The fundamental laws of physics, long thought to govern only the cold mechanics of the cosmos and the subatomic world, have been found to exert a surprisingly tight grip on the very machinery of biological life. Recent theoretical breakthroughs led by Kostya Trachenko, a physicist at Queen Mary University of London, suggest that the ability of liquids to flow—a prerequisite for cellular function—is governed by a narrow window of physical constants. If these universal numbers, such as the mass of an electron or the Planck constant, were altered by as little as a few percentage points, the resulting change in viscosity would render the universe a stagnant, lifeless expanse, even if stars and planets were still able to form.
This research introduces a new dimension to the "fine-tuning" problem in physics. For decades, scientists have noted that the universe seems uniquely calibrated to produce the heavy elements necessary for life, such as carbon and oxygen. However, Trachenko’s work, culminating in a series of papers between 2020 and 2025, suggests that the chemical ingredients for life are not enough. The physical properties of the medium in which those ingredients interact—the liquid state—must also fall within a specific range to allow for the movement of nutrients, the removal of waste, and the occurrence of vital chemical reactions.
The Architecture of the Physical World: Understanding Fundamental Constants
To understand the gravity of these findings, one must first consider the role of fundamental constants. These are the "fixed" numbers that define the strength of forces and the masses of particles in our universe. Key among them are the Planck constant ($h$), which dictates the scale of quantum effects; the charge of the electron ($e$); and the masses of fundamental particles like electrons and protons.
In the standard model of physics, these values are taken as given. There is no underlying mathematical reason why the electron must have its specific mass, yet its value influences the strength of chemical bonds and the structure of atoms. If the electromagnetic force were slightly stronger, atoms would hold onto their electrons too tightly for chemistry to occur. If it were weaker, stable molecules might never form. Trachenko’s research extends this sensitivity to the macroscopic world of fluid dynamics, revealing that the viscosity of a liquid—its internal friction or resistance to flow—is also a direct product of these quantum-scale constants.
A Chronology of Discovery: From Pure Physics to Biological Necessity
The path to this realization began in 2020, when Trachenko and his colleagues published a landmark study in Science Advances. They demonstrated that there is a theoretical lower limit to the viscosity of any liquid. While common experience suggests that liquids can be infinitely "thin" or "runny" if heated enough, the researchers found that quantum mechanics imposes a floor. This fundamental limit is determined by the ratio of the Planck constant to the mass of the molecules.
By 2023, the focus shifted from pure physics to the requirements of biology. In a subsequent analysis, Trachenko identified that the viscosity of water—the universal solvent for life—is not a random occurrence. Instead, it is positioned perfectly to allow for efficient diffusion. Diffusion is the process by which molecules move from areas of high concentration to low concentration. Within a living cell, diffusion is the primary mode of transport for oxygen, glucose, and signaling molecules.
The 2023 study concluded that if the fundamental constants were different, water could become as viscous as honey or tar. In such a universe, the "metabolic engine" of a cell would seize up. The time required for a protein to find its target or for an ion to cross a membrane would stretch from milliseconds to hours, making the rapid-fire chemical sequences required for life impossible.
The 2025 Breakthrough: The Quantum Signature in Human Blood
The most recent development in this field occurred in January 2025, with a study published in The European Physical Journal E. Trachenko and his team moved beyond simple liquids like water to investigate complex biological fluids, specifically human blood.
Blood is a non-Newtonian fluid, meaning its viscosity changes depending on how fast it is flowing. It is a dense suspension of red blood cells, white blood cells, platelets, and proteins. Despite this staggering complexity, the researchers found that blood’s viscosity remains remarkably close to the fundamental limit derived from universal constants.
This finding is particularly startling because red blood cells are macroscopic objects compared to atoms. However, the study suggests that when blood cells are packed closely together in capillaries, the thin layers of plasma between them behave according to quantum mechanical constraints. The "stickiness" of these interactions is governed by the same electron-scale physics that governs a glass of water. This suggests that the "window" for life is even narrower than previously thought, as it must account for both the molecular level of the cell and the systemic level of circulatory physics.
