 Hello, and welcome to our video book on how old is it? This is our fourth video book. The other three all started here in my backyard. The first one was, How far away is it? Where we started with direct measurement and triangulation in the backyard, and took it across the earth, the solar system, the galaxy, the Virgo supercluster, out to the farthest reaches of space. Our second video book was, How small is it? We started here, with a strand of hair, took it to the microscopic, all the way down to the tiniest elementary particles, quantum mechanics, the standard model of particle physics and the Higgs boson. Our third video book was, How fast is it? Where we started here, with a snail, moving across the tile, and took it to the speed of light, special relativity, general relativity, and gravitational waves. For this video book, we're not going to start in the backyard, we're going to start at the cosmos, the very beginning of the expansion of the universe, and over a number of chapters work our way to the backyard at the end. Our first chapter is on the Big Bang Theory, where we'll cover the cosmological principle, the idea of space expanding. We'll take a look at a Newton's view of how the universe would have expanded with his Newtonian mechanics, if he had given it a try. We'll look at how Einstein, equations would be used to describe it. We'll go into the observational evidence for the accelerating universe, Hubble's law, the cosmic microwave background that made all the difference, and then step by step, how we'll go back to the beginning, and then move back into the future. The chapters will cover not only how old is the universe, will cover how old is the sun, and the solar system, how old is the earth, how old is the moon, how old is the ground we're standing on, how old is the water in the swimming pool, we'll move on to how old is life, the vast array of living things around us, and we'll conclude with how old are human beings, and again we'll always go through the evidence that we have that leads us to our current thinking on these subjects. I trust you'll find it informative and entertaining. Thank you.