I am a philosopher of physics, lost artist, and Associate Professor at the LSE, where I direct the Centre for Philosophy of Natural and Social Sciences (CPNSS). Since 2019 I have also taught in the Department of Applied Mathematics and Theoretical Physics (DAMTP) at the University of Cambridge.
I work on foundational issues in quantum theory, spacetime and gravitation, thermodynamics, gauge physics, and other things that fill one with wonder about the world.
Bryan W Roberts is a philosopher of physics, Associate Professor of Philosophy, Logic and Scientific Method, and Director of the Centre for Philosophy of Natural and Social Sciences (CPNSS) at the London School of Economics. His fields of expertise lie in the intersection of philosophy and mathematical physics, with projects ranging from the arrow of time in particle physics, to the interpretation of general relativity, to the nature of the "observable", in addition to hosting a YouTube channel called Space, Time and Einstein. He has published in philosophy, physics, and history journals, receiving the Leverhulme Prize in 2017, an NSF grant in 2018, and a visiting Fellowship at Trinity College, Cambridge in 2019, during which time he taught in the Department of Applied Mathematics and Theoretical Physics (DAMTP) at the University of Cambridge. Dr Roberts received his Ph.D. in 2012 from the University of Pittsburgh under John Earman and John D. Norton, and then held the Provost's Postdoctoral Fellowship at the University of Southern California from 2012-2013, before finally settling in London at the LSE in 2013.
|Weak Interactions and the Curious Little Arrow of Time, given at the ETH in Zurich in 2015, for the D-Phys Workshop on Time in Physics.|
|The good news about killing people, given for the LSE Choice Group, 18 March 2020|
Why is gauge symmetry so important in modern physics, given that one must eliminate it when interpreting what the theory represents? In this paper we discuss the sense in which gauge symmetry can be fruitfully applied to constrain the space of possible dynamical models in such a way that forces and charges are appropriately coupled. We review the most well-known application of this kind, known as the 'gauge argument' or 'gauge principle', discuss its difficulties, and then reconstruct the gauge argument as a valid theorem in quantum theory. We then present what we take to be a better and more general gauge argument, based on Noether's second theorem in classical Lagrangian field theory, and argue that this provides a more appropriate framework for understanding how gauge symmetry helps to constrain the dynamics of physical theories.
Time reversal is a wonderfully strange concept. It sounds like science fiction at first blush, and yet plays a substantial role in the foundations of physics. This chapter introduces one little corner of the rich literature on time reversal, which deals with the question of what time reversal means. I begin with a presentation of the standard account of time reversal, with plenty of examples, followed by a popular non-standard account. I will then argue that, in spite of recent commentary to the contrary, the standard approach to the meaning of time reversal is the only one that is philosophically and physically viable. I conclude with a few open research problems about time reversal.
We criticise the claims of many expositions that the time-energy uncertainty principle allows both a violation of energy conservation and particle creation, provided that this happens for a sufficiently short time. But we agree that there are grains of truth in these claims: which we make precise and justify using perturbation theory.
Leibniz Equivalence is a principle of applied mathematics that is widely assumed in both general relativity textbooks and in the philosophical literature on Einstein's hole argument. In this article, I clarify an ambiguity in the statement of this Leibniz Equivalence, and argue that the relevant expression of it for the hole argument is strictly false. I then show that the hole argument still succeeds as a refutation of manifold substantivalism; however, recent proposals that the hole argument is undermined by principles of representational equivalence do not fare so well.
This special issue of Foundations of Physics collects together articles representing some recent new perspectives on the hole argument in the history and philosophy of physics. Our task here is to introduce those new perspectives.
We explore the ways that non-self-adjoint operators can be observables. There are in fact only four ways for this to occur: non-self-adjoint observables can either be normal operators, or be symmetric, or have a real spectrum, or have none of these three properties. I explore each of these four classes of observables, arguing that the class of normal operators provides an equivalent formulation of quantum theory, whereas the other classes considerably extend it.
This note argues that quantum observables can include not just self-adjoint operators, but any member of the class of normal operators, including those with non-real eigenvalues. Concrete experiments, statistics, and symmetries are all expressed in this more general context. However, this more general class of observables also introduces a new restriction on which sets of operators can be interpreted as observables at once. These sets are referred to here as 'sharp sets.'
This paper seeks to dispel three myths about the concept of time reversal in quantum theory, by providing a novel derivation of the meaning of time reversal in non-relativistic and relativistic contexts, without appeal to classical mechanics.
