ancient cells, having essentially invented photosynthesis together with redox‐based cellular circadian clocks some 2.7 billion years ago. Bioelectricity phenomena, based on redox homeostasis associated electron transfers in membranes and within protein complexes inserted in excitable membranes, play important roles, not only in the cellular circadian clocks and in anesthetics‐sensitive cellular sentience (awareness of environment), but (...) also in the coupling of single cells into tissues and organs of unitary multicellular organisms. This integration of cellular circadian clocks with cellular basis of sentience is an essential feature of the cognitive CBC‐Clock basis of cellular life. (shrink)

Recent work in the physics literature demonstrates that, in particular classes of rotating spacetimes, physical light rays in general do not traverse null geodesics. Having presented this result, we discuss its philosophical significance, both for the clock hypothesis (and, in particular, a recent purported proof thereof for light clocks), and for the operational meaning of the metric field. 1. Introduction2. Fletcher's Theorem2.1. Maudlin on the clock hypothesis in special relativity2.2. Fletcher’s result in special relativity2.3. Fletcher’s theorem in general relativity3. (...) Electromagnetism and the Geometrical-Optical Limit 3.1. Maxwell’s equations in curved spacetime3.2. The geometrical-optical limit3.3. Rotating spacetimes3.4. Aren’t Gödel spacetimes unphysical?4. The Clock Hypothesis and Chronogeometry 4.1. Natural and mathematical observations4.2. Clock registry discord4.3. Chronogeometry5. Conclusion. (shrink)

Circalunar clocks, which allow organisms to time reproduction to lunar phase, have been experimentally proven but are still not understood at the molecular level. Currently, a new generation of researchers with new tools is setting out to fill this gap. Our essay provides an overview of classic experiments on circalunar clocks. From the unpublished work of the late D. Neumann we also present a novel phase response curve for a circalunar clock. These experiments highlight avenues for molecular work (...) and call for rigor in setting up and analyzing the logistically complex experiments on circalunar clocks. Re‐evaluating classic experiments, we propose that (1) circalunar clocks in different organisms will have divergent mechanisms and physiological bases, (2) they may have properties very different from the well‐studied circadian clocks and (3) they may have close mechanistic and molecular relations to seasonal rhythms and diapause. (shrink)

A clock can do two things: it can give the time, and it can measure time. Perhaps the first function is the more humanly important. But one might say that a clock can only give the time by measuring time; at some point it is ‘fed’ the time, or the date, and if it subsequently keeps good time—measures time accurately—one can use it to read off later times or dates.

Scientists, both modern and contemporary, commonly try to discern patterns in nature. They also frequently use arguments by analogy to construct an understanding of the natural mechanisms responsible for producing such patterns. For Robert Boyle, the famous clock at Strasbourg provided a perfect paradigm for understanding the connection between these two scientific activities. Unfortunately, it also posed a serious threat to his realistic pretensions. All sorts of internal mechanisms could produce precisely the same movements across the face of a clock. (...) Given God's immense creative capacities, Boyle realized that standard epistemological constraints could never ensure, not even to the least degree of probability, that scientific theories about the unobservable mechanisms of nature were descriptively accurate. Like most moderns, he fortified his epistemology theologically in order to retain his realistic stance. John Locke, however, took counsel from Ecclesiastes to repudiate Boyle's realism, while Samuel Clarke mobilized biblical images to dismiss the clockwork paradigm altogether.A contemporary review of this modern controversy reveals that there is still much to learn from the clock at Strasbourg. Among other things, the realism/antirealism issue is of central importance to understanding today's science, Nancey Murphy's protests notwithstanding. Moreover, the kind of realistic stance that is essential, not only to the truth but to the very intelligibility of certain types of scientific explanation, demands more than the critical realism of Ian Barbour. To be taken seriously, the models used in such contexts must be taken literally. (shrink)

