One thing most often forgotten about the universe is it's scale. Sure everyone knows its huge, but jeez, noone really knows how huge! Theoretical limits are placed around 10-20 billion light years, since it couldnt expand at faster than the speed of light, but then you would have to define a boundary on one side of which there is a universe, and on the other side there is not. The wave/partoicle theory of the universe (to go a little off track for a second) (much like the wave/particle theory of energy) is interesting in the respect of said boundaries. The particle side of the universe, in the effect that the universe consists of matter and energy, is most familiar (and most vague as far as boundaries go). But consider that from an outside perspective the universe is throughly dense, and from our perspective the formations that we see as matter are wave fluctuations -- matter represents condensations in that wave. If you have a grasp of the time-space fabric described by Einstein (and many others) in his theories, you can illustrate this. Of course by wave i dont mean ripples, but waves which affect both space and time. Time itself, in effect, is part of that wave (represented by entropy) from its initial transmission at its own beginning (big bang, whatever). Now, to get back to the notion of a quiet universe, also consider that what we observe of the universe is NOT only space (stars, galaxies, etc) but also time. When we look at a quasar, for example, we can determine by its electromagnetic doppler shift that it is extremely far away (indeed, most distant of all other known objects). What we really "see" is the universe as it was billions of years ago, because that is how long it took the light from that object to reach us. So finding a civilization is like finding a needle in a haystack in a haystack of haystacks. (For those that are curious, the most recent pessimistic estimate of the civilization equation is 140,000 in our galaxy, and the optimistic is 600,000, which is of course based on an equation half of which factors we do not know)