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Monday, Nov 9, 2009
But were too afraid of quantum spookiness to ask.
Oct 20, 2005 | What is nanotechnology? Recent surveys indicate that most Americans don't have a clue. (The good news is that most of the rest of the world doesn't either.) Competing definitions are in circulation. The simplest, but least adequate, simply states that anyone manipulating matter at the dimensions of 100 nanometers or smaller is engaged in nanotechnology. How big is a nanometer? A billionth of a meter, but that definition doesn't mean much. If you split a human hair into a thousand equal parts, each part would be about 100 nanometers in diameter -- a nanohair, so to speak. But researchers on the frontier of nanotechnology have no interest in working with anything this bulky and cumbersome. They would argue, and quite rightly, that by the time you reach this scale most of the qualities unique to the nanoworld have either been used or lost.
A far more meaningful definition of nanotechnology is this: Nanotechnology is the set of tools necessary to design and build molecular devices with atomic precision. Molecular devices are the tiny machines that we use to construct things in the nanofuture. How big will they be? Start with atoms. Each atom is a blob of primordial universal stuff, a fraction of a nanometer in diameter. A standard baseball is about 3 inches in diameter, or about 7.5 centimeters. If we shrink this ball to one-millionth of its original size, it is now about 75 nanometers in diameter -- just below the NNI's upper limit of 100 nanometers. If we shrink it again so it's one-thousandth of the already tiny baseball, it will be less than one-tenth of a nanometer in diameter -- slightly smaller than a carbon atom (whose diameter is 0.154 nanometers, for those keeping score). For the nanoengineer, individual atoms are the components of a molecular device. In order to have moving parts, workspace, inputs, outputs, etc., a molecular device will need a few thousand atoms. This brings us back to about 100 nanometers, the generic upper size limit for nanotechnology. So why is the first definition poor and the second meaningful? The answer, like nanotechnology itself, lies outside the very limits of our physical world.
While the universe may hold wonders without end, our physical realm can be explained by a few simple yet profound rules of atomic behavior. These rules do not differ greatly from the ones envisioned by the first proponents of atom theory, the ancient Greek philosophers. The physical, or macroscopic, region of our senses and experience behaves in a manner fully consistent with this atomic theory of matter. In fact, the microscopic world of bacteria, viruses, and molecules looks just like our world, only much, much smaller. A bacterium swims in a drop of water much the way you or I swim in a pond. Actually, some swim, and some, like the intestinal bacterium E. coli, have a little propeller that looks and works a lot like an outboard motor. Bacteria, molecules, and even whole atoms are subject to the effects of heat and cold. When you fry an egg, it is the very proteins that denature and turn white. Molecules of air collide just like billiard balls, making endless bank shots off each other and the walls of the room.
Democritus of Abdera (ca. 460-370 BCE) laid down the basic principles of atomism. He proposed that atoms are separate from each other and distinguished in size, shape, position and arrangement. He further stated that atoms could overtake each other, collide, and interact to create "compound bodies." He also used atomism to formulate what we now call the law of conservation of energy (aka the first law of thermodynamics), by stating, "Nothing can be created out of nothing, nor can it be destroyed and returned to nothing." This may be the most famous and profound observation in all of science. Democritus was truly the grandfather of modern chemistry and the godfather of nanotechnology. His prescient ideas included the concepts of atomic weight, and the essential idea that atoms had chemical properties based on their size and shape. He believed that these chemical properties were responsible for material manifestations such as color and taste. His ideas were, in fact, correct -- but only for that which is atom-size or larger.
The kingdom of nanotechnology is infinitely more complex and mysterious than the atomic world first sketched out by Democritus because it spans both the atomic and the subatomic. Nanoengineers manipulate individual atoms by controlling their ability to chemically bond. But to bond, atoms must share tiny bits of themselves -- electrons. Electrons are subatomic particles, so a few rudimentary concepts from quantum mechanics must be used to characterize their behavior.
Quantum behavior is never seen in the "real" world, nor does it make logical sense. Consider one of the most famous findings of quantum mechanics, the so-called wave-particle duality. This expression refers to is the fact that all objects -- whether light or boulders -- exhibit at times a wavelike nature, at other times a particle-like nature. Electrons, for example, must behave like both waves and particles for the chemical bond to work. The intellectually challenging (not to say mind-boggling) part is that absolutely speaking, neither an electron nor any other object "is" either a particle or a wave: It simply exhibits wave or particle properties at different times.
This duality is necessary to make sense of subatomic behavior, but it would never do on the playground of life: Getting hit by a flashlight is not the same as getting hit by a flashlight beam. (Unless you have access to a subatomic-size flashlight, don't try to disprove this at home.) In order to manipulate matter one atom at a time -- that is, in order to do real nanotechnology -- it is necessary to dip below the atomic surface and capture a few denizens of the subatomic universe. We don't need to understand all the "deep things," just enough of them. And we do.
Most of us have a general understanding that once we shrink below the size of atoms things get exceedingly strange. We know the atom is made up of subatomic particles -- protons, neutrons and electrons -- and that subatomic particles follow the rules of quantum mechanics. In the quantum zone impossible things like "electron tunneling" begin to occur. This describes the phenomenon of electrons tunneling through an energy barrier and coming out on the other side without ever occupying the space in between. In our material plane, this would be equivalent to moving directly from one side of a brick wall to the other without ever passing through the wall or even the space occupied by the wall.
Another baffling example of quantum behavior is that under certain conditions, two particles will influence each other no matter how far apart they are. Quantum theory allows a single, pure quantum state -- a particular polarization, for example -- to be spread across two subatomic particles, such as a pair of simultaneously created photons. Such photons are said to be "entangled," and they remain entangled even when they fly apart. The uncanny result of this entanglement is that physically measuring one photon will instantaneously influence the properties of its twin, even if they are on opposite sides of the galaxy. Even Einstein thought this was too weird, because it violates a bedrock principle of the theory of relativity, that nothing can travel faster than the speed of light. Einstein said, "I cannot seriously believe in [the quantum theory] because it cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance." Yet, in an experiment funded in part by a telecommunications conglomerate, quantum "spookiness" was demonstrated at distances of greater than 10 kilometers. (The headline of the Science magazine article about this was, "Quantum Spookiness Wins, Einstein Loses in Photon Test.")
A real-world application for this unreal phenomenon would be "spooky encryption," in which one entangled particle goes off into the world with your data and the other to a secure location. Anyone trying to read your electronic file would change the entangled state of both particles, setting off an alarm. But what kind of force can affect two particles at exactly the same time across light-years of space? The ultimate causes may be unknown, but the reality is that phenomena completely impossible at the human scale are completely ordinary on the quantum scale.