In the eighteenth century, the sciences and their applications adopted a new attitude based on quantification and, increasingly, on a notion of precision. Within this process, instruments played a significant role. However, while new devices such as the micrometer, telescope, and pendulum clock embodied a formerly unknown potential of precision, this could only be realized by defining a set of practices regulating their application and control. The paper picks up the case of pendulum clocks used in eighteenth-century observatories in (...) order to show the process of learning in the course of which the pendulum clock first became a precision instrument. By examining the results of an especially developed statistical analysis, conducted to compare the performance of eighteenth-century clocks, it highlights the diversity of conditions, attitudes, and manners of handling that are characteristic for the epoch. In this way, it underlines the necessity of standardization of timekeeping practices rather than exclusively focusing on the technological development of clocks. Ultimately, the paper discusses the role of makers and users in order to show the evolution of a “precision instrument.”. (shrink)

On receiver-based teleosemantic theories of representation, the chemical states of the circadian clocks in animal, plant and cyanobacterial cells constitute signals of future states of affairs, often the rising and setting of the sun. This signalling is much more rigid than sophisticated representational systems like human language, but it is not simple on all dimensions. In most organisms the clock regulates many different circadian rhythms. The process of entrainment ensures that the mapping between chemical states of the clock and (...) the daily light-dark cycle is adjusted to deal with seasonal changes. In regulating anticipatory behaviour, the states of the clock look forward both to the time the behaviour is supposed to happen and the later time when the anticipated circumstances are supposed to arise. The case of the circadian clock shows that purely indicative signals can arise in very basic biological systems and brings into sharp relief the trade-offs involved in characterizing representational systems. On receiver-based teleosemantic theories, future-directed signals are not restricted to complex multicellular organisms but are ubiquitous in the biological world. (shrink)

This paper (i) gives necessary and sufficient conditions that clocks in an inertial lattice can be synchronized, (ii) shows that these conditions do not imply a universal light speed, and (iii) shows that the terrestrial redshift experiment provides evidence that clocks in a small inertial lattice in a gravitational field can be synchronized.

In the context of a parametric theory (with the time being a dynamical variable) we consider here the coupling between the quantum vacuum and the background gravitation that pervades the universe (unavoidable because of the universality and long range of gravity). We show that this coupling, combined with the fourth Heisenberg relation, would break the parametric invariance of the gravitational equations, introducing thus a difference between the marches of the atomic and the astronomical clocks. More precisely, they would be (...) progressively and adiabatically desynchronized with respect to one another in such a way that the latter would lag behind the former. This would produce a discrepancy between gravitational theory and observations, which use astronomical and atomic time respectively. It turns out that this result, surprising at it might be, is fully compatible with current physics, since it does not conflict with any known physical law or principle. We argue that this phenomenon must be studied, since it could have cosmological consequences. (shrink)

There are a number of problematic features within the current treatment of time in physical theories, including the “timelessness” of the Universe as encapsulated by the Wheeler–DeWitt equation. This paper considers one particular investigation into resolving this issue; a conditional probability interpretation that was first proposed by Page and Wooters. Those authors addressed the apparent timelessness by subdividing a faux Universe into two entangled parts, “the clock” and “the remainder of the Universe”, and then synchronizing the effective dynamics of the (...) two subsystems by way of conditional probabilities. The current treatment focuses on the possibility of using a realistic clock system; namely, a coherent-state description of a damped harmonic oscillator. This clock proves to be consistent with the conditional probability interpretation; in particular, a standard evolution operator is identified with the position of the clock playing the role of time for the rest of the Universe. Restrictions on the damping factor are determined and, perhaps contrary to expectations, the optimal choice of clock is not necessarily one of minimal damping. (shrink)

A passenger boards a fast train. It takes her some distance, makes a u-turn, and returns to the starting platform. She reports that according to her clock, the trip took n seconds. An observer on the platform, using his own clock, gets a different reading. He records a longer time interval m. These claims are compatible with the clocks being in perfect order. Modern Physics tells us that time is a relativistic notion. The duration of the trip, understood as (...) the temporal distance between the departure and the return event, will depend on the chosen frame of reference. The passenger and the observer belong to different frames. This is the source of the discrepancy. Suppose that the passenger and the observer speak a language that is like ours with possible differences arising from the assumption that no one in their community knows about modern physics. Let us call this language '19th Century English'. Imagine that the agents, in different conversations, utter sentences (1) and (2) respectively. (shrink)

