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Works by J. Brian Pitts
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J. Brian Pitts
How Dualists Should (Not) Respond to the Objection From Energy Conservation.Alin C. Cucu & J. Brian Pitts - 2019 - Mind and Matter 17 (1):95-121.details
The principle of energy conservation is widely taken to be a se- rious difficulty for interactionist dualism (whether property or sub- stance). Interactionists often have therefore tried to make it satisfy energy conservation. This paper examines several such attempts, especially including E. J. Lowe's varying constants proposal, show- ing how they all miss their goal due to lack of engagement with the physico-mathematical roots of energy conservation physics: the first Noether theorem (that symmetries imply conservation laws), its converse (that conservation (...) laws imply symmetries), and the locality of continuum/field physics. Thus the "conditionality re- sponse", which sees conservation as (bi)conditional upon symme- tries and simply accepts energy non-conservation as an aspect of interactionist dualism, is seen to be, perhaps surprisingly, the one most in accord with contemporary physics (apart from quantum mechanics) by not conflicting with mathematical theorems basic to physics. A decent objection to interactionism should be a posteri- ori, based on empirically studying the brain. (shrink)
Causal Closure of the Physical in Metaphysics
Classical Mechanics in Philosophy of Physical Science
Dualism, Misc in Philosophy of Mind
Interactionism in Philosophy of Mind
Conservation Laws and the Philosophy of Mind: Opening the Black Box, Finding a Mirror.J. Brian Pitts - 2020 - Philosophia 48 (2):673-707.details
Since Leibniz's time, Cartesian mental causation has been criticized for violating the conservation of energy and momentum. Many dualist responses clearly fail. But conservation laws have important neglected features generally undermining the objection. Conservation is _local_, holding first not for the universe, but for everywhere separately. The energy in any volume changes only due to what flows through the boundaries. Constant total energy holds if the global summing-up of local conservation laws converges; it probably doesn't in reality. Energy conservation holds (...) if there is symmetry, the sameness of the laws over time. Thus, if there are time-places where symmetries fail due to nonphysical influence, conservation laws fail there and then, while holding elsewhere, such as refrigerators and stars. Noether's converse first theorem shows that conservation laws imply symmetries. Thus conservation trivially nearly entails the causal closure of the physical. But expecting conservation to hold in the brain simply assumes the falsehood of Cartesianism. Hence Leibniz's objection begs the question. Empirical neuroscience is another matter. So is Einstein's General Relativity: far from providing a loophole, General Relativity makes mental causation _harder_. (shrink)
Change in Hamiltonian General Relativity From the Lack of a Time-Like Killing Vector Field.J. Brian Pitts - 2014 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 47:68-89.details
In General Relativity in Hamiltonian form, change has seemed to be missing, defined only asymptotically, or otherwise obscured at best, because the Hamiltonian is a sum of first-class constraints and a boundary term and thus supposedly generates gauge transformations. Attention to the gauge generator G of Rosenfeld, Anderson, Bergmann, Castellani et al., a specially _tuned sum_ of first-class constraints, facilitates seeing that a solitary first-class constraint in fact generates not a gauge transformation, but a bad physical change in electromagnetism or (...) General Relativity. The change spoils the Lagrangian constraints, Gauss's law or the Gauss-Codazzi relations describing embedding of space into space-time, in terms of the physically relevant velocities rather than auxiliary canonical momenta. But the resemblance between the gauge generator G and the Hamiltonian H leaves still unclear where objective change is in GR. Insistence on Hamiltonian-Lagrangian equivalence, a theme emphasized by Castellani, Sugano, Pons, Salisbury, Shepley and Sundermeyer among others, holds the key. Taking objective change to be ineliminable time dependence, one recalls that there is change in vacuum GR just in case there is no time-like vector field xi^a satisfying Killing's equation L_xi g_mn=0, because then there exists no coordinate system such that everything is independent of time. Throwing away the spatial dependence of GR for convenience, one finds explicitly that the time evolution from Hamilton's equations is real change just when there is no time-like Killing vector. The inclusion of a massive scalar field is simple. No obstruction is expected in including spatial dependence and coupling more general matter fields. Hence change is real and local even in the Hamiltonian formalism. The considerations here resolve the Earman-Maudlin standoff over change in Hamiltonian General Relativity: the Hamiltonian formalism is helpful, and, suitably reformed, it does not have absurd consequences for change and observables. Hence the classical problem of time is resolved. The Lagrangian-equivalent Hamiltonian analysis of change in General Relativity is compared to Belot and Earman's treatment. The more serious quantum problem of time, however, is not automatically resolved due to issues of quantum constraint imposition. (shrink)
Space and Time in Philosophy of Physical Science
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Space–Time Philosophy Reconstructed Via Massive Nordström Scalar Gravities? Laws Vs. Geometry, Conventionality, and Underdetermination.J. Brian Pitts - 2016 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 53:73-92.details
What if gravity satisfied the Klein-Gordon equation? Both particle physics from the 1920s-30s and the 1890s Neumann-Seeliger modification of Newtonian gravity with exponential decay suggest considering a "graviton mass term" for gravity, which is _algebraic_ in the potential. Unlike Nordström's "massless" theory, massive scalar gravity is strictly special relativistic in the sense of being invariant under the Poincaré group but not the 15-parameter Bateman-Cunningham conformal group. It therefore exhibits the whole of Minkowski space-time structure, albeit only indirectly concerning volumes. Massive (...) scalar gravity is plausible in terms of relativistic field theory, while violating most interesting versions of Einstein's principles of general covariance, general relativity, equivalence, and Mach. Geometry is a poor guide to understanding massive scalar gravity: matter sees a conformally flat metric due to universal coupling, but gravity also sees the rest of the flat metric in the mass term. What is the 'true' geometry, one might wonder, in line with Poincaré's modal conventionality argument? Infinitely many theories exhibit this bimetric 'geometry,' all with the total stress-energy's trace as source; thus geometry does not explain the field equations. The irrelevance of the Ehlers-Pirani-Schild construction to a critique of conventionalism becomes evident when multi-geometry theories are contemplated. Much as Seeliger envisaged, the smooth massless limit indicates underdetermination of theories by data between massless and massive scalar gravities---indeed an unconceived alternative. At least one version easily could have been developed before General Relativity; it then would have motivated thinking of Einstein's equations along the lines of Einstein's newly re-appreciated "physical strategy" and particle physics and would have suggested a rivalry from massive spin 2 variants of General Relativity. The Putnam-Grünbaum debate on conventionality is revisited with an emphasis on the broad modal scope of conventionalist views. Massive scalar gravity thus contributes to a historically plausible rational reconstruction of much of 20th-21st century space-time philosophy in the light of particle physics. An appendix reconsiders the Malament-Weatherall-Manchak conformal restriction of conventionality and constructs the 'universal force' influencing the causal structure. Subsequent works will discuss how massive gravity could have provided a template for a more Kant-friendly space-time theory that would have blocked Moritz Schlick's supposed refutation of synthetic _a priori_ knowledge, and how Einstein's false analogy between the Neumann-Seeliger-Einstein modification of Newtonian gravity and the cosmological constant \Lambda generated lasting confusion that obscured massive gravity as a conceptual possibility. (shrink)
General Relativity in Philosophy of Physical Science
Underdetermination of Theory by Data, Misc in General Philosophy of Science
Permanent Underdetermination From Approximate Empirical Equivalence in Field Theory: Massless and Massive Scalar Gravity, Neutrino, Electromagnetic, Yang–Mills and Gravitational Theories.J. Brian Pitts - 2010 - British Journal for the Philosophy of Science 62 (2):259-299.details
Classical and quantum field theory provide not only realistic examples of extant notions of empirical equivalence, but also new notions of empirical equivalence, both modal and occurrent. A simple but modern gravitational case goes back to the 1890s, but there has been apparently total neglect of the simplest relativistic analog, with the result that an erroneous claim has taken root that Special Relativity could not have accommodated gravity even if there were no bending of light. The fairly recent acceptance of (...) nonzero neutrino masses shows that widely neglected possibilities for nonzero particle masses have sometimes been vindicated. In the electromagnetic case, there is permanent underdetermination at the classical and quantum levels between Maxwell's theory and the one-parameter family of Proca's electromagnetisms with massive photons, which approximate Maxwell's theory in the limit of zero photon mass. While Yang–Mills theories display similar approximate equivalence classically, quantization typically breaks this equivalence. A possible exception, including unified electroweak theory, might permit a mass term for the photons but not the Yang–Mills vector bosons. Underdetermination between massive and massless (Einstein) gravity even at the classical level is subject to contemporary controversy. (shrink)
