Welcome
Welcome to the Laws of Nature Series web site. You will find the latest information regarding the planned events in the current series. Please contact us if you want to join our seminars and receive our newsletter. Further information about this initiative can be found in the about section.
Ongoing  Spring/Summer 2024 Series
Meetings begin with a gettogether at 15:45 and talks start sharply at 16:00. Each session comprises a 50+10 minutes talk+discussion.
Session  Speakers  Title 

15.04.2024, 16:00
Brussels time Collapse in quantum mechanics 
Tjerk Oosterkamp 
Cryogenic experiments for Penrosian collapseI will present a clock Gedanken experiment that gives an alternative derivation of the Penrose collapse time. We try to develop new technologies for precision mechanical experiments using low temperatures and low vibrations. With these experiments we can improve bounds on various theories such as those that combine gravity and quantum mechanics. 
07.05.2024, 16:00
Brussels time Mass in quantum mechanics 
Hendrik Ulbricht 
Largemass quantum systemsI will discuss recent results with levitated mechanical systems in experiments and explain possible implications for testing the laws of nature. 
14.05.2024, 16:00
Brussels time Chance and determinism 
Barry Loewer 
Chance in Physics and PhilosophyProbability is the most important concept in modern science, especially as nobody has the slightest notion what it means (Bertrand Russell, 1929 Lecture)."  My talk develops an account of laws and chances that is based on David Lewis' Best Systems Account and argues that I is superior to frequency, propensity, and purely subjective accounts. I show how this account applies to indeterministic laws and also allows for objective physical probabilities that are compatible with deterministic dynamical laws. This plies to classical statistical mechanics and Bohmian mechanics. I show how this account explains why objective probabilities guide credences and thus supports Lewis remark that he can "see dimly but well enough why chance is a guide to credence." 
11.06.2024, 16:00
Brussels time Foundations of quantum mechanics 
Tim Maudlin 
Fundamental Dynamics for Quantum Theory: Why Complex Numbers?There are fundamental dynamical equations that govern fundamental entities and emergent dynamical equations that (approximately) describe the dynamics of emergent entities. For example, there is the classical theory of fluid dynamics based on Newtonian physics that is used to describe water waves, even though the fundamental Newtonian dynamical equation is not a wave equation. One strong suggestion of quantum phenomena such as twoslit interference is that the fundamental dynamics of the quantum state (wavefunction) must be some sort of wave dynamics. I will discuss the fundamental mathematical features of the clearest example we have of fundamental wave dynamicsthe free Maxwellian electromagnetic fieldand then suggest how that gives insight into the structure of Schrödinger's equation in quantum theory, including motivating both the use of complex numbers in the wavefunction and the implementation of "timereversal" by complex conjugation. 
Completed  Autumn/Winter 2023/24 Series
Meetings begin with a gettogether at 15:45 and talks start sharply at 16:00. Each session comprises a 50+10 minutes talk+discussion.
Session  Speakers  Title 

30.11.2023, 16:00
Brussels time Beables for quantum fields 
Andrea Carosso 
Simulating Ontologies in QFT: Bohm and NelsonIn this talk I describe my recent work on simulating the beables implied by the Bohmian and Nelsonian approaches to quantum field theory, after a brief review of Nelson`s theory applied to the hydrogen atom. I employ the Schrödinger representation of QFT regularized on a spatial lattice, where quantum states are wave functions depending on field configurations, and whose squares determine the probability of a field beable taking on certain configurations across space. I focus mostly on the Nelsonian account, since it is understudied in the foundations literature, and because it turns out to provide intuitive pictures of the field beables corresponding to various states in QFT. For example, a very literal meaning is given to the colloquial statement that “particles are excitations of a field”, which otherwise does not have much weight in traditional approaches to QFT. The implications for wave function ontology will be discussed. Finally, I will comment on the case of interacting fields, and the prospects for describing particle creation and annihilation. Throughout the talk, I will show animations of the relevant beables in example cases. 
