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 beyond anything we know, just as the universe is bigger and the sub-atomic world is tinier than we know. No machine ever built even approaches a cell’s complexity and 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 quantum effects helped matter to evolve into life (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

If the quantum world can bypass classical laws, 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 life on earth needed to evolve. Our electric motors are only 25% efficient losing the rest to heat, but low-light bacteria photosynthesize 100% of light energy into chemical energy (Magdaong et al., 2014). This energy efficiency is impossible for heat engines by Carnot’s thermodynamic principle but bacteria seem to have evolved the molecular structure of a quantum heat engine (Al-Khalili & McFadden, 2014) p310 that can do what classical mechanics forbids:

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

A bacterium packs light receptive molecules called chromophores in a protein structure that also has reaction centers to convert light into chemical energy. It is a forest of chromophore antennae on a base structure with centers for energy conversion. When a photon hits an antenna, its energy must pass through a molecular forest of antennae to 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

As the photon pulse decays in nanoseconds, a single path 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 to survive, but how do they do it?

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

In physics, if one event creates two photons, they entangle, even when 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). While two entangled photons can only go in two ways, a photon entangled with many receptors can go in many ways to explore the many paths to a reactor all at once. An arriving photon received by many receptors spreads in a wavelike manner until the result collapses at a reaction center. If that doesn’t happen in one molecular cycle, the synchrony repeats until it does. The bacterium uses quantum entanglement to enhance photosynthesis and this molecular coherence can support 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 antennae vibrating in synchrony allow the photon interaction evolve down many paths simultaneously to find the fastest path to a reaction center before it collapses. Quantum coherence lets cells do many things at once. If light-harvesting bacteria achieved photosynthesis by coherence, the first step to all life on earth was a quantum effect.