Across a wide range of cultural forms, including philosophy, cultural theory, literature and art, the figure of the clock has drawn suspicion, censure and outright hostility. In contrast, even while maps have been shown to be complicit with forms of domination, they are also widely recognised as tools that can be critically reworked in the service of more liberatory ends. This paper seeks to counteract the tendency to see clocks in this way, arguing that they have many more interesting (...) possibilities than they are usually given credit for. An analysis of approaches to clocks in continental philosophy critiques the way they have too often been dismissed as unworthy of further analysis, and argues that this dismissal is based upon an inadequate understanding of how clocks operate. Seeking to move towards more critical and curious approaches, the paper draws inspiration from critical cartography in order to call for the development of a ‘critical horology’ which would emphasise both the fundamentally political nature of clocks, and the potential for designing them otherwise. A discussion of temporal design provides a range of examples of how clocks might open up new horizons within the politics of time. (shrink)

With the advent of colonial education, the school-going ‘child’ as a conceptual category became substantially complicated. Moreover, the seemingly progressive structure of nineteenth-century English Utilitarian thought was responsible for the association of primitivism with both the child and the colonized natives. The Utilitarian thought, along with the Sanskrit nitishastras, influenced the earliest Bengali textbooks of the nineteenth century, including that of Tarkalankar’s Sishusiksha and Vidyasagar’s Barnaparichay. In closely reading these influential primers, this paper attempts to show that the moral pedagogy (...) was a cryptic disciplinary measure to shape the child’s character, often employing the newly introduced tool of ‘clock-time’. As a critique of this, Rabindranath Tagore reinvents the ‘child’ by emphasizing the imaginative to open up a space for the literary. This paper will further attempt to argue that there is a significant shift from pedagogy to play when it comes to Tagore. The loaded idea of ‘ethical play’ forms the fundamental premise of Tagore’s philosophy of education. The ‘child’ has a complicated presence in Tagore’s oeuvre. He significantly deviates from the earlier tradition to inform his philosophy of education with a spontaneous sense of becoming (‘howa’) to develop an aesthetics of resistance. The paper will argue that ‘ethical play’, the philosophy of educating the child is nothing separated from his larger philosophical assumptions about the world and the Man. (shrink)

The twin paradox of relativity theory is reviewed. A distinction is made between physical clocks and biological ones. It is suggested that metabolic activity might be a better measure of aging than physical time. Further it is suggested that entropy changes representing metabolic activity would be a good way to describe aging. Using the above criterion it appears that a traveling twin will be older than his brother.

In this dissertation I examine how the English philosopher-theologian Samuel Clarke (1675--1729) attempted to reasonableness of Christianity and its compatibility with the new natural philosophy. In reaction to what he perceived as the problematic excesses of mechanical philosophy, with its looming threat of atheism, Clarke developed a series of arguments against atheism which aimed to show the shortcomings of a purely material or mechanical explanation of the universe, and demonstrate the overall `reasonability' of the Christian religion. Clarke aimed to demonstrate (...) the `reasonableness' of Christianity by turning the `mathematical' style of reasoning of the mechanical philosophy against his atheist adversaries. Clarke's writings offer us a valuable case-study for the complex interplay of philosophy, science and religion in England at the start of the eighteenth century, and the impact of mechanical philosophy on natural theology. This dissertation aims to improve our understanding of Clarke's philosophy through careful examination of its principal components: The active role of God in the world, the perfection of God's plan, the existence of immaterial substances and powers, and the subsequent reasonability of the Christian religion. Taken together, the four chapters show Clarke's solutions to the atheist threats, and provide a coherent picture of Clarke's ideas about the nature of God and God's role in the world. (shrink)

In mammals, a network of cellular circadian clocks organizes physiology and behavior along the 24‐h day cycle. The traditional hierarchical model of circadian clock organization with a central pacemaker and peripheral slave oscillators has recently been challenged by studies combining tissue‐specific mouse mutants with transcriptome analyses. First, a surprisingly small number of tissue rhythms are lost when only local clocks are ablated and, second, transcriptional circadian rhythms appear to be regulated by a complex mix of local and systemic (...) factors. As reviewed here, these findings suggest a more integrated model of clock network interaction with the central pacemaker as the main source of behavioral and systemic–physiological rhythms and peripheral clocks controlling some local rhythms while at the same time acting as gatekeepers that temporally adjust cellular responses to external stimuli. (shrink)

