With sadness we note the passing of Steven Weinberg. His influence on physics has of course been enormous, but – despite his public antipathy to ‘philosophy’ – his conceptual insights into quantum field theory and gravity (and more) have also greatly influenced many of us in philosophy of physics. Notably for me, his work on the renormalization group, the relation between fields and particle in QFT, and – especially relevant to this website – his contributions to our understanding of the scope and limits of gravity as a QFT. Beyond that of course are his amazing popular works in physics, that I expect helped bring many of us to physics in the first place.
Blog followers may be interested in the following interview of Tushar Menon by David Baker, on “Taking up Superspace”, a paper published in the project collection “Philosophy Beyond Spacetime” (OUP, 2021). https://www.youtube.com/watch?v=4Mj_3FZWMIM
We are delighted to announce that Mike Schneider (currently a postdoc at Pittsburgh) will be joining our group at UIC as a postdoctoral research fellow for 2021-22. If you don’t yet know Mike, you can read about his work on his website.
Please join us for a talk next week.
Wednesday, 14 April 2021 at 9:30am Chicago Time– Craig Callender (UCSD) and Eugene Chua (UCSD): No Time for Time from No-Time
Programs in quantum gravity often claim that time emerges from fundamentally timeless
physics. In the semiclassical time program time arises only after approximations are
taken. Here we ask what justifies taking these approximations and show that time seems
to sneak in when answering this question. This raises the worry that the approach is
either unjustified or circular in deriving time from no–time.
Join Zoom Meeting: https://uic.zoom.us/j/86317237897?pwd=dSt0N0JsRVVpbEx6Y0EyY1RwKzN4UT09
Meeting ID: 863 1723 7897
March 16 @ 12:00 pm – 1:30 pm Eastern Time (note that US clocks went forward on March 14th, and adjust to your local time accordingly!!!)
Nick Huggett, University of Illinois at Chicago / Center Senior Visiting Fellow
Missing the Point in Non-Commutative Field Theory
This will be an online lecture held via Zoom, and pre-registration is required. Please register here: https://pitt.zoom.us/webinar/register/WN_8cIVYSN0RfywEh4uJOp0MA
ABSTRACT: A non-commutative field theory (for scalar fields in this talk) introduces a fundamental area, as the measure of non-commutation (analogous to Planck’s constant), but does it signify a minimum area? Drawing on work with Fedele Lizzi (Napoli) and Tushar Menon (Cambridge) I will explain a sense in which this is correct, implying that points are ‘missing’. This situation raises several questions: how should the theory then be understood? Can its algebraic formulation be interpreted as describing the basic degrees of freedom of a world? And if so, how do we understand the ‘emergence’ of continuous, classical spacetime physics?
Join us online on Wednesday March 10 at 10.15am (Eastern) for Fay Dowker (Imperial) for “If Time Had No Beginning”. Details and registration are here: https://www.centerphilsci.pitt.edu/cosmology-beyond-spacetime/.
Abstract: Could the universe have had no beginning? I don’t mean, in raising thisquestion, to deny or throw doubt on Big Bang cosmology and the existence in the past of a hot, dense state of Planckian curvatureand temperature. But, in that case, how is the question to be interpreted given that—if we accept the standard cosmology— the Lorentzian manifold structure of spacetime breaks down at the Big Bang? Certainly, the *continuum* concept of timein our cosmological epoch “begins” at the Big Bang. Can we even ask what happened “before” that? The causal set approach to the problem of quantum gravity provides an arena in which to address the question of origins, in which it makes sense to ask what happened before the Big Bang and in which a clear distinction can be made between models of the universe which are “past infinite” and “past finite”. I will describe work with Stav Zalel and Bruno Bento in which we construct a framework for dynamics for causal sets which can result in past infinite universes.
Nick Huggett will be speaking online at the Oxford Philosophy of Physics seminar on Thursday 4th March, at 16.30 GMT. Details here: https://www.philosophy.ox.ac.uk/philosophy-of-physics-seminar#. Hope to see you there.
Title: Missing the point in (noncommutative) field theory.
Abstract: A non-commutative field theory (for scalar fields in this talk) introduces a fundamental area, as the measure of non-commutation (analogous to Planck’s constant), but does it signify a minimum area? Drawing on work with Fedele Lizzi (Napoli) and Tushar Menon (Cambridge) I will explain a sense in which this is correct, implying that points are ‘missing’. This situation raises several questions: how should the theory then be understood? Can its algebraic formulation be interpreted as describing the basic degrees of freedom of a world? And if so, how do we understand the ‘emergence’ of continuous, classical spacetime physics?
