There is a recent book on the market by John Hogan, published by Addison- Wesley titles The End of Science: facing the limits of Knowledge in the Twilight of the Scientific Age. For a book review and chapter excerpt, go to the Washington Post Book World section and look for the Sunday, August 11 issue.
Anyway, the idea is that we are not making any progress towards answering the 'big' questions, and some of the popular theories we have are, what Hogan calls, 'Ironic Science'. Like superstring theory, they promise a sweeping new understanding of the physical world, but they are not testable with any conceivable technology we are likely ever to develop. These theories are, therefore, technically falsifiable, but in practice not falsifiable. They are also developed through a plea of 'beauty' in the eyes of theoreticians who in very small numbers are the only ones able to 'see' the mathematical beauty. The rest of us scientists not fluent in the mathematics are doomed to only see the beauty through second-hand translators.
Hogan argues that there are several questions that define the foundations of science that we are not much closer to answering than we were a century ago such as 'Does life exist elsewhere?', 'How does consciousness emerge from a brain?', and 'What is the nature of matter?'. His reading on science is rather pessimistic since he considers the development of relativity, quantum theory and organic evolution as some type of window dressing that doesn't really get us closer to answering the Big Questions about life, matter and the universe. He also seems concerned that our theoretical revolutions are increasingly of the kind that pits one 'beautiful and untestable' theory against another so that in the end we may be left with a fragmented scientific world where in some sense you are free to choose the kind of answers to the Big Questions that you like, without much risk of contradiction.
My own impression from the ranks of the working scientist is that 'we' find these kind of summaries rather narrow minded. It is all too easy to draw a line and say 'Science will never advance beyond this point'. It has happened in the past. I think that at some point we will recognize that we are capable of asking zillions of questions that can never be answered, and that we will eventually decide that our understanding is 'good enough' for now. This will be hastened when society withdraws funding for the necessary research in view of other goals it wants to commit to. Meanwhile, what is the hurry? If it takes another 200 years to answer one of these questions, I think that's great. We need to leave something for the next generation! I find it pretty arrogant to propose that just because the current generations cannot see how to answer these perfectly reasonable questions, that we have to preordain the next 100 generations to believe with us that the search is pointless!
Anyone that says that science has a boundary doesn't understand what science is all about no matter how learned their prose. Many scientists are optimists, and even though the Superconducting Super Collider was 'killed' by Congress, perhaps that is just as well. In another 30 years engineers will develop ways of accelerating particles that will be 1000 times more efficient than the 'dinosaur' technologies we use today. The stimulus for this will be the realization that cheaper means must be found or society will not support the effort.