14.12.2023, 16:00
Brussels time Quantum gravity 
Daniele Oriti 
A foundational trefoil for spacetime: quantum gravity, hydrodynamics and cosmologyThe hydrodynamics of quantum fluids can be mapped to relativistic cosmological dynamics, and both share the same conformal symmetries, which can be unraveled via geometric methods in superspace. This suggests a more general correspondence between hydrodynamics and cosmology, and a picture of the universe as a quantum fluid of nonspatiotemporal building blocks. This picture is in fact realized also in some quantum gravity formalisms, like group field theory, spin foam models and lattice quantum gravity, in which an emergent cosmological dynamics can be extracted from the quantum dynamics of fundamental quantum simplices in a condensate phase. A key ingredient is the relational understanding of space and time, which makes superspace the natural arena for gravitational dynamics, as opposed to the "spacetime" manifold. These results suggest an exciting dialogue between quantum gravity, the theory of quantum fluids and cosmology, as well as a new direction for analogue gravity simulations in the lab. If we are lucky, that is, the expected trefoil fored by quantum gravity, hydrodynamics and cosmology, leading us to the foundations of spacetime, will turn out to be an even more intriguing quatrefoil. 
11.01.2024, 16:00
Brussels time Language of mathematics 
Dustin Lazarovici 
Why the Book of Nature is Written in the Language of Mathematics
Why is mathematics so successful in describing the natural world? More
profoundly, why are the fundamental laws of nature  as far as we know them
today  expressed in mathematical language?

18.01.2024, 16:00
Brussels time Gravitation and collapse 
Daniel Sudarsky 
Dynamical Reduction in General Relativistic ContextsSpontaneous collapse theories provide one of the most promising approaches to dealing with the "measurement problem" in Quantum Theory (QT) . Recent advances have provided versions of the theory that are compatible with special relativity. However, for a theory to be truly viable, it should also be made compatible with General Relativity (GR). I will describe some of the issues that arise when attempting to follow that path, and discuss some ideas about how these might be addressed. I will then argue that, in fact, it is in various situations where GR and QT come together, that these theories exhibit their potential in dramatic manner, offering plausible resolutions to issues that have remained unresolved for a long time. 
25.01.2024, 16:00
Brussels time Quantum decoherence 
Anirudh Gundhi 
Decoherence due to vacuum fluctuations?Previous works have suggested that even when the electron is prepared in a superposition of `here' and `there' in absolute vacuum, its interaction with the fundamentally unavoidable vacuum fluctuations of the electromagnetic field would lead to decoherence. This talk argues against this conclusion. Further, with the help of the mathematical formalism used in addressing this problem, the quantum mechanical version of the AbrahamLorentz equation will be derived (up to second order in the interactions), which is free of the pathologies of its classical counterpart. 
01.02.2024, 16:00
Brussels time Philosophy and physics 
Jacob Barandes 
New Prospects for a Causally Local Formulation of Quantum TheoryIt is difficult to extract trustworthy criteria for causal locality from the limited ingredients of textbook quantum theory. In the end, Bell humbly warned us that his famous theorem was based on principles that "should be viewed with the utmost suspicion." Remarkably, by stepping outside of the wavefunction paradigm, one can reformulate quantum theory in terms of oldfashioned configuration spaces and stochastic laws. These stochastic laws take the form of directed conditional probabilities, which provide a hospitable foundation for speaking about microphysical causal relationships. In this talk, I will argue that this alternative formulation of quantum theory does not suffer from the measurement problem, and that it deflates various exotic claims about superposition, interference, and entanglement. I will also use this new formulation to show directly that systems at spacelike separation cannot exert causal influences on each other, without any need for appeals to Bell's criteria. These results lead to a general interpretation of quantum theory that is arguably compatible with causal locality. 
22.02.2024, 16:00
Brussels time Testing collapse models 
Matteo Carlesso 
Testing collapse models in lab and spaceThe quantum measurement problem finds a possible solution in the socalled collapse models. They are a modification of quantum mechanics which establish a natural and universal mechanism for the quantumtoclassical transition. In turn, they also describe an objective way to determine which are the limits of quantum mechanics. Thus, testing collapse models is equivalent to testing the limits of quantum mechanics. In this talk, I will present my contributions to the theoretical and experimental endeavour for testing collapse models. 
