### Basic Notions

Basic Notions is a bi-weekly seminar at Wednesdays from 3:30pm to 4:30pm. Its format is hybrid (online/onsite). After the talk we go out for drinks in the Foodcourt.

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Organisers: Roland van der Veen and Kevin van Helden

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What is basic knowledge to one person may be rather mysterious to another. The plan of this seminar is to promote the communication between physics, astronomy and mathematics by having some informal discussions on basic notions relevant to everybody. The topic is intentionally rather broad, but since this is part of the Fundamentals of the Universe program, a few examples that come to mind could be 'duality', 'field', 'tensor', 'quantization', 'distribution', 'action', 'representation',...

Everybody is busy so the point is not to prepare a great and impressive presentation. Rather the converse: if you cannot speak about it unprepared then it may not be a basic notion for you. At any rate the level should not be higher than what a good bachelor student in her/his 3rd year can understand.

##### The cosmic microwave background - between theory and observation.

June 1st 2022

Alba Kalaja

The anisotropies imprinted in the CMB are our most important window into

the very early universe. In this session, I will explain the main features of such anisotropies and what they tell us about the initial conditions of the universe.

Time: 3:30pm - 4:30pm

Location: room 5161.0041b

##### A variational principle for integrable systems, symmetries, and discretisation &

Cold atoms and molecules

May 18th 2022

Mats Vermeeren & Steven Hoekstra

We will join together with the Floris Takens seminar in a mini symposium with two talks.

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Talk 1: A variational principle for integrable systems, symmetries, and discretisation (Mats Vermeeren, 3:00pm - 4:00pm)

Classical integrable systems are traditionally characterised by a condition formulated in terms of Hamiltonian mechanics. A Lagrangian theory of integrability exists as well, but it is a much more recent and lesser-known development. My talk will give an overview of this theory, known under the names "pluri-Lagrangian systems" and "Lagrangian multiforms".

Even though these ideas emerged from integrable systems, they apply more generally. A good way to think about Lagrangian multiforms is as a framework that captures a dynamical system together with its symmetries in a single variational principle. Compared to the Hamiltonian perspective, a variational principle has the advantage that it easily transforms between discrete and continuous settings. I will show glimpses of continuous, semi-discrete (differential-difference) and fully discrete Lagrangian multiforms.

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Talk 2: Cold atoms and molecules (Steven Hoekstra, 4:00pm - 5:00pm)

The research field of cold atoms and molecules is all about controlling the motion and the internal state of these small quantum systems. Following the amazing achievements with atoms that are cooled to quantum degeneracy (a new state of matter, called a bose-einstein-condensate) a few decades ago, the current focus in atomic, molecular and optical physics is on controlling - and using - more complicated systems, such as diatomic molecules. In my research we use cold and controlled molecules to probe fundamental physics, but cold molecules are also being explored to study for example cold chemistry (think of astrochemistry, chemical reactions in space) and even complicated solid state systems (in quantum simulation by an array of cold molecules in an optical lattice, for example). In my recently awarded VICI project we will cool take the next step to even more complicated systems (polyatomic molecules), specifically for a next-generation search for the electron's electric dipole moment. If this property would be detected, it would be a clear observation of physics beyond the standard model of particle physics. In this meeting I would like to present and discuss the basic notions of making, and using, cold atoms and molecules.

Time: 3:00pm - 5:00pm

Location: room 5161.0041b

##### The Ginzburg-Landau Equation

May 4th 2022

Riccardo Bonetto

The Ginzburg-Landau Equation (GLE) is among the most celebrated equations in nonlinear physics. Indeed, GLE arises in a wide range of phenomena such as superconductivity, superfluidity, second-order phase transitions, but also from biological models and chemical reactions. The universality of GLE follows from the fact that it describes the behaviour of a reaction-diffusion (extended) system near the threshold of instability.

The goal of this seminar is to derive via perturbation theory a 1D GLE from Swift-Hohenberg equation. We aim to emphasize the necessary mathematical techniques, and to highlight generic properties associated with reaction-diffusion systems.

Time: 3:30pm - 4:30pm

Location: room 5161.0267

##### Cosmological Inflation

April 20th 2022

Thomas Flöss

TBA

Time: 3:30pm - 4:30pm

Location: room 5161.0041b

##### Physics of Topological Phenomena

April 6th 2022

Guiseppe de Nittis & Max Lein

We will join the mini symposium organized by Marcello Seri. Prof. Giuseppe de Nittis (PUC, Santiago, Chile) and Prof. Max Lein (AIMR, Sendai, Japan) will give a pedagogical overview to the physics of topological phenomena, targeting both physicists and mathematicians.