We explore the facts and fiction regarding Curie's own example of Curie's principle. Curie's claim is vindicated in his suggested example of the electrostatics of central fields, but fails in many others. Nevertheless, the failure of Curie's claim is still of special empirical interest, in that it can be seen to underpin the experimental discovery of parity violation and of CP violation in the 20th century.
A supertask is a task that consists in infinitely many component steps, but which in some sense is completed in a finite amount of time. Supertasks were studied by the pre-Socratics and continue to be objects of interest to modern philosophers, logicians and physicists. The term “super-task” itself was coined by J.F. Thomson (1954). This encyclopedia article begins with an overview of the analysis of supertasks and their mechanics. We then discuss the possibility of supertasks from the perspective of general relativity.
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 really just three approaches currently being explored. I show how each is characterized by a symmetry principle, which provides a template for detecting T-violating laws even without knowing the laws of physics themselves. Each approach is illustrated with an example, and the prospects of each are considered in extensions of particle physics beyond the standard model.
Ashtekar (2013) 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.
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 beyond its standard formulation.
I clarify the sense in which classical mechanics is time reversal invariant. I first point out that some common folk wisdom about time reversal invariance is strictly incorrect, by showing some explicit examples in which classical time reversal invariance fails. I then propose two ways capture the sense in which classical mechanics is time reversal invariant.
There is a simple sense in which the standard formulation of Curie's Principle is false, when the symmetry transformation it describes is time reversal.
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 so does not apply to all potentially relevant quantum systems. Adopting an algebraic definition of degeneracy, this note shows that Kramers degeneracy can be derived more generally, for Hamiltonians with or without eigenvectors.
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 time is infinite, the result of an exponential dependence of distance on time. Instead, Galileo conflated it with the other motion that satisfies this ‘equal time’ property, instantaneous motion.
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.
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.
2012 Time, symmetry and structure: A study in the Foundations of Quantum Theory. Supervised by John Earman and John D. Norton, History and Philosophy of Science, University of Pittsburgh. Defended 20 May 2012. Pittsburgh ETD.
|2017 Leverhulme Prize (2018-2020)|
|National Science Foundation (NSF) Grant #1734155 "Extending the Observable", with collaborator Nicholas Teh, University of Notre Dame.|
|Audio BBC Crowd Science, "If a tree falls in a forest... does it make a sound?".|
|Audio BBC Radio 4 Moral Maze, "Is Science Morally Neutral?" 12 March 2016.|
Unfortunately, much of the recent outcry against artificial-intelligence weapons has been confused, conjuring robot takeovers of mankind. This scenario is implausible in the near term, but AI weapons actually do present a danger not posed by conventional, human-controlled weapons, and there is good reason to ban them. Intelligent weapons are too easily converted by software engineers into indiscriminate killing machines.
I animated and recorded a series of YouTube videos introducing Einstein's theories of space, time and gravity.
Philosophico-Scientific Adventures. I wrote an ebook introducing some topics in the philosophy of science. I'm continually developing it, adding chapters when I can, so please excuse any errors!
7 Steps to a Better Philosophy Paper. A short writing guide for beginners in philosophy: 7 steps, 10 tips, and only 4 pages!
Writing an MSc Dissertation. How to do the mammoth task of writing an MSc dissertation in the Department, which applies more broadly of course.
I am co-editor in chief of the BSPS Open book series, a free open access book series for philosophy of science.
I'm also a co-director of PhilSci-Archive, the field's main preprint server. If you're a philosopher of science that doesn't use PhilSci-Archive, stop what you're doing and go sign up! Visit us at philsci-archive.pitt.edu.
|Emacs Zen: I write everything in emacs. You can see my setup on github.|
|Be more efficient. The The Pomodoro Technique is hands-down the most important trick I used to complete my dissertation on time in grad school, and I still use it regularly. There are lots of free timer apps online.|
|Dirt Simple ToDo List: My work flow, explained as a screencast by me in 2010. I still do basically the same thing.|
|Handling academic citations. If you use something a lot, you may as well make it easier on yourself: screencast from 2009. Know a better way? Tell me!|
|Give better talks. Give better talks. Giving an academic talk? Read Paul Edwards' How to Give an Academic Talk, but also watch this video on how to give great talks in any context. Giving a talk on a technical subject? Check out this excellent advice from Bob Geroch and from David Tong.|