07.03.2024, 16:00
Brussels time Probabilistic Laws 
Eddy Keming Chen 
Algorithmic Randomness and Probabilistic LawsProbabilistic laws of nature, as they are usually understood, are extraordinarily permissive. For example, a probabilistic law of a coin toss experiment is compatible with any sequence of results, including the all heads sequence (HHHHH......) and the alternating headstails sequence (HTHTHT......). This feature can be problematic, as it gives rise to a variety of metaphysical and epistemological underdetermination. We consider two ways one might use algorithmic randomness to strengthen the content of a probabilistic law. They provide much tighter connections between probabilistic laws and their corresponding sets of possible worlds, and allow us to eliminate several philosophical problems about probabilistic laws. (Joint work with Jeffrey A. Barrett; paper version at https://arxiv.org/pdf/2303.01411.pdf) 
21.03.2024, 16:00
Brussels time Beyond the standard model 
Michael Drewsen 
Search for bosons beyond the Standard Model with atomic ionsBy combining highresolution spectroscopy of the 3d ^{2}D_{3/2}  3d ^{2}D_{5/2} interval with an accuracy of ~20 Hz using direct frequencycomb Raman spectroscopy with isotope shift measurements of the 4s ^{2}S_{1/2} ↔ 3d ^{2}D_{5/2} transition in all stable even isotopes of ^{A}Ca^{+} (A = 40, 42, 44, 46, and 48) at the accuracy of ~1 kHz, we have been able to carry out a King plot analysis with unprecedented sensitivity to coupling between electrons and neutrons by bosons beyond the Standard Model. Furthermore, we estimate that by improved spectroscopic techniques available, King plots based on data from spectroscopy on either Ca^{+}, Ba^{+} and Yb^{+} ions should be able to produce sensitivity to such potentially new bosons, which surpass other current methods in a broad mass range of 10 to 10^{8} eV/c^{2}. 
Laws of Nature Conference 2022
We are happy to annoce the Laws of Nature Conference 2022 remembering Detlef Dürr – please find all information following this link.
Completed  Autumn/Winter 2021/22 Series
Session  Speakers  Title 

05.10.2021, 16:00
Brussels time Between past and future 
Paula Reichert & Sheldon Goldstein 
Reichert: Arrow(s) of Time Without a Past HypothesisWe experience that entropy increases, thereby marking an arrow of time, although the underlying microscopic dynamics is timereversal invariant. This seemingly paradoxical fact has, to large extent, been explained by Boltzmann who showed that macroscopic irreversibility is grounded on timeasymmetric boundary conditions, namely on the fact that systems start from very special, lowentropy initial states. Eventually, this reasoning led to the past hypothesis: the postulate that the universe started from a very special, lowentropy initial macro state. Lately, this line of reasoning has been attacked. Physicists like Sean Carroll or Julian Barbour claim that one can dispose of the past hypothesis and instead obtains the arrow of time as a feature of a typical universe. In this talk, we study Boltzmann's statistical reasoning and the way in which the new proposals avoid the conclusion of a past hypothesis. We show how this rests on crucial conceptual differences with respect to Boltzmann's understanding of the universe. In detail, we study the Newtonian gravitational Nbody model and the way in which the notions of entropy and typicality figure in the absolute and relational description of that system. It turns out that a bigbanglike state, a state of apparently low entropy, is typical among relationally distinct solutions where it forms the midpoint of the evolution and thus grounds two arrows of time in an overall timesymmetric one past and two futures scenario. Goldstein: The Distinction Between Past and FutureI will discuss a variety of topics about time and its arrow  mathematical, physical, and metaphysical. 
09.11.2021, 16:00
Brussels time The shapes of things 
Flavio Mercati & Julian Barbour 
Mercati: Saving determinism in gravitational singularitiesI will review the results of a series of papers in which we showed that a variety of homogeneous solutions of General Relativity which have singularities are regularizable. This implies that each and every solution can be continued uniquely through the singularity, questioning a widelyheld expectation that gravitational singularities break down classical determinism, and require quantum effects to be resolved. The result concerns Bianchi IX cosmological models with a large class of scalar fields, Kantowskiâ€“Sachs universes, which describe the interior of a Schwarzschild black hole, and of homogeneous cosmologies coupled with gauge fields. Future plans to generalize the result will be discussed. Barbour: The Emergence of Local Laws of Motion.Maxwell, followed by Einstein, argued that the laws of nature are local and are to be expressed by partial differential equations that take the same form at each spacetime point. This is reflected in cosmology, in which any model of the universe in which the field equations of general relativity hold at each space point (with any acceptable energymomentum tensor on their righthand side) is assumed to be an acceptable model. I will argue that while this is a necessary condition something more ambitious may be needed to restrict possibilities. This is that there exists a master law of the universe from which local laws emerge that allow many more models of the universe than does the master law. I will give illustrative examples. 
07.12.2021, 16:00
Brussels time Quantum events, trees, and histories 
Jürg Fröhlich 
Fröhlich: The Appearance of Events in Quantum Mechanics  a New Dynamical Law of Nature [slides]
The purpose of this talk is to propose an extension of the standard formalism of QM and complete this theory in such a way that it makes sense. The extension, yielding a new Law of Nature, is called "ETH  Approach to QM." The ETH  Approach to QM supplies the fourth one of four pillars QM rests upon:
Core of the talk: Besides sketching the ETHApproach to QM, simple models of a very heavy atom coupled to the radiation field in a limit where the speed of light tends to ∞ will be discussed. These models illustrate the ETHApproach. 
