Kostya Trachenko published the work in The European Physical Journal E in January 2025, following up on an earlier study in Science Advances that looked at pure liquids rather than biological ones. That first paper argued that small shifts in constants such as the Planck constant would change how viscous liquids are, and that the shift needed to make life impossible is tiny: a change of only a few percent in viscosity would be enough to disrupt the processes that keep cells running. The usual illustration is water. If it were as viscous as tar, life as we know it would not exist.

The open question was whether that result held for a fluid as complex as blood, which carries cells, proteins and other components far beyond the simple molecular structure the original theory was built on. Trachenko's follow-up found that it does: blood's viscosity still tracks close to the theoretical value derived from fundamental constants, despite all that added complexity.

Taken together, the two studies point to a double constraint on the physical constants that govern the universe. Those constants have to allow stars to forge heavy elements in the first place, and separately, they have to permit liquids to flow efficiently enough for cells to function. A universe could satisfy the first condition and fail the second.

The findings rest on theoretical models rather than experiments that vary the constants directly, since the constants cannot be dialed up or down in a lab.