Has the universe always existed or was it created from nothing? Is it finite or infinite in extent? If it is finite, does it have an edge? Until the 1920's, scientists by and large left these kinds of questions to religion and philosophy. Then Hubble found that the universe is expanding, as predicted by Einstein's theory of General Relativity. Now we have plenty of evidence that, as far in the sky as our instruments can see, it all started about 14 billions years ago with a Big Bang. Our notions of space and time, and of the ultimate structure of matter, have evolved into a theory wilder than imagination, in which matter and antimatter are created from pure energy and an entire galaxy can disappear into a black hole. This theory claims to explain what has happened since the Big Bang, but the end of the story is nowhere in sight. What is the nature of the dark matter and dark energy that seem to control the evolution of the universe? Did the Big Bang really originate everything, or was there something before? Is this the only possible universe, or the best of all possible universes, or did it turn out this way by chance? We will discuss what is known, what is still uncertain or speculative, and what appear to be the ultimate limits of human ability to know, with readings from books by Steven Hawking and Brian Greene, and current articles in newspapers and journals such as Scientific American.