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From Steam Engines to Life?

What is the state of thermodynamics on the 100th anniversary of the death of Lord Kelvin?

Mark Haw

Open Universe, Open Life

The thermodynamics of open systems remains a controversial area, sparking debate reminiscent of similar controversies over complexity and the emergence of life. The similarities are not accidental: All these ideas pit the spontaneous creation of complexity or order against the Second Law's mandate for disorder.

But debate alone will not solve the problem. Perhaps the best way to learn more about non-equilibrium and open-system thermodynamics is not to formulate grand theories, but to study their consequences in the form of palpable objects, actual pieces of matter. Kelvin's profound ideas about energy led to a fundamental revolution in modern science but were firmly anchored to a solid reality in the industrial engineering of Victorian Britain.

Which brings us back to microscopic engines: the most interesting objects in which the two themes of modern thermodynamics—microscopic scales and open systems—join. Although studies of individual proteins are important foundation stones, the cell depends on millions of molecules in a complex network of machines, their functions interlocked across a range of scales. Such interplay is possible precisely because these living engines are open to fluctuations and not isolated from their environment. It may be that the complex functions of matter that we call life are nothing more than this multiscale interplay of engines, a network through which energy is transformed again and again, as microscopic machines swap and shift matter—manipulate entropy—in a thermodynamical cycle the likes of which Kelvin could hardly have imagined.

If so, then the theory that accommodates living engines will require both a thermodynamics of microscopic matter, and a thermodynamics of open systems. Current research is providing progress in each of these, but the challenge may be to match them together, to join the palpable chemical reality of protein engines to the heady concepts of non-equilibrium thermodynamics and self-organization. That may lead us, finally, to the second revolution—the thermodynamics of life.

Kelvin's theory of thermodynamics was only one product of his long, intensely curious life. At retirement, he declared that despite half a century of work he felt he understood little more about the nature of the physical world than he had all those years ago, staring down at the water of the Walsall canal. Now, a century after his death, the science of thermodynamics that Kelvin pioneered is indeed more puzzling, more profound, more tantalizing, more practically relevant, and just plain more fascinating, than ever.

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