Is Quantum Mechanics Controlling Your Thoughts?
weirdest realm may be responsible for photosynthesis, our sense of smell, and
even consciousness itself.
Fleming sits down at an L-shaped lab bench, occupying a footprint about
the size of two parking spaces. Alongside him, a couple of off-the-shelf
lasers spit out pulses of light just millionths of a
Peering deep into these
proteins, Fleming and his colleagues at the
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
Quantum mechanics holds that any given particle has a chance of being in a whole range of locations and, in a sense, occupies all those places at once. Physicists describe quantum reality in an equation they call the wave function, which reflects all the potential ways a system can evolve. Until a scientist measures the system, a particle exists in its multitude of locations. But at the time of measurement, the particle has to “choose” just a single spot. At that point, quantum physicists say, probability narrows to a single outcome and the wave function “collapses,” sending ripples of certainty through space-time. Imposing certainty on one particle could alter the characteristics of any others it has been connected with, even if those particles are now light-years away. (This process of influence at a distance is what physicists call entanglement.) As in a game of dominoes, alteration of one particle affects the next one, and so on.
The implications of all this are mind-bending. In the macro world, a ball never spontaneously shoots itself over a wall. In the quantum world, though, an electron in one biomolecule might hop to a second biomolecule, even though classical laws of physics hold that the electrons are too tightly bound to leave. The phenomenon of hopping across seemingly forbidden gaps is called quantum tunneling.
From tunneling to entanglement, the special properties of the quantum realm allow events to unfold at speeds and efficiencies that would be unachievable with classical physics alone. Could quantum mechanisms be driving some of the most elegant and inexplicable processes of life? For years experts doubted it: Quantum phenomena typically reveal themselves only in lab settings, in vacuum chambers chilled to near absolute zero. Biological systems are warm and wet. Most researchers thought the thermal noise of life would drown out any quantum weirdness that might rear its head.
Yet new experiments keep
finding quantum processes at play in biological systems, says Christopher Altman,
a researcher at the Kavli Institute of Nanoscience in the
INTO THE LIGHT
The secret, Fleming and his colleagues found, is quantum physics.
To unearth the bacteria’s inner workings, the researchers zapped the connective proteins with multiple ultrafast laser pulses. Over a span of femtoseconds, they followed the light energy through the scaffolding to the cellular reaction centers where energy conversion takes place.
Then came the revelation: Instead of haphazardly moving from one connective channel to the next, as might be seen in classical physics, energy traveled in several directions at the same time. The researchers theorized that only when the energy had reached the end of the series of connections could an efficient pathway retroactively be found. At that point, the quantum process collapsed, and the electrons’ energy followed that single, most effective path.
Electrons moving through a leaf or a green sulfur bacterial bloom are effectively performing a quantum “random walk”—a sort of primitive quantum computation—to seek out the optimum transmission route for the solar energy they carry. “We have shown that this quantum random-walk stuff really exists,” Fleming says. “Have we absolutely demonstrated that it improves the efficiency? Not yet. But that’s our conjecture. And a lot of people agree with it.”
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
TUNNELING FOR SMELL
What is really happening,
In the quantum world, an electron from one biomolecule might hop to another, though classical laws of physics forbid it.
“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
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
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