Elated by the finding, researchers are looking to mimic nature’s quantum ability to build solar energy collectors that work with near-photosynthetic efficiency. Alán Aspuru-Guzik, an assistant professor of chemistry and chemical biology at Harvard University, heads a team that is researching ways to incorporate the quantum lessons of photosynthesis into organic photovoltaic solar cells. This research is in only the earliest stages, but Aspuru-Guzik believes that Fleming’s work will be applicable in the race to manufacture cheap, efficient solar power cells out of organic molecules.
TUNNELING FOR SMELL
Quantum physics may explain the mysterious biological process of smell, too, says biophysicist Luca Turin, who first published his controversial hypothesis in 1996 while teaching at University College London. Then, as now, the prevailing notion was that the sensation of different smells is triggered when molecules called odorants fit into receptors in our nostrils like three-dimensional puzzle pieces snapping into place. The glitch here, for Turin, was that molecules with similar shapes do not necessarily smell anything like one another. Pinanethiol [C10H18S] has a strong grapefruit odor, for instance, while its near-twin pinanol [C10H18O] smells of pine needles. Smell must be triggered, he concluded, by some criteria other than an odorant’s shape alone.
What is really happening, Turin posited, is that the approximately 350 types of human smell receptors perform an act of quantum tunneling when a new odorant enters the nostril and reaches the olfactory nerve. After the odorant attaches to one of the nerve’s receptors, electrons from that receptor tunnel through the odorant, jiggling it back and forth. In this view, the odorant’s unique pattern of vibration is what makes a rose smell rosy and a wet dog smell wet-doggy.
In the quantum world, an electron from one biomolecule might hop to another, though classical laws of physics forbid it.
In 2007 Turin (who is now chief technical officer of the odorant-designing company Flexitral in Chantilly, Virginia) and his hypothesis received support from a paper by four physicists at University College London. That work, published in the journal Physical Review Letters, showed how the smell-tunneling process may operate. As an odorant approaches, electrons released from one side of a receptor quantum-mechanically tunnel through the odorant to the opposite side of the receptor. Exposed to this electric current, the heavier pinanethiol would vibrate differently from the lighter but similarly shaped pinanol.
“I call it the ‘swipe-card model,’?” says coauthor A. Marshall Stoneham, an emeritus professor of physics. “The card’s got to be a good enough shape to swipe through one of the receptors.” But it is the frequency of vibration, not the shape, that determines the scent of a molecule.
THE GREEN TEA PARTY
Even green tea may tie into subtle subatomic processes. In 2007 four biochemists from the Autonomous University of Barcelona announced that the secret to green tea’s effectiveness as an anti-oxidant—a substance that neutralizes the harmful free radicals that can damage cells—may also be quantum mechanical. Publishing their findings in the Journal of the American Chemical Society, the group reported that antioxidants called catechins act like fishing trollers in the human body. (Catechins are among the chief organic compounds found in tea, wine, and some fruits and vegetables.)
Free radical molecules, by-products of the body’s breakdown of food or environmental toxins, have a spare electron. That extra electron makes free radicals reactive, and hence dangerous as they travel through the bloodstream. But an electron from the catechin can make use of quantum mechanics to tunnel across the gap to the free radical. Suddenly the catechin has chemically bound up the free radical, preventing it from interacting with and damaging cells in the body.
Quantum tunneling has also been observed in enzymes, the proteins that facilitate molecular reactions within cells. Two studies, one published in Science in 2006 and the other in Biophysical Journal in 2007, have found that some enzymes appear to lack the energy to complete the reactions they ultimately propel; the enzyme’s success, it now seems, could be explained only through quantum means.
QUANTUM TO THE CORE
Stuart Hameroff, an anesthesiologist and director of the Center for Consciousness Studies at the University of Arizona, argues that the highest function of life—consciousness—is likely a quantum phenomenon too. This is illustrated, he says, through anesthetics. The brain of a patient under anesthesia continues to operate actively, but without a conscious mind at work. What enables anesthetics such as xenon or isoflurane gas to switch off the conscious mind?
Hameroff speculates that anesthetics “interrupt a delicate quantum process” within the neurons of the brain. Each neuron contains hundreds of long, cylindrical protein structures, called microtubules, that serve as scaffolding. Anesthetics, Hameroff says, dissolve inside tiny oily regions of the microtubules, affecting how some electrons inside these regions behave.
He speculates that the action unfolds like this: When certain key electrons are in one “place,” call it to the “left,” part of the microtubule is squashed; when the electrons fall to the “right,” the section is elongated. But the laws of quantum mechanics allow for electrons to be both “left” and “right” at the same time, and thus for the microtubules to be both elongated and squashed at once. Each section of the constantly shifting system has an impact on other sections, potentially via quantum entanglement, leading to a dynamic quantum-mechanical dance.
It is in this faster-than-light subatomic communication, Hameroff says, that consciousness is born. Anesthetics get in the way of the dancing electrons and stop the gyration at its quantum-mechanical core; that is how they are able to switch consciousness off.
It is still a long way from Hameroff’s hypothetical (and experimentally unproven) quantum neurons to a sentient, conscious human brain. But many human experiences, Hameroff says, from dreams to subconscious emotions to fuzzy memory, seem closer to the Alice in Wonderland rules governing the quantum world than to the cut-and-dried reality that classical physics suggests. Discovering a quantum portal within every neuron in your head might be the ultimate trip through the looking glass.