Empirically Equivalent Theories in General Philosophy of Science
Philosophy of Physical Science, Misc in Philosophy of Physical Science
Gauge-Invariant Localization of Infinitely Many Gravitational Energies From All Possible Auxiliary Structures.J. Brian Pitts - unknowndetails
The problem of finding a covariant expression for the distribution and conservation of gravitational energy-momentum dates to the 1910s. A suitably covariant infinite-component localization is displayed, reflecting Bergmann's realization that there are infinitely many gravitational energy-momenta. Initially use is made of a flat background metric (or rather, all of them) or connection, because the desired gauge invariance properties are obvious. Partial gauge-fixing then yields an appropriate covariant quantity without any background metric or connection; one version is the collection of pseudotensors (...) of a given type, such as the Einstein pseudotensor, in _every_ coordinate system. This solution to the gauge covariance problem is easily adapted to any pseudotensorial expression (Landau-Lifshitz, Goldberg, Papapetrou or the like) or to any tensorial expression built with a background metric or connection. Thus the specific functional form can be chosen on technical grounds such as relating to Noether's theorem and yielding expected values of conserved quantities in certain contexts and then rendered covariant using the procedure described here. The application to angular momentum localization is straightforward. Traditional objections to pseudotensors are based largely on the false assumption that there is only one gravitational energy rather than infinitely many. (shrink)
Absolute Objects and Counterexamples: Jones--Geroch Dust, Torretti Constant Curvature, Tetrad-Spinor, and Scalar Density.J. Brian Pitts - 2006 - Studies in History and Philosophy of Modern Physics 37:347-71.details
James L. Anderson analyzed the novelty of Einstein's theory of gravity as its lack of "absolute objects." Michael Friedman's related work has been criticized by Roger Jones and Robert Geroch for implausibly admitting as absolute the timelike 4-velocity field of dust in cosmological models in Einstein's theory. Using the Rosen-Sorkin Lagrange multiplier trick, I complete Anna Maidens's argument that the problem is not solved by prohibiting variation of absolute objects in an action principle. Recalling Anderson's proscription of "irrelevant" variables, I (...) generalize that proscription to locally irrelevant variables that do no work in some places in some models. This move vindicates Friedman's intuitions and removes the Jones-Geroch counterexample: some regions of some models of gravity with dust are dust-free and so naturally lack a timelike 4-velocity, so diffeomorphic equivalence to (1,0,0,0) is spoiled. Torretti's example involving constant curvature spaces is shown to have an absolute object on Anderson's analysis, viz., the conformal spatial metric density. The previously neglected threat of an absolute object from an orthonormal tetrad used for coupling spinors to gravity appears resolvable by eliminating irrelevant fields. However, given Anderson's definition, GTR itself has an absolute object (as Robert Geroch has observed recently): a change of variables to a conformal metric density and a scalar density shows that the latter is absolute. (shrink)
Philosophy of Physics, Miscellaneous in Philosophy of Physical Science
Einstein׳s Physical Strategy, Energy Conservation, Symmetries, and Stability: "But Grossmann & I Believed That the Conservation Laws Were Not Satisfied".J. Brian Pitts - 2016 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 54:52-72.details
Recent work on the history of General Relativity by Renn, Sauer, Janssen et al. shows that Einstein found his field equations partly by a physical strategy including the Newtonian limit, the electromagnetic analogy, and energy conservation. Such themes are similar to those later used by particle physicists. How do Einstein's physical strategy and the particle physics derivations compare? What energy-momentum complex did he use and why? Did Einstein tie conservation to symmetries, and if so, to which? How did his work (...) relate to emerging knowledge of the canonical energy-momentum tensor and its translation-induced conservation? After initially using energy-momentum tensors hand-crafted from the gravitational field equations, Einstein used an identity from his assumed linear coordinate covariance x'=Mx to relate it to the canonical tensor. Usually he avoided using matter Euler-Lagrange equations and so was not well positioned to use or reinvent the Herglotz-Mie-Born understanding that the canonical tensor was conserved due to translation symmetries, a result with roots in Lagrange, Hamilton and Jacobi. Whereas Mie and Born were concerned about the canonical tensor's asymmetry, Einstein did not need to worry because his Entwurf Lagrangian is modeled not so much on Maxwell's theory as on a scalar theory. Einstein's theory thus has a symmetric canonical energy-momentum tensor. But as a result, it also has 3 negative-energy field degrees of freedom. Thus the Entwurf theory fails a 1920s-30s a priori particle physics stability test with antecedents in Lagrange's and Dirichlet's stability work; one might anticipate possible gravitational instability. This critique of the Entwurf theory can be compared with Einstein's 1915 critique of his Entwurf theory for not admitting rotating coordinates and not getting Mercury's perihelion right. One can live with absolute rotation but cannot live with instability. Particle physics also can be useful in the historiography of gravity and space-time, both in assessing the growth of objective knowledge and in suggesting novel lines of inquiry to see whether and how Einstein faced the substantially mathematical issues later encountered in particle physics. This topic can be a useful case study in the history of science on recently reconsidered questions of presentism, whiggism and the like. Future work will show how the history of General Relativity, especially Noether's work, sheds light on particle physics. (shrink)
A First Class Constraint Generates Not a Gauge Transformation, But a Bad Physical Change: The Case of Electromagnetism.J. Brian Pitts - unknowndetails
In Dirac-Bergmann constrained dynamics, a first-class constraint typically does not _alone_ generate a gauge transformation. By direct calculation it is found that each first-class constraint in Maxwell's theory generates a change in the electric field E by an arbitrary gradient, spoiling Gauss's law. The secondary first-class constraint p^i,_i=0 still holds, but being a function of derivatives of momenta, it is not directly about E. Only a special combination of the two first-class constraints, the Anderson-Bergmann -Castellani gauge generator G, leaves E (...) unchanged. This problem is avoided if one uses a first-class constraint as the generator of a _canonical transformation_; but that partly strips the canonical coordinates of physical meaning as electromagnetic potentials and makes the electric field depend on the smearing function, bad behavior illustrating the wisdom of the Anderson-Bergmann Lagrangian orientation of interesting canonical transformations. The need to keep gauge-invariant the relation dot{q}- dH/dp= -E_i -p^i=0 supports using the primary Hamiltonian rather than the extended Hamiltonian. The results extend the Lagrangian-oriented reforms of Castellani, Sugano, Pons, Salisbury, Shepley, _etc._ by showing the inequivalence of the extended Hamiltonian to the primary Hamiltonian even for _observables_, properly construed in the sense implying empirical equivalence. Dirac and others have noticed the arbitrary velocities multiplying the primary constraints outside the canonical Hamiltonian while apparently overlooking the corresponding arbitrary coordinates multiplying the secondary constraints _inside_ the canonical Hamiltonian, and so wrongly ascribed the gauge quality to the primaries alone, not the primary-secondary team G. Hence the Dirac conjecture about secondary first-class constraints rests upon a false presupposition. The usual concept of Dirac observables should also be modified to employ the gauge generator G, not the first-class constraints separately, so that the Hamiltonian observables become equivalent to the Lagrangian ones such as the electromagnetic field F. (shrink)
Gauge Theories in Philosophy of Physical Science
Conservation of Energy: Missing Features in Its Nature and Justification and Why They Matter.J. Brian Pitts - 2021 - Foundations of Science 26 (3):559-584.details
Misconceptions about energy conservation abound due to the gap between physics and secondary school chemistry. This paper surveys this difference and its relevance to the 1690s–2010s Leibnizian argument that mind-body interaction is impossible due to conservation laws. Justifications for energy conservation are partly empirical, such as Joule's paddle wheel experiment, and partly theoretical, such as Lagrange's statement in 1811 that energy is conserved if the potential energy does not depend on time. In 1918 Noether generalized results like Lagrange's and proved (...) a converse: symmetries imply conservation laws and vice versa. Conservation holds if and only if nature is uniform. The rise of field physics during the 1860s–1920s implied that energy is located in particular places and conservation is primordially local: energy cannot disappear in Cambridge and reappear in Lincoln instantaneously or later; neither can it simply disappear in Cambridge or simply appear in Lincoln. A global conservation law can be inferred in some circumstances. Einstein's General Relativity, which stimulated Noether's work, is another source of difficulty for conservation laws. As is too rarely realized, the theory admits conserved quantities due to symmetries of the Lagrangian, like other theories. Indeed General Relativity has more symmetries and hence more conserved energies. An argument akin to Leibniz's finally gets some force. While the mathematics is too advanced for secondary school, the ideas that conservation is tied to uniformities of nature and that energy is in particular places, are accessible. Improved science teaching would serve the truth and enhance the social credibility of science. (shrink)
