Obstacles

Starfarers, 18.

A later Andersonian theme is that slower than light interstellar travel, even if started, might involve too much effort, energy, expenditure etc for too little profit, return, whatever and might therefore decline. By Chapter 18, this seems to be happening both to the Kith and to the starfaring civilization that Envoy is aimed towards. A variation on this is that, if the ruling intelligences become electronic, post-organic, whatever, then they might lose interest in empirical exploration. The latter happens in the Harvest Of Stars Tetralogy and in The Boat Of A Million Years although post-organics spread through the galaxy and beyond in Genesis. 

A related issue is as follows. If we detect something interesting, e.g., five thousand light-years away and if we then set out to investigate it close up but we travel at sub-light speed, then will whatever it was still be there when we get there? When approached, the starfaring civilization is seen to be drastically contracting - which returns us to the first point.

In Starfarers, as in The Boat Of A Million Years, the characters find ways to sustain interstellar travel despite such obstacles.