Month: September 2024

What is entropy? by John C. Baez

Once there was a thing called Twitter, where people exchanged short messages called ‘tweets’. While it had its flaws, I came to like it and eventually decided to teach a short course on entropy in the form of tweets. This little book is a slightly expanded version of that course.
It’s easy to wax poetic about entropy, but what is it? I claim it’s the amount of information we don’t know about a situation, which in principle we could learn. But how can we make this idea precise and quantitative? To focus the discussion I decided to tackle a specific puzzle: why does hydrogen gas at room temperature and pressure have an entropy corresponding to about 23 unknown bits of information per molecule? This gave me an excuse to explain these subjects:
• information
• Shannon entropy and Gibbs entropy
• the principle of maximum entropy
• the Boltzmann distribution
• temperature and coolness
• the relation between entropy, expected energy and temperature • the equipartition theorem
• the partition function
• the relation between entropy, free energy and expected energy • the entropy of a classical harmonic oscillator
• the entropy of a classical particle in a box
• the entropy of a classical ideal gas.

Read the full book at: math.ucr.edu

Augmenting the availability of historical GDP per capita estimates through machine learning

Philipp Koch, Viktor Stojkoski, and César A. Hidalgo

PNAS 121 (39) e2402060121

The scarcity of historical GDP per capita data limits our ability to explore questions of long-term economic development. Here, we introduce a machine learning method using detailed data on famous biographies to estimate the historical GDP per capita of hundreds of regions in Europe and North America. Our model generates accurate out-of-sample estimates (R2 = 90%) that quadruple the availability of historical GDP per capita data and correlate positively with proxies of economic output such as urbanization, body height, well-being, and church building activity. We use these estimates to reproduce the reversal of fortunes experienced by southern and northern Europe and the historical role played by Atlantic ports. These findings show that machine learning can effectively augment the historical availability of economic data.

Read the full article at: www.pnas.org

Typicality, entropy and the generalization of statistical mechanics

Bernat Corominas-Murtra, Rudolf Hanel & Petr Jizba

EPJ B Volume 97, article number 129, (2024)

When at equilibrium, large-scale systems obey conventional thermodynamics because they belong to microscopic configurations (or states) that are typical. Crucially, the typical states usually represent only a small fraction of the total number of possible states, and yet the characterization of the set of typical states—the typical set—alone is sufficient to describe the macroscopic behavior of a given system. Consequently, the concept of typicality, and the associated Asymptotic Equipartition Property allow for a drastic reduction of the degrees of freedom needed for system’s statistical description. The mathematical rationale for such a simplification in the description is due to the phenomenon of concentration of measure. The later emerges for equilibrium configurations thanks to very strict constraints on the underlying dynamics, such as weekly interacting and (almost) independent system constituents. The question naturally arises as to whether the concentration of measure and related typicality considerations can be extended and applied to more general complex systems, and if so, what mathematical structure can be expected in the ensuing generalized thermodynamics. In this paper, we illustrate the relevance of the concept of typicality in the toy model context of the “thermalized” coin and show how this leads naturally to Shannon entropy. We also show an intriguing connection: The characterization of typical sets in terms of Rényi and Tsallis entropies naturally leads to the free energy and partition function, respectively, and makes their relationship explicit. Finally, we propose potential ways to generalize the concept of typicality to systems where the standard microscopic assumptions do not hold.

Read the full article at: link.springer.com

Young Scientist Award for Socio- and Econophysics (sponsored by CFM)

The Young Scientist Award for Socio- and Econophysics of the German Physical Society (DPG) recognizes outstanding original contributions that use physical methods to develop a better understanding of socio-economic problems. The annually awarded prize is endowed with EUR 7,500 and is intended for young scientists (f/m) below the age of 40 at the time of submission deadline (15. October). The division of socio-economic physics (SOE) is a division of the German Physical Society (DPG) devoted to the “Physics of Socio-Economic Systems”. Its aims are to foster research on these topics and to coordinate our activities and those of similar societies across Europe, and to interest young physicists in economic, urban, and social problems. The prize is awarded during the meeting of the Section of condensed matter (SKM) of the DPG.

The price is sponsored by Capital Fund Management (CFM).

More at: www.dpg-physik.de

Sustainable Visions: Unsupervised Machine Learning Insights on Global Development Goals

Alberto García-Rodríguez, Matias Núñez, Miguel Robles Pérez, Tzipe Govezensky, Rafael A. Barrio, Carlos Gershenson, Kimmo K. Kaski, Julia Tagüeña

The United Nations 2030 Agenda for Sustainable Development outlines 17 goals to address global challenges. However, progress has been slower than expected and, consequently, there is a need to investigate the reasons behind this fact. In this study, we used a novel data-driven methodology to analyze data from 107 countries (2000−2022) using unsupervised machine learning techniques. Our analysis reveals strong positive and negative correlations between certain SDGs. The findings show that progress toward the SDGs is heavily influenced by geographical, cultural and socioeconomic factors, with no country on track to achieve all goals by 2030. This highlights the need for a region specific, systemic approach to sustainable development that acknowledges the complex interdependencies of the goals and the diverse capacities of nations. Our approach provides a robust framework for developing efficient and data-informed strategies, to promote cooperative and targeted initiatives for sustainable progress.

Read the full article at: arxiv.org