Classical oscillator networks reproduce the math that made photosynthesis look quantum

Quantumlike, in the sense Scholes uses it, is a statement about equations. Many interacting oscillating parts, each of them classical, can add up to a collective whole whose behavior obeys the same mathematics that makes predictions about the quantum world ^[8]. Nothing in the network has to hold a superposition or stay entangled. Nothing has to survive the warmth of a cell. The claim explains less than the coherence account that followed the 2007 result ^[3], and it is easier to defend.

"Maybe quantum biology, at the biggest scales, means using 3 1/2 billion years of evolution to work out how to get the functionality that you could get from quantum systems," Scholes said ^[9].

His own follow-up experiments, on photosynthesizing proteins and pigments, came away with conclusions similar to the 2007 work ^[4]. He now doubts that quantum effects play a role in life ^[5]. Quanta's account does not describe the experiments or reanalyses that changed his mind. So one prominent chemist's reversal is documented, and the field has not retracted anything.

What the new papers show is that complex networks of classical objects can produce phenomena that mathematically mimic quantum objects ^[7]. That is a result about networks. Markus Müller, a physicist at the Institute for Quantum Optics and Quantum Information in Vienna, said Scholes has shown how quantumlike behavior can emerge from relatively unremarkable complex networks, of the sort that abound in nature ^[11]; Müller also noted that people working on the foundations of quantum mechanics have spent decades exploring how to classically re-create aspects of the quantum world ^[10]. That such networks are common does not show that any organism depends on the collective state one of them can produce.

The observation that needs explaining has not moved. Photosynthetic organisms convert almost every incoming photon into useful chemical energy ^[2]. Coherence was the proposed explanation for that efficiency ^[1].

The pull toward quantum explanations of life is old. Niels Bohr, in a 1929 lecture, said quantum mechanics "may perhaps be of decisive importance, particularly in the discussion of the position of living organisms in our picture of the world" ^[14], seventy-eight years before the 2007 coherence claim ^[18]. Pascual Jordan spent decades arguing that life amplifies quantum indeterminism to macroscopic scales and made that the basis of human thought and free will ^[15]; J.B.S. Haldane echoed him in a 1934 paper ^[16]. Jordan joined the Nazi Party and its paramilitary forces in 1933 and damaged quantum biology's credibility by trying to link the two ^[17].

Against that history, the current proposal asks for much less. It asks which equations describe a system of coupled classical parts, and it can be checked without ever detecting a quantum state in a leaf. Sabre Kais, a quantum chemist at North Carolina State University who develops quantum computing algorithms for complex systems ^[13], said "Classical systems can mimic some of the key features of quantum information" and called it "an exciting new direction" ^[12].