Lee's Fest: Quantum Gravity and the Nature of Time

Jun 2, 2025, 8:00 a.m. → Jun 6, 2025, 5:15 p.m. America/Toronto

PI/3-394 - Skyroom (Perimeter Institute for Theoretical Physics)

 

What is time? Is it fundamental or emergent? This question lies at the foundation of contemporary physics and provides a key to unlocking some of its most challenging open problems, from quantum gravity to cosmology. The quest to understand time extends beyond the realm of physics, providing a privileged standpoint to address questions in diverse fields such as philosophy, mathematics, and computer science.

In this conference, we explore the nature of time from many different perspectives. This is the occasion to honor Perimeter’s “Master of Time,” Lee Smolin, and to celebrate his seminal scientific contributions. Lee Smolin is a founding faculty member of Perimeter Institute and a primary inspiration behind its spirit and design. This is an opportunity to journey back in time to the origins of some of the groundbreaking initiatives that Lee helped develop, and to look forward to future developments inspired by his achievements. The conference focuses on time but also on the foundations of quantum mechanics and the quest for quantum gravity, particularly Loop Quantum Gravity, of which Lee Smolin is a co-creator. In the spirit of Lee Smolin, the conference celebrates the interdisciplinary nature of the journey toward quantum gravity, with contributions from physics, mathematics, computer science, and philosophy.

 

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Scientific Organizers
Laurent Freidel (Perimeter Institute)
Maïté Dupuis (Perimeter Institute)
Dongxue Qu (Perimeter Institute)
Francesca Vidotto (Western University)

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Speakers

• Niayesh Afshordi (University of Waterloo)
• Stephon Alexander (Brown University)
• Giovanni Amelino-Camelia (University of Naples Federico II)
• Julian Barbour (Independent)
• Bianca Dittrich (Perimeter Institute)
• Fay Dowker (Imperial College)
• Avshalom Elitzur (Chapman University)
• Lucien Hardy (Perimeter Institute)
• Viqar Husain (University of New Brunswick)
• Jenann Ismael (Johns Hopkins University)
• Ted Jacobson (Maryland University)
• Jaron Lanier (Microsoft Research)
• Etera Livine (Lyon, Ecole Normale Superieure)
• João Magueijo (Imperial College London)
• Seth Major (Hamilton College)
• Carlo Rovelli (Aix-Marseille University)
• Simon Saunders (Oxford University)
• Simone Speziale (Aix-Marseille University)
• Francesca Vidotto (Western University)
• Steven Weinstein (University of Waterloo) 

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Credit: Artwork by Kaća Bradonjić

 

Mon, June 2

8:30 a.m. → 9:15 a.m. Registration

9:15 a.m. → 9:30 a.m. Opening Remarks

Speakers: Marcela Carena (Perimeter Institute for Theoretical Physics), Laurent Freidel (Perimeter Institute for Theoretical Physics)

9:30 a.m. → 10:30 a.m. One of us would be superfluous

I will tell stories. About Lee's physics. About his insights that have shaped many of the ideas that we take for granted today. From the birth of Loop Quantum Gravity to the discreteness of physical space.

Speaker: Carlo Rovelli (Aix-Marseille University)

10:30 a.m. → 11:00 a.m. Break

11:00 a.m. → 12:00 p.m. Quantum Foundations

Speaker: Lucien Hardy (Perimeter Institute for Theoretical Physics)

12:00 p.m. → 1:00 p.m. Lunch

1:00 p.m. → 2:00 p.m. Cosmology, Quantum Gravity and a Constant

Cosmological data is consistent with a positive cosmological constant. In this talk I discuss an approach pioneered by Smolin that uses a non-perturbative exact quantization of gavity with a cosmological constant in the Ashtekar formalism. I discuss follow up work by the Author and his collaborators that address some conceptual and potential physical predictions of this approach. I end with a discussion of Smolin's cosmic natural selection as a predictive mechanism which also had consequences in particular Anthrophic landscape realizations in string theory.

