Biology, meet quantum physics
January 16, 2009 | 7:54 am
Most young scholars study photosynthesis, the process by which plants and some microorganisms convert sunlight into fuel.
Those middle school biology lessons generally steer clear of the topic of quantum mechanics, the physics of the subatomic world.
But it turns out the same rules that govern subatomic particles are at work in sun-gobbling plants, according to research at the University of California, Berkeley, and at Washington University in St. Louis.
According to a recent article in Discover magazine, electrons moving through a plant use quantum tunneling, the phenomenon of hopping spontaneously from one location to another, to make the process of photosynthesis more efficient than any energy-converting process created by man.
According to the article:
On the face of things, quantum mechanics and the biological sciences do not mix. Biology focuses on larger-scale processes, from molecular interactions between proteins and DNA up to the behavior of organisms as a whole; quantum mechanics describes the often-strange nature of electrons, protons, muons and quarks–the smallest of the small…
Yet new experiments keep finding quantum processes at play in biological systems… With the advent of powerful new tools like femtosecond (10-15 second) lasers and nanoscale-precision positioning, life’s quantum dance is finally coming into view.
As new scientific tools are developed, the prospect of understanding processes like photosynthesis at a much deeper level is becoming stronger. For example, the Linac Coherent Light Source, due for first light this year at SLAC National Accelerator Laboratory, is an X-ray laser driven by a particle accelerator that will allow physicists to watch chemical reactions that previously occurred too quickly to observe.
The Discover article points out that new studies of photosynthesis may lend some credibility to past hypotheses involving quantum mechanics.
In 1996, biophysicist Luca Turin controversially suggested human smell receptors performed quantum tunneling to distinguish between odors. In 2007, biochemists from the Autonomous University of Barcelona said that green tea acted as an anti-oxidant through a similar process.
And Sir Roger Penrose, Oxford University physicist, and Stuart Hameroff, an anesthesiologist and director of the Center for Consciousness Studies at the University of Arizona, have argued that our very consciousness is governed by the laws of quantum gravity. These arguments are also very controversial, with Max Tegmark, MIT cosmologist, publishing some forceful rebuttals.
But with new results and new tools that can explore the quantum domain of biological systems, perhaps some day quantum physics will make it into the biology classroom after all.
Kathryn Grim
Posted in Uncategorized |
1 Comment »
January 21st, 2009 at 3:01 pm
Hmmm. Electron transfer on femtosecond scales is a far cry from quantum computation.
Were I a short-tempered fellow, I’d ask whether anybody actually researches Hameroff’s claims before writing about them. His assertions grow wilder the more closely they are studied; Litt et al. (2006) is a good antidote. (It should be noted that Hameroff has tried to respond to this article, but when I found his response on the Net, it was so full of blatant comprehension failures and absurd claims — ignoring everything that has ever been learned about emergent properties, for starters — that I can only hope it was a joke of some kind.)
Penrose has made various remarks to the effect that Gödel’s Incompleteness Theorems imply that classical computation cannot support human thought; to put it briefly, Gödel’s theorems imply no such thing. (Look up Scott Aaronson’s “Quantum Computing Since Democritus” lecture on Penrose for an accessible rebuttal, and see Greg Egan’s short story “Oracle” for an interesting companion piece.) All the proposals about microtubules and so forth are attempted solutions to a non-problem.
The notion that quantum mechanics is relevant to biology is not itself controversial. Read Watson’s The Double Helix: if you can get past the crude and sexist talk of how Rosalind Franklin could have been attractive if she’d only done something with her hair, you can see that people in the 1950s actually attempted to calculate using quantum chemistry how DNA nucleotides would stick together. This avenue of investigation goes back to Linus Pauling in the 1930s, whose work on the essentially quantum properties of interatomic bonds saturated the chemistry curriculum during World War II.
(For that matter, quantum mechanics was explained — badly — in my ninth-grade biology textbook, when it talked about what molecules are. Quantum physics is already in the biology classroom.)
Philosophically, the question is not whether quantum physics is necessary to answer some questions about biological systems — it is — but at what point a classical description becomes adequate or, in practical terms, necessary.