The metaphor of momentum is often used in relation to technological innovation and, more specifically, to claim that an emerging technology is gaining relevance and is edging towards commercialization. Even though the use of this metaphor is typically quite casual and superficial, a closer look at its origins in physics and its treatment in the scientific literature reveals that there is much more to gain from it.

Our observations

• In the 1960s, historian of technology Thomas P. Hughes, proposed the metaphor of momentum to describe the way in which technological systems are formed and gain stability. It was his answer to the debate over technological versus social determinism; emerging systems are relatively flexible at first (and mostly the product of human agency), but over time they become more stable and eventually they are virtually inert and beyond deliberate human control.
• In physics, momentum is the product of an object’s mass and speed in a given direction ( = m). The more momentum an object has, the more difficult it is to slow it down or change its course. In other words, very heavy objects (e.g. an oil tanker) can have tremendous momentum even at very low speeds. On the other hand, light objects (e.g. a bullet) can have large momentum when they travel at very high speed.
• Hughes argued that in the case of (emerging) technologies, the metaphorical “mass” can be interpreted to be the structural components of an emerging system. These include the number of businesses that are committed to a technology’s development and commercialization (and their cumulative investments), but also supportive infrastructures (i.e. sunk costs) and softer factors such as regulations, design standards or other institutions (e.g. a favorable shift in norms; growing societal concern over privacy adds to momentum for more secure digital technology).
• Metaphorically, “speed” can be understood as the pace of technological development (e.g. scientific or engineering breakthroughs). In that case, a novel technology with few committed developers can pick up momentum rapidly when technological progress is evident and, as a consequence, additional actors are likely to jump on the bandwagon and further spur development. Such breakthroughs can also affect the “direction” of the emerging system as specific design options may gain the upper hand (e.g. the battle between AC and DC power in the emerging electricity system).
• This conception of momentum ties in the so-called Collingridge dilemma, regarding the (un)desired implications of technological designs; at first, we don’t know what a technology really entails and what its impact will be and by the time we finally understand it, it is too late to change anything. This is true for technologies that raise obvious ethical questions (e.g. genetic ngineering), but also, for example, for the smartphone, which has a much more profound societal impact than we could ever have imagined.

Connecting the dots

In times of rapid technological change, the same questions come up time and time again; will this technology make it to market, when will it be “ready” and what will be its impact? For each of these questions, the momentum metaphor is often used as merely a rhetorical tool to claim that a technology is on a sure path to success. However, there is more to gain from the metaphor when we unpack its meaning in physics. It invites us to look at three dimensions of technological change: mass, speed and directionality. In other words, we should consider how many organizations are developing, supporting or advocating the technology and how powerful they are, how much has been invested (e.g. in production capacity) and to what extent a supportive infrastructure or institutional framework has been constructed. If there is no such infrastructure or framework (yet), probably because some technological hurdles still need to be taken, the question is how fast the technology is progressing.This could relate to performance (e.g. the reliability of self-driving cars), efficiency (e.g. of a solar panel), costs (e.g. $/kWh in a li-ion battery) or a combination of factors. No technological trajectory is ever straightforward and many design choices are made in the process that may change the direction of developments. Such changes may come about as different stakeholders have different preferences (e.g. because some design option better suits their competences or interests) or because technological breakthroughs favor one option over the other (e.g. the success of batteryelectric vehicles killed momentum for the hydrogen car). To illustrate, there are different design options for nuclear fusion reactors and a breakthrough for one of those options would not only add momentum to nuclear fusion in general, it would also steer the emerging system in that particular direction.Besides scientific or engineering breakthroughs (i.e. internal factors), external forces working on the system may also add (or reduce) momentum or change the course of developments. Growing societal pressure or regulatory push may incentivize developers to invest more time and money and could also attract additional developers or investors. Especially in a technology’s early stages, momentum is very much the product of rhetoric and persuasion. Interested actors will seek to convince others of the virtues of some option to get them to jump on the bandwagon and create a self-fulfilling prophecy. In some cases, this includes heavy lobbying with governments to set up support programs, in other cases, the commitment of one or more powerful actor(s) (e.g. market leaders) may be enough to persuade others to join as well. This does not mean that the technology will necessarily prove successful; technological progress may be disappointing and actors may lose interest. In this respect, the momentum metaphor partly overlaps with Gartner’s hype cycle model, which states that technologies are typically hyped in their early stages and that they will go through a phase of disappointment before they eventually find success. However, while the hype cycle is essentially deterministic (by implying that every technology follows this path to success), the concept of momentum allows for a greater variety of pathways and outcomes.

Implications

• Momentum can be gained and lost, and to truly understand a technological trajectory, one must understand not only the rate of technological progress, but also its structural components (committed actors, infrastructure and supportive institutions) and the (societal and political) force-field that propels it or slows it down.
• On a case-by-case basis, momentum can be quantified (and tracked over time) by identifying the key proxies for mass (e.g. levels of investments, number and type of businesses involved), speed (e.g. key parameters of performance) and direction (e.g. the major design options) of the emerging system.
• The momentum metaphor is not only applicable to technological development. In (geo-)politics, for instance, the same dynamics can be discerned. A seemingly small conflict may pick up momentum when events take place in rapid succession and nations respond with increasingly heavy measures. As a result, developments may spin out of control, become unstoppable and lead to a major conflict that no one intended in the beginning (e.g. the current tit-for-tat tariffs between China and the U.S., which can result into a protectionist regime change in the global trading system).