14 found
Order:
  1. Bryan W. Roberts (2011). Group Structural Realism. British Journal for the Philosophy of Science 62 (1):47-69.
    We present a precise form of structural realism, called group structural realism , which identifies ‘structure’ in quantum theory with symmetry groups. However, working out the details of this view actually illuminates a major problem for structural realism; namely, a structure can itself have structure. This article argues that, once a precise characterization of structure is given, the ‘metaphysical hierarchy’ on which group structural realism rests is overly extravagant and ultimately unmotivated.
    Direct download (12 more)  
     
    Export citation  
     
    My bibliography   10 citations  
  2. Bryan W. Roberts (2015). Comment on Ashtekar: Generalization of Wigner׳s Principle. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 52:21-23.
    Ashtekar has illustrated that two of the available roads to testing for time asymmetry can be generalized beyond the structure of quantum theory, to much more general formulations of mechanics. The purpose of this note is to show that a third road to T-violation, which I have called "Wigner's Principle," can be generalized in this way as well.
    Direct download (7 more)  
     
    Export citation  
     
    My bibliography   2 citations  
  3.  26
    Bryan W. Roberts (2016). Three Myths About Time Reversal in Quantum Theory. Philosophy of Science.
    Many have suggested that the transformation standardly referred to as `time reversal' in quantum theory is not deserving of the name. I argue on the contrary that the standard definition is perfectly appropriate, and is indeed forced by basic considerations about the nature of time in the quantum formalism.
    Direct download (4 more)  
     
    Export citation  
     
    My bibliography  
  4.  82
    Bryan W. Roberts (2011). How Galileo Dropped the Ball and Fermat Picked It Up. Synthese 180 (3):337-356.
    This paper introduces a little-known episode in the history of physics, in which a mathematical proof by Pierre Fermat vindicated Galileo’s characterization of freefall. The first part of the paper reviews the historical context leading up to Fermat’s proof. The second part illustrates how a physical and a mathematical insight enabled Fermat’s result, and that a simple modification would satisfy any of Fermat’s critics. The result is an illustration of how a purely theoretical argument can settle an apparently empirical debate.
    Direct download (9 more)  
     
    Export citation  
     
    My bibliography  
  5.  34
    Bryan W. Roberts (2015). Three Merry Roads to T-Violation. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 52:8-15.
    This paper is a tour of how the laws of nature can distinguish between the past and the future, or be T-violating. I argue that, in terms of the basic argumentative structure, there are basically just three approaches currently being explored. The first is an application of Curie's Principle, together with the CPT theorem. The second route makes use of a principle due to Pasha Kabir which allows for a direct detection. The third route makes use of a Non-degeneracy Principle, (...)
    Direct download (9 more)  
     
    Export citation  
     
    My bibliography   1 citation  
  6.  88
    Bryan W. Roberts (2013). The Simple Failure of Curie's Principle. Philosophy of Science 80 (4):579-592.
    I point out a simple sense in which the standard formulation of Curie’s principle is false when the symmetry transformation it describes is time reversal.
    Direct download (11 more)  
     
    Export citation  
     
    My bibliography   2 citations  
  7. Bryan W. Roberts (2014). A General Perspective on Time Observables. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 47:50-54.
    I propose a general geometric framework in which to discuss the existence of time observables. This frameworks allows one to describe a local sense in which time observables always exist, and a global sense in which they can sometimes exist subject to a restriction on the vector fields that they generate. Pauli's prohibition on quantum time observables is derived as a corollary to this result. I will then discuss how time observables can be regained in modest extensions of quantum theory (...)
    Direct download (10 more)  
     
    Export citation  
     
    My bibliography  
  8.  33
    Bryan W. Roberts (2012). Time, Symmetry and Structure: A Study in the Foundations of Quantum Theory. Pittsburgh D-Scholarship Dissertation.
    This dissertation is about the sense in which the laws of quantum theory distinguish between the past and the future. I begin with an account of what it means for quantum theory to make such a distinction, by providing a novel derivation of the meaning of "time reversal." I then show that if Galilei invariant quantum theory does distinguish a preferred direction in time, then this has consequences for the ontology of the theory. In particular, it requires matter to admit (...)
    Direct download  
     
    Export citation  
     
    My bibliography   1 citation  
  9.  41
    Bryan W. Roberts (2012). Kramers Degeneracy Without Eigenvectors. Physical Review A 86 (3):034103.
    Wigner gave a well-known proof of Kramers degeneracy, for time reversal invariant systems containing an odd number of half-integer spin particles. But Wigner's proof relies on the assumption that the Hamiltonian has an eigenvector, and thus does not apply to many quantum systems of physical interest. This note illustrates an algebraic way to talk about Kramers degeneracy that does not appeal to eigenvectors, and provides a derivation of Kramers degeneracy in this more general context.
    Direct download (4 more)  
     
    Export citation  
     
    My bibliography   1 citation  
  10.  23
    Bryan W. Roberts (2016). Curie’s Hazard: From Electromagnetism to Symmetry Violation. Erkenntnis 81 (5):1011-1029.
    Pierre Curie claimed that a symmetry of a cause must be found in the produced effects. This paper shows why this principle works in Curie’s example of the electrostatics of central fields, but fails in many others. The failure of Curie’s claim is then shown to be of special empirical interest, in that this failure underpins the experimental discovery of parity violation and of CP violation in the twentieth century.
    Direct download (3 more)  
     
    Export citation  
     
    My bibliography  
  11.  18
    Bryan W. Roberts, Disregarding the 'Hole Argument'.
    Jim Weatherall has suggested that Einstein's hole argument, as presented by Earman and Norton, is based on a misleading use of mathematics. I argue on the contrary that Weatherall demands an implausible restriction on how mathematics is used. The hole argument, on the other hand, is in no new danger at all.
    Direct download (4 more)  
     
    Export citation  
     
    My bibliography  
  12.  46
    John D. Norton & Bryan W. Roberts (2012). Galileo's Refutation of the Speed-Distance Law of Fall Rehabilitated. Centaurus 54 (2):148-164.
    Galileo's refutation of the speed-distance law of fall in his Two New Sciences is routinely dismissed as a moment of confused argumentation. We urge that Galileo's argument correctly identified why the speed-distance law is untenable, failing only in its very last step. Using an ingenious combination of scaling and self-similarity arguments, Galileo found correctly that bodies, falling from rest according to this law, fall all distances in equal times. What he failed to recognize in the last step is that this (...)
    Direct download (9 more)  
     
    Export citation  
     
    My bibliography  
  13.  12
    Bryan W. Roberts, Does Quantum Time Have a Preferred Direction?
    This paper states and proves a precise sense in which, if all the measurable properties of an ordinary quantum mechanical system are ultimately derivable from position, then time in quantum mechanics can have no preferred direction. In particular, I show that when the position observable forms a complete set of commuting observables, Galilei invariant quantum mechanics is guaranteed to be time reversal invariant.
    No categories
    Direct download (2 more)  
     
    Export citation  
     
    My bibliography  
  14.  12
    Bryan W. Roberts (2013). When We Do Have a Classical Arrow of Time. Philosophy of Science 80 (5):1112-1124.
    I point out that some common folk wisdom about time reversal invariance in classical mechanics is strictly incorrect, by showing some explicit examples in which classical time reversal invariance fails, even among conservative systems. I then show that there is nevertheless a broad class of familiar classical systems that are time reversal invariant.
    Direct download (9 more)  
     
    Export citation  
     
    My bibliography