That title is literally true. Over 90 percent of what actually is there can’t be seen. Thus, astrophysicists and cosmologists now speak of “dark energy” and “dark matter” which together account for the continuing and eternal expansion of the universe until everything will be too far away to be seen at all. This kind of thing does, perhaps, reduce American politics and troubles to their comparative triviality. Our guide to the universe in this broadcast is Michael Turner,  the discoverer of dark energy and a man who talks about cosmology with enough excitement and lucidity to create the illusion, at least, of comprehension in his listeners.