Einstein’s equivalence principle has a number of problems, and it is often applied incorrectly. Clocks on the earth do not seem to be affected by the sun’s gravitational potential. The most commonly accepted reason given is a faulty application of the equivalence principle. While no valid reason is available within either the special or general theories of relativity, ether theories can provide a valid explanation. A clock bias of the correct magnitude and position dependence can convert the Selleri transformation (...) of ether theories into an apparent Lorentz transformation, which gives rise to an apparent equivalence of inertial frames. The results indicate that the special theory is invalid and that only an apparent relativity exists. (shrink)

Pandemic disruptions to schooling threw into sharper relief the entanglements of economy, gender norms, and education that had been there, and throughout the modern world, all along. The particular entanglement this paper aims to unravel is the reliance of education on a certain kind of attentiveness, historically provided by a feminized teaching force and mothers, that itself rests on the cultivation of particular sensibilities regarding time.

When addressing the notion of proper time in the theory of relativity, it is usually taken for granted that the time read by an accelerated clock is given by the Minkowski proper time. However, there are authors like Harvey Brown that consider necessary an extra assumption to arrive at this result, the so-called clock hypothesis. In opposition to Brown, Richard TW Arthur takes the clock hypothesis to be already implicit in the theory. In this paper I will present a view (...) different from these authors by taking into account Einstein’s notion of natural clock and showing its relevance to the debate. (shrink)

Somites are transient structures which represent the most overt segmental feature of the vertebrate embryo. The strict temporal regulation of somitogenesis is of critical developmental importance since many segmental structures adopt a periodicity based on that of the somites. Until recently, the mechanisms underlying the periodicity of somitogenesis were largely unknown. Based on the oscillations of c-hairy1 and lunatic fringe RNA, we now have evidence for an intrinsic segmentation clock in presomitic cells. Translation of this temporal periodicity into a spatial (...) periodicity, through somite formation, requires Notch signaling. While the Hox genes are certainly involved, it remains unknown how the metameric vertebrate axis becomes regionalized along the antero–posterior (AP) dimension into the occipital, cervical, thoracic, lumbar, and sacral domains. We discuss the implications of cell division as a clock mechanism underlying the regionalization of somites and their derivatives along the AP axis. Possible links between the segmentation clock and axial regionalization are also discussed. BioEssays 22:72–83, 2000. ©2000 John Wiley & Sons, Inc. (shrink)

Somites are transient structures which represent the most overt segmental feature of the vertebrate embryo. The strict temporal regulation of somitogenesis is of critical developmental importance since many segmental structures adopt a periodicity based on that of the somites. Until recently, the mechanisms underlying the periodicity of somitogenesis were largely unknown. Based on the oscillations of c-hairy1 and lunatic fringe RNA, we now have evidence for an intrinsic segmentation clock in presomitic cells. Translation of this temporal periodicity into a spatial (...) periodicity, through somite formation, requires Notch signaling. While the Hox genes are certainly involved, it remains unknown how the metameric vertebrate axis becomes regionalized along the antero–posterior (AP) dimension into the occipital, cervical, thoracic, lumbar, and sacral domains. We discuss the implications of cell division as a clock mechanism underlying the regionalization of somites and their derivatives along the AP axis. Possible links between the segmentation clock and axial regionalization are also discussed. (shrink)

A core principle of modern science holds that a scientific explanation must not attribute will or agency to natural phenomena.The Restless Clock examines the origins and history of this, in particular as it applies to the science of living things. This is also the story of a tradition of radicals—dissenters who embraced the opposite view, that agency is an essential and ineradicable part of nature. Beginning with the church and courtly automata of early modern Europe, Jessica Riskin guides us through (...) our thinking about the extent to which animals might be understood as mere machines. We encounter fantastic robots and cyborgs as well as a cast of scientific and philosophical luminaries, including Descartes and Leibnitz, Lamarck and Darwin, whose ideas gain new relevance in Riskin's hands. The book ends with a riveting discussion of how the dialectic continues in genetics, epigenetics, and evolutionary biology, where work continues to naturalize different forms of agency.The Restless Clock reveals the deeply buried roots of current debates in artificial intelligence, cognitive science, and evolutionary biology. (shrink)