Time: 2:30pm - 4:50pm

Location: room 5173.0050 or online

##### Philosophy of Science - part 2

March 23rd 2022

Simon Friedrich

â€‹Are there regions where the laws and constants of nature are different, perhaps in spatio-temporally separate universes? In this talk, I review the debate about whether the existence of such universes can be inferred from the "fine-tuning" of the laws of nature for life. And I consider suggested attempts to make concrete multiverse theories testable.

Time: 1:00pm - 2:00pm

Location: room 5113.0202 or online

##### Philosophy of Science - part 1

March 16th 2022

Simon Friedrich & Sean Gryb

We give a general overview of key debates in the philosophy of science. We first outline why it is not at all obvious what it means for a scientific theory to be "confirmed." Next, we consider whether Popper's falsificationism provides an attractive answer to this challenge, and we provide a glimpse at Bayesian and (post-) Kuhnian developments. Finally, to round off our panorama of philosophy of science, we explain why the notion of explanation in the sciences is tricky and why "cause" may not be the kind of physical notion that physicists sometimes take it to be.

Time: 1:00pm - 2:00pm

Location: room 5113.0202 or online

##### Supersymmetry

February 23th 2022

Boudewijn Bosch

##### Moment maps

February 9th 2022

Tamás Görbe

Momentum maps allow us to obtain conserved quantities in Hamiltonian systems with symmetry. In this talk, I'll explain how momentum maps are constructed and give examples of momentum maps (including the conservation of linear and angular momentum).

Time: 3:30pm - 4:30pm

Location: room 5161.0222 or online

##### The early Universe

January 26th 2022

Sophie van Mierlo

In this talk, I will discuss the conditions of the Universe when the first galaxies came into existence by giving a quick overview of galaxy formation in LCDM. In addition, I will go over various theories regarding the reionization of the early, neutral Universe, as it not yet well established when and how it happened exactly.

Time: 3:30pm - 4:30pm

Location: online

##### Actions and Angles

December 8th 2021

Orlin Koop

Actions and Angles constitute a system of phase-space coordinates that is widely used in Galactic studies to describe orbits of bodies in a Galactic Gravitational potential.

In this talk I will introduce what Actions and Angles are and why they are of interest, and I will point out the intricacies and problems we currently still have while using Actions and Angles with our current datasets.

Time: 3:30pm - 4:30pm

Location: room 5115.0020 or online

##### Fiber Bundles

November 24th 2021

Eric Pap

In mathematics, it is common to think of spaces as being composed of `fibers', so that the space is a `fiber bundle'. Picking an element of each fiber gives a way to unify functions, vector fields, k-forms and gauge fields. We will consider these notions of `local triviality' and `section' hands-on, in which we can recognize basics as `expressing in local coordinates' and `gauge fixing'.

Time: 3:30pm - 4:30pm

Location: room 5115.0014 or online

##### Neural networks

November 10th 2021

Jann Aschersleben

Machine learning algorithms can appear as black boxes that magically return the correct answers of a complex problem. I will introduce the very basic principles of artificial neural networks and how they learn to solve a problem from labelled training data.

Time: 3:30pm - 4:30pm

Location: room 5161.0289 or online

##### My name is Theory, Category Theory

October 27th 2021

Jorge Becerra

I will give a down-to-earth, non-technical overview of some basic concepts of category theory that are transversal in mathematics and physics, giving many different examples. I will also illustrate how this framework arises naturally in physics.

Time: 3:30pm - 4:30pm

Location: room 5161.0289 or online

##### Tensors

October 13th 2021

Martijn Kluitenberg

Some might say a tensor is "something that transforms like a tensor," while others might say that it's "an element of a tensor space." I will not try to answer the question "What is a tensor?" but I will try to explain the relationship between the previous two useless answers.

Time: 3:30pm - 4:30pm

Location: room 5161.0289 or online

##### Quantum calculus

September 29th 2021

Jeffrey Weenink

Quantum calculus, is first your university year of math without limits. A lot of easy results can be restated in this simple formalism. It's especially useful in non-commutative (i.e. quantum) settings, where it is a more natural language instead of the standard calculus and algebra.

Time: 3:30pm - 4:30pm

Location: room 5161.0289 or online

##### Space according to the functions on it.

September 13th 2021

Roland van der Veen

Think of some space X. How will you describe it? How can you communicate what's happening inside? How can you do calculations with it? In answering such questions you will probably have used certain functions on X. In fact the outcome of any measurement you do on X would be a function on X, so I will argue that the space of functions Fun(X) is more fundamental than X itself. If that is so then it seems a good idea to reformulate basic notions of geometry on X directly in terms of Fun(X). Taking this to the extreme we can forget about X and just work with some set of functions Fun(X). This point of view is especially useful if X is behaving badly and/or we want to quantize. One of the founders of this subject is Shahn Majid and he will tell us less basic things about it in our September 24 fundamentals of the universe symposium.