Einstein׳s Equations for Spin 2 Mass 0 From Noether׳s Converse Hilbertian Assertion.J. Brian Pitts - 2016 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 56:60-69.details
An overlap between the general relativist and particle physicist views of Einstein gravity is uncovered. Noether's 1918 paper developed Hilbert's and Klein's reflections on the conservation laws. Energy-momentum is just a term proportional to the field equations and a "curl" term with identically zero divergence. Noether proved a \emph{converse} "Hilbertian assertion": such "improper" conservation laws imply a generally covariant action. Later and independently, particle physicists derived the nonlinear Einstein equations assuming the absence of negative-energy degrees of freedom for stability, along (...) with universal coupling: all energy-momentum including gravity's serves as a source for gravity. Those assumptions imply that the energy-momentum is only a term proportional to the field equations and a symmetric curl, which implies the coalescence of the flat background geometry and the gravitational potential into an effective curved geometry. The flat metric, though useful in Rosenfeld's stress-energy definition, disappears from the field equations. Thus the particle physics derivation uses a reinvented Noetherian converse Hilbertian assertion in Rosenfeld-tinged form. The Rosenfeld stress-energy is identically the canonical stress-energy plus a Belinfante curl and terms proportional to the field equations, so the flat metric is only a convenient mathematical trick without ontological commitment. Neither generalized relativity of motion, nor the identity of gravity and inertia, nor substantive general covariance is assumed. The more compelling criterion of lacking ghosts yields substantive general covariance as an output. Hence the particle physics derivation, though logically impressive, is neither as novel nor as ontologically laden as it has seemed. (shrink)
The Nontriviality of Trivial General Covariance: How Electrons Restrict 'Time' Coordinates, Spinors Fit Into Tensor Calculus, and of a Tetrad is Surplus Structure.J. Brian Pitts - 2012 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 43 (1):1-24.details
It is a commonplace in the philosophy of physics that any local physical theory can be represented using arbitrary coordinates, simply by using tensor calculus. On the other hand, the physics literature often claims that spinors \emph{as such} cannot be represented in coordinates in a curved space-time. These commonplaces are inconsistent. What general covariance means for theories with fermions, such as electrons, is thus unclear. In fact both commonplaces are wrong. Though it is not widely known, Ogievetsky and Polubarinov constructed (...) spinors in coordinates in 1965, enhancing the unity of physics and helping to spawn particle physicists' concept of nonlinear group representations. Roughly and locally, these spinors resemble the orthonormal basis or "tetrad" formalism in the symmetric gauge, but they are conceptually self-sufficient and more economical. The typical tetrad formalism is de-Ockhamized, with six extra field components and six compensating gauge symmetries to cancel them out. The Ogievetsky-Polubarinov formalism, by contrast, is Ockhamized, with most of the fluff removed. As developed nonperturbatively by Bilyalov, it admits any coordinates at a point, but "time" must be listed first. Here "time" is defined in terms of an eigenvalue problem involving the metric components and the matrix $diag$, the product of which must have no negative eigenvalues in order to yield a real symmetric square root that is a function of the metric. Thus even formal general covariance requires reconsideration; the atlas of admissible coordinate charts should be sensitive to the types and \emph{values} of the fields involved. Apart from coordinate order and the usual spinorial two-valuedness, Ogievetsky-Polubarinov spinors form, with the metric, a nonlinear geometric object, for which important results on Lie and covariant differentiation are recalled. Such spinors avoid a spurious absolute object in the Anderson-Friedman analysis of substantive general covariance. They also permit the gauge-invariant localization of the infinite-component gravitational energy in General Relativity. Density-weighted spinors exploit the conformal invariance of the massless Dirac equation to show that the volume element is absent. Thus instead of an arbitrary nonsingular matrix with 16 components, 6 of which are gauged away by a new local $O$ gauge group and one of which is irrelevant due to conformal covariance, one can, and presumably should, use density-weighted Ogievetsky-Polubarinov spinors coupled to the 9-component symmetric square root of the part of the metric that fixes null cones. Thus $\frac{7}{16}$ of the orthonormal basis is eliminated as surplus structure. Greater unity between spinors and tensors and the like is achieved, such as regarding conservation laws. Regarding the conventionality of simultaneity, an unusually wide range of $\epsilon$ values is admissible, but some extreme values are inadmissible. Standard simultaneity uniquely makes the spinor transformation law linear and independent of the metric, because transformations among the standard Cartesian coordinate systems fall within the conformal group, for which the spinor transformation law is linear. The surprising mildness of the restrictions on coordinate order as applied to the Schwarzschild solution is exhibited. (shrink)
Space-Time Constructivism Vs. Modal Provincialism: Or, How Special Relativistic Theories Needn't Show Minkowski Chronogeometry.J. Brian Pitts - 2017 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 67:191-198.details
Already in 1835 Lobachevski entertained the possibility of multiple geometries of the same type playing a role. This idea of rival geometries has reappeared from time to time but had yet to become a key idea in space-time philosophy prior to Brown's _Physical Relativity_. Such ideas are emphasized towards the end of Brown's book, which I suggest as the interpretive key. A crucial difference between Brown's constructivist approach to space-time theory and orthodox "space-time realism" pertains to modal scope. Constructivism takes (...) a broad modal scope in applying to all local classical field theories---modal cosmopolitanism, one might say, including theories with multiple geometries. By contrast the orthodox view is modally provincial in assuming that there exists a _unique_ geometry, as the familiar theories have. These theories serve as the "canon" for the orthodox view. Their historical roles also suggest a Whiggish story of inevitable progress. Physics literature after c. 1920 is relevant to orthodoxy primarily as commentary on the canon, which closed in the 1910s. The orthodox view explains the spatio-temporal behavior of matter in terms of the manifestation of the real geometry of space-time, an explanation works fairly well within the canon. The orthodox view, Whiggish history, and the canon have a symbiotic relationship. If one happens to philosophize about a theory outside the canon, space-time realism sheds little light on the spatio-temporal behavior of matter. Worse, it gives the _wrong_ answer when applied to an example arguably _within_ the canon, a sector of Special Relativity, namely, _massive_ scalar gravity with universal coupling. Which is the true geometry---the flat metric from the Poincare' symmetry group, the conformally flat metric exhibited by material rods and clocks, or both---or is the question faulty? How does space-time realism explain the fact that all matter fields see the same curved geometry, when so many ways to mix and match exist? Constructivist attention to dynamical details is vindicated; geometrical shortcuts can disappoint. The more exhaustive exploration of relativistic field theories in particle physics, especially massive theories, is a largely untapped resource for space-time philosophy. (shrink)
Why the Big Bang Singularity Does Not Help the Kal M Cosmological Argument for Theism.J. Brian Pitts - 2008 - British Journal for the Philosophy of Science 59 (4):675-708.details
The cosmic singularity provides negligible evidence for creation in the finite past, and hence theism. A physical theory might have no metric or multiple metrics, so a 'beginning' must involve a first moment, not just finite age. Whether one dismisses singularities or takes them seriously, physics licenses no first moment. The analogy between the Big Bang and stellar gravitational collapse indicates that a Creator is required in the first case only if a Destroyer is needed in the second. The need (...) for and progress in quantum gravity and the underdetermination of theories by data make it difficult to take singularities seriously. The singularity exemplifies the sort of gap that is likely to be closed by scientific progress, obviating special divine action. The apparent irrelevance of cardinality to practices of counting infinite sets in classical field theory and Fourier analysis is noted. Introduction The Doctrine of Creation and Its Warrant Cardinality and Sizes of Infinity Modern Cosmology and Creation Tolerance or Intolerance toward Singularities? Leibniz against Incompetent Watchmaker? Induction from Earlier Theories' Breakdown? Stellar Collapse Implies Theistic Destroyer Stacking the Deck for GTR Quantum Gravity Tends to Resolve Singularities Vicious God-of-the-Gaps Character Fluctuating or Inaccessible Warrant Big Bang Cosmology Not Especially Congenial to Faith CiteULike Connotea Del.icio.us What's this? (shrink)
