This is a book that was written ages ago, in 1979. Dr. Asimov takes on the question of whether we are alone in the galaxy, and he takes a fairly straightforward and conservative (in his estimation) approach to determining an estimate of how many technological civilizations there are in our Galaxy alone.

He comes up with the number 390 million, and further extrapolates that most of them would be more advanced than we are. He makes a lot of assumptions, for example, he assumes (optimistically, he admits) that our civilization will continue to last on Earth as long as Earth is able to support life, which he suggests is about 7.4 billion more years, and then that this is the average duration of a civilization. (Therefore, only 1/1,500,000 of the civilizations in the galaxy are at or below our level of sophistication and advancement.)

It's fascinating to "watch" Dr. Asimov manipulate the science to come up with the numbers he comes up with, starting with the total number of stars in the galaxy, which he estimates at 300 billion, and whittling it down based on estimates based on the best scientific data available to him at the time. By the end, you are almost awed by the potential number of civilizations - not just life bearing planets, but ones that develop an advanced civilization.

So then, he goes on to ask, why haven't we found any evidence of them? He talks about the physics limiting the reality of interstellar travel, the energy expenditures, the times involved, and the difficulties of finding likely targets for exploration. He talks about the difficulties in detecting the various potential signals that an advanced civilization might send out, and whether we are too 'primitive' to detect such signals, or whether said signals are just not at high enough energy to be detected by our efforts to do so to date. (Remember, this was written in 1979.)

In the end, Dr. Asimov suggests that the efforts themselves to expand beyond our world and to detect extraterrestrial civilizations will lead to profit and to helping ourselves. "Let us strive to inherit the Universe that is waiting for us; doing so alone, if we must, or in company with others - if they are there."

We have so many problems here in the United States, and in the world, that at this point in history (2008), any sort of effort like this might be impossible, at least politically. But perhaps having a goal to inspire us and to influence us would be a good thing, and help us to surmount some of these issues that seem so important.