Sound propagation within certain non-relativistic condensed matter models obeys a relativistic wave equation despite such systems admitting entirely non-relativistic descriptions. A natural question that arises upon consideration of this is, “do devices exist that will experience the relativity in these systems?” We describe a thought experiment in which ‘acoustic observers’ possess devices called sound clocks that can be connected to form chains. Careful investigation shows that appropriately constructed chains of stationary and moving sound clocks are perceived by observers (...) on the other chain as undergoing the relativistic phenomena of length contraction and time dilation by the Lorentz factor, \, with \ the speed of sound. Sound clocks within moving chains actually tick less frequently than stationary ones and must be separated by a shorter distance than when stationary to satisfy simultaneity conditions. Stationary sound clocks appear to be length contracted and time dilated to moving observers due to their misunderstanding of their own state of motion with respect to the laboratory. Observers restricted to using sound clocks describe a universe kinematically consistent with the theory of special relativity, despite the preferred frame of their universe in the laboratory. Such devices show promise in further probing analogue relativity models, for example in investigating phenomena that require careful consideration of the proper time elapsed for observers. (shrink)

In her articles on the clock paradox and the relativity of time Luise Lange (1891–1978) defends the theory of relativity against philosophical refutations, by showing that the apparent clock paradox is not a paradox, but merely conflicts with common sense and is based on a misunderstanding of the theory. The following study explores, contextualizes and analyzes Lange’s clear and sophisticated contribution to the debate on the clock paradox for the first time.

Over the last few decades there have been several calls for a “big picture” of the history of science. There is a general need for a concise overview of the rise of modern science, with a clear structure allowing for a rough division into periods. This essay proposes such a scheme, one that is both elementary and comprehensive. It focuses on four machines, which can be seen to have mediated between science and society during successive periods of time: the clock, (...) the balance, the steam engine, and the computer. Following an extended developmental phase, each of these machines came to play a highly visible role in Western societies, both socially and economically. Each of these machines, moreover, was used as a powerful resource for the understanding of both inorganic and organic nature. More specifically, their metaphorical use helped to construe and refine some key concepts that would play a prominent role in such understanding. In each case the key concept would at some point be considered to represent the ultimate building block of reality. Finally, in a refined form, each of these machines would eventually make its entry in scientific research, thereby strengthening the ties between these machines and nature. (shrink)

We present Backward Clock, an original counterexample to Robert Nozick’s truth-tracking analysis of propositional knowledge, which works differently from other putative counterexamples and avoids objections to which they are vulnerable. We then argue that four ways of analysing knowledge in terms of safety, including Duncan Pritchard’s, cannot withstand Backward Clock either.

1. Introduction. The germ of the clock paradox was contained in Einstein's fundamental paper on the special theory of relativity, where he declares that the retardation of a moving clock “still holds good if the clock moves from A to B in any polygonal line, and also when the points A and B coincide.” This remark soon gave rise to a criticism which was to play a prominent role in the discussions of the consistency of the theory of relativity. It (...) was charged that this theory allows the paradoxical conclusion that at the instant of the return of a moving clock U1 to its point of departure A, the time shown by Ul is both earlier and later than the corresponding reading of a clock U2 which has remained stationary at A during U1's journey. Critics based this contention on the following assumptions, for which they claimed the sanction of relativity: The relative motion of U1 and U2 is such that the kinematic process seen by an observer on one of these clocks is of the same character as that seen by an observer on the other, and this symmetry allows each of these two clocks to be used as a reference frame from which to describe the motion of the other, and there is reciprocity between these two reference frames such that in each of them, the moving clock must be slow upon returning to the stationary one. (shrink)

We consider a sequence of absolute-space kinematical theories which differ more or less from the special theory of relativity (STR) in the amount of clock retardation which they predict, but which agree with STR with respect to roundtrip light experiments, such as Michelson-Morley and Kennedy-Thorndike. This sequence of theories is imbedded in the synchrony-free formulation of STR developed by Winnie by modifying the equal passage time principle. The paper has bearing on the relationship between the slow clock transport behavior of (...) clocks and the one-way velocity of light. Experiments which claim to measure the latter are discussed. (shrink)

The discoveries, advancements and continuing controversies in the field of molecular evolution are reviewed. Topics summarized are (1) the evolution of the genetic code, (2) gene evolution including the demonstration of homology, estimation of sequence divergence, phylogenetic trees, the molecular clock and the origin of genes and gene families by various genetic mechanisms, and (3) eukaryotic genome evolution, including the highly repeated satellite sequences, the interspersed and potentially mobile repeated sequences and the unique sequence fraction of the genome.

