Time isotropy,Lorentz transformation and inertial frames

Homogeneity of Euclidean space and time, spatial isotropy, principle of relativity and the existence of a finite speed limit (or its variants) are commonly believed to be the only axioms required for developing the special theory of relativity (Lorentz transformations). In this paper, however, it is pointed out that the Lorentz transformation for a boost cannot actually be derived without the explicit assumption of time isotropy (viz. time-reversal symmetry) which is logically independent of the other postulates of relativity. Postulating time isotropy also restores the symmetry between space and time in the postulates of relativity (i.e. time and space share the same symmetries then). Time isotropy also helps explain naturally one key general feature of the fundamental physical laws, viz. their time-reversal symmetry. But inertial frames are defined in influential texts as frames having space-time homogeneity and spatial isotropy only. Inclusion of time isotropy in that definition is thus suggested.     

On the time reversal invariance of classical electromagnetic theory

David Albert claims that classical electromagnetic theory is not time reversal invariant. He acknowledges that all physics books say that it is, but claims they are “simply wrong” because they rely on an incorrect account of how the time reversal operator acts on magnetic fields. On that account, electric fields are left intact by the operator, but magnetic fields are inverted. Albert sees no reason for the asymmetric treatment, and insists that neither field should be inverted. I argue, to the contrary, that the inversion of magnetic fields makes good sense and is, in fact, forced by elementary geometric considerations. I also suggest a way of thinking about the time reversal invariance of classical electromagnetic theory—one that makes use of the invariant four-dimensional formulation of the theory—that makes no reference to magnetic fields at all. It is my hope that it will be of interest in its own right, Albert aside. It has the advantage that it allows for arbitrary curvature in the background spacetime structure, and is therefore suitable for the framework of general relativity. The only assumption one needs is temporal orientability.     

Prospects for a new account of time reversal

In this paper I draw the distinction between intuitive and theory-relative accounts of the time reversal symmetry and identify problems with each. I then propose an alternative to these two types of accounts that steers a middle course between them and minimizes each account׳s problems. This new account of time reversal requires that, when dealing with sets of physical theories that satisfy certain constraints, we determine all of the discrete symmetries of the physical laws we are interested in and look for involutions that leave spatial coordinates unaffected and that act consistently across our physical laws. This new account of time reversal has the interesting feature that it makes the nature of the time reversal symmetry an empirical feature of the world without requiring us to assume that any particular physical theory is time reversal invariant from the start. Finally, I provide an analysis of several toy cases that reveals differences between my new account of time reversal and its competitors.     

The forecasting attributes of trend- and difference-stationary representations for macroeconomic time series

We analyse the forecasting attributes of trenc and diffence-stationary representations of the U.S. macroeconomic time series sudied by Nelson and Plosser (1982). Predictive densities based on models estimated for these series (which terminate in 1970) are compared with subsequent realizations compiled by Schotman and van Dijk (1991) which terminate in (1988). Predictive densities obtained using the, extended series are also derived to assess the impact of the subsequent realization on long-range forecasts. Of particular interest are comparisons of the average intervals of predictive densities corresponding to the competing specifications In general, we find that coverage intervals based on diference-stationary specifications are far wider than those based or. trend-stationary specifications for the real series, and slightly wider for the nominal series. This additional width is often a virtue in forecasting nuninal series over the 1971-1988 period, as the inflation experienced durnig this time was unprecedented in the 1900s. However, the evolution of the real series has been relatively stable in the 1900s, hence the uncertainty associated with difference-stationary specifications generally seems excessive for these data.     

Minimal length in quantum gravity and the fate of Lorentz invariance

The paper highlights a recent debate in the quantum gravity community on the status of Lorentz invariance in theories that introduce a fundamental length scale, and in particular in deformed special relativity. Two arguments marshaled against that theory are examined and found wanting.     

Medical representations of the body in Japan: gender, class, and discourse in the eighteenth century

This paper examines the introduction of European anatomy to Japan via translated medical texts in the eighteenth century. It argues how detailed illustrations of the body found in the texts presented a new discourse by which to objectify and control the body, and new metaphors and analogies by which to view society. Inspection of bodily parts through dissection and the reading of anatomical texts marked a transition to Western forms of science, to 'reliable' knowledge which was certified by the social status of the author. By looking at one important text, the Kaitai shinsho [A New Book of Anatomy] (1774), it will be shown that changes in representations of the body reflect the social construction of gender.     

Probability,arrow of time and decoherence

This paper relates both to the metaphysics of probability and to the physics of time asymmetry. Using the formalism of decoherent histories, it investigates whether intuitions about intrinsic time directedness that are often associated with probability can be justified in the context of no-collapse approaches to quantum mechanics. The standard (two-vector) approach to time symmetry in the decoherent histories literature is criticised, and an alternative approach is proposed, based on two decoherence conditions (‘forwards’ and ‘backwards’) within the one-vector formalism. In turn, considerations of forwards and backwards decoherence and of decoherence and recoherence suggest that a time-directed interpretation of probabilities, if adopted, should be both contingent and perspectival.     