Speaker: Stephon Alexander (Brown University)

2:00 p.m. → 2:30 p.m. Break

2:30 p.m. → 3:30 p.m. Philosophy: Perspectives on the Universe

Speaker: Steven Weinstein

3:30 p.m. → 5:00 p.m. Reception

Tue, June 3

9:00 a.m. → 9:15 a.m. To Lee, with best wishes

I will make a few remarks of both scientific and personal nature to celebrate Lee's contributions to our field.

Speaker: Abhay Ashtekar (Pennsylvania State University)

9:15 a.m. → 9:30 a.m. Gravitational collapse, shock waves and white holes

I will describe an effective quantum gravity model for dust collapse that predicts a shock wave as the end point of a black hole, and smooth metrics for black hole to white hole transitions.

Speaker: Viqar Husain (University of New Brunswick)

9:30 a.m. → 9:45 a.m. Building and (hints of) seeing gravitational statistical mechanics

A statistical mechanics of geometry based on the quasi-local energy of constantly accelerating observers outside black holes is proposed. By assuming particle statistics for the geometric quanta, the geometry condenses in the large area limit, providing a quantum gravity cutoff for the entropy of the thermal atmosphere of geometric excitations. These excitations model the fluctuating shape of the black hole" and form an effectively two dimensional quantum thermal geometric atmosphere. The entropy from theseDebye" excitations is proportional to the area. Prospects of for the observation of the fluctuations are briefly discussed.

Speaker: Seth Major (Hamilton College)

9:45 a.m. → 10:00 a.m. Conference Talk

Speaker: Bianca Dittrich (Perimeter Institute for Theoretical Physics)

10:00 a.m. → 11:00 a.m. Q&A/Panel Discussion: Foundations of Loop Quantum Gravity

Panel discussion featuring the morning's speakers.

Speakers: Abhay Ashtekar (Pennsylvania State University), Bianca Dittrich (Perimeter Institute for Theoretical Physics), Seth Major (Hamilton College), Viqar Husain (University of New Brunswick)

11:00 a.m. → 11:30 a.m. Break

11:30 a.m. → 11:45 a.m. Principle and constructive theories of physical probability

I show how to make sense of physical probability even for a single atom at a single time in an otherwise empty universe. The ideas are in https://arxiv.org/abs/2404.12954 and http://arxiv.org/abs/2505.06983. As applied to the EPRB setup, probability defined in this way is perfectly local.

Speaker: Simon Saunders (University of Oxford)

11:45 a.m. → 12:00 p.m. The Elusiveness of Time

Lee’s most philosophical work is a probing challenge to the "timeless" view prevailing in much of physics. I’’ll say why I think he is right that the idea of the universe as a fixed totality of events is a mirage, and one that arises– as he argued – from extending techniques appropriate for open subsystems to the universe as a whole. Time (for any system in the universe) is irresolubly open-ended, ongoing, and incomplete.

Speaker: Jenann Ismael (Johns Hopkins University)

12:00 p.m. → 12:30 p.m. Q&A/Panel Discussion: Philosophy of Time

Speakers: Jenann Ismael (Johns Hopkins University), Simon Saunders (University of Oxford)

12:30 p.m. → 1:30 p.m. Lunch

1:30 p.m. → 1:45 p.m. Quantum gravity and the Born rule

Speaker: Antony Valentini

1:45 p.m. → 2:00 p.m. Causality and flow of time in realist quantum models

In a series of papers [Phys. Rev. D 102, 124027 (2020)], [Phys. Rev. D 102, 124028 (2020)] I had the pleasure to explore with Cortês, Elitzur and Smolin realist formulations of quantum theory which obey either retrocausality or disordered causality. After briefly presenting these works, I will attempt to extend them by addressing time as a quantum observable using the Page-Wootters formalism. Within this framework, the clock is treated as a quantum subsystem, endowing the remainder of the system with a notion of time through entanglement. I will show the fruitfulness of this approach by deriving new time-energy uncertainty relations [Quantum 6, 683 (2022)] and by elucidating aspects of dynamical nonlocality [Phys. Rev. A 105, 042207 (2022)]. Furthermore, I will demonstrate that in the post-Newtonian regime, perspective-dependent non-unitarity and a distinct form of time–asymmetry naturally emerge when the clocks experience acceleration or gravitational effects [Commun. Phys. 5, 298 (2022)]. Finally, I will discuss the more recent works viewing all the above as spatiotemporal quantum reference frames [Phys. Rev. A 109, 032205 (2024)], [arXiv:2503.20090].

