• Physics 17, 182
New Theory Challenges Traditional Thermodynamics in Living Systems
A groundbreaking new theory that reinterprets the second law of thermodynamics includes active biological systems like migrating cells and traveling birds. This development opens up a new understanding of how living organisms operate far from thermal equilibrium.
Figure 1:
A biological cell (black outline) crawling on a substrate extracts energy from its environment (purple arrows) and converts that energy into self-propelled motion (green arrow). Sorkin and colleagues have derived an equivalent of the second law of thermodynamics for living systems, which establishes a relation between such a cell’s active uptake of energy and its random-looking path (blue line) in terms of entropy production. The outlines show the migrating cell at regular time intervals, with microscopy images at the start and end.
The Evolution of Understanding Life’s Physics
In 1944, Erwin Schrödinger published a seminal work titled “What is Life?” where he explored the nature of living systems using the principles of statistical physics. Schrödinger proposed that organisms maintain order by minimizing their own entropy, or disorder. In his view, what organisms consume is not just energy, but negative entropy that helps them function away from thermal equilibrium.
Schrödinger’s ideas posed a profound question about whether the second law of thermodynamics, which states that the total entropy of a closed system must always increase over time, holds for living systems. This question has intrigued scientists for decades.
A New Perspective on the Second Law
Researchers Benjamin Sorkin from Tel Aviv University and his team have advanced this discussion by developing a new theory that generalizes the second law of thermodynamics to encompass active biological systems. Their approach uses information theory to derive key thermodynamic quantities and relationships applicable to living systems.
The team focused on a critical concept in stochastic thermodynamics known as informatic entropy production, which quantifies the irreversibility of microscopic processes. Without relying on the Einstein relation, a principle that relates the rates of transport processes to thermodynamic temperatures, they derived a generalized nonequilibrium temperature. This temperature is a crucial component of their theory.
Impressively, when the Einstein relation is assumed, the generalized temperature reduces to the conventional thermodynamic temperature, demonstrating that the new theory is consistent with existing principles under certain conditions. However, it also offers a broader framework applicable to a wider range of biological systems.
Implications and Future Directions
The derivation of a new second law for living systems represents a significant advancement in our understanding of biophysics. By not requiring the Einstein relation, Sorkin’s theory could be considered a form of ‘athermal dynamics,’ addressing the unique characteristics of active biological systems.
However, the theory makes assumptions, such as the system being overdamped and Markovian. These assumptions can break down in specific scenarios, such as systems with position-dependent fluctuations or non-Markovian dynamics, like migrating cells.
Despite these limitations, the theory’s potential is expansive. Schrödinger himself foresaw the possibility that living matter might involve “other laws of physics” beyond those currently known. Modern research, like Sorkin’s work, aligns with this vision, promising to uncover new scientific truths.
Final Thoughts
This new theory challenges traditional views on thermodynamics and opens new avenues for research in biophysics. By providing a framework to understand the entropy production in active biological systems, scientists can better appreciate the intricate mechanisms that sustain life.
As the field progresses, further refinements to the theory are likely, potentially leading to even more comprehensive models of biological function. The work of Sorkin and his colleagues underscores the ongoing quest to reconcile the principles of physics with the complex dynamics of living systems.
Stay tuned for more breakthroughs in this exciting area of study. The future of biophysics holds numerous possibilities as we continue to explore the profound interplay between life and thermodynamics.
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