I've long been convinced that intelligent species exist, but only for very short periods of time cosmologically speaking. I now believe that those species probably exist near the peak of their technological capabilities for only an extremely short time, probably less than 500 years, depending mainly on their rate of reproduction (less fertile species exist longer).

The reason is twofold: first, we develop on spheres where stored resources are axiomatically finite, and secondly our techological development allows us to rapdly dominate all the resources of that sphere. This leads automatically to a situation of overshoot, where the easily available stored resources support exponential population growth, followed by a Malthusian collapse. The time required to enter that overshoot depends on three things - the availability of resources, the overall fertility of the species, and their ingenuity. A reduction an any of these factors leads to a broader curve (slower ascent and descent) without changing its fundamental shape.

I no longer see expansion into space as a saviour. the reason is that the growing ability to exploit local resources causes the population to start exploding well in advance of the development of pinnacle technologies like mass space flight. I also expect that the utilization of renewables would not play a major role in saving a species, because by the time the need to collect such diffuse energy was obvious it would be too late due to exponential population pressure and the depletion of the foundational stored energy sources.

I'm obviously guilty of massive anthropocentrism here, because my primary assumption is that intelligent species arise in conditions much like those we have here. Still, it seems like a reasonable first approximation.

This could lead to new ways of gathering energy, much more efficient ways of using energy and enourmous cultural changes that could challange our old notions of what it is to be human and what life and death is. There is physical "room" for very intresting things, if we work on it.

Technologies that are practical for the 3rd world might be things like solar cookers that are easily made with materials that are available in the 3rd world.  It would eliminate the need to collect firewood, and reduce pressures on deforestation.  At least for a while - increasing human population would eventually overwhelm any ecosystem.

It's all a matter of priorities.

There were commercial plane flights about a decade after the Wright Brother first flew.  Not so with spaceflight.  Why?  Because the problems are harder to solve.  

Tainter takes a quantitative approach, as much as possible.  He looks at the number of patents granted, for example:

He also considers the money companies spend on R&D vs. the payback on their investment, and the benefits of medicine.  

The declining productivity of the United States health care system illustrates clearly the historical development of a problem-solving field. Rescher (1980) points out: Once all of the findings at a given state-of-the-art level of investigative technology have been realized, one must move to a more expensive level.... In natural science we are involved in a technological arms race: with every victory over nature the difficulty of achieving the breakthroughs which lie ahead is increased.

The declining productivity of medicine is due to the fact that the inexpensive diseases and ailments were conquered first (the basic research that led to penicillin costing no more than $20,000), so that those remaining are more difficult and costly to resolve (Rescher 1978). And as each increasingly expensive disease is conquered, the increment to average life expectancy becomes ever smaller.

Note that this does not literally mean the end of science.  It's more like "peak science."  Yes, there will always be more knowledge out there.  But it will be more difficult to extract, and more difficult to turn into a useful form.  If it weren't, it would have already been discovered.

I've been saying for a long time over on my site that the two technological areas that will have a huge impact on our energy situation are nanotech (as above) and genetic engineering (cheaper, more efficient biofuels processing).  These are extremely high multiplier areas, where even a single, seemingly minor breakthrough can be scaled up to broad application and have a huge impact on world energy markets.

They're not the "holy cow!" level of advancement like General Relativity or DNA, obviously, but I wouldn't trade them for anything right about now.