Speaker: Prof. Eliahu Cohen (Bar-Ilan University)

2:00 p.m. → 2:15 p.m. Reassessing the i.i.d. Assumption in Probability Assignments in Quantum Gravity

I will examine a foundational assumption in quantum probability assignments, that experimental data arise from an identically and independently distributed (i.i.d.) ensemble. However, this assumption becomes problematic in the regime of quantum gravity. I will outline a proposal to resolve this issue by leveraging the tool of quantum reference frames in the measurement context.

Speaker: Lin-Qing Chen (IQOQI Vienna & University of Vienna)

2:15 p.m. → 2:30 p.m. Conference Talk

Speaker: Francesca Vidotto (Western U. & IEM-CSIC Madrid)

2:30 p.m. → 3:30 p.m. Q&A/Panel Discussion: Time and the Quantum

Speakers: Avshalom Elitzur (Chapman University), Eliahu Cohen, Francesca Vidotto (Western U. & IEM-CSIC Madrid), Lin-Qing Chen (IQOQI Vienna & University of Vienna)

3:30 p.m. → 4:00 p.m. Break

4:00 p.m. → 5:00 p.m. Artistic Moment

5:00 p.m. → 5:45 p.m. Free Time

6:00 p.m. → 8:00 p.m. Banquet

Wed, June 4

9:00 a.m. → 9:15 a.m. Lee Smolin: His Important Critical Role with Regard to Unconventional Physical Theories

Speaker: Roger Penrose

9:15 a.m. → 9:30 a.m. GRB neutrinos and quantum-gravity-induced in-vacuo dispersion

I report on recent progress of investigations of in-vacuo dispersion for GRB neutrinos, also highlighting the connection with a previous study done in collaboration with Lee Smolin investigating in-vacuo dispersion for GRB photons. The present status of IceCube neutrino observations provides preliminary encouragement for a scenario based on in-vacuo dispersion and the KM3-230213A neutrino recently annouced by KM3NeT fits rather naturally within the in-vacuo-dispersion scenario motivated by IceCube data.

Speaker: Giovanni Amelino-Camelia (University of Naples Federico II)

9:30 a.m. → 9:45 a.m. Dark Matter as the leftover of historical violations of the Hamiltonian constraint

If the Hamiltonian constraint were ever violated (in the early Universe, at high energies, etc), its subsequent restoration could never erase a memory effect of the original violation. Depending on the technicalities of restoration, the memory effect may be as boring as something which mimics standard dark matter, or an anisotropic extension of dark matter... Or, as crazy as something that acts like a dust fluid capable of attracting other matter but being attracted to nothing. Attracting without being attracted: we discuss how it might be possible in a relativistic theory of gravity, its implications to the foundations of physics (specifically Dirac's algebra of constraints underpinning relativistic physics), and what its observational hallmarks might be.

Speaker: João Magueijo (Imperial College London)

9:45 a.m. → 10:00 a.m. Tempus Discretum: On the nature of cosmic time

What if the cosmic clock actually ticks? In this talk, I will explore growing evidence—from the structure of the cosmos to the frontiers of quantum gravity—that time may not be continuous, but fundamentally discrete. By rethinking the flow of time as a sequence of quantized events, we uncover surprising connections that challenge our classical intuitions and open new paths in fundamental physics.

Speaker: Niayesh Afshordi (University of Waterloo)

10:00 a.m. → 11:00 a.m. Q&A/Panel Discussion: Cosmology, Phenomenology and Time

11:00 a.m. → 11:30 a.m. Break

11:30 a.m. → 11:45 a.m. Thank You, Lee - Video Greetings

11:45 a.m. → 12:30 p.m. Conversation between Lee Smolin and the participants on Quantum Gravity (1)

12:30 p.m. → 1:30 p.m. Lunch

1:30 p.m. → 1:45 p.m. Homogeneity of orientations in Spin-foams

The original Spin-foam model, the Ponzano-Regge Spin-foam model of 3D gravity with zero cosmological constant, has two properties in seeming contradiction: (1.) Its connection representation consists in the imposition of exact flatness, and (2.) Its leading order large spin asymptotics consists in Regge calculus, modified to include an additional local discrete orientation variable for each tetrahedron, which, when fixed inhomogeneously, leads to critical point equations for the edge lengths which do not imply flatness, but rather spikes. We explore the possibility that this tension is resolved through the existence of a neglected critical point equation imposing homogeneity of the orientation variables. Such an elimination of local variation of the orientation variables in the large spin limit would additionally be consistent with classical 3D gravity, in which non-degeneracy of the triad ensures its orientation is global. The possibility of the existence of a similar neglected critical point imposing homogeneity of orientations in 4D spin-foam models is also considered.

