"There is an enormous variety of things that we never dreamed of, like... black holes, s, quasars, all these unbelievably active goings-on in the universe... [I]n Aristotle's time the universe... was supposed to be quiescent, it was supposed to be perfect and peaceful, and nothing ever happened in the ; and that remained true... throughout all of the revolutions... It remained the general view of astronomers... through Copernicus, and Galileo, and Newton, and everybody else... until just the last 30 years, and now we know it's not like that at all. In fact the universe is full of violent events, and fantastic strong gravitational fields, and collapsed objects, and huge outpourings of energy. ...The things we understand least are the quasars... the most violent and... energetic objects in the universe, and they're totally... mysterious... and... they're rather frequent; and nobody ever dreamed that they existed... [E]ven after they were found it took a long time before people took them seriously. Nature's imagination is always richer than ours."