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Unformatted text preview: 1 Scaling & Scaling & Scaling & Scaling & Physical Laws Physical Laws Physical Laws Physical Laws Introduction Introduction Introduction Introduction The physical laws that control everything we see are themselves universal (as far as we are aware). Yet how they act, and how we perceive them, depends very much on the scale over which these laws apply. For example, gravity is important to you and to me right now; it literally keeps us in our place. It acts as it does because of our relationship with the mass of the earth. Gravity is relatively weak and does its thing over large distances (over which distances other forces have long since effectively decayed to zero); gravity dominates the mechanics of large masses. On the other extreme, at the nuclear level, gravity is quite irrelevant but very short-range forces are predominant that affect, and effect, nuclear (and subnuclear) motions. In between these extremes of scale there are different forces at work. The Laws of Nature appear quite different from each other. These forces act in evidently unrelated ways but what they cause to happen may be different faces of the same phenomenon. The grossest laws of which we are aware relate gravity and distance, speed, and mass via relativity. We observe many aspects of long distance forces at the everyday level, for example the motion of the moon around the earth. But, as we know, at smaller scales, quantum mechanics rules electrons and atoms; at yet smaller scales, quantum mechanics and relativity interact to give us “quantum electrodynamics". At even smaller scales the laws are dictated by "quantum chromodynamics" and at the smallest scales presently conceived, “strings" may relate all of the above including gravity and quantum mechanics. The emerging new technology "Nanotechnology” is the application of forces over a length scale of relatively large molecules so that these forces can influence how these molecules will move and orientate. This motion is called " self-assembly " and lies at the heart of nanotechnology. Self-assembly means that Nature is doing the hard work to construct the molecular grouping you desire. This may be in the context of organic 2 compounds, inorganic structures, or living systems. In any case, the final product should have relied on molecular assembly to create the product rather than a series of anthropomorphically imposed synthetic steps. Unfortunately today there is no systematic approach to the study of the forces of self-assembly; each case is a special case; indeed in the vast majority of self-assembly processes it is not possible to quantitatively predict behavior. The forces for self-assembly must operate at a scale commensurate with the reactive elements being assembled. At the smallest scale of interest in nanotechnology, these reactions are just classical chemical reactions in which forces are often short range and move only small molecular subassemblies such as chemical radicals. Of course, there is also a blurred line between ordinary chemical reactions and those to which the sobriquet...
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This note was uploaded on 02/21/2009 for the course PHY A10 taught by Professor Tawfiq during the Fall '08 term at University of Toronto.
- Fall '08