Speaker: Prof. Jonathan Engle (Florida Atlantic University)

1:45 p.m. → 2:00 p.m. Conference Talk

Speaker: Simone Speziale (Aix-Marseille Université)

2:00 p.m. → 2:15 p.m. Bulk-Boundary in Spinfoams

Spinfoams define a path integral for quantum gravity based on topological quantum field theory (TQFT). Following Lee’s early intuitions about the implementation of the holographic principle in the formalism, I will explain how the bulk dynamics arises as a network of boundary theories and draw lessons about the bulk-boundary relations. Diving into the example of 3d quantum gravity, this is illustrated by a beautiful holographic-like duality with the 2d inhomogeneous Ising model, with an underlying emergent supersymmetry, opening an intriguing interplay with the world of statistical physics with an elegant geometric formula for the zeroes of the Ising partition function.

Speaker: Etera Livine (École Normale Supérieure de Lyon)

2:15 p.m. → 2:30 p.m. Time in quantum gravity.

In this talk, I will investigate the possibility of time being a fundamental physical entity in quantum gravity.

I will briefly review the different notions of time in classical and quantum mechanics and then focus on explaining the fundamental clash that exists between the notions of time in Quantum Field theory and general relativity. This clash, related to the so-called problem of time, is at the core of the fundamental difficulty of quantizing gravity. I will review how recent results in Quantum gravity allow a surprising resolution of this fundamental puzzle through the presence of a quantum anomaly, which promotes time to a fundamental quantum observable in quantum gravity.

Speaker: Laurent Freidel (Perimeter Institute for Theoretical Physics)

2:30 p.m. → 3:30 p.m. Q&A/Panel Discussion: Time in Loop Quantum Gravity

Speakers: Etera Livine (French National Centre for Scientific Research (CNRS)), Jonathan Engle (Florida Atlantic University), Laurent Freidel (Perimeter Institute for Theoretical Physics), Simone Speziale (Aix-Marseille University)

3:30 p.m. → 4:00 p.m. Break

4:00 p.m. → 4:30 p.m. Artistic Moment

7:00 p.m. → 9:00 p.m. Public Lecture - Niaysh Afshordi (Ticket Required)

Thu, June 5

9:00 a.m. → 9:15 a.m. Conference Talk

Speaker: Renate Loll (Radboud Universiteit Nijmegen)

9:15 a.m. → 9:30 a.m. Three for Lee

I will present three results:
1. Violation of positivity of energy in the extension of classical General Relativity provided by Ashtekar's polynomial formulation by virtue of its admittance of initial data with degenerate (densitized) triads.
2. Consistency of Propagation in the sense articulated by Lee with the apparent ``ultralocal'' action of the Hamiltonian constraint in LQG.
3. An explicit demonstration of the consistency of area discreteness with Lorentz Invariance for an LQG type quantization of
free scalar field theory on 1+1 flat spacetime formulated in a diffeomorphism invariant disguise.

The first two results were obtained as answers to direct questions from Lee, the third is a new result and all three are motivated by issues connected with Dynamics, and hence, Time in LQG.

Speaker: Madhavan Varadrajan

9:30 a.m. → 9:45 a.m. Being, Becoming and Experience in Quantum Gravity

In causal set quantum gravity, spacetime is Being and the process of the birth of the atoms of spacetime is Becoming. This process coordinates with our experience of the passage of time.

