Physicists: We Need a Fourth Law of Thermodynamics

SadaNews - Thermodynamics, which involves quantities such as heat and entropy (a measure of disorder in a system), provides tools to determine how far an ideal system of particles is from a state of equilibrium and stability.

However, when it comes to life, it is not clear that our current laws of thermodynamics are sufficient. Now, scientists may have taken the first step toward establishing a new law.

The Dynamics of Life

Thermodynamics is crucial for life because being out of equilibrium is one of its key properties. But because cells are filled with particles that actively consume energy, the state of a cell differs from, for example, a bunch of beads floating in a liquid.

For instance, cells have a "set point," meaning they behave as if they follow an internal thermostat. There is a feedback mechanism that returns it to the set point, allowing it to continue functioning. This type of behavior may not easily be captured by classical thermodynamics.

To understand how "disequilibrium" in living systems differs from that in inanimate systems, N. Narinder and Elizabeth Fischer-Friedrich at the Technical University of Dresden in Germany turned to HeLa human cells – a line of cancer cells commonly used in scientific research that were taken without consent from a woman named Henrietta Lacks in the 1950s.

First, the researchers used chemicals to halt the cells mid-cell division. Then they probed their outer membranes with a tip of an atomic force microscope to assess how fluctuations in each cell's membrane changed when the researchers intervened in some cellular processes.

The scientists found that for these fluctuations, no single standard thermodynamic "recipe" fully explained the behavior of an inanimate system. Specifically, the idea of "effective temperature" was found to be inaccurate. This concept aims to capture something akin to our understanding of how temperature increases when we bring a system like a pot of water out of equilibrium by heating it.

Time Asymmetry

The team concluded that there exists a more useful physical quantity for capturing the degree of disequilibrium in life, which is "time reversal asymmetry." This property explores how a biological process would differ if it were to occur backward instead of forward in time.

The presence of time reversal asymmetry may be directly related to the fact that biological processes serve a purpose such as survival and reproduction, says Fischer-Friedrich.

When it comes to life, it is not clear that our laws of thermodynamics are sufficient, or as Chase Broedersz at the Vrije Universiteit Amsterdam in the Netherlands says, "We know in biology that there are many processes that really depend on the system being out of equilibrium, but it’s actually important to understand how far the system is from equilibrium," adding that the new study identifies valuable new tools to establish that.

Ultimately, the team wants to derive something akin to a fourth law of thermodynamics that applies only to living matter where processes have a set point, says Fischer-Friedrich.

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