Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100

that can create anything you want. Other scientists, however, are skeptical.
    The late Nobel laureate Richard Smalley, for example, raised the problem of “sticky fingers” and “fat fingers” in an article in
Scientific American
in 2001. The key question is: Can a molecular nanobot be built that is nimble enough to rearrange molecules at will? He said the answer was no.
    This debate spilled open when Smalley squared off with Drexler in a series of letters, reprinted in the pages of
Chemical and Engineering News
in 2003 to 2004. The repercussions of that debate are being felt even today. Smalley’s position was that the “fingers” of a molecular machine would not be able to perform this delicate task for two reasons.
    First, the “fingers” would face tiny attractive forces that would make them stick to other molecules. Atoms stick to each other, in part, because of tiny electrical forces, like the van der Waals force, that exist between their electrons. Think of trying to repair a watch when your tweezers are covered with honey. Assembling anything as delicate as watch components would be impossible. Now imagine assembling something even more complicated than a watch, like a molecule, that constantly sticks to your fingers.
    Second, these fingers might be too “fat” to manipulate atoms. Think of trying to repair that watch wearing thick cotton gloves. Since the “fingers” are made of individual atoms, as are the objects being manipulated, the fingers may simply be too thick to perform the delicate operations needed.
    Smalley concluded, “ Much like you can’t make a boy and a girl fall in love with each other simply by pushing them together, you cannot make precise chemistry occur as desired between two molecular objects with simple mechanical motion. … Chemistry, like love, is more subtle than that.”
    This debate goes to the very heart of whether a replicator will one day revolutionize society or be treated as a curiosity and relegated to the trash bin of technology. As we have seen, the laws of physics in our world do not easily translate to the physics of the nanoworld. Effects that we can ignore, such as van der Waals forces, surface tension, the uncertainty principle, the Pauli exclusion principle, etc., become dominant in the nanoworld.
    To appreciate this problem, imagine that the atom is the size of a marbleand that you have a swimming pool full of these atoms. If you fell into the swimming pool, it would be quite different from falling into a swimming pool of water. These “marbles” would be constantly vibrating and hitting you from all directions, because of Brownian motion. Trying to swim in this pool would be almost impossible, since it would be like trying to swim in molasses. Every time you tried to grab one of the marbles, it would either move away from you or stick to your fingers, due to a complex combination of forces.
    In the end, both scientists agreed to disagree. Although Smalley was unable to throw a knockout punch against the molecular replicator, several things became clear after the dust settled. First, both agreed that the naive idea of a nanobot armed with molecular tweezers cutting and pasting molecules had to be modified. New quantum forces become dominant at the atomic scale.
    Second, although this replicator, or universal fabricator, is science fiction today, a version of it already exists. Mother Nature, for example, can take hamburgers and vegetables and turn them into a baby in just nine months. This process is carried out by DNA molecules (which encode the blueprint for the baby) that guide the actions of ribosomes (which cut and splice the molecules into correct order) using the proteins and amino acids present in your food.
    And third, a molecular assembler might work, but in a more sophisticated version. For example, as Smalley pointed out, bringing two atoms together does not guarantee a reaction. Mother Nature often gets around this problem by employing a third party, an enzyme in a water solution, to facilitate a chemical reaction. Smalley pointed out that many chemicals found in computers and the electronics industry cannot be dissolved in water. But Drexler countered by saying that not all chemical reactions involve water or enzymes.
    One possibility, for example, is called self-assembly, or the bottom-up approach. Since antiquity, humans have used the top-down approach to building. With tools like a hammer and saw, one begins to cut wood and then