WATCH: Unit 2 Overview - The Big Bang

Hello! This is a time machine. And for today's lesson I'm going to take us back. Back 13 billion years. [whirring noises] Unfortunately, the maximum it can go is four  seconds so I'll just be really descriptive. [instrumental music] Hi, I'm Rachel Hansen. And this is Unit 2  The Big Bang. Check this out. This picture may be the closest thing we have to a time machine   because it's showing us something from 13 billion years ago. How? Well, not by using an ordinary camera.    This image was taken by the Hubble Space Telescope in 2003. There are 10,000 galaxies in this picture.    Some of those tiny red ones are so far away that the light from them that's reaching us today is  from, yes, 13 billion years ago. This picture lets us peer back into the earliest days of our universe.  And this is only a sliver of our night sky.   If you were standing on earth and looking up this image occupies a space just one tenth the size of the full moon. To make this one tiny picture of  our unimaginably huge universe it took hundreds   of scientists and engineers, 400 orbits around  earth, four months, and one awesome telescope. But it also took thousands of years and  generations of thinkers taking chances, making mistakes, and progressing our understanding  of the size nature and origins of the universe. Edwin Hubble, that's the guy who the telescope is  named for, first proved in 1924 that other galaxies existed. He showed us that the universe  was so much bigger than we thought. But he didn't stop there. In 1929, he formulated Hubble's Law. Not the kind of law where you get in trouble for breaking it, but one of those "This  is just how it is" laws.   Hubble's law helped provide evidence that the universe is expanding. His work supports a theory proposed by Georges Lemaitre just two years earlier. the Big Bang Theory. [instrumental music] That probably sounds like way too much science for a history class. But that's like saying  that a history of Rome has too many Romans. Science is a part of history. And history  can help us explain how we know what we know. It shows us how science changed over time. And it can reveal how changes in our knowledge transformed our societies. Take Edwin Hubble. It's thanks to his discoveries that we understand the size and origins of our universe.   But he built on the ideas and discoveries of other astronomers in the early 20th century. like Henrietta Levitt, Albert Einstein, Harlow Shapley, and Georges Lemaitre. And these scholars built on the work of scholars from centuries earlier   Ancient Greeks like Claudius Ptolemy asserted  that the universe revolved around the earth. Generations of Arab, Persian, Chinese, and other  astronomers improved on Ptolemy's calculations. Then, in the 16th century, Nicholas Copernicus asserted that, actually, the sun sat at the center of the cosmos. Everyone was like, "Wait, what?" From there, step by step, discovery by discovery we moved closer to the understandings that  allowed Hubble to make his breakthrough.   And his breakthroughs allowed later  astronomers to improve on his work, and develop new ideas and discoveries, refining  our understanding of space-time, the earliest   days of our universe, and how to capture a  picture like this. Even today, our understanding of the beginning of time in our universe continues to evolve with each new discovery. [instrumental music] In Unit 1, we defined Big History. It's the modern scientific origin story backed by historical and scientific evidence that tells the history  of the universe and our place in it. You learned that this class is about the history of human thought. If this were a science class, we'd teach what scientists discovered and how they did it. But this course, this history course, is about learning how our knowledge of the universe and everything in it has changed over time. That means that, sometimes, we'll need some knowledge of scientific concepts. So, while this unit may seem like it's all about  the Big Bang, it's really about the way humans have answered the question: Where did we come from? In the first unit, we also examined the concept of scale   and how our perspective changes whether we're zooming in on a tiny grain of sand or out to an entire planet. Then we explored how different human societies explain the origins of our world. We also learned about claim testing and how you can evaluate the narratives you encounter. And finally, we met eight new friends,  the thresholds of increasing complexity. Each threshold marks a moment in time when  just the right ingredients came together under just the right goldilocks conditions to  create something more complex in our universe. The Big Bang is the first threshold of increasing complexity. [instrumental music] What is the Big Bang? And how do we know  that it's the origin story of our universe? Those are the two big questions you'll tackle  in this unit. The Big Bang is a scientific theory. It claims that the universe started out  incredibly, unimaginably small, hot, and dense. Then, for some reason we still don't know, it  rapidly expanded.   This was the beginning of time and space and everything else in our universe. all the ingredients for stars, planets, mountains, polar bears, daffodils, and your lunch were born in this instant. But, how did scientists come up with the theory? It took centuries of careful observations, the development of new technologies, and new ways of thinking to get a 21st century model of our universe. In this unit, they'll travel back in time to meet scholars like Ptolemy Nasir al-Din al-Tusi, Copernicus, Galileo, and Hubble.  You'll ask how each explained the origins of the universe and how each built on older knowledge  to update our modern scientific origin story. The way that humans build and improve on knowledge  over time is called collective learning, and you're going to hear a lot more about it throughout this course. And guess what, we still don't know everything. Each generation of scholars continues to build on the past. In this unit, you'll also see how different disciplines study the origins of the universe in different ways. Scholars from a wide variety of disciplines  such as physics, astronomy, cosmology, chemistry, geology, biology, and history have all helped  us understand the universe and our place in it. That's a lot of information in one short video. So let's do a quick recap. Big History is organized around eight thresholds of increasing complexity.   And the first is, say it with me, the Big Bang. Now, we don't know a lot about what happened  before the big bang, but we do have a lot of   evidence about what happened in the moments just after as the universe was born, expanded, and cooled over time. We also have centuries of scholarly works on the history of the universe. these scholars are legitimate authorities, who used  evidence to develop ideas that were then shared,   tested, and improved upon by other scholars  over time. I don't want to brag, but I just name dropped not one, but two claim testers, evidence and authority, to help explain the Big Bang. As you go through the lessons in this unit,  think about the evidence that supports the Big Bang Theory. Also think about the authorities who support, extend, or challenge this evidence. Then, as you move through the unit put  the evidence and authority together   with your intuition and logic to evaluate the Big Bang Theory. When you use all four of the claim testers to evaluate a particular topic   you're well on your way to becoming a big historian. I wonder if this thing can go four seconds into the future. [whirring noises] [instrumental music] It worked! What did I miss?