Life on the Edge

The coming age of quantum biology

Johnjoe McFadden & Jim Al-Khalili

MY RATING +2 (Highly Recommended)

TLDR

“What I cannot create, I do not understand” - Richard Feynman

Are quantum mechanical phenomena the heart of Life? Is it likely that many of Life’s most important biological processes are highly dependent on the nature of the quantum world? This book seems to think the answer to both is: yes, it’s very likely Life’s most fundamental processes occur on a scale ruled by quantum mechanical laws. Experiments as recent as 2015 are finally revealing that processes like photosynthesis & cellular respiration utilize quantum effects like tunneling and superposition to achieve a level of efficiency and order greater than can be accounted for by thermodynamic laws alone.

The Quantum World
Wave-Particle Duality
Tunneling
Entanglement
Enzymes & Respiration
Photosynthesis
Olfaction & Magnetoreception Brain & Quantum Computing
Genetics & Evolution
History of Quantum Theory
EPR Paradox
Final Thoughts
References

The Quantum World

Quantum mechanics describes the behavior of atomic and subatomic particles: protons, electrons, etc. These atomic structures behave in unintuitive ways. A growing field of quantum biology is attempting to identify ways in which Life has taken advantage of quantum phenomena to achieve its structures and processes.

Wave-Particle Duality

The de Broglie hypothesis proposes all matter can have both wave- and particle-like behavior. The infamous Double Slit Experiment illustrates this duality well. The consequences of this phenomenon are philosophic; the nature of the universe is so unintuitive that there is no real world physical analogy with which to relate. Quantum theory has developed a multitude of interpretations. This is where we get the idea of the multiverse, based on the Many-worlds interpretation.

Tunneling

Tunneling represents the most fundamental process in physics.¹ This phenomenon allows particles to “tunnel” through an energy barrier despite not having the required energy to do so according to classical physics.

Physicists introduced the name tunneling for a classical forbidden process, which the theory of quantum mechanics explained around 1927: A ball, for instance, can- not overcome a hill if its kinetic energy is less than the hill’s gravitational potential energy. In this case the ball rolls back. However, quantum mechanics explained that the ball has a tiny probability of getting to the other side of the hill. Similarly, an α-particle leaves the attractive nuclear potential well despite having a small energy, thereby producing radioactivity.¹ - Tunneling, Compendium of Quantum Physics

We now understand processes like radioactive decay and nuclear fusion (like the fusion of hydrogen atoms into helium that powers our sun) are possible due to tunneling.

Entanglement

Entanglement allows the quantum states of pairs or groups of particles to be synchronized in such a way that measurement of one particle will be correlated with measurement of the other particles. This effect occurs instantaneously across any distance in space. If the state of one particle is known, the state of the other entangled particle, no matter where it is in the universe, is also known. Entanglement is what Einstein referred to as “spooky action at a distance” and what led him to believe that quantum mechanics was an incomplete model of reality. See the EPR paradox.

Enzymes & Respiration

Enzymes are biological catalysts. They speed up chemical reactions, sometimes millions of times faster than the reaction could proceed otherwise. Biological chemical reactions like cellular respiration, in which a highly coordinated transfer of electrons during a sequence of chemical reactions is used to convert chemical energy stored in the bonds of glucose molecules into energy stored in bonds of ATP molecules, a form of cellular fuel, would essentially be impossible without coordination of enzymes. We evolved lungs to supply oxygen to the final stage of this cascade of reactions, to act as the final electron acceptor to transform O₂ into CO₂ and H₂O.
The puzzle of respiration is how these enzymes are able to transfer electrons so efficiently across what are known to be very large molecular gaps between the enzymes, several tens of angstroms wide (a distance of many atoms).

In 1966, Don DeVault & Britton Chance published Studies of Photosynthesis Using a Pulsed Laser, the first experimental evidence that enzymes use quantum tunneling during electron transfer. DeVault & Chance found the rate of electron-hopping in respiratory enzymes did not drop at low temperatures. They measured the rate of electron transfer in cells of a photosynthetic bacterium Chromatium using pulses of light from a ruby laser. They found the rate of transfer decreased steadily with temperature until 35 K, after which the rate remained constant. The lack of temperature dependence below 35 K is evidence of transfer by quantum tunneling. In other words, even when the the energy of the reactants was extremely low, there is a still some finite minimum probability that electrons will tunnel to complete the reaction. If tunneling did not occur, we would expect the rate of the reaction to continue decreasing with temperature below 35 K.

It took several years to theoretically explain the temperature results in the DeVault & Chance experiment. In 1974, J.J. Hopfield published Electron Transfer Between Biological Molecules by Thermally Activated Tunneling, in which he develops a theoretical model for this tunneling that matches the results from the DeVault & Chance experiment.

Photosynthesis

Brain & Quantum Computing

Genetics & Evolution

History of Quantum Theory

EPR Paradox

Final Thoughts

I really enjoyed this book. A fantastic introduction to and summary of the concepts of quantum mechanics and the growing field of quantum biology. Quantum mechanics is mind-boggling at times, yet it remains the most accurate model we have of atomic behavior; the authors do well at presenting these concepts in a digestible way. Certainly, that mysterious phenomenon Life has utilized the quantum nature of this universe; that Life, arising consequently from the nature of this universe, should be correlated with that nature is very likely.

References

1. Greenberger, Daniel, & Hentsche. Compendium of Quantum Physics
2. This Book 3. Steven Weinberg. The Trouble With Quantum Mechanics, https://www.nybooks.com/articles/2017/01/19/trouble-with-quantum-mechanics/