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

valve can control a huge volume of water, the transistor allows a tiny flow of electricity to control a much larger flow, thereby amplifying its power.
    At the heart of this revolution is the computer chip, which can contain hundreds of millions of transistors on a silicon wafer the size of your fingernail. Inside your laptop there is a chip whose transistors can be seen only under a microscope. These incredibly tiny transistors are created the same way that designs on T-shirts are made.
    Designs on T-shirts are mass-produced by first creating a stencil with the outline of the pattern one wishes to create. Then the stencil is placed over the cloth, and spray paint is applied. Only where there are gaps in the stencil does the paint penetrate to the cloth. Once the stencil is removed, one has a perfect copy of the pattern on the T-shirt.
    Likewise, a stencil is made containing the intricate outlines of millions of transistors. This is placed over a wafer containing many layers of silicon, which is sensitive to light. Ultraviolet light is then focused on the stencil, which then penetrates through the gaps of the stencil and exposes the silicon wafer.
    Then the wafer is bathed in acid, carving the outlines of the circuits and creating the intricate design of millions of transistors. Since the wafer consists of many conducting and semiconducting layers, the acid cuts into the wafer at different depths and patterns, so one can create circuits of enormous complexity.
    One reason why Moore’s law has relentlessly increased the power of chips is because UV light can be tuned so that its wavelength is smaller and smaller, making it possible to etch increasingly tiny transistors onto silicon wafers. Since UV light has a wavelength as small as 10 nanometers (a nanometer is a billionth of a meter), this means that the smallest transistor that you can etch is about thirty atoms across.
    But this process cannot go on forever. At some point, it will be physically impossible to etch transistors in this way that are the size of atoms. You can even calculate roughly when Moore’s law will finally collapse: when you finally hit transistors the size of individual atoms.
    Around 2020 or soon afterward, Moore’s law will gradually cease to hold true and Silicon Valley may slowly turn into a rust belt unless a replacementtechnology is found. According to the laws of physics, eventually the Age of Silicon will come to a close, as we enter the Post-Silicon Era. Transistors will be so small that quantum theory or atomic physics takes over and electrons leak out of the wires. For example, the thinnest layer inside your computer will be about five atoms across. At that point, according to the laws of physics, the quantum theory takes over. The Heisenberg uncertainty principle states that you cannot know both the position and velocity of any particle. This may sound counterintuitive, but at the atomic level you simply cannot know where the electron is, so it can never be confined precisely in an ultrathin wire or layer and it necessarily leaks out, causing the circuit to short-circuit.
    The end of Moore’s law. Chips are made the same way as designs on T-shirts. Instead of spray painting over a stencil, UV light is focused on a stencil, burning an image onto layers of silicon. Acids then carve out the image, creating hundreds of millions of transistors. But there is a limit to the process when we hit the atomic scale. Will Silicon Valley become a rust belt?
    We will discuss this in more detail in Chapter 4 , when we analyze nanotechnology. For the rest of this chapter, we will assume that physicists have found a successor to silicon power, but that computer power grows at a much slower pace than before. Computers will most likely continue to grow exponentially, but the doubling time will not be eighteen months, but many years.
    MIXING REAL AND VIRTUAL REALITY
    By midcentury, we should all be living in a mixture of real and virtual reality. In our contact lens or glasses, we will simultaneously see virtual images superimposed on the real world. This is the vision of Susumu Tachi of Keio University in Japan and many others. He is designing special goggles that blend fantasy and reality. His first project is to make things disappear into thin air.
    I visited Professor Tachi in Tokyo and witnessed some of his remarkable experiments in mixing real and virtual reality. One simple application is to make an object disappear (at least in your