Science as we understand it starts with the ancient Greeks, this extraordinary culture that lived in the Aegean part of the Mediterranean about 2,500 years ago. Over a span of a few hundred years, a small number of extraordinary thinkers, philosophers of the time, came up with strikingly prescient ideas about nature and the universe. They didn't always agree, and they weren't observational scientists, they were philosophers, so we can see striking divergence in the ideas they had. Consider this on the possibility of life and the universe. Epicurus saying, there must be infinite worlds both like and unlike this world. And going on to speculate about creatures and perhaps intelligent creatures on those worlds. That's a strikingly modern statement that fits completely with modern astrobiology. And yet from the same time, we also have the statement of Aristotle that this world must be unique, the earth, there can be no other world. And the dominant philosopher of the time, his opinion held, and so forward into history the idea of the Earth as unique and esteemed amongst objects and of course, the center of the universe held sway. >> More than 25 centuries ago, among the Greek islands, here with the vibrant crossroads of Africa, Asia and Europe, philosophers began to devise rational theories about the world around them. The wondrous waves and foams of nature, they said, could be understood. [MUSIC] One Greek thinker suggested that the earth actually moved around around the sun. [MUSIC] Another thought that everything, the work of men and nature was made of pattern, too small to see. [MUSIC] Others estimated the sizes of the Earth and moon, and the distances between them, and reasoned that both were spheres. [MUSIC] But it would be many centuries before we had the tools to extend our vision and confirm the wisdom of these early thinkers. In the meantime, people around the world gazed on the stars and give them names, most assumed that the earth was the centre of an unchanging universe. >> We will talk about the contribution of the ancient Greeks to science but they made an extraordinary set of contributions to other fields as well. Obviously to philosophy and logic, the foundational pieces of the scientific method. But they also gave us more strikingly modern ideas on systems of government, of law, and of the city state. They had ideas in theater and music and arts that are still used to the present day. While other ideas on medicine were perhaps a little archaic, they also contain some rudiments of modern ideas. In mathematics, they came up with the ideas of geometry, algebra, the notion of infinity, and even the concept of irrational numbers. And then, strikingly for people who may never have traveled more than a few dozen miles in their lives. Any educated ancient Greek knew that the Earth was round, suspected that the Sun was larger than the Earth and had the idea of a vast universe, much larger than the Earth itself. What allowed a small set of people, basically a set of interrelated city states in the Aegean Peninsula, to come up with such radical ideas, so advanced for their time? Nobody really knows but unlike the fixed civilizations of Greece, Mesopotamia, and Babylon, the Greeks were mobile, they lived by trade and by their wits. They travelled the Aegean carrying things like the Antikythera mechanism, trading in ideas and artefacts and technologies that they knew had value. Because they were mobile and lived by trade and commerce, they were open to ideas they had to be, that's how they survived. The also esteemed thought and rational thought above all things and they implemented it in their society in every way that they could. They were also a small, nimble society, not too large they did indeed depend on slaves for that small set of thinkers to be able to think the way they did. But otherwise, they were democratic in their implementation of the rule of law. Key to what the Greeks did in science and why they did something that other cultures before them didn't, was they made mental models of nature. Other cultures were willing to track emotions in the night sky and indeed see patterns, but they never went to a general principle or an abstract idea of what they saw, they just took took it to be the way they saw it. The Greeks were making mental models and they were using mathematics to understand the patterns of nature in an abstract way and rather than a literal way. This is the rudiment of the scientific method. One example will show this in mathematics. The Egyptians used to survey the Egyptian Nile Valley which flooded every year, because during the floods, all the lines and demarcations with property were obliterated. And so they developed the surveying techniques to resurvey the plots of land in the Nile Delta. To lay out these right angle triangles, they kept enormous loops of rope knotted in increments that corresponded to perfect triangles. For instance, 3 squared plus 4 squared equals 5 squared. So they would keep the triad of numbers that led to perfect triangles. Meaning they would stretch these lobes into right angle triangles of different sides and put a rectilinear grid in place every year. But the Greeks were maintaining warehouse full of the loops of lobes never went to the general case. That felt to Pythagoras who invented the Pythagorean theorem. Which we know from the wizard it was defines intelligence. A squared plus b squared equals c squared. What he is doing is abstracting into algebra the general case. Pythagoras knew this was a big invention an innovation. Legend has it that he sacrificed 100 oxen to the gods when he came up with his Pythagorean theorem and he wasn't a rich man, that was a lot of oxen. So the mathematics that was applied to the natural world and it became the basis of the scientific method, dates back to these times. Now it wasn't always esteemed in those times Pythagoras ran what in Modern Age we would probably characterize as a cult. He and his followers lived in an island in the Aegean Sea. They'd been hounded off the Greek homeland and there was an indication he would have been killed if