Kevin Kelly has a great new essay up, "Was Moore's Law Inevitable?", examining a series of examples of exponential growth in technological capability from a wide range of fields - and makes the very interesting point that all these examples are "prisoner[s] of physics, the periodic table, manufacturing technology and economics" - but some of them proceed rapidly and some do not. The interesting question is why?
One answer he gives is in the "scale-down" of solid-state technologies: it has proven relatively easy to pack more stuff into smaller areas, and so technical advances related to increasing smallness are ripe for this sort of growth. But other examples don't have that smallness aspect, and yet grew exponentially just the same: the growth of the railroads in the 19th century, the increase in the speed of aircraft in the first half of the 20th century, the cost per unit for DNA sequencing in recent years. Examples that are not growing rapidly now where it would seem very useful if they were include such things as the cost per unit production of solar cells, or the energy storage capacity per unit volume or mass of batteries. Every technology seems like it would benefit from a Moore's law-type progression - so why are we seeing it for some but not for others?
This all suggested to me that the key criterion in whether a technological trend follows a “Moore’s law” of rapid growth or not is the level of continuing investment society puts into that technology, relative to the real costs and constraints of chemistry/physics/information.
If the level of investment is high enough, rapid (2-year or faster doubling) growth comes naturally and is driven by continued demand against the falling cost. If the level of investment is lower than some threshold (solar cells, batteries, spaceflight, …) then growth in technical capability is forced to a much slower curve, constrained by the ratio of investment level to that threshold.
I would guess the threshold investment level also grows exponentially with that capability level, and when the curves of available investment capital vs. threshold cross, you hit the top of that S curve and innovation slows again. But new technology ideas can drop that threshold and re-ignite growth again…
The level of investment capital available would be constrained in a market economy by the basic level of demand for whatever product it is, and the availability of alternative technologies. For example, in energy markets the availability of fossil fuels as alternatives greatly suppresses the level of investment available in solar photovoltaics or batteries. An argument for government intervention?