Technological momentum is a theory about the relationship between technology and society over time. The term was originally developed by the historian of technology Thomas P. Hughes.

Hughes's thesis is a synthesis of two separate models for how technology and society interact. One, technological determinism, claims that society itself was modified by the introduction of a new technology in an irreversible and irreparable way -- for example, the introduction of the automobile has influenced the manner in which American cities are designed, a change that can clearly be seen when comparing the pre-automobile cities on the East Coast to the post-automobile cities on the West Coast. Technology, under this model, self-propagates itself as well -- there is no turning back once adoption has taken place, and the very existence of the technology means that it will continue to exist in the future.

The other model, social determinism, claims that society itself controls how a technology is used and developed -- for example, the rejection of nuclear power technology in the USA amid the public fears after the Three Mile Island incident.

Technological momentum takes the two models and adds time as the unifying factor. In Hughes's theory, when a technology is young, deliberate control over its use and scope is possible and enacted by society. However as a technology matures, and becomes increasingly enmeshed in the society where it was created, its own deterministic force takes hold. In other words, Hughes's says that the relationship between technology and society always starts with a social determinism model, but evolves into a form of technological determinism over time and as its use becomes more prevalent and important.

An example of this can be found in the QWERTY keyboard. The original reason for the QWERTY key arrangement came from mechanical requirements in the first typewriters -- frequently-used pairs of letters were separated in an attempt to stop the typebars from intertwining and becoming stuck, thus forcing the typist to manually unstick the typebars and also frequently blotting the document. The QWERTY arrangement was purposefully chosen for a specific purpose, and could have been a variety of other arbitrary possibilities. Over time, though, the mechanical limitations of the early typewriters were solved, and of course modern computer keyboards have no such limitations. Yet the QWERTY arrangement is still used in a majority of keyboards using the Roman character set, and there has been some discussion as to whether more efficient keyboard arrangements exist (such as the Dvorak layout). However, to implement other arrangements would be difficult, if not impossible, in countries where QWERTY is currently used, because it would involve the re-learning of typing for anyone currently using QWERTY, and would cost millions of dollars in replacing keyboards. In a free-market democracy, this is not a feasible option, so QWERTY will continue to be the typing style favored, even if its original technological purpose has long since ceased to exist. The existence and use of the QWERTY layout -- as a technology -- compels its future use. In Hughes's model, it has moved from social determinism into a period of technological determinism, out of the control of individuals in society.

References

Thomas P. Hughes, "Technological momentum," in Albert Teich, ed., Technology and the Future, 8th edn., 2000.