Nineteenth Arnold Sommerfeld Lecture Series, Two of the most amazing ideas in physics are the holographic

principle and quantum error correction. The holographic principle

asserts that all the information contained in a region of space is

encoded on the boundary of the region, albeit in a highly scrambled

form. Quantum error correction is the foundation of our hope that

large-scale quantum computer can be operated to solve hard

problems. I will argue that these two ideas are closely related, and

will describe quantum codes which realize the holographic

principle. These codes provide simplified models of quantum

spacetime, opening new directions in the study of quantum gravity,

though many questions remain.

Twentieth Arnold Sommerfeld Lecture Series, Global symmetries and gauge symmetries have played a crucial role in physics. The

idea of duality demonstrates that gauge symmetries can be emergent and might not

be fundamental. During the past decades it became clear that the circle of ideas

about emergent gauge symmetries and duality is central in different branches of

physics including Condensed Matter Physics, Quantum Field Theory, and Quantum

Gravity. We will review these developments, which highlight the unity of physics.

Twentieth Arnold Sommerfeld Lecture Series, A combination of ideas originating from Condensed Matter physics, Supersymmetric Field Theory, and AdS/CFT has led to a detailed web of conjectured dualities. These relate the long distance behavior of different short distance theories. These dualities clarify a large number of confusing and controversial issues in Condensed Matter physics and in the study of 2+1 dimensional quantum field theory.

Twentyfirst Arnold Sommerfeld Lecture Series, Superconductivity, the ability of certain materials to conduct electricity with

no resistance whatsoever, has fascinated scientists since its discovery by

Kammerlingh-Onnes in 1911. While much has been understood, the question

of predicting which materials will become superconducting, and at what

temperatures, remains one of the grand challenges of modern materials

theory. This talk will outline the evolution of our understanding as the subject

has progressed from its primitive beginnings through the ''bronze age''

marked by the 1986 discovery of high temperature superconductivity in

copper-oxide compounds to the present-day ''iron age'' of the Fe-As based

superconducting materials. The current status of the theory of the origin of

superconductivity will be described.

Twentyfirst Arnold Sommerfeld Lecture Series, This talk will present an overview of recent progress towards a solution of one

of the grand-challenges of modern science: understanding the properties of

interacting electrons in molecules and solids. After an introduction to the

physics I will argue our theoretical understanding of a basic model system,

the two dimensional Hubbard model, has reached the level that we can say

with confidence that its superconducting properties capture key aspect of the

high-Tc superconductivity in copper-oxide materials. I will then summarize

the current status of our extension of the methods to fully physically realistic

systems, emphasizing the areas of theoretical uncertainty and the prospects

for resolution.

Twentyfirst Arnold Sommerfeld Lecture Series, Advances in light sources and time resolved spectroscopy have made it

possible to excite specific atomic vibrations in solids and to observe the

resulting changes in electronic properties. I argue that in narrow-band

systems the dominant symmetry-allowed coupling between electron density

and dipole active modes implies an electron density-dependent squeezing of

the phonon state which provides an attractive contribution to the electron-electron

interaction, independent of the sign of the bare electron-phonon

coupling and with a magnitude proportional to the degree of laser-induced

phonon excitation. Reasonable excitation amplitudes lead to non-negligible

attractive interactions that may cause significant transient changes in

electronic properties including superconductivity. The mechanism is

generically applicable to a wide range of systems, offering a promising route

to manipulating and controlling electronic phase behavior in novel materials.

Twentieth Arnold Sommerfeld Lecture Series, 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.

Sixteenth Arnold Sommerfeld Lecture Series, The Principle of Least Action is both profound and practical. Since its first formulation by Maupertuis and Euler nearly three centuries ago, the Principle has been, and continues to be, a formidable battlehorse for penetrating unchartered territory in

theoretical physics. The Principle, its connection with, and implications for, our ideas of symmetry, space, time, quantum mechanics, thermodynamics and gravitation, are glanced at.

Fifteenth Arnold Sommerfeld Lecture Series, A piece of paper or candy wrapper crackles when it is crumpled. A magnet crackles when you change its magnetization slowly. The earth crackles as the continents slowly drift apart, forming earthquakes. Crackling noise happens when a material, when put under a slowly increasing strain, slips through a series of short, sharp events with an enormous range of sizes. There are many thousands of tiny earthquakes each year, but only a few huge ones. The sizes and shapes of earthquakes show regular patterns that they share with magnets and many other systems. This suggests that there must be a shared scientific explanation. We shall hear about crackling noise and that it is a symptom of a surprising truth: the system behaves the same on small, medium, and large scales.

Fifteenth Arnold Sommerfeld Lecture Series, “With four parameters I can fit an elephant; with five I can make it wag its tail.” Systems biology models of the cell have an enormous number of reactions between proteins, RNA, and DNA whose rates (parameters) are hard to measure. Models of climate change, ecosystems, and macroeconomics also have parameters that are hard or impossible to measure directly. If we fit these unknown parameters, fiddling with them until they agree with past experiments, how much can we trust their predictions? Multiparameter fits are sloppy; the parameters can vary over enormous ranges and still agree with past experiments. Nonetheless, they can often make useful predictions about future experiments, even allowing for these huge parameter uncertainties: a few stiff combinations of parameters govern the behavior. Third, these sloppy models all appear strikingly similar to one another – for example, the stiffnesses in every case we’ve studied are spread roughly uniformly over a range of over a million. We will use ideas and methods from differential geometry to explain what sloppiness is and why it happens so often. Finally, we shall show that models in physics are also sloppy – that sloppiness makes science possible.