text: The Knowledge Emporium: ET - please phone!
  ET - please phone!
  This argument can be generalized to state that once an intelligent species develops the technology to rapidly increase its numbers, its days are numbered. In the case of our own species – and almost certainly any alien species - the crucial technology was agriculture, which permitted food to be produced rather than obtained from the wild, and thus permitted far larger populations to be sustained than was possible with hunter gathering. Complex societies soon followed: chiefdoms, then city-states and then empires, all with ever-increasing populations. Eventually mechanization of agricultural methods coupled with advances in medical science led to the rapid population increases of the last century.
  We turn, therefore, to the last of the possibilities listed above. Could interstellar travel be impossible or, at any rate be so difficult as to be rarely undertaken? What is known as the "technological ceiling" of the Universe defines the fundamental limits of what even the most advanced technology can accomplish. The best-known example of such a limit is Einstein's prohibition on any object or signal exceeding the speed of light.
  Unfortnately, it might not be as simple as that. It could be that our Universe has a low "technological ceiling". On this picture, our scientists could very likely understand the underlying principles behind the technology of a civilisation tens or even hundreds of millions years older than our own. Arthur C. Clarke's well-known Third Law stating that "any sufficiently-advanced technology is indistinguishable from magic" might turn out to be wrong.