Three technologies I predict will be the origin of transformative technological changes in the coming century are:
- molecular manufacturing
- artificial intelligence or brain-computer interfaces, but not both
- solar or nuclear energy, but not both
By origin, I mean that a particularly large breakthrough in one of those areas will have effects that ripple into every other field of technology and science as well as politics. For example, molecular manufacturing will make it easier to build anything, which will have completely transformative effects in building construction, aerospace and space travel, cybernetics, etc. I wouldn't list "cybernetics" as an item on this list, because it's an example of a technology that will accelerate rapidly when enabled by advances in another area -- in this case, the quick fabrication of nanostructured materials, actuators, and sensors. Molecular manufacturing will open the floodgates of cybernetics, not the other way around.
In the same way, I believe that brain-computer interfaces will either progress to the point where creating a theory of intelligence for AI programming becomes a lot easier, or we create advanced AI before sophisticated brain-computer interfaces (BCI) and use it to make critical breakthroughs in analyzing the huge amounts of biological data necessary to implement BCI.
My model of future technological advances is not like a line of marching soldiers, where each field progresses steadily along, but more like a fireworks factory going up in flames: one spark ignites numerous powder kegs and the whole thing goes up in a great explosion. My current idea is that the spark will be something involving intelligence enhancement technology, either brain-computer interfaces using arrays of billions of nanowires as interface mechanisms, or artificial intelligence based on some scheme of merging together statistical inference with sequential decision theory. Although, in retrospect, it is possible that molecular manufacturing may be the key spark, as when this is introduced, it will be a tremendous enabler for both AI and BCI research. This is primarily through the nine-or-more orders of magnitude computing power increase it will offer, unless the availability of such resources are restricted through regulation.
For solar vs. nuclear energy, I do think that one will dominate the 21st century, but can't tell which yet. Anyone who says one or the other will definitely dominate is intellectually biased. Fossil fuels are obviously on their way out. Solar can be distributed everywhere, which is good, but it produces negligible power relative to harnessing the nuclear strong force (the strongest force in the universe), and consumes real estate. When we can manufacture carbon nanotubes in ton quantities, they will be available for covering the walls of reactor cores, as well as pipes able to hold extremely high-pressure steam, which will miniaturize nuclear power plants while maintaining energy output. With these infrastructural improvements, the large, clumsy plants of the past will seem like ancient history. Irrational environmentalist hangups over nuclear power could evaporate, as we see them doing so today, and the world could embrace the power of the atom. On the other hand, high-efficiency solar cells laid down in the world's deserts by autonomous robots could power all of human civilization, if deployed aggressively enough, making nuclear somewhat unnecessary for the near term. Only the future will tell.