Philosophy of Cosmology in Philosophy of Physical Science
General Relativity, Mental Causation, and Energy Conservation.J. Brian Pitts - forthcoming - Erkenntnis:1-43.details
The conservation of energy and momentum have been viewed as undermining Cartesian mental causation since the 1690s. Modern discussions of the topic tend to use mid-nineteenth century physics, neglecting both locality and Noether's theorem and its converse. The relevance of General Relativity has rarely been considered. But a few authors have proposed that the non-localizability of gravitational energy and consequent lack of physically meaningful local conservation laws answers the conservation objection to mental causation: conservation already fails in GR, so there (...) is nothing for minds to violate. This paper is motivated by two ideas. First, one might take seriously the fact that GR formally has an infinity of rigid symmetries of the action and hence, by Noether's first theorem, an infinity of conserved energies-momenta. Second, Sean Carroll has asked how one should modify the Dirac–Maxwell–Einstein equations to describe mental causation. This paper uses the generalized Bianchi identities to show that General Relativity tends to exclude, not facilitate, such Cartesian mental causation. In the simplest case, Cartesian mental influence must be spatio-temporally constant, and hence 0. The difficulty may diminish for more complicated models. Its persuasiveness is also affected by larger world-view considerations. The new general relativistic objection provides some support for realism about gravitational energy-momentum in GR. Such realism also might help to answer an objection to theories of causation involving conserved quantities, because energies-momenta would be conserved even in GR. (shrink)
Equivalent Theories Redefine Hamiltonian Observables to Exhibit Change in General Relativity.J. Brian Pitts - unknowndetails
Change and local spatial variation are missing in canonical General Relativity's observables as usually defined, an aspect of the problem of time. Definitions can be tested using equivalent formulations of a theory, non-gauge and gauge, because they must have equivalent observables and everything is observable in the non-gauge formulation. Taking an observable from the non-gauge formulation and finding the equivalent in the gauge formulation, one requires that the equivalent be an observable, thus constraining definitions. For massive photons, the de Broglie-Proca (...) non-gauge formulation observable A_{\mu} is equivalent to the Stueckelberg-Utiyama gauge formulation quantity A_{\mu} + \partial_{\mu} \phi, which must therefore be an observable. To achieve that result, observables must have 0 Poisson bracket not with each first-class constraint, but with the Rosenfeld-Anderson-Bergmann-Castellani gauge generator G, a tuned sum of first-class constraints, in accord with the Pons-Salisbury-Sundermeyer definition of observables. The definition for external gauge symmetries can be tested using massive gravity, where one can install gauge freedom by parametrization with clock fields X^A. The non-gauge observable g^{\mu\nu} has the gauge equivalent X^A,_{\mu} g^{\mu\nu} X^B,_{\nu}. The Poisson bracket of X^A,_{\mu} g^{\mu\nu} X^B,_{\nu} with G turns out to be not 0 but a Lie derivative. This non-zero Poisson bracket refines and systematizes Kuchař's proposal to relax the 0 Poisson bracket condition with the Hamiltonian constraint. Thus observables need covariance, not invariance, in relation to external gauge symmetries. The Lagrangian and Hamiltonian for massive gravity are those of General Relativity + \Lambda + 4 scalars, so the same definition of observables applies to General Relativity. Local fields such as g_{\mu\nu} are observables. Thus observables change. Requiring equivalent observables for equivalent theories also recovers Hamiltonian-Lagrangian equivalence. (shrink)
Null Cones and Einstein's Equations in Minkowski Spacetime.J. Brian Pitts & W. C. Schieve - 2004 - Foundations of Physics 34 (2):211-238.details
If Einstein's equations are to describe a field theory of gravity in Minkowski spacetime, then causality requires that the effective curved metric must respect the flat background metric's null cone. The kinematical problem is solved using a generalized eigenvector formalism based on the Segré classification of symmetric rank 2 tensors with respect to a Lorentzian metric. Securing the correct relationship between the two null cones dynamically plausibly is achieved using the naive gauge freedom. New variables tied to the generalized eigenvector (...) formalism reduce the configuration space to the causality-respecting part. In this smaller space, gauge transformations do not form a group, but only a groupoid. The flat metric removes the difficulty of defining equal-time commutation relations in quantum gravity and guarantees global hyperbolicity. (shrink)
Equivalent Theories and Changing Hamiltonian Observables in General Relativity.J. Brian Pitts - 2018 - Foundations of Physics 48 (5):579-590.details
Change and local spatial variation are missing in Hamiltonian general relativity according to the most common definition of observables as having 0 Poisson bracket with all first-class constraints. But other definitions of observables have been proposed. In pursuit of Hamiltonian–Lagrangian equivalence, Pons, Salisbury and Sundermeyer use the Anderson–Bergmann–Castellani gauge generator G, a tuned sum of first-class constraints. Kuchař waived the 0 Poisson bracket condition for the Hamiltonian constraint to achieve changing observables. A systematic combination of the two reforms might use (...) the gauge generator but permit non-zero Lie derivative Poisson brackets for the external gauge symmetry of General Relativity. Fortunately one can test definitions of observables by calculation using two formulations of a theory, one without gauge freedom and one with gauge freedom. The formulations, being empirically equivalent, must have equivalent observables. For de Broglie-Proca non-gauge massive electromagnetism, all constraints are second-class, so everything is observable. Demanding equivalent observables from gauge Stueckelberg–Utiyama electromagnetism, one finds that the usual definition fails while the Pons–Salisbury–Sundermeyer definition with G succeeds. This definition does not readily yield change in GR, however. Should GR's external gauge freedom of general relativity share with internal gauge symmetries the 0 Poisson bracket, or is covariance sufficient? A graviton mass breaks the gauge symmetry, but it can be restored by parametrization with clock fields. By requiring equivalent observables, one can test whether observables should have 0 or the Lie derivative as the Poisson bracket with the gauge generator G. The latter definition is vindicated by calculation. While this conclusion has been reported previously, here the calculation is given in some detail. (shrink)
Empirical Equivalence, Artificial Gauge Freedom and a Generalized Kretschmann Objection.J. Brian Pitts - unknowndetails
Einstein considered general covariance to characterize the novelty of his General Theory of Relativity (GTR), but Kretschmann thought it merely a formal feature that any theory could have. The claim that GTR is ``already parametrized'' suggests analyzing substantive general covariance as formal general covariance achieved without hiding preferred coordinates as scalar ``clock fields,'' much as Einstein construed general covariance as the lack of preferred coordinates. Physicists often install gauge symmetries artificially with additional fields, as in the transition from Proca's to (...) Stueckelberg's electromagnetism. Some post-positivist philosophers, due to realist sympathies, are committed to judging Stueckelberg's electromagnetism distinct from and inferior to Proca's. By contrast, physicists identify them, the differences being gauge-dependent and hence unreal. It is often useful to install gauge freedom in theories with broken gauge symmetries (second-class constraints) using a modified Batalin-Fradkin-Tyutin (BFT) procedure. Massive GTR, for which parametrization and a Lagrangian BFT-like procedure appear to coincide, mimics GTR's general covariance apart from telltale clock fields. A generalized procedure for installing artificial gauge freedom subsumes parametrization and BFT, while being more Lagrangian-friendly than BFT, leaving any primary constraints unchanged and using a non-BFT boundary condition. Artificial gauge freedom licenses a generalized Kretschmann objection. However, features of paradigm cases of artificial gauge freedom might help to demonstrate a principled distinction between substantive and merely formal gauge symmetry. (shrink)
Progress and Gravity: Overcoming Divisions Between General Relativity and Particle Physics and Between Physics and HPS.J. Brian Pitts - 2017 - In Khalil Chamcham, Joseph Silk, John D. Barrow & Simon Saunders (eds.), The Philosophy of Cosmology. Cambridge University Press. pp. 263-282.details