Data and Analysis: The Narrow Window of Habitability
The implications of a "narrow window" can be quantified. Trachenko’s models suggest that a change of just 2% to 3% in the Planck constant or the electron charge would have catastrophic effects on biological viability:
- Increased Viscosity: If constants shifted to increase viscosity, blood would become too thick for the heart to pump without requiring pressures that would rupture vessel walls. On a cellular level, the cytoplasm would become a "glassy" state, halting the Brownian motion essential for enzymes to function.
- Decreased Viscosity: Conversely, if viscosity were significantly lower, liquids would lack the structural integrity to support stable membranes. The controlled, directional flow required for biological processes would give way to chaotic turbulence, disrupting the delicate gradients of ions that cells use to generate energy.
This creates a paradox for the "Multiverse" theory, which suggests that our universe is just one of many, each with different physical constants. If Trachenko’s analysis is correct, the vast majority of these universes would be "stillborn"—not because they lack stars, but because their chemistry is locked in a frozen or sluggish state.
Comparison with Stellar Nucleosynthesis
For decades, the primary evidence for a fine-tuned universe was the "triple-alpha process." This is the nuclear reaction inside stars that produces carbon. In the 1950s, physicist Fred Hoyle famously predicted a specific energy state in the carbon nucleus—now called the Hoyle State—that must exist for carbon to be produced in large quantities. If the strong nuclear force or the electromagnetic force were slightly different, this resonance would not exist, and the universe would contain almost no carbon.
Trachenko’s work adds a second, independent layer of fine-tuning. He notes that the constants required for star formation and those required for liquid flow are not necessarily the same. A universe could theoretically exist where the Hoyle State allows for carbon production, but where the electron mass makes water as thick as pitch. The fact that our universe satisfies both conditions—the creation of elements and the fluid dynamics required to use them—suggests a level of "cooperation" between different branches of physics that scientists are only beginning to explore.
Broader Implications and Scientific Reaction
The scientific community has reacted to these findings with a mix of intrigue and cautious skepticism. While the mathematical link between constants and viscosity is robust, some biophysicists argue that life is incredibly adaptable. Extremophiles on Earth, for instance, survive in high-pressure, high-temperature environments where water behaves differently.
However, Trachenko’s argument is not about the adaptability of life, but about the fundamental limits of the liquid state itself. Even the most resilient extremophile still relies on the movement of molecules. If the physics of the universe prevents that movement, biology never gets the chance to adapt.
This research also impacts the search for extraterrestrial life. Traditionally, the "habitable zone" around a star is defined by the temperature at which liquid water can exist. Trachenko’s work suggests that we must also consider the "physical habitability" of the universe itself. If we were to find a planet with liquid ammonia or methane, the same fundamental constraints on viscosity would apply, potentially limiting the types of biochemistry that could emerge there.
Conclusion: A New Evolutionary Perspective on Physics?
One of the most provocative suggestions arising from this work is the idea that the laws of physics themselves might have undergone a form of selection or evolution. Trachenko posits that the "fine-tuning" of multiple independent processes—stellar nucleosynthesis and liquid viscosity—might point toward a deeper, yet undiscovered principle of nature that favors complexity and stability.
As we look at a glass of water or feel the pulse of blood in our veins, we are witnessing the manifestation of the deepest constants of the cosmos. The fact that water flows and blood circulates is not a mundane detail of daily life, but a profound testament to the specific calibration of the universe. This research reminds us that life is not an accidental passenger in a cold, mechanical universe, but is deeply woven into the very fabric of physical law. The mystery of why these constants have the values they do remains, but the realization that our existence depends on the "runniness" of the world provides a new and vital lens through which to view our place in the stars.
