When physicists ask why life exists, they start with stars. Nuclear reactions inside them produce the carbon and oxygen biology runs on. Get those constants right and, the thinking goes, and life will eventually follow.
A new study points to another requirement for life as we know it – one that has nothing to do with nuclear reactions, and everything to do with how liquids flow.
Liquid flow and cell chemistry
Kostya Trachenko, Professor of Physics at Queen Mary University of London (QMUL), has spent years asking what limits a liquid’s flow. Cells depend on motion at very small scales.
Proteins fold, nutrients diffuse, molecular motors haul cargo, and waste gets pushed out. None of it happens without viscosity behaving the way it does in water.
Change how thick or thin a liquid runs, and cell chemistry can slow, stall, or run out of balance. Trachenko’s question was whether the laws governing that one number reach further than anyone had guessed.
A floor for liquids
His earlier work in 2020 found something unexpected. Viscosity in any liquid has a hard floor – a value it cannot drop below no matter how hot or pressurized it gets.
That floor depends on the deepest constants in physics: the Planck constant, the electron mass, the electron’s charge.
Water, helium, mercury, molten metals – their viscosity minima all trace back to those same numbers, confirmed across decades of data.
Blood at the boundary
The newer paper carries that floor into biology. Human blood operates within a narrow viscosity range – push it outside that window in either direction and the cardiovascular system stops working.
Trachenko ran the numbers. A change of only a few percent in the Planck constant or the electron charge would push blood viscosity outside that healthy range.
Water alongside it would run either thick like tar or absurdly thin. Cellular chemistry would collapse, and the kind of life we recognize never gets off the ground.
Until this paper, no one had connected the constraints on how fluids must flow inside organisms directly to the constants of fundamental physics. Trachenko did.
A bio-friendly window
Out of that math falls a striking conclusion. The fundamental constants sit inside a very narrow window. Inside it, liquids stay runny enough for life. Outside it, the chemistry of cells stops.
“Understanding how water flows in a cup turns out to be closely related to the grand challenge to figure out fundamental constants,” Trachenko said.
The window spans the Planck constant, electron charge, proton mass, and electron mass. Each is squeezed from at least one side. Small variations threaten the diffusion rates and flow speeds biology depends on.
Researchers had long suspected the constants were tuned to allow stars and heavy atoms. No one had shown they must also work for liquid-based life to function. Until now.
Beyond stars and atoms
Fine-tuning arguments usually live in cosmology – focused on star formation, the production of carbon, and the strength of nuclear forces. Stars produce elements, planets host chemistry, life follows. End of story.
Trachenko’s paper opens a door 15 orders of magnitude below a star’s core. Even in a universe that makes carbon and oxygen, no living thing might emerge if those liquids refuse to flow properly.
A separate study on liquid behavior at tiny physical scales has since picked up the same thread, confirming that everyday fluid dynamics traces back to the deepest physical laws.
Multiple rounds of tuning
That redundancy bothered Trachenko. A single round of tuning would have produced atoms and stars, but the second layer of bio-friendly flow looks suspiciously convenient.
He proposes the constants were tuned multiple times, separately. Each round producing a new sustainable structure – atoms first, then stars, then something as subtle as the thickness of a liquid.
Trachenko sees a parallel with biological evolution. Unrelated lineages can independently arrive at similar traits – eyes developed separately in vertebrates and in octopuses. A more recent paper extends the conjecture into molecular machines inside cells.
The paper is a mathematical argument – no experiment has directly tested what happens to cells when fundamental constants shift.
Nailing down the precise window boundaries will also need biological input, and the multiple-tuning conjecture remains speculative by Trachenko’s own description.
Liquid viscosity and life
Before this paper, fine-tuning arguments about the chemistry required for life stopped at atomic nuclei and the heavy elements stars produce. They now reach all the way down to living cells.
The question of why our Universe permits life now has a calculable requirement: liquid viscosity must fall inside a tight window set by the Planck constant, electron charge, and proton and electron masses.
For physics, that puts a new check on any future theory attempting to explain why the fundamental constants have the values they do.
Biology gets something too – a way to ask which life processes break first as viscosity climbs, touching pharmacology, blood disorders, and the search for life on worlds where chemistry runs on different liquids.
The deepest laws of physics, it turns out, can be read in how water moves through a glass on a kitchen counter.
The study is published in Science Advances.
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