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.
Green algae may rely on quantum computing to turn sunlight into food.
Petr Znachor/Nikon Small World
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 Netherlands. With the advent of powerful new tools like femtosecond (10-15 second) lasers and nanoscale-precision positioning, lifes quantum dance is finally coming into view.
INTO THE LIGHT
One of the most significant quantum observations in the life sciences comes from Fleming and his collaborators. Their study of photosynthesis in green sulfur bacteria, published in 2007 in Nature [subscription required], tracked the detailed chemical steps that allow plants to harness sunlight and use it to convert simple raw materials into the oxygen we breathe and the carbohydrates we eat. Specifically, the team examined the protein scaffold connecting the bacterias external solar collectors, called the chlorosome, to reaction centers deep inside the cells. Unlike electric power lines, which lose as much as 20 percent of energy in transmission, these bacteria transmit energy at a staggering efficiency rate of 95 percent or better.
The secret, Fleming and his colleagues found, is quantum physics.
To unearth the bacterias 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.
(An equivalent process maybe happening in the brain. During a thought, our neural patterns fire in many areas of the brain while looking for a path of least resistance. Please see fMRI Neuroscience Advances in Mind Reading Scans)
Electrons moving through a leaf or a green sulfur bacterial bloom are effectively performing a quantum random walka sort of primitive quantum computationto 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 thats our conjecture. And a lot of people agree with it…
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 lifeconsciousnessis likely a quantum phenomenon too (so that’s where it started with Hameroff!). 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 Hameroffs 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.