## Reality as a Vector in Hilbert Space

**Sean M. Carroll**

I defend the extremist position that the fundamental ontology of the world consists of a vector in Hilbert space evolving according to the Schrödinger equation. The laws of physics are determined solely by the energy eigenspectrum of the Hamiltonian. The structure of our observed world, including space and fields living within it, should arise as a higher-level emergent description. I sketch how this might come about, although much work remains to be done.

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## On modelling bicycle power-meter measurements

**Tomasz Danek, Michael A. Slawinski, Theodore Stanoev**

We combine power-meter measurements with GPS measurements to study the model that accounts for the use of power by a cyclist. The model takes into account the change in elevation and speed along with adverse effects of air, rolling and drivetrain resistance. The focus is on estimating the resistance coefficients using numerical optimization techniques to maintain an agreement between modelled and measured power-meter values, which accounts for the associated uncertainties. The estimation of coefficients is performed for two typical scenarios of road cycling under windless conditions, along a course that is mainly flat as well as a course of near constant inclination. Also, we discuss relations between different combinations of two model parameters, where other quantities are constant, by the implicit function theorem. Using the obtained estimates of resistance coefficients for the two courses, we use the mathematical relations to make inferences on the model and physical conditions. Along with a discussion of results, we provide two appendices. In the first appendix, we illustrate the importance of instantaneous cadence measurements. In the second, we consider the model in constrained optimization using Lagrange multipliers.

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## Uncertainty and the weirdness of classical physics

Edwin Steiner explore the concepts of uncertainty and probability as aspects of the common empirical basis of classical and quantum physics.

## Antimatter and other deep mysteries

**Public lecture by Dr. Gerald Gabrielse**

Our universe is made of matter. Yet the Big Bang produced essentially equal amounts of matter and antimatter according to our most fundamental understanding of the building blocks of nature. The inability of our fundamental theory to describe this basic feature of our universe is the great frustration of modern physics. In this one-hour lecture, held on Feb. 19, 2021, Dr. Gerald Gabrielse, Northwestern University, gives an introduction to antimatter and matter, explains the theoretical framework that explains particle interactions, and gives examples of attempts to solve the mystery of antimatter.

Dr. Gerald Gabrielse, a member of the National Academy of Science and the American Academy of the Arts and Sciences, is a Trustees Professor at Northwestern University. His vision, techniques and measurements started low-energy antiproton and antihydrogen research at the European laboratory CERN. He has made the most precise measurement of a property of an elementary particle, the electron’s magnet, to test the Standard Model’s most precise prediction. His test of whether the electron charge is spherical is one of the most sensitive tests for physics beyond the Standard Model.

## Elementary Particles: What are they? Substances, elements and primary matter

**D-M. Cabaret, T. Grandou, G-M. Grange, E. Perrier**

The most successful “Standard Model” allows one to define the so-called “Elementary Particles”. Now from another point of view, philosophical, how can we think of them? Which kind of a status can be attributed to Elementary Particles and their associated quantised fields? Beyond the unprecedented efficiency and reach of quantum field theories the current paper attempts at understanding the nature of what we talk about, the enigmatic reality of the quantum world.

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## Towers on the Moon

**Sephora Ruppert, Amia Ross, Joost Vlassak, Martin Elvis**

The lunar South pole likely contains significant amounts of water in the permanently shadowed craters there. Extracting this water for life support at a lunar base or to make rocket fuel would take large amounts of power, of order Gigawatts. A natural place to obtain this power are the “Peaks of Eternal Light”, that lie a few kilometers away on the crater rims and ridges above the permanently shadowed craters. The amount of solar power that could be captured depends on how tall a tower can be built to support the photovoltaic panels. The low gravity, lack of atmosphere, and quiet seismic environment of the Moon suggests that towers could be built much taller than on Earth. Here we look at the limits to building tall concrete towers on the Moon. We choose concrete as the capital cost of transporting large masses of iron or carbon fiber to the Moon is presently so expensive that profitable operation of a power plant is unlikely. Concrete instead can be manufactured in situ from the lunar regolith. We find that, with minimum wall thicknesses (20 cm), towers up to several kilometers tall are stable. The mass of concrete needed, however, grows rapidly with height, from ∼ 60 mt at 1 km to ∼ 4,100 mt at 2 km to ∼10^{5} mt at 7 km and ∼10^{6} mt at 17 km.

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