I recently wrote about how the formation and removal of reverse salients influence the path of technological progress. As explained by Thomas P. Hughes, “As [a technological] system evolves toward a goal, some components fall behind or out of line. As a result of the reverse salient, growth of the entire enterprise is hampered, or thwarted, and thus remedial action is required.” Reverse salients are progress’s sticking points.

As one reverse salient is overcome, a new one forms. What’s interesting is that, as a system advances, problems that were considered “solved” become problems again. Reverse salients form in the same places over and over again.

A great current example, described in a new Economist article, is refrigeration. For many years, refrigeration was a solved problem. The reigning technology for cooling – “draw heat from the thing you want to cool by evaporating a liquid next to it, and then dump that heat by pumping the vapour elsewhere and condensing it” – was good enough. Now, though, refrigeration has again become a reverse salient, at least in computing systems. Not only has the dissipation of heat from microprocessors become a problem in computer design, but the cost of the electricity needed to cool the air around computers has made refrigeration a reverse salient in data center design as well.

Reverse salients attract the attention of inventors, and, as the Economist relates, some interesting new ideas are emerging for how to cool chips, ranging from paraelectric films to thermoelectric materials to newfangled radiators. I would expect we’ll see a burst of innovation in designing more efficient air-conditioning as well. When it comes to technological systems, problems rarely stay solved for long.