The Science of Discworld IV

limitations on the energy needed to put a person or cargo in orbitaround the Earth could, in principle, be overcome by changing the context. If you use a rocket, the amount of energy needed to get a 100-kilogramme man up to synchronous orbit can be calculated using Newton’s laws of motion. It is the difference in potential energy caused by the planet’s gravity well. You can’t change that, so at first the limitation seems foolproof.
    In the mid-1970s, however, a wholly new suggestion was made: the space bolas. Essentially this is a giant Ferris wheel in orbit. The traveller gets into the cabin as it swings past the upper atmosphere, and gets out again when it approaches the furthest point from Earth. A succession of such gadgets can deposit him in synchronous orbit a few weeks later.
    A third step in the ladder of technology, not practical yet but already being discussed by engineers, is the space elevator. The science fiction writer and futurologist Arthur C. Clarke was one of several people who had this idea: take a ‘rope’ up to synchronous orbit and let it down to an equatorial landing-strip. The result would be a material link from a point in synchronous orbit to the ground. Once this is set up, a system of cabins and pulleys-and-weights like those used in skyscraper elevators could take a person up to orbit very efficiently. Counterweights, or another man coming down, would reduce the cost to that of the energy required to override friction.
    The point is not whether we can do this yet. We can’t; even carbon-fibre ‘rope’ is too weak. But the space elevator shows how a design trajectory can take a function away from its earliest, primitive constraints, so that a whole new set of rules applies, and the old limitations become … not invalid, but irrelevant.
    More familiar examples of this ‘transcendent’ process are writing and telecommunication. The first attempts at writing probably involved scratches on rock or bark, and these matured in two directions – pictorial and phonetic writing. Pictorial writing, such as ancient Egyptian hieroglyphs and modern Chinese, has found it difficult to move up the technological ladder. They are not evenat the rocket stage; fireworks, perhaps. Phonetic writing was more suitable for printing – the space bolas stage of the technology. This was improved as far as the great newspaper printing presses of the twentieth century and the electric typewriter. Then came the space elevator stage, word processing by computer. Ironically, this may just have saved Chinese ideograms, now easily typeset by computer, from oblivion. A further stage is starting to appear with eBooks and iPads. Eventually, all writing might be virtual, encoded in physically tiny memories until it needs only to be actualised on screens and in minds.
    Communication at a distance started with semaphore and chains of watch-fires on hilltops. Navies developed coded systems of flags for communication between ships. Discworld inventors developed the clacks, a mechanical telegraph with repeaters at limit-of-sight, aided by telescopes, while we used a signal-box and mechanical linkages to signal to trains miles from the box. With electricity came the ability to send signals via cables, and the telegraph was born. Several different coding systems for commercial transactions, and a primitive fax machine, were in commercial use before 1900. All these were rocket-ships. Then came the telephone, which uses sound waves to modulate an electrical signal. Much capital investment went into wiring the countryside and undersea cables to connect the continents. These heroic ventures were comparable, in technical difficulty, with putting up a space bolas now. Meanwhile ‘wireless’ began to be used: radio, and later television. With mobile phone technology, depending upon billions of pounds of investment in immensely sophisticated base stations and in research to improve and develop the handsets, we are now beginning the space elevator stage of telephone technology.
    We can compare these technical innovations to developments in organic evolution. We analyse the development of mammals on two scales, to show how the evolutionary process outgrows its initialconstraints and achieves new properties and functions as the trajectory changes direction. We choose the two scales to emphasise that this is not a description of what actually happens during organic evolution.
    We have already met the question of the extent of