Speaker: Fay Dowker (Imperial College London)

9:45 a.m. → 10:00 a.m. It Feels Like the Old Days: From Loop Quantum Gravity to Conformal Graphs

Speaker: Tim Koslowski (Universität Würzburg and Technical University of App. Sci. Würzburg)

10:00 a.m. → 11:00 a.m. Q&A/Panel Discussion: Perspectives on Time and Quantum Gravity

Speakers: Fay Dowker (Imperial College London), Madhavan Varadarajan, Renate Loll (Radboud Universiteit Nijmegen), Tim Koslowski (Universität Würzburg and Technical University of App. Sci. Würzburg)

11:00 a.m. → 11:30 a.m. Break

11:30 a.m. → 12:30 p.m. Conversation between Lee Smolin and the participants on Quantum Gravity (2)

12:30 p.m. → 1:30 p.m. Lunch

1:30 p.m. → 1:45 p.m. Conference Talk

Speaker: Julian Barbour

1:50 p.m. → 2:05 p.m. Quantum Physics needs Philosophy, but shouldn't trust it

Lee Smolin is fully aware that quantum physics has deep philosophical implications (about the nature of reality, time and space, observation, etc.). However, when philosophers engage in quantum theories, they often succumb to idealist temptations (consciousness creates reality, etc.). My aim as a philosopher is to bring out and clarify these implications which often appear inconsistent

Speaker: Slavoj Zizek (University of Ljubljana)

2:10 p.m. → 2:25 p.m. Spin Networks

Speaker: Ted Jacobson (University of Maryland, College Park)

2:30 p.m. → 2:45 p.m. Conference Talk

Speaker: Jaron Lanier (Microsoft Research New York City)

2:50 p.m. → 3:30 p.m. Conversation: Lee Smolin and Special Guest

3:30 p.m. → 4:00 p.m. Break

7:00 p.m. → 9:00 p.m. Movie Night - Ticket Required

Fri, June 6

10:15 a.m. → 11:00 a.m. Contributed Talks

10:25 a.m. No time machine on the cheap: why semiclassical wormholes won’t do

If you can control a wormhole, you can time-travel. The issue is whether they can exist at all. Wormhole solutions in general relativity have spectacular local and global features. Invariantly, a wormhole throat is an outer marginally trapped surface satisfying additional constraints. Some of its properties — like violation of the energy conditions — it shares with black holes that are required to trap light in finite time for a distant observer. This condition may be contentious for black and white holes, but it is the essential part of what “traversable” means.

Standard traversable wormholes, such as those described by the Ellis-Morris-Thorne or Simpson-Visser metrics, are static and spherically symmetric. We show that no dynamical solution of the semiclassical Einstein equations can asymptote to these geometries. Conversely, dynamical solutions that do exist either fail to yield a traversable static limit, or breach quantum energy inequalities that bound violations of the null energy condition, or lead to divergent tidal forces. These conclusions hold independently of the choice of quantum fields. Such symmetric wormholes, therefore, are ruled out in semiclassical gravity — making time travel a costlier proposition.

Speaker: Prof. Danie Terno (Macquarie Univerisry)

10:35 a.m. The problem of time and evolving constants of motion: the cosmological case

I present a cosmological toy model of the resolution of the problem of time based on the Page-Wootters formalism but written in terms of evolving constants of motion. The use of these quantities resolves the issues, e.g., the incorrect propagators, etc., of the Page-Wootters formalism, and points to some interesting preliminary results.

Speaker: Prof. Saeed Rastgoo (University of Alberta)

10:45 a.m. Q&A

11:00 a.m. → 11:30 a.m. Break

11:30 a.m. → 12:30 p.m. Contributed Talks

11:30 a.m. Emergence of (Space)-Time from Fluctuations

Based on a previously published model of a quantum gravity path integral, expressed in spectral-geometric variables (Phys. Rev. Lett. 131, 211501), co-authored with M. Reitz and A. Kempf, I study the emergence of Lorentzian signature and time dimension from quantum fluctuations, and argue the physical intuition behind it via a known condensed matter phenomenon.

