Classical Networks Mimic Quantum Math in Biology

Chemist Gregory Scholes of Princeton University is now skeptical that quantum effects play a role in life. He proposes that life might imitate quantum phenomena using complex networks of classical objects, producing 'quantumlike' behavior instead.

Scholes and colleagues have published several papers over the past three years demonstrating this concept. They show that interacting, oscillating parts in a network can sum to a collective whole whose mathematics mirrors that of quantum systems. These states are not truly quantum but arise from classical interactions.

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.

The Historical Allure of Quantum Biology

The idea of linking life's mysteries to quantum mechanics is nearly a century old. Quantum pioneer Niels Bohr suggested in a 1929 lecture that the new theory might be key for understanding living organisms. His contemporary, Pascual Jordan, wrote extensively on Quantenbiologie, arguing life could amplify quantum indeterminacy to macroscopic scales, a view echoed by geneticist J.B.S. Haldane in 1934.

These early thinkers sought to explain puzzling classical-scale properties of life with counterintuitive quantum laws. Genuine quantum states involve superposition and coherence, where particles exist in multiple configurations at once. Such states are delicate and easily destroyed by environmental noise like heat, a process called decoherence. In a warm, wet cell, decoherence should be nearly instantaneous.

While simple quantum effects like particle tunneling occur in biology, Scholes notes they are fleeting and unavoidable even in non-living chemistry. The core question for quantum biology has been whether life can maintain long-lived coherence as a functional resource.

The Photosynthesis Disappointment

The search for such quantum coherence focused intensely on photosynthesis. Photosynthetic organisms convert almost every absorbed photon into chemical energy with nearly perfect efficiency. Scientists hypothesized that quasiparticles called excitons might use quantum coherence to explore multiple simultaneous paths to a reaction center, avoiding loss.

In 2007, Graham Fleming of the University of California, Berkeley, published evidence from laser experiments on bacterial light-harvesting complexes that seemed to show coherence. Other researchers, including Scholes, found similar 'beats' in their data. However, later analysis revealed these beats reflected a resonance from wiggling molecular bonds, not long-lived quantum coherence.

"People were disappointed," said Richard Cogdell, a photobiologist at the University of Glasgow. The hope for a special quantum mechanism in biology faded. While quantum effects are still hypothesized for other biological processes like bird navigation, definitive evidence remains elusive.

A New Direction: Quantumlike Networks

Scholes's current work shifts focus from finding genuine quantum effects to explaining how classical systems can mimic them. Researchers in quantum foundations have long explored classical recreations of quantum aspects. Markus Müller, a physicist at the Institute for Quantum Optics and Quantum Information in Vienna, said Scholes has shown how such quantumlike behavior can emerge from unremarkable complex networks common in nature.

Sabre Kais, a quantum chemist at North Carolina State University, called it "an exciting new direction." The implication is that evolution may have crafted classical biological networks that mathematically emulate quantum efficiency without the fragility of true quantum states.

This perspective redefines the potential scope of quantum biology. It suggests the field's biggest insight may not be about quantum physics in cells, but about the sophisticated classical engineering that evolution has achieved.