March 30, 2022, 7:30 p.m.
Sitterzaal

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Big ice and Sea level rise

Michiel van den Broeke

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The climate is changing, land ice is melting and sea levels are rising. Only several decades ago, it was unknown how fast the big ice sheets of Greenland and Antarctica would react to a warming atmosphere and ocean. But smart satellites that were recently launched can directly measure mass changes at the surface of the earth. They showed beyond a doubt that the big ice sheets are melting, and that their mass loss accelerates. This is cause for concern, because together these ice sheets contain sufficient water to raise global sea levels by tens of metres. In this presentation we travel to the ice sheets of Greenland and Antarctica, and learn about processes that determine their mass balance, how it is currently changing and what we can expect for the not too distant future. We also look back into the distant past, to put the current changes in a context of past natural climate variability

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April 6, 2022, 7:30 p.m.
Sitterzaal

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Atom-by-atom engineering of novel states of matter

Cristiane Morais Smith

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Feynman’s original idea of using one quantum system that can be manipulated at will to simulate the behavior of another more complex one has flourished during the last decades in the field of cold atoms. More recently, this concept started to be developed in nanophotonics and in condensed matter. In this talk, I will discuss a few recent experiments, in which 2D electron lattices were engineered on the nanoscale using STM manipulation of adatoms on the surface of copper. First, I will show that it is possible to control the geometry of the lattice [1] and the orbital degrees of freedom [2] by building different Lieb lattices [1,2]. Then, I will show how to realize topological states of matter using the same procedure. We investigate the robustness of the zero modes in a breathing Kagome lattice, which is the first experimental realization of a designed electronic higher-order topological insulator [3], and the fate of the edge modes in a Kekule structure, upon varying the type of boundary of the sample [4]. Finally, we will control the effective dimension of the electronic structure by creating a Sierpinski gasket [5-7], which has dimension D = 1.58. The realization of this first quantum fractal opens the path to electronics in fractional dimensions. In addition, our recent investigation of quantum transport in fractals by using photonic quantum simulators might shed some light on the issue of consciousness

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June 1, 2022, 7:30 p.m.
Sitterzaal

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Thinking Effectively About Gravity

Clifford Burgess

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We live at a time of contradictory messages about how successfully we understand gravity. General Relativity seems to work well in the Earth’s immediate neighborhood, but arguments abound that it needs modification at very small and/or very large distances. This talk tries to put this discussion into the broader context of similar situations in other areas of physics, and summarizes some of the lessons which our good understanding of gravity in the solar system and elsewhere has for proponents for its modification over very long and very short distances. The main message is mixed: On one hand short-distance quantum effects are notoriously difficult to control in gravity and cosmology seems to like features (like light scalars and small vacuum energies) that are not generic to the long-wavelength limit of fundamental theories. These are crucial clues that would be silly to ignore. On the other hand, General Relativity successfully passes many stringent new observational tests and also seems to be almost unique in its ability to reconcile quantum effects with gravity on longer distances without being inconsistent. Neither of these seems to offer much scope for modification. I try to organize what the successes of GR might be telling us, and provide a score-card about it says about the various alternatives that have been proposed.

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• June 1, 2022, 7:30 p.m. CE Clifford Burgess (Mc Master University, Hamilton Canada) Thinking Effectively About Gravity