The Milky Way: summary and outlook

Extract

First let me review the historical discussions presented during our symposium: the papers by Paul, Gingerich, Hoskin and Smith. I was greatly impressed by the power of abstract human thought in its confrontation with resistant reality. On the one hand we see again and again extraordinary prescience, where abstract beliefs based on little or no empirical evidence–like the island-universe hypothesis–turn out to be, in their essentials, true. Clearly, we often know more than we know that we know. On the other hand, there are repeated instances of resistance to the most obvious truth due to ingrained beliefs. These may be termed conspiracies of silence. Van Rhijn and Shapley agreed about few things. But one of them was that there was no significant absorption of light in the Galaxy. Yet the most conspicuous feature of the night sky is the Milky Way, and the second most conspicuous feature is the dark rift through its middle. What looks to the most untutored eye like a “sandwich” was modeled as an oblate spheroid. These eminent scientists must have known about the rift, but somehow wished it away in their analyses. I find that very curious. Other examples from earlier times abound. We all know that the Crab supernova was seen from many parts of the globe but, though it was bright enough to be detected by the unaided eye in daylight, its existence was never–so far as we know–recorded in Europe. It did not fit in with the scheme of things, so it was not seen.