Reflective equilibrium between physics and philosophy, and between GR and particle physics, is fruitful and rational. I consider the virtues of simplicity, conservatism, and conceptual coherence, along with perturbative expansions. There are too many theories to consider. Simplicity supplies initial guidance, after which evidence increasingly dominates. One should start with scalar gravity; evidence required spin 2. Good beliefs are scarce, so don't change without reason. But does conservatism prevent conceptual innovation? No: considering all serious possibilities could lead to Einstein's equations. (...) GR is surprisingly intelligible. Energy localization makes sense if one believes Noether mathematics: an infinity of symmetries shouldn't produce just one energy. Hamiltonian change results from Lagrangian-equivalence. Causality poses conceptual questions. For GR, what are canonical 'equal-time' commutators? For massive spin 2, background causality exists but is violated. Both might be cured by engineering a background null cone respected by a gauge groupoid. Perturbative expansions can enlighten. They diagnose Einstein's 1917 'mass'-Lambda analogy. Ogievetsky-Polubarinov invented an infinity of massive spin 2 gravities---including ghost-free de Rham-Gabadadze-Tolley theories!---perturbatively, and achieved the impossible : spinors in coordinates. (shrink)
Underconsideration in Space-Time and Particle Physics.J. Brian Pitts - unknowndetails
The idea that a serious threat to scientific realism comes from unconceived alternatives has been proposed by van Fraassen, Sklar, Stanford and Wray among others. Peter Lipton's critique of this threat from underconsideration is examined briefly in terms of its logic and its applicability to the case of space-time and particle physics. The example of space-time and particle physics indicates a generic heuristic for quantitative sciences for constructing potentially serious cases of underdetermination, involving one-parameter family of rivals T_m that work (...) as a team rather than as a single rival against default theory T_0. In important examples this new parameter has a physical meaning and makes a crucial _conceptual_ difference, shrinking the symmetry group and in some case putting gauge freedom, formal indeterminism vs. determinism, the presence of the hole argument, etc., at risk. Methodologies akin to eliminative induction or tempered subjective Bayesianism are more demonstrably reliable than the custom of attending only to "our best theory": they can lead either to a serious rivalry or to improved arguments for the favorite theory. The example of General Relativity vs. massive spin 2 gravity, a recent topic in the physics literature, is discussed. Arguably the General Relativity and philosophy literatures have ignored the most serious rival to General Relativity. (shrink)
Irrelevant Conjunction and the Ratio Measure or Historical Skepticism.J. Brian Pitts - 2013 - Synthese 190 (12):2117-2139.details
It is widely believed that one should not become more confident that all swans are white and all lions are brave simply by observing white swans. Irrelevant conjunction or "tacking" of a theory onto another is often thought problematic for Bayesianism, especially given the ratio measure of confirmation considered here. It is recalled that the irrelevant conjunct is not confirmed at all. Using the ratio measure, the irrelevant conjunction is confirmed to the same degree as the relevant conjunct, which, it (...) is argued, is ideal: the irrelevant conjunct is irrelevant. Because the past's really having been as it now appears to have been is an irrelevant conjunct, present evidence confirms theories about past events only insofar as irrelevant conjunctions are confirmed. Hence the ideal of not confirming irrelevant conjunctions would imply that historical claims are not confirmed. Confirmation measures partially realizing that ideal make the confirmation of historical claims by present evidence depend strongly on the (presumably subjective) degree of belief in the irrelevant conjunct. The unusually good behavior of the ratio measure has a bearing on the problem of measure sensitivity. For non-statistical hypotheses, Bayes' theorem yields a fractional linear transformation in the prior probability, not a linear rescaling, so even the ratio measure arguably does not aptly measure confirmation in such cases. (shrink)
Bayesian Reasoning, Misc in Philosophy of Probability
Induction in General Philosophy of Science
Some Thoughts on Relativity and the Flow of Time: Einstein's Equations Given Absolute Simultaneity.J. Brian Pitts - 2004 - Chronos 6.details
The A-theory of time has intuitive and metaphysical appeal, but suffers from tension, if not inconsistency, with the special and general theories of relativity (STR and GTR). The A-theory requires a notion of global simultaneity invariant under the symmetries of the world's laws, those ostensible transformations of the state of the world that in fact leave the world as it was before. Relativistic physics, if read in a realistic sense, denies that there exists any notion of global simultaneity that is (...) invariant under the symmetries of the world's laws. If physics is at least a decent guide to metaphysics--as sympathies for scientific realism would suggest--then relativistic physics supports the B-theory. If there were a physically natural way to modify the symmetries of the physical laws so as to remove those that are repugnant to the A-theory, while retaining empirical adequacy, then such an altered physics might be attractive to the A-theorist and would weaken the support given by relativity to the B-theory. I exhibit a way to do so here, displaying a Lagrangian density explicitly containing distant simultaneity, yet implying Einstein's field equations. The modification involves a change in the nature of the lapse function and makes use of the Dirac-Bergmann formalism of constrained dynamics, which recently has been discussed much by John Earman. Here this formalism is adapted slightly to permit both local and global generalized coordinates. A classification of senses in which time might be absolute or not is made along the way. Some suggestions for extending the work by finding a first principles motivation are made. An appendix outlines an argument why many local presents are insufficient and a global present is attractive, while two more appendices review the Dirac-Bergmann apparatus for GTR and then apply it to the theory at hand. (shrink)
A-Theories of Time in Metaphysics
B-Theories of Time in Metaphysics
Nonsingularity of Flat Robertson–Walker Models in the Special Relativistic Approach to Einstein's Equations.J. Brian Pitts & W. C. Schieve - 2003 - Foundations of Physics 33 (9):1315-1321.details
Recently the neglected issue of the causal structure in the flat space-time approach to Einstein's theory of gravity has been substantially resolved. Consistency requires that the flat metric's null cone be respected by the null cone of the effective curved metric. While consistency is not automatic, thoughtful use of the naive gauge freedom resolves the problem. After briefly recapitulating how consistent causality is achieved, we consider the flat Robertson–Walker Big Bang model. The Big Bang singularity in the spatially flat Robertson–Walker (...) cosmological model is banished to past infinity in Minkowski space-time. A modified notion of singularity is proposed to fit the special relativistic approach, so that the Big Bang becomes nonsingular. (shrink)
Special Relativity in Philosophy of Physical Science
Time and Fermions: General Covariance Vs. Ockham's Razor for Spinors.J. Brian Pitts - unknowndetails
It is a commonplace in the foundations of physics, attributed to Kretschmann, that any local physical theory can be represented using arbitrary coordinates, simply by using tensor calculus. On the other hand, the physics and mathematics literature often claims that spinors \emph{as such} cannot be represented in coordinates in a curved space-time. These commonplaces are inconsistent. What general covariance means for theories with fermions is thus unclear. In fact both commonplaces are wrong. Though it is not widely known, Ogievetsky and (...) Polubarinov constructed spinors in coordinates in 1965, enhancing the unity of physics and helping to spawn particle physicists' concept of nonlinear group representations. Roughly and locally, OP spinors resemble the orthonormal basis or tetrad formalism in the symmetric gauge, but they are conceptually self-sufficient and more economical. The typical tetrad formalism is thus de-Ockhamized, with six extra field components and six compensating gauge symmetries to cancel them out. As developed nonperturbatively by Bilyalov, OP spinors admit any coordinates at a point, but `time' must be listed first; `time' is defined in terms of an eigenvalue problem involving the metric components and the matrix $diag$, the product of which must have no negative eigenvalues. Thus even formal general covariance requires reconsideration; the atlas of admissible coordinate charts should be sensitive to the types and \emph{values} of the fields involved. Apart from coordinate order and the usual spinorial two-valuedness, Ogievetsky-Polubarinov spinors form, with the metric, a nonlinear geometric object. Important results on Lie and covariant differentiation are recalled and applied. The rather mild consequences of the coordinate order restriction are explored in two examples: the question of the conventionality of simultaneity in Special Relativity, and the Schwarzschild solution in General Relativity. (shrink)
Null Cones in Lorentz-Covariant General Relativity.J. Brian Pitts & W. C. Schieve - unknowndetails
The oft-neglected issue of the causal structure in the flat spacetime approach to Einstein's theory of gravity is considered. Consistency requires that the flat metric's null cone be respected, but this does not automatically happen. After reviewing the history of this problem, we introduce a generalized eigenvector formalism to give a kinematic description of the relation between the two null cones, based on the Segre' classification of symmetric rank 2 tensors with respect to a Lorentzian metric. Then we propose a (...) method to enforce special relativistic causality by using the gauge freedom to restrict the configuration space suitably. A set of new variables just covers this smaller configuration space and respects the flat metric's null cone automatically. Respecting the flat metric's null cone ensures that the spacetime is globally hyperbolic, indicating that the Hawking black hole information loss paradox does not arise in the special relativistic approach to Einstein's theory. (shrink)
