Category Archives: Uncategorized

April 14th: Callender and Chua speak

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

Passcode: RMvp1pYM

Huggett speaks this week

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?

Talk this week: Fay Dowker

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. 

Huggett speaks

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?

Talk this week: Chris Smeenk

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.

2021 Summer Institute

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).

This week’s speaker – Lee Smolin

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.

Talk this week: Vidotto

Please join us (virtually) on Feb 17, at 10:15ET for Francesca Vidotto, speaking on “Quantum Gravity in Practice”. Full details and registration at https://www.centerphilsci.pitt.edu/cosmology-beyond-spacetime/.

Abstract: I present a recent concrete calculation in Spinfoam Cosmology -the application of the covariant LQG techniques to the cosmos- as an example to discuss a number of conceptual issues that are at the core of quantum gravity and cosmology. These include: What are the observables when localization does not rely on background space and time? What are the degrees of freedom? What is the role of quantum fluctuations of spacetime? What’s the interplay between the Planck scale and the cosmological scale? How should we think about time in this picture?

Talk this week: Wüthrich

On Wednesday February 10th, our very own Christian Wüthrich will present  “Laws Beyond Spacetime”, as part of our online seminar series at the Pittsburgh Center for Philosophy of Science. Please join us. Full details and registration at https://www.centerphilsci.pitt.edu/cosmology-beyond-spacetime/.

Abstract: Quantum gravity’s suggestion that spacetime may be emergent and so only exist contingently would force a radical reconception of extant analyses of laws of nature. Humeanism presupposes a spatiotemporal mosaic of particular matters of fact on which laws supervene. I will show how the Humean supervenience basis of non-modal facts can be reconceived, avoiding a reliance on fundamental spacetime. However, it is unclear that naturalistic forms of Humeanism can maintain their commitment to there being no necessary connections among distinct entities. This talk is based on a joint project with Vincent Lam.

Talk this week

The first talk of our seminar series – by Nick Huggett – is on Wednesday February 3rd, at 9.15 CST.

Laws for Nowhere: the standard concept of law is, I suggest, significantly spatiotemporal, posing the question of how there can be laws in non-spatiotemporal theories, and most pointedly how laws could hold in non-spatiotemporal regions of spacetime. I describe a couple of quantum gravity models of the Big Bang (in string theory and group field theory), in a provisional attempt to demonstrate how such questions might arise.

Please come via zoom, or watch on Facebook. Details at https://www.centerphilsci.pitt.edu/cosmology-beyond-spacetime/.