QR6.3.1 Cell Unity

A cell has about 42 million protein molecules working together in the most complex system mankind has ever witnessed. It has been called the third infinity because its complexity is just as far beyond anything we know as the universe is bigger than we know and the sub-atomic world is tinier than we know. No machine ever built even approaches a cell’s complexity, so the chance that trillions of atoms randomly formed millions of proteins in a primal “stew” is effectively zero. Evolution clearly needed help and the emerging field of quantum biology argues that it got it from quantum effects (McFadden & Al-Khalili, 2018). 

Quantum effects like entanglement were critical to the evolution of matter, stars and galaxies but until recently seemed to play no part in life. No-one doubted that quantum weirdness rules the atomic world but quantum states collapsed too quickly to affect the macro-world of biology:

On the face of it, quantum effects and living organisms seem to occupy utterly different realms. The former are usually observed only on the nanometer scale, surrounded by hard vacuum, ultra-low temperatures and a tightly controlled laboratory environment. The latter inhabit a macroscopic world that is warm, messy and anything but controlled. A quantum phenomenon such as ‘coherence’, in which the wave patterns of every part of a system stay in step, wouldn’t last a microsecond in the tumultuous realm of the cell. Or so everyone thought. But discoveries in recent years suggest that nature knows a few tricks that physicists don’t: coherent quantum processes may well be ubiquitous in the natural world.(Ball, 2011) p272

The quantum world can bypass classical laws so one expects life to use that power if it can, and it had billions of years to do so. Biologists just had to look to find quantum effects in cells:

“…something quantum mechanical is going on inside living cells, whether it’s in photosynthesis, whether it’s in enzyme catalysis,[16] [17] [18] whether it’s in mutations of DNA,[19] [24] even more controversially the way we smell, the theories of olfaction,[25] or magnetoreception, the way certain animals can sense the Earth’s magnetic field, the chemical compass that allows them to detect the orientation of the field relies on quantum effects, quantum entanglement.[26] [27] [28]” (Al-Khalili & Lilliu, 2020)

The best-known example is photosynthesis, the process that sustains complex life on earth. It began over three billion years ago when bacteria harvested the sun’s light to create the oxygen that later life needed. Our electric motors are 25% efficient, losing the rest to heat, but low-light bacteria convert 100% of light energy into chemical energy (Magdaong et al., 2014). This energy efficiency is impossible for heat engines by Carnot’s law but bacteria have evolved a quantum heat engine (Al-Khalili & McFadden, 2014) p310 that can do what classical physics forbids:

natural selection has come up with ways for living systems to naturally exploit quantum phenomena (O’Callaghan, 2018).

Photosynthetic bacteria have light receptive molecules called chromophores that absorb light energy and send it to reaction centers that convert it into chemical energy. These “antennae” sit on a protein structure and when they register a photon, its energy must pass through a molecular forest of other antennae to reach the nearest reaction center, but:

The problem, of course, is which route this energy transfer should take. If it heads in the wrong direction, randomly hopping from one molecule to the next in the chlorophyll forest, it will eventually lose its energy rather than delivering it to the reaction center.(Al-Khalili & McFadden, 2014) p126

The photon pulse decays in nanoseconds, so it should often go down a dead-end and die out but instead, nearly every photon arrives at a reaction center. This helps bacteria competing in the light-starved depths of the sea survive, but how do they do it?

Studies show that the chromophores of bacteria vibrate in step to give quantum beats (Engel, 2007), allowing their electromagnetic fields to cohere and entangle (Maiuri, 2018). Entanglement in physics occurs at the atomic scale or near absolute zero. It is a fragile quantum state that should quickly collapse in a warm cell but identical matter entities close enough for their quantum fields to overlap will always entangle (Lo Franco & Compagno, 2016). Densely packed chromophores vibrating in synchrony satisfy this demand, so they entangle to act as one system.

Entanglement in physics is illustrated by entangled photons going in opposite directions (Aspect et al., 1982). What looks like two photons going separate ways is actually one entity, so if either photon interacts, both respond (3.8.5). If entangled photons can go in two ways, a photon entangled with many receptors can explore all the paths to a reactor at once. Once received, the energy spreads down all paths like a wave until it collapses at a reaction center. If that doesn’t happen in one molecular cycle, the synchrony repeats until it does. The bacterium uses quantum coherence to enhance photosynthesis in a way that supports the known transfer times: 

Coherent quantum beats have been observed in most light harvesting systems, where the coherences are stable over a time scale that is commensurate with the relevant energy transfer times.(Scholes Group, 2018)   

Chromophore molecules vibrating in synchrony let photon energy evolve down many paths simultaneously to find a reaction center before it decays. If light-harvesting bacteria achieved photosynthesis by coherence, all life on earth began with a quantum effect.