The Anderson-Friedman Absolute Objects Program: Several Successes, One Difficulty.J. Brian Pitts - unknowndetails
The Anderson-Friedman absolute objects project is reviewed. The Jones-Geroch dust 4-velocity counterexample is resolved by eliminating irrelevant structure. Torretti's example involving constant curvature spaces is shown to have an absolute object on Anderson's analysis. The previously neglected threat of an absolute object from an orthonormal tetrad used for coupling spinors to gravity appears resolvable by eliminating irrelevant fields and using a modified spinor formalism. However, given Anderson's definition, GTR itself has an absolute object (as Robert Geroch has observed recently): a (...) change of variables to a conformal metric density and a scalar density shows that the latter is absolute. (shrink)
On the Form of Parametrized Gravitation in Flat Spacetime.J. Brian Pitts & W. C. Schieve - 1999 - Foundations of Physics 29 (12):1977-1985.details
In a framework describing manifestly covariant relativistic evolution using a scalar time τ, consistency demands that τ-dependent fields be used. In recent work by the authors, general features of a classical parametrized theory of gravitation, paralleling general relativity where possible, were outlined. The existence of a preferred "time" coordinate τ changes the theory significantly. In particular, the Hamiltonian constraint for τ is removed From the Euler-Lagrange equations. Instead of the 5-dimensional stress-energy tensor, a tensor comprised of 4-momentum density mid flux (...) density only serves as the source. Building on that foundation, in this paper we develop a linear approximate theory of parametrized gravitation in the spirit of the flat spacetime approach to general relativity. Using a modified form of Kraichnan's flat spacetime derivation of general relativity, we extend the linear theory to a family of nonlinear theories in which the flat metric and the gravitational field coalesce into a single effective curved metric. (shrink)
On Parametrized General Relativity.J. Brian Pitts & W. C. Schieve - 1998 - Foundations of Physics 28 (9):1417-1424.details
A physical framework has been proposed which describes manifestly covariant relativistic evolution using a scalar time τ. Studies in electromagnetism, measurement, and the nature of time have demonstrated that in this framework, electromagnetism must be formulated in terms of τ-dependent fields. Such an electromagnetic theory has been developed. Gravitation must also use of τ-dependent fields, but many references do not take the metric's dependence on τ fully into account. Others differ markedly from general relativity in their formulation. In contrast, this (...) paper outlines steps towards a τ-dependent classical intrinsic formulation of gravitation, patterned after general relativity, which we call parametrized general relativity (PGR). Given the existence of a preferred foliation, the Hamiltonian constraint is removed. We find that some nonmetricity in the connection is allowed, unlike in general relativity. Conditions on the allowable nonmetricity are found. Consideration of the initial value problem confirms that the metric signature should normally be O(3, 2) rather than O(4, 1). Following the lead of earlier works, we argue that concatenation (integration over τ) is unnecessary for relating parametrized physics to experience, and propose an alternative to it. Finally, we compare and contrast PGR with other relevant gravitational theories. (shrink)
Synopsis and Discussion. Workshop: Underdetermination in Science 21-22 March, 2009. Center for Philosophy of Science.Greg Frost-Arnold, J. Brian Pitts, John Norton, John Manchak, Dana Tulodziecki, P. D. Magnus, David Harker & Kyle Stanford - manuscriptdetails
This document collects discussion and commentary on issues raised in the workshop by its participants. Contributors are: Greg Frost-Arnold, David Harker, P. D. Magnus, John Manchak, John D. Norton, J. Brian Pitts, Kyle Stanford, Dana Tulodziecki.
Absolute Objects, Counterexamples and General Covariance.J. Brian Pitts - unknowndetails
The Anderson-Friedman absolute objects program has been a favorite analysis of the substantive general covariance that supposedly characterizes Einstein's General Theory of Relativity (GTR). Absolute objects are the same locally in all models (modulo gauge freedom). Substantive general covariance is the lack of absolute objects. Several counterexamples have been proposed, however, including the Jones-Geroch dust and Torretti constant curvature spaces counterexamples. The Jones-Geroch dust case, ostensibly a false positive, is resolved by noting that holes in the dust in some models (...) ensure that no physically relevant nonvanishing timelike vector field exists there, so no absolute object exists. The Torretti constant curvature spaces case, allegedly a false negative, is resolved by testing an irreducible piece of the metric, the conformal metric density of weight -2/3, for absoluteness; this geometric object is absolute. A new counterexample is proposed involving the orthonormal tetrad said to be necessary to couple spinors to a curved metric. The threat of finding an absolute object in GTR + spinors is overcome by the use of an alternative spinor formalism that takes a symmetric square root of the metric (with the help of the matrix diag(-1,1,1,1)), eliminating 6 of the 16 tetrad components as irrelevant. The importance of eliminating irrelevant structures, as Anderson emphasized, is clear. The importance of the choice of physical fields is also evident. A new counterexample due to Robert Geroch and Domenico Giulini, however, finds an absolute object in vacuum GTR itself, namely the scalar density $g$ given by the metric components' determinant. Thus either the definition of absoluteness or its use to analyze GTR's substantive general covariance is flawed. Anderson's belief that all absolute objects are nonvariational (that is, not varied in a suitable action principle) and vice versa is also falsified by the Geroch-Giulini counterexample. However, it remains plausible that all nonvariational fields are absolute, so adding nonvariationality as a necessary condition for absoluteness, as Hiskes once suggested, would likely leave no useful work to the Anderson-Friedman condition of sameness in all models. Simply having only variational fields in an action principle (suitably free of irrelevant fields) might be a satisfactory analysis of substantive general covariance, if one exists. This proposal also resembles the suggestion that GTR is "already parameterized," if one decides to parameterize theories by defining the nonvariational fields in terms of preferred coordinates called clock fields. More questions need to be addressed. Which fields should be tested for absoluteness: only primitive fields (which ones?), or all or some (which?) of their concomitants also? Geroch observes that some kinds of geometric objects, such as tangent vectors, scalar densities, and tangent vector densities of non-unit weight, satisfy the condition of sameness in all models if they merely fail to vanish. If these "susceptible" geometric objects can hardly help being absolute, to what degree are they, or the theories harboring them, responsible for this absoluteness? The answer to this question helps to determine the significance of the Geroch-Giulini counterexample. (shrink)
Change in Hamiltonian General Relativity with Spinors.J. Brian Pitts - 2021 - Foundations of Physics 51 (6):1-30.details
In General Relativity in Hamiltonian form, change has seemed to be missing, defined only asymptotically, or otherwise obscured at best, because the Hamiltonian is a sum of first-class constraints and a boundary term and thus supposedly generates gauge transformations. By construing change as essential time dependence, one can find change locally in vacuum GR in the Hamiltonian formulation just where it should be. But what if spinors are present? This paper is motivated by the tendency in space-time philosophy tends to (...) slight fermionic/spinorial matter, the tendency in Hamiltonian GR to misplace changes of time coordinate, and the tendency in treatments of the Einstein-Dirac equation to include a gratuitous local Lorentz gauge symmetry along with the physically significant coordinate freedom. Spatial dependence is dropped in most of the paper, both restricting the physical situation and largely fixing the spatial coordinates. In the interest of including all and only the coordinate freedom, the Einstein-Dirac equation is investigated using the Schwinger time gauge and Kibble-Deser symmetric triad condition are employed as a \ version of the DeWitt-Ogievetsky-Polubarinov nonlinear group realization formalism that dispenses with a tetrad and local Lorentz gauge freedom. Change is the lack of a time-like stronger-than-Killing field for which the Lie derivative of the metric-spinor complex vanishes. An appropriate \-friendly form of the Rosenfeld-Anderson-Bergmann-Castellani gauge generator G, a tuned sum of first class-constraints, is shown to change the canonical Lagrangian by a total derivative, implying the preservation of Hamilton's equations. Given the essential presence of second-class constraints with spinors and their lack of resemblance to a gauge theory, it is useful to have an explicit physically interesting example. This gauge generator implements changes of time coordinate for solutions of the equations of motion, showing that the gauge generator makes sense even with spinors. (shrink)
Einstein and Religion.J. Brian Pitts - 2003 - Philosophia Christi 5 (2):655-659.details
God and the Nature of Time.J. Brian Pitts - 2007 - Philosophia Christi 9 (1):231-235.details
