Where physics meets biology: More information

Davies replies: I greatly appreciate this helpful feedback on my article “Does new physics lurk inside living matter? ” Julian Ting raises a question about quantum tunneling through organic molecules. Single-molecule conductance experiments are now established technology and are being developed for DNA sequencing. Ting is correct that the geometrical configuration of the molecule can be extremely important, especially in the case of folded versus unfolded peptides.

However, although individual organic molecules may be insulators or conductors, I am unaware of any simple relationship between single-molecule conductance values and bulk conductance values. The full details of the claimed “quantum criticality” of key biological models may be found in the paper by Gábor Vattay and coauthors, ¹ which I cited in my article. I discuss other examples of quantum tunneling in organic molecules in my book The Demon in the Machine: How Hidden Webs of Information Are Solving the Mystery of Life (2019). The discussion there includes the important work of my Arizona State University colleague Stuart Lindsay on tunneling through nucleotides and peptides.

Edwin Kerr touches on what I regard as one of the deepest outstanding challenges in explaining life’s origin: the emergence of encrypted-information processing—what biologists call translation (from the 4-letter DNA alphabet to the 20-letter amino-acid alphabet). All known terrestrial life uses a common code, an encryption–decryption system. There is no agreement about how the specific coding assignments, or indeed any coding assignments, first evolved. How did such “software” come out of chemistry—that is, “hardware”? As Kerr surmises, I do indeed think that this transition is where new physics may lie. I should clarify, however, that the accumulation of information in living matter is entirely consistent with the second law of thermodynamics: Living organisms are open systems, and they export entropy into their surroundings to pay for the information gained.

Finally, I am grateful to Akira Hasegawa for emphasizing the astonishing thermodynamic efficiency of the human brain, which deploys legions of Maxwell-demon-like molecules to operate gated ion channels that enable information to propagate between neurons with relatively little waste heat.