Time: 3:30pm - 4:30pm

Location: room 5161.0041b or online

##### Partitioning an n-cube

July 8th 2021

Nikolay Martynchuk

Time: 2:00pm - 3:00pm

Location: online

##### Basics of General Relativity

June 17th 2021

Ema Dimastrogiovanni

Time: 2:00pm - 3:00pm

Location: online

##### The Geometric Nature of Fundamental Physics

June 3rd 2021

Bram Brongers

We will explore the Wu-Yang dictionary, which established a deep connection between the geometry of principal bundles and particle physics, in the 1970s. The primary aim is to explain the mathematical/geometric perspective of what a gauge theory is.

Time: 2:00pm - 3:00pm

Location: online

##### The Solvability of the Hard Problem of Consciousness

May 6th 2021

Jelmar de Vries

In this presentation, we will explore a proof showing that no theory (physical or otherwise) can explain the qualitative experience that humans have. We will also have a brief look at the implications of this proof.

Time: 2:00pm - 3:00pm

Location: online

##### (Super-)Integrable Planetary Systems

April 22nd 2021

Dijs de Neeling

We'll talk about Liouville integrability in the context of planetary systems. How is integrability defined? And what is super-integrability? What are the consequences for systems that posses these properties?

Time: 2:00pm - 3:00pm

Location: online

##### What is a tropical variety?

April 4th 2021

Oliver Lorscheid

Time: 2:00pm - 3:00pm

Location: online

##### Quantum entanglement

March 25th 2021

Martine Schut

I'll discuss quantum entanglement. How do we define it? How is it useful? And how do we measure it? To answer these questions we will probably talk a bit about the density matrix formalism as well.

Time: 2:00pm - 3:00pm

Location: online

##### Meta-stable quantum mechanics

March 3rd 2021

Giovanni van Marion

A hot particle is trapped in the local minimum of some potential and is trying to tunnel out. How can we compute its decay rate? I will discuss this problem from various angles and how it connects to my research.

Time: 2:00pm - 3:00pm

Location: online

##### Reduction in physics

February 25th 2021

Myrthe Scheepers

The notion of reduction is of great importance in describing the relation between different theories in physics, but different examples seem to indicate different characteristics of that relation. So what are our requirements for theory reduction?

Time: 2:00pm - 3:00pm

Location: online

##### Dynamics of the Kuramoto model

February 2nd 2021

Nico Moro

##### Geometry of Maxwell's equations

January 28th 2021

Kevin van Helden

In physics, everybody is familiar with the theory of electromagnetism. The equations behind this theory are known as the Maxwell equations, and they relate the electric and the magnetic field by derivatives, divergences and rotations. There is also a different approach to writing those equations, and that involves exterior derivatives and differential forms. We will explore this path and see how these approaches are related.

Time: 2:00pm - 3:00pm

Location: online

##### Group theory

January 7th 2021

Roland van der Veen

To kick off the new year let's have a chat about symmetry. Here's a fun fact to get us started: take the multiplication table of any group and interpret it as a square matrix with whose entries are independent variables. The determinant of that matrix will factor into the "elementary particles of the group", the irreducible representations.

Time: 2:00pm - 3:00pm

Location: online

##### Field theory

December 10th 2020

Johannes Lahnsteiner

I will give a short overview of field theory and its significance in theoretical physics. I will sketch how to define, organize, and use field theories by reviewing the hallmark examples of 20th-century physics: Einstein gravity, the standard model of particle physics, and effective field theories in condensed matter physics. The focus will lie on unpacking the jargon and the general structure of these examples.

Time: 1:00pm - 2:00pm

Location: online

##### Conjugation and adjoint actions

November 19th 2020

Eric Pap

How does conjugation appear in practice? What groups are connected to conjugation? How does a bracket relate to conjugation? Handout available here

Time: 2:00pm - 3:00pm

Location: online

##### Hamiltonian Mechanics

November 5th 2020

Federico Zadra

I will explain how this construction appears to be the natural choice in some physical problem, how symplectic geometry and in other geometrical frameworks enter in physics.

Time: 2:00pm - 3:00pm

Location: online

##### Active vs passive

October 22nd 2020

Diederik Roest

Time: 2:00pm - 3:00pm

Location: online

##### The dual of a vector space

October 8th 2020

Roland van der Veen

Some topics we may to touch on: Is the dual of the dual the same as the original? How do you raise an index? What is the transpose? and why not just pick a metric/inner product? What is the Dirac delta function? What happens when you tensor with the dual?

Time: 2:00pm - 3:00pm

Location: online