The Relevance of Irrelevance: Absolute Objects and the Jones-Geroch Dust Velocity Counterexample, with a Note on Spinors.J. Brian Pitts - unknowndetails
James L. Anderson analyzed the conceptual novelty of Einstein's theory of gravity as its lack of ``absolute objects.'' Michael Friedman's related concept of absolute objects has been criticized by Roger Jones and Robert Geroch for implausibly admitting as absolute the timelike 4-velocity field of dust in cosmological models in Einstein's theory. Using Nathan Rosen's action principle, I complete Anna Maidens's argument that the Jones-Geroch problem is not solved by requiring that absolute objects not be varied. Recalling Anderson's proscription of (globally) (...) ``irrelevant'' variables that do no work (anywhere in any model), I generalize that proscription to locally irrelevant variables that do no work in some places in some models. This move vindicates Friedman's intuitions and removes the Jones-Geroch counterexample: some regions of some models of gravity with dust are dust-free, and there is no good reason to have a timelike dust 4-velocity vector there. Eliminating the irrelevant timelike vctors keeps the dust 4-velocity from counting as absolute by spoiling its neighborhood-by-neighborhood diffeomorphic equivalence to (1,0,0,0). A more fundamental Gerochian timelike vector field presents itself in gravity with spinors in the standard orthonormal tetrad formalism, though eliminating irrelevant fields might solve this problem as well. (shrink)
What Are Observables in Hamiltonian Theories? Testing Definitions with Empirical Equivalence.J. Brian Pitts - unknowndetails
Change seems missing in Hamiltonian General Relativity's observables. The typical definition takes observables to have $0$ Poisson bracket with \emph{each} first-class constraint. Another definition aims to recover Lagrangian-equivalence: observables have $0$ Poisson bracket with the gauge generator $G$, a \emph{tuned sum} of first-class constraints. Empirically equivalent theories have equivalent observables. That platitude provides a test of definitions using de Broglie's massive electromagnetism. The non-gauge ``Proca'' formulation has no first-class constraints, so everything is observable. The gauge ``Stueckelberg'' formulation has first-class constraints, (...) so observables vary with the definition. Which satisfies the platitude? The team definition does; the individual definition does not. Subsequent work using the gravitational analog has shown that observables have not a 0 Poisson bracket, but a Lie derivative for the Poisson bracket with the gauge generator $G$. The same should hold for General Relativity, so observables change locally and correspond to 4-dimensional tensor calculus. Thus requiring equivalent observables for empirically equivalent formulations helps to address the problem of time. (shrink)


Daisy came into my life as result of a staying-over. She was 2 years old then. We remained together for 15 years, so the staying-over took a little while longer than expected.
She was very ladylike. Always softspoken, sweet and gentle in behaviour.
She has gone through quite a bit with me. Five houses, two women, you name it.
She never had any trouble adjusting. After yet another move, she would look around the new home - everything pretty much still in boxes - and she just accepted it, as long as I was there with her.
Sorry to have put you through all this, dear Daisy.
I'll see you at the Rainbow Bridge.


This ride has been established by the Matakana Cycle Trail Trust and takes you from Matakana to Omaha and Point Wells. The ride is recommended for more confident cyclists as it includes sections on gravel roads.
A mix of off-road shared paths, cycle lanes and quiet roads with 50km – 70km hour speed limits.
Caution is required if crossing Matakana bridge from the township.
The Matakana trails ride has fantastic views and many points of interest including café's, wineries and roadside stalls offering fresh produce. The track goes through farmland as well as bush and quiet communities.
Along the way 8 ceramic sculptural markers feature stylised maps of the area's topography. These indicate selected features like lakes, roads and buildings encountered along the route. Some are paired to hold macrocarpa slab bench seats that offer a place to rest and contemplate the landscape.
The path itself is predominantly gravel, and there are sections of gravel road so road bikes are not recommended. There is one steep section up and down to Takatu Road.
The Matakana Cycle Trail Trust has worked extensively with community members, authorities and private land owners to develop these cycling and walking trails.
Swimming spot at high tide near Omaha.
Ride on the left and pass on the right.


The FWC recently provided employers with an unintentional lesson in how not to handle sick leave – what can HR learn from this?
The controversial resignation of FWC vice-president Michael Lawler who took sick leave at full pay for more than nine months while helping his partner fight a Federal Court ruling serves as a key example of how not to handle long-term sick leave, says McDonald Murholme managing direct Alan McDonald.
"The resignation of vice-president Lawler brings to a conclusion reputational damage to the Fair Work Commission," McDonald told HC Online.
"The Commission has been criticised for paying sick leave to the vice-president while he appears to work to assist his partner Kathy Jackson in the Federal Court," he says.
McDonald points out that a sick or injured employee must not work, even in a voluntary capacity, for someone else while claiming sick leave from their employer.
Lawler continued to collect his $430,000 salary during his sick leave, while helping his partner, former Health Services Union official Kathy Jackson, fight a Federal Court ruling that she misappropriated $1.4 million of union funds.
FWC president Iain Ross told a Senate hearing in October that he had approved 215 days of sick leave for Lawler on the basis that he was medically unfit to perform his duties, the ABC reported.
"He did not seek and I did not approve leave for the purpose of assisting his partner in legal proceedings," Ross told the hearing.
But because Mr Lawler was a statutory office holder, the FWC was powerless to sack him, as a vote by both houses of Parliament would have been required to remove him from his position.
A week ago, former Federal Court Judge Peter Heeley received an independent report on Lawler's conduct while at the FWC.
McDonald welcomed Lawler's resignation and says while the Government was too slow to remove him from his position, should make public the findings of the Heeley report.
"It is not surprising that there would be a lot of public interest in this matter because the Fair Work Commission should comply with excepted standards," he says.
McDonald said that the report should have been published in the interests of transparency and to help avoid such a mistake in the future.
He said the issue was very sensitive for the FWC president, since Lawler's payments were based on a very high salary and using public money.
"The president felt constrained to act because Lawler was appointed by the Executive Council, not him," McDonald explains.
As there appeared to be a very poor relationship between the vice-president and the president, the ability of the president to quietly influence Lawler's conduct failed, Murholme says.
"So it was a combination of factors unlikely to be repeated which caused this terrible example of how not to deal with a long term sick leave situation to occur," he told HC Online.
He says the good news is that a replacement for Lawler's role should not be required, because there are already three vice-presidents in the FWC where traditionally there have only been two.
"Around $1 million a year can be saved by not reappointing another vice-president," McDonald says.
Lawler resigned from his position of as a presidential member of the Fair Work Commission on March 03, 2016.


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An Electric Feel – Jaguar iPace 400PS HSE
Before I go off and talk about the new Jaguar iPace, I want to make it clear that this isn't coming from a die-hard combustion engine fanatic -it also isn't going to be some preachy piece about how this is the future and we all need to get on board or we will definitely die in a 500-degree snowstorm. It is quite simply a review of a car that I lived with for a week, just like any other car.
When I found out I was going to be testing the new fully electric offering from Jaguar, I didn't really know how I felt. I've driven electric cars in the past and some of them were terrible, and some were alright, but none of them have wowed me. This isn't because they were electric, though, it was more because the cars just left me feeling a little numb or underwhelmed. Even the "all-singing, all-dancing" Tesla Model X felt more like a new phone than a car. It was great to play with but the drive offered little to the soul. So, as a big lover of Jaguar, am I going to be pleasantly surprised or left feeling a bit empty and disappointed?
The new iPace was delivered on a Friday to my office which is always exciting but also a bit frustrating as the first time I would properly get to drive the car would be on the rather mundane 10-mile drive home at the end of the day. Fortunately, we had made plans to drive into the City (London) the next day and stay at a hotel that had assured me they had electric charging points. My first impression of the car as it rolled off the back of the truck was one of reserved excitement and optimism. Had Jaguar done it, had they made an electric car that actually felt like a car? As far as looks went, it was safe to say that the iPace was a handsome brute. That unmistakable open-mouthed grill and its sweeping roofline made it look undeniably Jaguar and the huge 22″ wheels gave it a sort of "Hot Wheels" toy car look as they filled the 4 corners of the body.