11.01.2022, 16:00
Brussels time Typicality, probability, and physics 
Barry Loewer & Dustin Lazarovici 
Probability and Typicality; Friends or Foes?Typicality and probability approaches to statistical mechanics are often thought of as radically different and competing. In my talk I will describe a probabilistic approach based on David Lewis' Best System Humean account of probability called "the Mentaculus" and a typicality approach based on work by Goldstein, Lazarovici, Hubert and others and argue that while there are some important differences they are more similar than initial appearances. Typicality as a Way of Reasoning in PhysicsBuilding on Barry Loewer's talk, I will argue for aspects of typicality that distinguish it from probability. I will present a view that grounds objective probabilities in a more fundamental notion of typicality and regards typicality not as part of the physical laws but as a way of reasoning about them. 
01.02.2022, 16:00
Brussels time Causal fermion systems 
Felix Finster 
An introduction to causal fermion systems and the causal action principle [slides]
The theory of causal fermion systems is an approach to describe fundamental physics. It gives quantum mechanics, general relativity and quantum field theory as limiting cases and is therefore a candidate for a unified physical theory. Moreover, causal fermion systems provide a general framework for modelling and analyzing nonsmooth spacetime structures. The dynamics of a causal fermion system is described by a nonlinear variational principle, the causal action principle.
The continuum limit of causal fermion systems and quantum states [slides]The goal of my second talk is to outline how to get a connection between the causal action principle and usual physical equations formulated in Minkowski space or curved spacetime. On the level of an interaction via classical bosonic fields, this connection is made precise in the socalled continuum limit. I will explain schematically how the analysis in the continuum limit works. In order to get the connection to quantum field theory, a recent approach is to construct a distinguished state at a fixed time, being a positive functional on the algebra generated by fermionic and bosonic field operators. As an outlook, I will explain the general structure of the resulting quantum dynamics. 
Completed  Spring/Summer 2021 Series
Session  Speakers  Title 

08.04.2021, 16:00
Brussel time There's plenty of room at the bottom 
Roger Penrose 
Penrose: How the Large and Small Interrelate in General Relativity and Quantum MechanicsDespite much theorizing on how quantum theory might modify general relativity at extremely tiny scales, thereby resolving the spacetime singularity problem, there are strong reasons for believing that this cannot provide an overall solution. On the other hand, conformal geometry, relating large to smalla remote expanding future to an initiating big bangleads to important thermodynamical insights and confirmed observations of previously unexpected effects. On the quantum side, the most troublesome and fundamental issue is the measurement problemor collapse of the wavefunctionand here I argue that it is in the large effects of tiny gravitational fields where we must find our answers. 
06.05.2021, 16:00
Brussel time Towards exact theories of nature 
Robert Wald & Michael Kiessling 
Wald: Point Particles and SelfForce in ElectromagnetismPoint charges are a very useful idealization in electromagnetism. Although they are commonly treated as though they are fundamental, they have infinite selfenergy and mathematical inconsistencies arise if one tries to describe their selfconsistent motion. On the other hand, the selfconsistent motion of distributions of continuous charged matter is entirely well defined in classical Maxwell theory. I will describe how to take a mathematically rigorous point particle limit of continuous charged matter wherein the charge and mass scale to zero in proportion to the size of the body. Lorentz force motion is obtained in this limit and selfforce arises as a perturbative correction. It is shown how to obtain selfconsistent motion that respects causality and does not admit spurious runaway solutions. Kiessling: Revisiting the 1920s  with the benefit of hindsight [slides]The 1927 Solvay Conference is perhaps the most renowned physics meeting of the 20th century. An eminently distinguished group of physicists had been invited to discuss the apparent breakthroughs that had happened in the previous two years, in the hope perhaps to come to a common understanding of what had been accomplished. Instead, as one participant (Langevin) later wrote, at the 1927 Solvay conference the confusion of ideas reached its peak. Given the fact that nowadays professional physicists typically disagree with each other about what quantum theory really says about nature, it is fair to say that the confusion has not been cleared up yet. In this talk I will argue that by the end of 1927 we may well have been on the way to a meaningful and accurate quantum mechanics of electrons, nuclei, and photons that does not suffer from the infamous measurement problem of what came to be known as orthodox (standard textbook) quantum mechanics. For this it would have only been necessary that Luis de Broglie, Max Born, and Erwin Schrödinger would have listened to each other more carefully and with an open mind. 
