Sommerfeld Lecture Series (ASC)

Populations and communities rarely evolve in static environments; their fitness landscapes fluctuate across space and time, forming what may be called a noisy seascape. This talk examines how such variability modifies classical models of population dynamics and community stability. Beginning from the logistic equation, I will show how spatiotemporal fluctuations in fitness lead naturally to power-law population statistics and, under certain conditions, to the empirical (fractional) Richards growth law. Extending these ideas to interacting species reveals that the combined effects of dispersal and environmental noise can stabilize large, diverse communities despite strong competitive interactions. The resulting framework connects extinction, growth, and coexistence within a unified view of life on a noisy seascape.

Active systems are driven out of equilibrium by exchanging energy and momentum with their environment. This endows them with anomalous mechanical properties which leads to rich phenomena when active fluids are in contact with boundaries, inclusions, or disordered potentials. Indeed, studies of the mechanical pressure of active fluids and of the dynamics of passive tracers have shown that active systems impact their environment in non-trivial ways, for example, by propelling and rotating anisotropic inclusions. Conversely, the long-ranged density and current modulations induced by localized obstacles show how the environment can have a far-reaching impact on active fluids. This is best exemplified by the propensity of bulk and boundary disorder to destroy bulk phase separation in active matter, showing active systems to be much more sensitive to their surroundings than passive ones.

Quantum physics teaches us that even the emptiest vacuum is teeming with fluctuations of electromagnetic fields. When these fluctuations are confined between objects, they produce measurable forces: the Casimir effect describes an attraction between uncharged conductors arising solely from the confinement of the quantum void. In this talk, I will explore how this subtle quantum phenomenon connects to ideas of attraction, repulsion, and mechanical work. After introducing the origin and measurement of the Casimir force, I will discuss whether it can be made repulsive, and why true levitation remains elusive in equilibrium. Extending these ideas beyond equilibrium reveals new possibilities: radiation pressure from heat, nonreciprocal materials that generate motion and work without contact, and rotating bodies that spontaneously emit light. Together, these examples show how the restless quantum vacuum continues to surprise us.

Cosmic strings are linear defects that could be formed at a phase transition in the early universe. Strings are predicted in a wide class of particle physics models. In particular, fundamental strings of superstring theory can have astronomical dimensions and play the role of cosmic strings. I will discuss recent progress in understanding the evolution of cosmic strings and possible ways of detecting them.

In recent decades, physicists and astronomers have discovered two beautiful

Standard Models, one for the quantum world of extremely short distances, and one

for the universe as a whole. Both models have had spectacular success, but there are

also strong arguments for new physics beyond these models. In this lecture, we will

review these models, their successes and their shortfalls. We will describe how

experiments in the near future could point to new physics suggesting a profound

conceptual revolution, which could change our view of the world.

Aside from enabling revolutionary future technologies, quantum

information science is providing powerful new tools for attacking

deep problems in fundamental physical science. In particular, the

recent convergence of quantum information and quantum gravity is

sparking exciting progress on some old and very hard questions.

From copper-oxide superconductors to rare-earth compounds, materials with strong electronic correlations have focused enormous attention over the last two decades. Solid-state chemistry, new elaboration techniques and improved experimental probes are constantly providing us with examples of novel materials with surprising electronic properties, the latest example being the recent discovery of iron-based high-temperature superconductors.

In this colloquium, I will emphasize that the classic paradigm of solid-state physics, in which electrons form a gas of wave-like quasiparticles, must be seriously revised for strongly correlated materials. Instead, a description accounting for both atomic-like excitations in real-space and quasiparticle excitations in momentum space is requested. I will review how Dynamical Mean-Field Theory -an approach that has led to significant advances in our understanding of strongly correlated materials- fulfills this goal.

New frontiers are also opening up, which bring together condensed-matter physics and quantum optics. `Artificial materials' made of ultra-cold atoms trapped by laser beams can be engineered with a remarkable level of controllability, and allow for the study of strong- correlation physics in previously unexplored regimes.

Which property of a material is more familiar to us than its color? And yet, the strange laws of quantum mechanics, which rule atoms, electrons and photons, are key to the understanding of this most beautiful feature! The invention and engineering of novel materials has shaped human civilization, from the Bronze age to the Silicon age. This lecture is an invitation to explore materials down to the scale of their intimate constituents – atoms and electrons. We'll address questions such as: do we master quantum mechanics well enough today to explain how materials behave from the only knowledge of the atoms which build them? Have we reached the stage where the principles of quantum mechanics allow for the design of a novel material with specific functionalities?

When we think about evolution, it is typically in the context of

natural history, seeking an explanation for the amazing diversity of life. Yet evolution is not only the matter of the past, but an ongoing dynamical process linking the past with the future. Evolutionary

dynamics is particularly apparent in rapidly mutating microbes and

viruses. For example, the virus causing seasonal flu continuously evolves to escape human immunity generated by previous

infections: because of this process, we get the flu again and again.

Can we understand evolutionary dynamics well enough to predict

the future, at least far enough to help with the flu vaccine updates?

This talk will review basic mechanisms of evolutionary dynamics and discuss some of the old and new approaches to evolutionary

forecasting and the challenges that they face. Surprisingly, ideas

from Theoretical Physics can be helpful in understanding

evolutionary dynamics.

Does the world embody beautiful ideas? Pythagoras and Plato intuited that it should, Newton and Maxwell showed, in impressive examples, how it could. Modern physics demonstrates, in depth and detail, that it does. I will narrate, through notable examples, how the concept of beauty in physical law has evolved – and how it continues to guide our quest for ultimate understanding.