5.30.2017

Recent advances in entropies

The pace of advance in physics the past few decades has been staggering, and is often difficult to convey. This article in the Journal of Applied Physics by Bejan and Errera (ungated version here) does an excellent job of bridging the divide, and is a remarkable translation of concepts from "nonlinear" and information physics into prose:
During the 20th century, statistical thermodynamics, quantum mechanics, information theory, and computer science have changed the scientific discourse on everything, from science itself to what life is. Instead of terms and images that did not require an advanced education, today it seems that legitimacy on this topic comes from speaking a language of disorder, uncertainty, scale, emergence, chaos, entropies of many types, and, above all, “information.” The fact that few seem to understand this kind of talk is going unnoticed, obviously, because the world does not speak jargon. 
This does not have to continue this way. In this article, we go against this movement and draw attention to a simple truth: words have meaning. We review the key words of the  discourse and start with the observation that information is not knowledge. 
“Every professor…one day discovers to his great surprise that the elements of his teaching which stay with his students are not the things which were “in the program” but those other things he has communicated unknowingly to his best students.
(Jean) Jaure`s said it well: One does not teach what one knows, but what one is. The computer knows many things, it can even know everything; but it is not. It is incapable of forming minds since it has no ends to offer them. But it is quite capable of reducing minds to an official conformity.” 
The computer “is not” because it is nothing more than an extension of the human who uses it to move (to live) more easily. It is one artifact among very many. On the other hand, you “are,” with or without that artifact. With what you are, you make decisions (purposeful choices and changes), and as a consequence you and your group move (live) more easily and with longer lasting power. 
Those whose mother language is not English have to learn English, and along the way they acquire the habit of checking the dictionary. We did this ourselves, as students and now while writing this article. 

I think it is worth ruminating on that last point. 

5.24.2017

Free energy sources in the very long run

Judson - 2017 - The energy expansions of evolution
The history of the life–Earth system can be divided into five ‘energetic’ epochs, each featuring the evolution of life forms that can exploit a new source of energy. These sources are: geochemical energy, sunlight, oxygen, flesh and fire. The first two were present at the start, but oxygen, flesh and fire are all consequences of evolutionary events. Since no category of energy source has disappeared, this has, over time, resulted in an expanding realm of the sources of energy available to living organisms and a concomitant increase in the diversity and complexity of ecosystems. These energy expansions have also mediated the transformation of key aspects of the planetary environment, which have in turn mediated the future course of evolutionary change. Using energy as a lens thus illuminates patterns in the entwined histories of life and Earth, and may also provide a framework for considering the potential trajectories of life–planet systems elsewhere. 
Free energy is a universal requirement for life. It drives mechanical motion and chemical reactions—which in biology can change a cell or an organism. Over the course of Earth history, the harnessing of free energy by organisms has had a dramatic impact on the planetary environment. Yet the variety of free-energy sources available to living organisms has expanded over time. These expansions are consequences of events in the evolution of life, and they have mediated the transformation of the planet from an anoxic world that could support only microbial life, to one that boasts the rich geology and diversity of life present today. Here, I review these energy expansions, discuss how they map onto the biological and geological development of Earth, and consider what this could mean for the trajectories of life–planet systems elsewhere.
Worth reading in its entirety for the log-timescale perspective on energy budgets alone, but also as a fantastic piece of science writing and communication. "Of all the planets and moons in the Solar System, Earth is the only one to have fire..."