Later On

A blog written for those whose interests more or less match mine.

First Support for a Physics Theory of Life

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Natalie Wolchover writes in Quanta:

The biophysicist Jeremy England made waves in 2013 with a new theory that cast the origin of life as an inevitable outcome of thermodynamics. His equations suggested that under certain conditions, groups of atoms will naturally restructure themselves so as to burn more and more energy, facilitating the incessant dispersal of energy and the rise of “entropy” or disorder in the universe. England said this restructuring effect, which he calls dissipation-driven adaptation, fosters the growth of complex structures, including living things. The existence of life is no mystery or lucky break, he told Quanta in 2014, but rather follows from general physical principles and “should be as unsurprising as rocks rolling downhill.”

Since then, England, a 35-year-old associate professor at the Massachusetts Institute of Technology, has been testing aspects of his idea in computer simulations. The two most significant of these studies were published this month — the more striking result in the Proceedings of the National Academy of Sciences (PNAS) and the other in Physical Review Letters (PRL). The outcomes of both computer experiments appear to back England’s general thesis about dissipation-driven adaptation, though the implications for real life remain speculative.

“This is obviously a pioneering study,” Michael Lässig, a statistical physicist and quantitative biologist at the University of Cologne in Germany, said of the PNAS paper written by England and an MIT postdoctoral fellow, Jordan Horowitz. It’s “a case study about a given set of rules on a relatively small system, so it’s maybe a bit early to say whether it generalizes,” Lässig said. “But the obvious interest is to ask what this means for life.”

The paper strips away the nitty-gritty details of cells and biology and describes a simpler, simulated system of chemicals in which it is nonetheless possible for exceptional structure to spontaneously arise — the phenomenon that England sees as the driving force behind the origin of life. “That doesn’t mean you’re guaranteed to acquire that structure,” England explained. The dynamics of the system are too complicated and nonlinear to predict what will happen.

The simulation involved a soup of 25 chemicals that react with one another in myriad ways. Energy sources in the soup’s environment facilitate or “force” some of these chemical reactions, just as sunlight triggers the production of ozone in the atmosphere and the chemical fuel ATP drives processes in the cell. Starting with random initial chemical concentrations, reaction rates and “forcing landscapes” — rules that dictate which reactions get a boost from outside forces and by how much — the simulated chemical reaction network evolves until it reaches its final, steady state, or “fixed point.”

Often, the system settles into an equilibrium state, where it has a balanced concentration of chemicals and reactions that just as often go one way as the reverse. This tendency to equilibrate, like a cup of coffee cooling to room temperature, is the most familiar outcome of the second law of thermodynamics, which says that energy constantly spreads and the entropy of the universe always increases. (The second law is true because there are more ways for energy to be spread out among particles than to be concentrated, so as particles move around and interact, the odds favor their energy becoming increasingly shared.)

But for some initial settings, the chemical reaction network in the simulation goes in a wildly different direction: In these cases, it evolves to fixed points far from equilibrium, where it vigorously cycles through reactions by harvesting the maximum energy possible from the environment. These cases “might be recognized as examples of apparent fine-tuning” between the system and its environment, Horowitz and England write, in which the system finds “rare states of extremal thermodynamic forcing.”

Living creatures also maintain steady states of extreme forcing: We are super-consumers who burn through enormous amounts of chemical energy, degrading it and increasing the entropy of the universe, as we power the reactions in our cells. The simulation emulates this steady-state behavior in a simpler, more abstract chemical system and shows that it can arise “basically right away, without enormous wait times,” Lässig said — indicating that such fixed points can be easily reached in practice.

Many biophysicists think something like what England is suggesting may well be at least part of life’s story. But whether England has identified the most crucial step in the origin of life depends to some extent on the question: What’s the essence of life? Opinions differ.

Form and Function

England, a prodigy by many accounts who spent time at Harvard, Oxford, Stanford and Princeton universities before landing on the faculty at MIT at 29, sees the essence of living things as the exceptional arrangement of their component atoms. “If I imagine randomly rearranging the atoms of the bacterium — so I just take them, I label them all, I permute them in space — I’m presumably going to get something that is garbage,” he said earlier this month. “Most arrangements [of atomic building blocks] are not going to be the metabolic powerhouses that a bacterium is.”

It’s not easy for a group of atoms to unlock and burn chemical energy. To perform this function, the atoms must be arranged in a highly unusual form. According to England, the very existence of a form-function relationship “implies that there’s a challenge presented by the environment that we see the structure of the system as meeting.”

But how and why do atoms acquire the particular form and function of a bacterium, with its optimal configuration for consuming chemical energy? England hypothesizes that it’s a natural outcome of thermodynamics in far-from-equilibrium systems.

The Nobel-Prize-winning physical chemist Ilya Prigogine pursued similar ideas in the 1960s, but his methods were limited. Traditional thermodynamic equations work well only for studying near-equilibrium systems like a gas that is slowly being heated or cooled. Systems driven by powerful external energy sources have much more complicated dynamics and are far harder to study.

The situation changed in the late 1990s, when the physicists Gavin Crooks and Chris Jarzynski derived “fluctuation theorems” that can be used to quantify how much more often certain physical processes happen than reverse processes. These theorems allow researchers to study how systems evolve — even far from equilibrium. England’s “novel angle,” said Sara Walker, a theoretical physicist and origins-of-life specialist at Arizona State University, has been to apply the fluctuation theorems “to problems relevant to the origins of life. I think he’s probably the only person doing that in any kind of rigorous way.”

Continue reading.

Life as a natural result of matter, energy, and the second law of thermodynamics, which seems to be a primal force. Everything then follows by one or another sort of selection (shades of Darwinian evolution) until life emerges and then evolution speeds up a lot, and then memes emerge and evolution speeds up more.

What is missing in the discussion is line-drawing and emergent phenomena: as life is an emergent phenomenon from thermodynamically driven chemical reactions. Interesting book: The Emergence of Everything. Also interesting: The Evolution of Everything. Different authors, though.

Written by LeisureGuy

26 July 2017 at 12:10 pm

Posted in Books, Evolution, Science

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