Imagine a universe where stars still shine, planets still form, and water exists, but the liquids are so thick that living cells can barely function. Even with the chemical ingredients necessary for life, the conditions could make living organisms impossible. Scientists have discovered a remarkable connection between the fundamental laws of physics and life’s ability to exist. Their findings suggest that even relatively small changes in some of the universe’s most basic physical constants could dramatically alter the way liquids flow, potentially preventing essential biological processes from taking place. The discovery, detailed in a study published in Science Advances, came from physicist Kostya Trachenko of Queen Mary University of London. Their theoretical analysis identified an additional constraint on the values of fundamental physical constants: they must allow liquids to move in a way that supports life within and between cells. The work raises a deep question about the universe. Why do the fundamental laws of nature have values that seem so suitable for the existence of life? The fundamental constants that shape our universe The fundamental physical constants are numbers that govern the functioning of the universe. Examples include the mass and electrical charge of an electron and Planck’s constant, which plays a central role in quantum mechanics, the branch of physics that describes matter and energy at extremely small scales. These quantities are generally considered universal and do not change over time. Its values influence everything from the behavior of atoms and chemical bonds to the nuclear reactions that power stars and produce elements essential for life. Despite their importance, scientists still don’t know why these constants have the particular values we observe. An important clue emerged in 2020, when Trachenko and his colleagues showed that fundamental physical constants impose a lower limit on the viscosity of liquids. Viscosity describes the force with which a fluid resists flow. Water has a relatively low viscosity and pours easily, while honey and tar are much more viscous and move slowly. The researchers showed that there is a fundamental limit to the freedom with which a fluid can flow, a limit that is ultimately related to the basic constants of nature. The 2023 study took this connection much further by examining its implications for biology. Why small changes in physics could make life impossible Every living cell depends on the movement of molecules. Nutrients must get to the places where they are needed, waste products must be transported, and countless chemical reactions must occur in a liquid environment. Another important process is diffusion, the natural spread of particles through a fluid. Diffusion helps molecules move around cells and enables many of the chemical interactions necessary for life. If the viscosity of these fluids changed too much, these processes could be seriously altered. Liquids that are too thick could prevent vital materials from moving efficiently, while excessively low viscosity could also interfere with the controlled flow necessary for biological functions. Trachenko explained the surprising connection: “Understanding how water flows in a cup turns out to be closely related to the great challenge of discovering the fundamental constants. Life processes within and between living cells require movement and it is viscosity that sets the properties of this movement. If the fundamental constants change, the viscosity would change too much impacting life as we know it. For example, if water were as viscous as tar, life would not exist in its current form or would not exist in absolute. This applies beyond water, so all life forms that use the liquid state for function would be affected.” The implications extend beyond water. Although all known life depends on water, hypothetical organisms in other parts of the universe could depend on different liquids. The same fundamental physical limitations would continue to influence the behavior of these liquids. Trachenko suggested that the range of constants compatible with cellular life might be surprisingly narrow. “Any change in the fundamental constants, including an increase or a decrease, would be equally bad news for flow and for liquid-based life. We expect the window to be quite narrow: for example, the viscosity of our blood would become too thick or too thin for the body to function with just a small percentage change in some fundamental constants such as Planck’s constant or the charge of electrons.” These predictions come from theoretical models rather than experiments in which scientists actually changed fundamental constants. The precise limits that different life forms could tolerate remain uncertain. A cosmic mystery that was billions of years in the making What makes the findings especially intriguing is that the same fundamental constants that influence liquid flow also govern the nuclear reactions responsible for creating heavy elements inside stars. Long before the first living cells appeared, stars produced elements such as carbon and oxygen that would eventually become essential components of living organisms. Physicists have long investigated whether the constants that govern these nuclear processes must be within certain ranges for complex matter to exist. But the ability to create the chemical ingredients of life does not necessarily guarantee that life can function. Trachenko’s analysis showed that some physical properties governing liquid flow could change without altering the combinations of constants needed to produce heavy nuclei in stars. In other words, a hypothetical universe could still produce the elements necessary for life and at the same time have liquids so viscous that cellular processes could not operate. That means the conditions necessary to support life may involve more than the ability to form stars, planets, and complex chemistry. The physical properties of liquids could impose additional requirements on the fundamental constants of the universe. Follow-up research reveals surprising connection to blood Research continued beyond the original discovery. In a follow-up study published in January 2025 in The European Physical Journal E, Trachenko and colleagues examined how fundamental physical constants influence more complicated biological fluids, particularly blood. Unlike water, blood is a complex mixture containing plasma, red blood cells, platelets, and other components. Its viscosity depends not only on the molecular properties but also on how these components interact. For example, red blood cells can form clumps that increase resistance to flow. As blood moves faster, those clumps can break up, allowing it to flow more easily. This behavior makes blood considerably more complicated than a simple liquid. The researchers found something unexpected. Despite the enormous complexity of blood and the relatively large size of red blood cells, its viscosity remains surprisingly close, on a fundamental physical scale, to a theoretical value derived from basic physical constants. They proposed that interactions between closely spaced blood cells may help explain this connection. Although red blood cells are much larger than atoms, the forces that act when their surfaces approach each other involve distances small enough for molecular and quantum effects to matter. The 2025 analysis also highlighted a major complication. Estimating which fundamental constants are compatible with life requires taking into account both the intrinsic properties of liquids, determined by fundamental physics, and the additional effects created by interactions between cells and molecules. These findings offer a more detailed framework for investigating the connection between the basic physical properties of the universe and the biological processes that depend on them. Could the laws of physics have evolved? The research also points to an even deeper mystery: why do fundamental constants have values that allow so many different physical processes to work together? One speculative possibility raised by Trachenko is that multiple forms of adjustment may be involved. The values that allow stars to make heavy elements and those that allow liquids to support cellular life may represent separate requirements. He suggested an intriguing analogy with biological evolution, in which different useful characteristics can arise through separate processes. Perhaps some broader evolutionary principle could help explain how nature arrives at combinations of physical properties capable of supporting stable structures and increasingly complex systems. For now, this remains a conjecture. Scientists have not established that fundamental constants evolve through such a mechanism, nor have they determined why those constants have their observed values. Still, the connection between liquid flow and fundamental physics opens up another way to investigate one of the biggest unanswered questions in science. Something as common as water moving through a glass, or blood circulating through the body, may contain clues to why the universe has the physical properties that make life possible.
