This is knowing the universe. The History and Philosophy of Astronomy. I'm Chris Impey, Distinguished Professor of Astronomy in the Department of Astronomy at the University of Arizona. In this module, we'll look at gravity. Gravity, the force that holds us to the earth. The force we fight against all of our lives. The first person to truly understand gravity was Isaac Newton, a giant in the history of Science whose work we'll consider now. We're also reaching the culmination of what we'll call the first Copernican Revolution. The history of astronomy has distanced us in cosmic importance from being the center of the universe. In the Greek times with the geocentric cosmology to the inside of Copernicus that we were not the center, that the sun was the center, but it's still a small universe. In the 19th century, we'll see that other stars were realized to be at enormous distances, so our universe gets larger and larger, and our sun is just one of many stars. In the 20th century, we learned that there are other galaxies, systems of stars, enormous, containing hundreds of billions of stars. Then later we find that we're not even the typical form of matter that the universe is made of. The current frontiers of the Copernican Revolution revolve around the possibility that there are other forms of life in the universe, that Biology is not unique to the earth. The possibility out of modern cosmology that we might live in a multiverse, a system of many universes that all spawned at the time of the big bang. That's speculation for the moment. But basically, we've seen a dizzying progression in the last 2,000 years in terms of our place in the universe. It takes people a while to get used to this progression. Why the big secret people are smart, they can handle it? A person is smart, people are dumb, panicky, dangerous animals, and you know it. Fifteen hundred years ago, everybody knew the Earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and 15 minutes ago you knew that people were alone on this planet. Imagine what you'll know tomorrow. One of the remarkable things about people, and I think makes us unique amongst the species of the Earth with some of whom we share high intelligence, perhaps are dolphins and sea creatures like whales, and land creatures like elephants and gorillas and apes, our chimp cousins. But we can hold the universe in our heads as can certain cartoon characters. Wow. We're looking at Isaac Newton. Here are some views on his history in the place of the world and his history in the role of Science for the last 400 years. He said, "I do not know what I may appear to the world, but to myself, I seem to have been only like a boy playing on the seashore, and diverting myself on now and then finding a smoother pebble or a prettier shell than ordinary. While the great truth of knowledge lay undiscovered all before me". This is a remarkable quote because it shows his humility in the face of nature and the fact that as brilliant as he was, he didn't think he understood everything. He also was famously to have said, "If I have seen further, it is by standing on the shoulders of giants". Now this is a double-edged sword because this was a letter to Robert Hooke, with whom he had bitter rivalries throughout his entire career. Robert Hooke had dwarfism, and it's possible that this quote is even a slight against his rival Robert Hooke. Newton was a complex character as we'll see, brilliant in his Science, but a little bit of a sociopath. Newton, however, was aware that he was standing on the shoulders of giants that came before him. Let's review the history from Copernicus to Newton. That's the end of this topic.