Speaker: Dr Barbara Soda (Perimeter Institute)

11:40 a.m. Quantum reconstruction in terms of imaginary time

Modern quantum simulations methods often use a fictitious imaginary time introduced by Feynman to exactly transform static quantum problems to dynamic imaginary time classical ones [1]. In addition to imaginary time simulation methods such as centroid molecular dynamics and path integral Monte Carlo, one can apply this quantum-classical isomorphism to self-consistent field theory (SCFT). An advantage of the field-theoretic perspective is that it can be exactly transformed into quantum density functional theory (DFT), meaning that the theorems of DFT (Hohenberg-Kohn and Mermin theorems) prove an equivalence between classical imaginary time SCFT dynamics and static quantum results [2]. Since imaginary time is assigned the same properties as regular time, one can replace the imaginary time in the SCFT equations with real time (a Wick rotation), which gives the equations of time-dependent DFT. The time-dependent DFT theorem (Runge-Gross theorem) then proves that one obtains all results of standard quantum mechanics from this imaginary time classical starting point. These results make it very tempting to consider treating imaginary time as an element of reality. This quantum reconstruction from imaginary time will be discussed, including a speculative look at treating imaginary time in the context of special relativity, with a preliminary comparison to the deformed special relativity of Magueijo and Smolin.

[1] D. M. Ceperely, Reviews of Modern Physics 67, 279 (1995)
[2] R. B. Thompson, Journal of Chemical Physics 150, 204109 (2019)
[3] J. Magueijo and L. Smolin, Physical Review D 67, 044017 (2003)

Speaker: Prof. Russell Thompson (University of Waterloo)

11:50 a.m. Lorentzian Quasicrystals and the Irrationality of Spacetime

Ordered structures that tile the plane in an aperiodic fashion - thus lacking translational symmetry - have long been considered in the mathematical literature. A general method for the construction of quasicrystals is known as cut-and-project ($\mathsf{CNP}$ for short), where an irrational slice "cuts" a higher-dimensional space endowed with a lattice and suitably chosen lattice points are further "projected down" onto the subspace to form the vertices of the quasicrystal. However, most of the known examples of $\mathsf{CNP}$ quasi-tilings are Euclidean. In this talk, after presenting the main ingredients of the Euclidean prescription, we will extend it to Lorentzian spacetimes and develop Lorentzian $\mathsf{CNP}$. This will allow us to discuss the first ever examples of Lorentzian quasicrystals, one in $(1+1)$- and another in $(1+3)$-dimensional spacetime. Finally, we will argue why the latter construction might be relevant for our Lorentzian spacetime. In particular, we shall appreciate how the picture of a quasi-crystalline spacetime could provide a potentially new string-compactification scheme that can naturally accommodate for the hierarchy problem and the smallness of our cosmological constant. Lastly, we will comment on its relevance to quantum geometry and quantum gravity; first, as a conformal Lorentzian structure of no intrinsic scale, and second through the connection of quasicrystals to quantum error-correcting codes.

Speaker: Mr Sotirios Mygdalas (Perimeter Institute for Theoretical Physics and University of Waterloo)

12:30 p.m. → 2:00 p.m. Lunch

2:00 p.m. → 4:00 p.m. Poster Session

2:00 p.m. Complexity, scaling, and a phase transition

We investigate the holographic complexity of CFTs compactified
on a circle with a Wilson line, dual to magnetized solitons in AdS$_4$ and
AdS$_5$. These theories have a confinement-deconfinement phase transition
as a function of the Wilson line, and the complexity of formation acts as
an order parameter for this transition. Through explicit calculation,
we show that proposed complexity functionals based on volume and action
obey a scaling relation with radius of the circle and further prove that
a broad family of potential complexity functionals obeys this scaling behavior.
As a result, we conjecture that the scaling law applies to
the complexity of conformal field theories on a circle in more general
circumstances.