Inside, it's also exactly what you would expect from this marque. Vibrant but soft red leather and dark wood and all the fancy new tech that is slowly creeping its way into all the JLR cars. The only thing that wasn't present that I think should have been was the rotary gear selector, I know it makes sense and saves space to just have buttons for selecting drive, reverse, neutral and park, but it would have been nice to keep as it's a nice little quirk in so much of the range. On the flip-side, it did create some extra room for my phone which seems to get bigger and bigger every time I upgrade!
Like so many other new cars, screens are the most prominent features upfront. Everything is now powered through three screens on the dash. A nice wide binnacle, an infotainment touchscreen and the new lower touchscreen for all your convenience and comfort settings like climate control and heated seats. I didn't like it in the Range Rovers I've driven, but in the iPace it felt more relevant, although this might change as soon as the sun reappears and highlights all the finger smudges on all the displays. One other thing worth noting about the interior compared to the exterior is just how compact it feels. From the outside, the car is huge. It dwarfs all the hatchbacks in the office car park and felt nearly as wide as the Range Rover, but inside, it all feels much smaller. The black headlining and tinted glass roof probably played a part in this too by making the cabin feel darker. It wasn't bad, just not as airy and spacious as the exterior suggests.
Jaguar has also done a great job combating the legroom issue that has always bothered me about the Tesla Model S. Due to the floor being used to house the batteries, you essentially lose a good few inches of legroom and if you sit in the back, you tend to end up with your knees up by your ears and on a long drive, it really isn't a comfortable experience. In the iPace, however, the rear seat bases seem to be a bit more sloped back, lifting your legs a bit and giving you a hint of more space.
The main factor that has put me off electric cars in the past has been the way the lackluster drive has been overcompensated by gimmicks and pointless "easter eggs" – I get it, it's cool to have a fireplace option on the dash for a bit of fun, but if I'm parting with a sizeable amount of cash, I want to drive it every day and get the same special feel it gave me on day one, and I've just not had that yet. With the iPace it's already on to a good start as there don't seem to be any of these gimmicks. It's all very much the same as the other road cars JLR produces, which is what I want.
On the road there is definitely a difference, the main one being the obvious – the sound, or should I say the lack of it. It must be so difficult to design a car that is essentially silent as you need to find a way to reduce all the other exterior noises that are normally masked by a combustion engine. Road/tyre noise and wind noise are the two main contributors that come to mind. Fortunately for this car, the combination of double glazed windows and a fantastic Meridian sound system means it is wonderfully peaceful inside and you can crank up your favourite Opera and enjoy the tranquility. There's also some rather nice mood lighting that can be customised to your liking that gives night drives a rather zen-like feel.
This particular iPace is the 400PS HSE AWD, meaning "the one with all the bells and whistles" and a part of that is a 90kWh battery pack producing 400PS of power that will literally catapult you from 0-62mph in 4.5 seconds and provide a claimed range of up to 292 miles, but this really does need to be taken with a pinch of salt. Acceleration-wise, I've driven plenty of faster cars in my days but none of them has planted me back into my seat the way an EV does. The thrust is so instant that it's like a boot to the chest as you're pinned back, it's an incredible feeling that never gets old, no matter how detrimental that may be to your battery range! On the motorway the iPace behaves just as you would expect any Jaguar too, it's quiet, civilised and comfortable and cruises along with no drama at all. It's only really on those twisty roads where the differences between the EV and conventional ICE cars appear. Obviously, the car is heavy. the entire floor is batteries, but this creates a bit of a conflicting sensation for the driver – on the one side, there is a lot of weight to shift in the corners, so obviously it's never going to corner like a Caterham, but on the other side, there's a low centre of gravity and some pretty even weight distribution so you don't get extreme body roll like in a full-sized SUV, it sort of messes with your senses but also makes it a surprising amount of fun. The only real issue comes when it's time to stop. The braking is good, but there is an obvious amount of force to deal with.
All-in-all, Jaguar has done a great job here. They've done something no other manufacturer has been able to do in my opinion, and that is they have created an EV that feels like a car to drive. This, to me, is big, as it proves that the drivetrain isn't everything when it comes to making a car. I thought I would miss the grumble of a proper Jag V8 under the bonnet but they have done such a great job creating a typically luxury car inside that it didn't feel any different to a well kitted XF or even XJ. It says a lot that Jaguar didn't throw in loads of token EV toys and features and instead focused on making a very good car as, until the release of the Porsche Taycan, it is the only one that seems to have stayed true to its roots.
It's not all sunshine and happy faces though, there are still some issues that bug me. Admittedly, most of these issues can be remedied with better infrastructure and if the government really wants to ban the sale of ICE vehicles in 2035, they are seriously going to need to dip their hands in their pockets and make some drastic changes. I said earlier that I was going to drive the iPace to London for the weekend – a 140 mile round trip for us. Now, I know the car claims to return 292 miles to a charge and I am also aware that the more realistic average range is claimed to be 258 miles, but after doing the trip and driving in what I consider to be 100% normal driving conditions (light traffic, a bit of motorway and a bit of city) the overall average range was a worrying 180 miles. This was not remedied at the hotel either when it turned out there were no charging points, despite being told there were over the phone. Fortunately, we managed to do the journey there and back in one charge but when I got home there were only 20 miles of range left. I plugged the charger into my garage 3-pin socket and left it for 11 hours – this managed to charge the car up to 55% – claiming just over 120 miles.
Now, first off, if I owned an EV, I would have a proper charger installed that would solve the latter of the issues, but I'm fortunate to have a garage and have off-road parking, but what are the people who only have on-street parking going to do? Run extension cables across the pavement? The city I live in currently has 6 public charging stations. 6. Wow… The other thing that really winds me up, probably rather irrationally, is the battery saving "eco" mode in the car, designed to get the most out of your range. Basically, this switches off all the lovely electrical functions you paid extra to have in your car. Heated seats, climate control, heated steering wheel etc… Manufacturers need to be a lot more honest with their range claims and if you're speccing up all these lovely options, the average range needs to be representative of this. I do think there is a positive future for both EVs and, more specifically, the iPace, but there are still a lot of external factors that need to be addressed if the masses are expected to adapt and adopt. The issues aside, the Jaguar iPace really is a great car and, in my opinion, leagues ahead of Tesla when it comes to creating a proper car.
As always, a big thank you to Jaguar UK for the car – you can read more about the iPace and build your own on the online configurator HERE
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redpajama_set_name: RedPajamaCommonCrawl


Leading a bunch of liars?
The now changed and revamped Malawi Congress Party (MCP) has just been caught in a web of lies with the aim of either boosting their morale or sowing seeds of discrepancy in other parties and even both.
MCP, now an unashamed user of social media, has suddenly resorted to using a number of social media channels to either tout their candidate, Rev. Dr. Lazarous Chakwera, or make baseless and confusing assumptions as recent revelations have come to reveal.
Earlier this week, MCP made the nation believe that DPP strongman in the Northern region district of Nkhatabay, Symon Vuwa Kaunda, was contemplating ditching his party to join MCP. However, the former minister of information has distanced himself from such allegations and has labeled them malicious.
"I'm still with the DPP and my goal is to see to it that Peter Mutharika wins the next election," said Kaunda, an alleged accomplice in the alleged crime of treason that Mutharika is answering together with five others including Kaunda.
So far, through the same social networks, MCP has hinted that it not only was Kaunda who was praying to join them but also the current Minister of Information, Moses Kunkuyu, and current speaker of Parliament, Henry Chimunthu Banda.
With the current and strong denial of the MCP propaganda by Kaunda, however, it gets hard to believe if what the MCP has been alleging has any elements of truth to it or is simply an attempt at sowing seeds of confusion in other parties so that they get a better leverage.


Point Loma's make-you-drool cookie shop, The Cravory, is celebrating three years of sweet success.
In honor of their perfectly-baked birthday, they'll offer $1 cookies for all signature and February cookie flavors on Tuesday, Feb. 21. This deal is only available in the Point Loma store from 10 a.m. to 8 p.m.
The Cravory's success is largely due to the the two young entrepreneurs, Nate Ransom and Adam Koven, who co-founded the cookie concept in 2009. With daily updates to the menu, The Cravory has developed more than 3,500 unique cookie flavors and has grown the production to include monthly cookie box subscriptions.
Learn how to make cookies like The Cravory here.