Please join us online at 10am (Eastern) on 3/3/21 for “Decoupling from the Initial State?” by Chris Smeenk (Western): details and registration at https://www.centerphilsci.pitt.edu/cosmology-beyond-spacetime/.
Abstract: According to inflationary cosmology, the universe passed through a transient phase of exponential expansion that leaves several characteristic imprints in the universe’s post-inflationary state. This paradigm has enjoyed considerable phenomenological success, as a wide range of inflationary models are compatible with observations. The extent to which this success lends credibility to inflation has been a subject of ongoing debate. Here I will focus on whether the predictions of inflation are robust to changes in high-energy physics, or to features of the pre-inflationary initial state. The prospect of describing the early universe successfully without resolving the mysteries of quantum gravity has always been one of inflation’s appealing features. I will review arguments that inflation does not decouple from high energy physics in the same sense as other effective field theories in physics. Establishing how inflation can be implemented in a theory of quantum gravity is an ongoing challenge, and doing so is needed to address several long-standing foundational questions.
Morzine, France 27 June – 2 July 2021: International Summer Institute in the PHILOSOPHY OF COSMOLOGY and the PHILOSOPHY OF QUANTUM GRAVITY
In recent years, the philosophy of quantum gravity and the philosophy of cosmology have emerged as new fields in their own right, with several summer schools dedicated to each. However, they remain largely unconnected, even though their intersection promises new scientific insights of great significance to philosophical question and the advancement of physics. This Summer Institute proposes to address conceptual, metaphysical, and epistemological implications of big bang, black hole, and multiverse models in quantum gravity: the fundamental nature of space and time, especially the beginning of spacetime, ‘before’ time or ‘outside’ space; the multiverse; the nature of physical law; and how we might have knowledge of such things. These are just some of the questions that we will discuss in this Summer Institute, which addresses graduate students and postdocs from philosophy of physics and related fields. Application details https://beyondspacetime.net/2021summerinstitute/
Faculty: Karen Crowther (Oslo), Nick Huggett (Illinois at Chicago), Mairi Sakellariadou (King’s College London), Chris Smeenk (Western), Francesca Vidotto (Western), David Wallace (Pittsburgh), Christian Wüthrich (Geneva).
Please join us (online) on Wednesday February 24th, for a talk by Lee Smolin, titled “Temporal naturalism”. The abstract is below, we start at 10am ET, and full details including registration are at https://www.centerphilsci.pitt.edu/cosmology-beyond-spacetime/.
Abstract: I discuss the progress of a research program called temporal naturalism, whose aim is to reframe naturalism and relationalism based on the hypotheses that time is fundamental, while space is emergent. By the fundamentality of time we mean that all that is real are causal processes that continually make definite facts out of previously indefinites possibilities, thereby producing novel events out of predecessor events.
Good beables to construct such a theory from are the views of events, which describe what properties an event was endowed with from its predecessor events, such as energy and momentum. Thus there is a single universe made up of partial views of itself.
In a relational setting and with no distance, coordinates, fields, trajectories to draw from, the dynamics must be formulated in terms of views, and in particular in terms of differences amongst views. The change between the view of an event and its immediate predecessors provides a notion of kinetic energy while potential energy is related to the variety, which is the total diversity of present causally unrelated views. This is enough to derive a version of many body quantum theory; which lives in a space that we show emerges from the solutions of the theory. Thus the program shows promise of reconciling both the problems of quantum foundations and quantum gravity, within a single completion.
The part of the program just described has been developed under the names of energetic causal sets and the causal theory of views. Another key aspect is the view that the laws of physics cannot be fixed, but must evolve, in a way as to explain howthe choices the universe has made of the fundamental forces and particles have come about through an evolutionary, dynamical process. If there is time I will discuss three realizations of this idea: cosmological natural selection, the principle of precedence and the hypothesis that the vacua of quantum fields can learn to navigate a landscape of possible laws, usingthe same mechanisms that allow a deep neural network to learn.
This work has appeared in six books and a number of papers; key collaborators have included Julian Barbour,Fotini Markopoulou, Stuart Kauffman, Joao Magueijo, Stephon Alexander, Roberto Mangabeira Unger, Jaron Lanier, Marina Cortes, Andrew Liddle and Clelia Verde.