Speaker: Jiayue Yang

2:05 p.m. The Surrational Materialism of the Path Integral

In recent debates on the ontology of quantum mechanics, Slavoj Žižek suggests that the Feynman path integral entails a subtle backward in time element, aligning this claim with his broader philosophical framework, which emphasizes symbolic mediation and retroactive causality . Žižek’s interpretation portrays the path integral as fundamentally indifferent to the direction of time, situating time within the domain of symbolic constructs and ontological incompleteness, devoid of immanent operativity. While this interpretation certainly aligns with his critique of metaphysical closure, it reduces time to a relational contingency imposed externally upon quantum systems, rendering the latter detached from the intrinsic operativity of time. I intend to challenge such a reading by advocating a metaphysics of the path integral that reclaims time as a generative, ontological force. Rather than suggesting a reversal or indifference to time, the Feynman path integral, when recast under the auspice of a new metaphysical intuition, reveals the return of time, and not a time reversal, as an immanent operator – a fractalized, recursive principle that undergirds quantum systems. Far from negating the irreversible arrow of time, the path integral reveals it as a field of individuation, not as a passive backdrop but as an asymmetric and creative force central to the genesis of quantum phenomena. Thus, Feynman’s path integral, traditionally interpreted as the summation over all spatial paths between two points, can be reimagined as a summation over internal temporal configurations. Then, each path becomes an expression of the particle’s fractalized internal temporality rather than an external spatial trajectory. That’s why at this point, terms like “path” and “trajectory” persist out of habit, because what the particle, say, an electron, traverses are more aptly described as circuits, diagrams, or even ritornellos , reflecting the necessity for a new imagination, a reimagined, temporally attuned perspective regarding the path integral.

Speaker: Ms Esterina Celami (PhD researcher)

2:10 p.m. Origins of Thermalization in Quantum Cosmology

We investigate how accelerated frames influence the cosmic evolution of a semi-classical universe
and propose that these effects can lead to thermalization at the quantum cosmological level. Our
primary research question is whether transformations in super-space, the configuration space of
the gravitational field can yield a mixed (and thus thermal) density matrix for the universe.
To address this, we apply a specific change of coordinates in super-space and analyze the WKB
wavefunction, revealing that it undergoes a Bogoliubov transformation. This transformation, in
turn, generates a mixed density matrix, signifying the emergence of thermal behavior.
Notably, our approach clarifies that this thermalization does not mirror the standard concept of
particle creation in uniformly accelerated (Rindler) observers; rather, it reflects a subtler
phenomenon linked to the geometry of super-space itself. We further demonstrate that the superspace transformation can be viewed as a double Rindler transformation of real space-time
coordinates, highlighting the deep geometric parallels between cosmological and accelerated
frames. These results suggest that acceleration-driven thermalization may play an important role
in semi-classical cosmology, offering new insights into how quantum and geometric effects
intertwine to shape the early universe.

Speaker: Mr Michael Osei (University of Lethbridge)

2:15 p.m. Shocks but not cataclysms: continuous dynamical extension beyond shell crossings

During the gravitational collapse of pressureless fluids in spherical symmetry, matter particles may collide with each other, forming what are called shell crossing surfaces. The differential equations governing the system become indeterministic at these surfaces, beyond which, therefore, the evolution of matter has to be determined by some other mechanism. This can be done by writing the equations in coordinates in which they turn out to be hyperbolic conservation laws; extensions beyond shell crossings can be formulated as weak solutions to a conservation law. But distinct ways of writing the conservation law yield distinct extensions. We show that the demand of metric continuity across a shell crossing gives a unique extension.

Speaker: Hassan Mehmood (University of New Brunswick)

2:20 p.m. Hydrogenic entanglement as a test for ER = EPR

The ER = EPR conjecture states that entangled particles are connected by microscopic worm holes. We look at some potential consequences of this "worm-hole-mediated entanglement." In particular, we see how they ought to affect the spectra of some well-known quantum systems in physics, such as the Hydrogen atom. Since the effects are significant but not observed experimentally, we are lead to believe that ER might not be EPR. We also suggest some experiments that could possibly be realized in the near future in order to strengthen our conclusion. At the end, we present some of our assumptions (like an electron is a point particle) as likely caveats to our approach.

Speaker: Irfan Javed (University of New Brunswick)

2:25 p.m. Semiclassical static solutions in spherically symmetric gravity

We use the Hamiltonian version of the semiclassical Einstein equation to study gravity coupled to a real scalar field. Starting from the full Einstein-Klein-Gordon system, we restrict to the spherically symmetric sector and derive the phase space equations of motion. In the semiclassical regime, we could do away with the scalar field equations and replace the scalar field variables by their expectations, which, in turn, could be viewed as free functions of the radial coordinate. This allows us to numerically find various static geometries, such as Boson stars, worm holes, and black holes. Our results are significant as they incorporate full backreaction of quantum matter on classical gravity.