Quantum mechanics,time and ontology

Against what is commonly accepted in many contexts, it has been recently suggested that both deterministic and indeterministic quantum theories are not time-reversal invariant, and thus time is handed in a quantum world. In this paper, I analyze these arguments and evaluate possible reactions to them. In the context of deterministic theories, first I show that this conclusion depends on the controversial assumption that the wave-function is a physically real scalar field in configuration space. Then I argue that answers which restore invariance by assuming the wave-function is a ray in Hilbert space fall short. Instead, I propose that one should deny that the wave-function represents physical systems, along the lines proposed by the so-called primitive ontology approach. Moreover, in the context of indeterministic theories, I argue that time-reversal invariance can be restored suitably redefining its meaning.     

Pregnancy following segmental isthmic reversal of the rabbit oviduct

Summary Microsurgical reversal of a segment of rabbit proximal tubal isthmus has been followed by normal pregnancy in the first two animals to undergo the procedure. Establishment of pregnancy despite radical modification of the oviduct furnishes the opportunity to gain new insights into the mechanisms controlling tubal ovum transport and emphasizes the evolving feasibility and importance of tuboplastic microsurgery both as a research tool and clinical procedure.This study was partly supported by an N.I.H. Institutional Research Grant.Supported by the Rockefeller Foundation.     

Unit roots versus other types of time heterogeneity,parameter time dependence and superexogeneity

This paper stresses the restrictive nature of the standard unit root/cointegration assumptions and examines a more general type of time heterogeneity, which might characterize a number of economic variables, and which results in parameter time dependence and misleading statistical inference. We show that in such cases ‘operational’ models cannot be obtained, and the estimation of time‐varying parameter models becomes necessary. For instance, economic processes subject to endemic change can only be adequately modelled in a state space form. This is a very important point, because unstable models will break down when used for forecasting purposes. We also discuss a new test for the null of cointegration developed by Quintos and Phillips (1993), which is based on parameter constancy in cointegrating regressions. Finally, we point out that, if it is possible to condition on a subset of superexogenous variables, parameter instability can be handled by estimating a restricted system. Copyright © 2002 John Wiley & Sons, Ltd.     

Spontaneous reversal of ethinyl estradiol-induced cholestasis in the rat

Summary The spontaneous reversal of ethinyl estradiol-induced cholestasis has been documented 7 days after the last estrogen administration in the rat. This finding supports the hypothesis that estrogens produce only a transient functional failure of the hepatocytic structures responsible for bile secretion.Supported by Research grant CT-77, 0153304 from Consiglio Nazionale delle Ricerche, Rome, Italy.     

β-Ergokryptine,a new alkaloid of the ergotoxine group

Zusammenfassung Es wird die Isolierung eines neuen Isomeren des Ergokryptins beschrieben, das sich von diesem nur durch den Ersatz des Leucin-Restes durch den Isoleucin-Rest im Peptidteil des Moleküls unterscheidet. Das neue Isomere soll als-Ergokryptin und das früher beschriebene Alkaloid als-Ergokryptin bezeichnet werden. Die beiden Isomeren, ebenso ihre Dihydro-Derivate, unterscheiden sich pharmakologisch nur ganz unwesentlich.

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Mitteilung über Mutterkornalkaloide (65. Mitteilung:H. Ott, A. Hofmann andA. J. Frey, J. Am. chem. Soc.88, 1251 (1966)).     

Amido,ureido and urethano neighbouring group participation

Zusammenfassung Bei der Ionisation eines 2-substituierten 1-Äthylhalogenides oder -toluolsulfonates mit Beteiligung benachbarter Amidgruppen handelt es sich entweder um eine Ionisation (Reaktionsgeschwindigkeitskonstantek ) mit Beteiligung der neutralen Amidgruppe, oder um eine Zyklisierung (Reaktionsgeschwindigkeitskonstantek ), bei der die anionische Form der Amidgruppe beteiligt ist. Solche Zyklisierungen sind von der Basenkonzentration abhängig; die gemessene Reaktionsgeschwindigkeitskonstantek ₂ ist gleichK k ^bO , wobeiK die Gleichgewichtskonstante für die Neutralisation des Substratmoleküls ist. Unter neutralen Bedingungen in 80% igem Äthanol ist die beobachtete Sequenz fürk Werte für verschiedene benachbarte Gruppen die folgende: Benzamido > Ureido > Urethano > Azetoxy, während in äthanolischer Natriumäthoxyd-Lösung die Sequenz die folgende ist: Urethano > Benzamido > Ureido.     

Reticulate evolution and cladism: Tests for the direction of evolution

Summary Reticulate evolution between ancestral-descendant lineages can be critically tested for by investigating the relationship between out-group and mid-point roots on numerically derived cladograms. The western grass-snake provides a worked example for the theoretical test.