03.06.2021, 16:00
Brussel time Beyond quantum gravity 
Francesca Vidotto & Stefano Liberati 
Vidotto: If you want to build a universe from scratch you must first invent a quantum state of the geometryThe application of the covariant LQG techniques to the universe allows to compute cosmological observable in the deep quantum regime of the early universe. In particular, it is possible to define a cosmological quantum state and study its property. This approach differs from the standard procedure in cosmology, where a primordial vacuum state needs to be assumed to provide the initial condition of the successive evolution. In this talk I will present how such a quantum state can be constructed, providing a spinfoam analogue of the HartleHawking wave function of the universe. I will emphasize the conceptual steps that need to be taken in defining the appropriate observable and the relevant degrees of freedom. I will present the first results obtained with improved numerical techniques. Liberati: Hearts of Darkness: probing of black holes inside outBlack holes are the purest expression of gravity and at the same time the places where our best theory of gravitation, Einstein General Relativity, meets its demise in the form of singularities. We know, however, that any successful theory of quantum gravity should be able to resolve these uncharted regions, but can they do so without showing any modification outside the event horizon? can real black holes be undistinguishable from the one predicted by general relativity? The recent direct observation of these tantalising objects represents an unprecedented possibility to answer these questions. In this talk, we shall explore on general grounds what alternative objects we can expect from a quantum gravity induced regularisation of singularities and discuss what observations can or will tell us about their nature. 
01.07.2021, 16:00
Brussel time Future of quantum foundations 
Siddhant Das & Sandro Donadi 
Das: Can we fix quantum arrival times before 2026?I will discuss the problem of predicting the arrival (or detection) time of a quantum particle on a detector surface that remains unresolved despite the timehonoured empirical successes of quantum mechanics. Given that arrivaltime or timeofflight (TOF) measurements are the quintessence of standard experimental techniques of atomic and particle physics, this is particularly striking. Drawing upon the early history of this issue, I will discuss many (disparate) theoretical predictions for the TOF distribution of a particle suggested in the literature. These are informed by various semiclassical heuristics, principles, extensions, or (for want of a better word) "interpretations" of quantum theory. Next, I will describe a socalled "backwall" experimentan arrivaltime experiment developed in collaboration with my late (and truly great) advisor Prof. Detlef Dürr that can reliably distinguish the aforementioned proposals. A key feature of our setup is that the particle is escaping a potential barrier (the backwall) in the direction of a distant detector, as opposed to moving completely freely. Without the backwall, most proposals become nearly indistinguishable, which renders usual experimental tests inconclusive. I will also describe a concrete iontrap implementation of the backwall experiment doable with presentday technology. Time permitting, I will mention a version of this experiment featuring a spin1/2 particle as an electron whose de BroglieBohm analysis predicts, thanks to quantum backflow, intriguing spindependent arrivaltime distributions hitherto unknown, demanding experimental inspection. Donadi: Collapse Models: State of the Art and Future PerspectivesCollapse models solve the measurement problem by modifying the Schrödinger equation, adding new terms which describe spontaneous localization in space of the wavefunction. Because of these additional terms, collapse models make different predictions compared to Quantum Mechanics, so they can be experimentally tested. In this talk, we will give an introduction to the most important collapse models and to the state of the art of the bounds on their phenomenological parameters, coming from different experiments. We then also discuss possible improvements of these bounds as well as theoretical developments of the models. 
Moderated by: Dr. Paula Reichert
About
Laws of Nature Series is a new initiative to promote the exchange of physical, philosophical, and mathematical ideas in the field of the foundations of quantum physics.
Currently, this initiative is organized by
 Angelo Bassi from the University of Trieste,
 Dirk  André Deckert from the LMU Munich, and
 Paula Reichert from the LMU Munich, and
 Ward Struyve from the KU Leuven.
Format
The Laws of Nature Series comprises a Spring and Autumn Series each comprising online colloquia held in the form of themed sessions on Zoom. The session theme can be found in the first column of the schedules. The current chosen format for each session is a 50 minutes talk followed by a 10 minutes discussion. Meetings begin with a gettogether at 15:45 and talks start sharply at 16:00.
Contact
If you are interested in joining our seminar community, please contact us by email and state your full name and institution. We will then put you on our email newsletter in which the latest schedule announcements as well as all information to join the respective online meetings will be posted ahead of time. Please understand that anonymous emails will be disregarded.
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