Speaker: Irfan Javed (University of New Brunswick)

2:40 p.m. Semiclassical Mixmaster Universe

We present a semiclassical study of the Mixmaster cosmology minimally coupled to a massive scalar field in the Hamiltonian formalism, with focus on three distinct scenarios: the classical cosmology coupled to the quantized scalar field, and "effective" cosmology, with spacetime discreteness corrections, coupled to the classical scalar field, and to the quantized scalar field. We find several results: (i) the effective cosmology undergoes several small bounces before expanding, with scalar field excitations rising through the bounce; (ii) anisotropies rise and fall as the universe undergoes a bounce, a feature that is enhanced with matter; (iii) Lyapunov exponents reveal that chaos is reduced in the effective systems compared to the classical case.

Speaker: Mr Muhammad Muzammil (University of New Brunswick)

2:55 p.m. The Local Many Worlds Interpretation and Quantum Gravity

The Local Many Worlds Interpretation (LMWI) of quantum mechanics, unlike the Everett Many Worlds interpretation, is an entirely separable Lorentz covariant theory in spacetime. LMWI explains observed violations of Bell inequalities using a straightforward locally causal mechanism, which requires multiple local worlds for each observer. An extension of this model to treat gravity works by reinterpreting topologically flat curved spacetime where free objects follow geodesics, as flat spacetime with gravitation effects on objects caused by massless particles leaving the source mass at c. A mass in a spatial superposition produces a superposition of these gravitational effects on the flat spacetime, instead of a superposition of differently curved spacetimes. We thus have a superposition of gravitational force on another mass, as well as superpositions of the local energy density due to the massless gravity-carrying particles, which effect the local rates of clocks, which correspond to many different local worlds of the affected mass. This generalization of LMWI is undeveloped, but it seems like a promising new approach to quantum gravity, and I will try to explain the basic ideas.

Speaker: Mordecai Waegell (Institute for Quantum Studies, Chapman University)

3:10 p.m. When Nothing Ticked: Physical and Geometrical Time in Early-Universe Cosmology

The notion of time arises in two fundamentally distinct frameworks: physical time, grounded in operational standards such as atomic transitions or electromagnetic oscillations, and geometrical time, typically defined through coordinate choices and metric structures. This distinction becomes particularly problematic in the early universe, where traditional physical clocks—based on stable, observable periodic processes—are unavailable. In such regimes, theorists rely on mathematically defined constructs like conformal time $\eta=\int \frac{d t}{a(t)}$ to describe temporal evolution. While conformal time clarifies causal structure and underpins key predictions in inflationary cosmology, its status as a physically interpretable clock—connected to observable processes—remains deeply unclear. This ambiguity complicates efforts to define observables, specify initial conditions, and evaluate the singularity structure of early-universe models.

Christof Wetterich (2024) recently proposed photon-based clocks as physically meaningful, frame-invariant measures that seemingly bridge these two conceptions. However, under the extreme conditions of the early universe—where quantum gravitational effects become significant—can clocks grounded solely in classical geometry and quantum fields on fixed backgrounds remain coherent operational standards?

This paper examines this tension, arguing that a consistent and physically meaningful definition of early-universe clocks requires a quantum gravity context. Photon-based clocks, though attractive for their theoretical consistency, fundamentally depend on the assumption that photons maintain stable frequencies and coherent propagation even in regimes approaching quantum-gravitational breakdown. This assumption, I argue, is neither trivial nor necessarily justified within a semi-classical approximation that couples quantum electrodynamics to a classical gravitational background. Without direct linkage to empirical observables—such as primordial fluctuations or model-independent correlations—neither conformal nor field-based clocks meet the criteria of physical measurement.

I contend that this dilemma drives cosmologists toward two paths: either developing new methods for empirically grounding theoretical clocks or reconceiving cosmological clocks as inferential constructs—epistemic tools embedded within theoretical models rather than direct standards of measurement. This discussion is relevant not only for theoretical cosmologists seeking operational robustness but also for philosophers of cosmology concerned with how time is defined, measured, and conceptualized in the absence of observers, instruments, or classical reference systems.

Speaker: Ms Asya Ciftci (McGill University)