Period homeostasis is the defining characteristic of a biological clock. Strict period homeostasis is found for the ultradian clocks of eukaryotic microbes. In addition to being temperature-compensated, the period of these rhythms is unaffected by differences in nutrient composition or changes in other environmental variables. The best-studied examples of ultradian clocks are those of the ciliates Paramecium tetraurelia and Tetrahymena sp. and of the fission yeast, Schizosaccharomyces pombe. In these single cell eukaryotes, up to seven different parameters display (...) ultradian rhythmicity with the same, species- and strain-specific period. In fission yeast, the molecular genetic analysis of ultradian clock mechanisms has begun with the systematic analysis of mutants in identified candidate genes. More than 40 “clock mutants” have already been identified, most of them affected in components of major regulatory and signalling pathways. These results indicate a high degree of complexity for a eukaryotic clock mechanism. BioEssays 22:16–22, 2000. ©2000 John Wiley & Sons, Inc. (shrink)

It is the prevailing paradigm in contemporary physics to model the dynamical evolution of physical systems in terms of a real parameter conventionally denoted as 't' ('little tee'). We typically call such dynamical models laws of nature' and t we call 'physical time'. It is common in the philosophy of time to regard t as time itself, and to take the global structure of general relativity as the ultimate guide to physical time, and so consequently the true nature of time. (...) In this paper we defend the idea that physical time, t, is rather better defined as an operational modelling parameter: we measure relations between changing physical quantities using bespoke physical systems---i.e. clocks---that coordinate local coincidences. We argue that the sorts of physical systems that make good clocks---what we call precision clocks---are those that exhibit self-sustained oscillations known as limit cycles, which are ubiquitous in open, driven, stable, dissipative systems. We develop the physical and philosophical ramifications of this conception of physical time, particularly the notion that physical time does not track something 'out there' in the world. As a result, we speculate that physical time is perhaps not as different from manifest time as many philosophers of time (and apparently general relativity) seem to suggest. (shrink)

This essay proposes that the only publication of the Accademia del Cimento, referred to as Saggi,Footnote11 Accademia del Cimento, Saggi di naturali esperienze fatte nell’ Accademia del Cimento sotto la protezione del serenissimo principe Leopoldo di Toscana e descritte dal segretario di essa Accademia (Firenze: Per Giuseppe Cocchini, 1667). had as one of its main goals the celebration of the House of Medici’s paternity of cutting-edge experiments and instruments during the reign of Grand Duke Ferdinando II. These included Ferdinando II’s (...) thermometers and hygrometers, Torricelli’s experiment and barometer, and Galileo’s pendulum as a clock-regulator. It seems that this agenda went unnoticed, not at the time of its initial circulation, but rather in modern historiography. Christiaan Huygens’s challenged invention of the pendulum clock provides a case study to explore the agenda of this publication and the problem of defining an invention in seventeenth-century Europe. This paper presents for the first time the document that attests to when the first specimen of Huygens’s clock arrived in Florence, disproving the previously believed date of September 1657. The paper argues that over the last two centuries, this error has made the Medici narratives of this dispute appear inconsistent and marginalized them. In light of this new find, they must be reconsidered. (shrink)

A vast network of cellular circadian clocks regulates 24‐hour rhythms of behavior and physiology in mammals. Complex environments are characterized by multiple, and often conflicting time signals demanding flexible mechanisms of adaptation of endogenous rhythms to external time. Traditionally this process of circadian entrainment has been conceptualized in a hierarchical scheme with a light‐reset master pacemaker residing in the hypothalamus that subsequently aligns subordinate peripheral clocks with each other and with external time. Here we review new experiments using (...) conditional mouse genetics suggesting that resetting of the circadian system occurs in a more “federated” and tissue‐specific fashion, which allows for increased noise resistance and plasticity of circadian timekeeping under natural conditions. (shrink)