he'd gone back. His followers were like accolights or cult followers nothing Pythagoras wrote survives to us. Everything we know about him comes from his followers and their descendants. And Pythagoras went further, he went to the limit, suggesting that the universe itself is a mathematical entity. As we'll see when we get to cosmology, that's a strikingly modern idea. With the mathematical theories of general relativity and perhaps string theory underlying nature at the deepest and most profound level in modern scientific theorizing. Pythagoras may have been right. A great example of the application of both logic and mathematics to the everyday world and the astronomical world comes in the fact that the average educated Greek knew that the earth was round and how large it was. Think how striking that is millenia ago when none of these people would have travelled more than a few dozen miles in their lives. The logic behind this was fairly simple, it started with the observation of the lunar eclipse where the earth's shadow travels across the moon. Understanding the illumination of the earth, sun and the moon, the Greeks knew that that was the situation during a lunar eclipse. And so they could see that the earth projected a circular shadow onto the moon. And they knew that the only object where regardless of its orientation, it cast a circular shadow is a sphere. So for them, logically, it was self-evident that the Earth was a sphere. As for the size of the sphere, they make another observation. Knowing that on a certain day of the year, the sun casts no shadow at a certain time in a certain place, they would then make the same observation in a place a known distance away, several hundred miles. And at that distance, the Earth casts a shadow with an angle that can be measured. And then it is simple geometry of similar triangles to infer the diameter or circumference of the Earth knowing only the angle cast by that shadow and the distance between those two points on the Earth's surface. They actually got the size of the earth accurate to about 5%, which may have been fortuitous because their linear distance measurement on the earth was perhaps not that precise. But the principle was valid, so the Greeks absolutely knew the size of the earth. A separate piece of logic lead to the inference that the earth was larger than the moon and smaller than the sun. And that led one Greek thinker, 2,000 years ago before Copernicus, to speculate on a heliocentric model. So they were strikingly modern in their views of space and time. They were also asking profound questions, and two examples will give a sense of this. Plato had a colleague called Archytas. Archytas wondered about the universe. Was it finite or infinite? It's a dichotomy and it's very profound. In the analogy, he used, he imagined a warrior, a spear carrier who went to the edge of the universe as far as they could travel and herald their spear. What do you imagine Archytas said should happen? Should the sphere travel forever, and into what? Or will the sphere hit a boundary or a barrier or the limit? And then what is that substance, and what's beyond that substance? So in this logic, Archytas knew that if there were a boundary or a barrier or a container, then something has to contain the container. And so in his logic, it was more rational to imagine that the universe was infinite. And so in Greek philosophy at that time, the dominant idea was of an infinite universe. 100 or so years later, Democritus made an analogous thought experiment, this time going in the downward direction. He imagined a sharp knife and a stone. You cut the stone into smaller and smaller pebbles until it becomes a grain of sand. And then perhaps you can do the experiment but you imagine cutting it in half and half and half again until it's almost too small to see on a tip of your finger. Now you can do the experiment, but the thought experiment continues. And how does it end? To democratize, there are only two outcomes. Either you reach a fundamental invisible indivisible object, he called it an atom, or you carry on the process forever generating infinitely small subunits. And to him, it was apparent, logically, that an infinite progression would continue, and so he imagined an indivisible element called an atom. He hypothesized atoms and also inferred that the properties of normal material like its texture or its smell or its taste, would be secondary properties not held by the individual atoms themselves. Another strikingly modern idea, 2,000 years before we had the ability to prove that atoms exist. These were the powerful thought processes the Greeks used to address each situations where they had no apparatus, no equipment to do observation and of course no telescope. As I've mentioned, the dominant philosopher of the Greek age was Aristotle. Aristotle believed that the earth was unique, motionless, spherical, and the center of the universe. Why did he believe that? Because the alternative to put the earth in motion around the sun which was speculated by a couple of Greek philosophers would mean the earth was in motion and yet we felt no motion. If we think about it, knowing the size of the Earth, if the Earth is in motion and at a degree latitude, the Earth must be spinning about 700 miles an hour, no such motion was obvious. So to Aristotle, it was self evidence that the Earth could not be moving. And if it was stationary, it was most sensibly the center of the Universe. So that is called the geocentric model that came to us from the Greeks. But there's a fly in the ointment of this model, and it comes from those moving objects in the night sky, the planets, especially Mars. When you observe Mars carefully over a period of years, there are some times when in it's normal, steady motion through the fixed pattern of the stars, it appears to reverse course for a few months and then resume it's normal motion. That so called retrograde motion was strange anomaly, also observed for Jupiter and Satan. And had no natural explanation in a geocentric model why the earth is at the center of universe and the planet simply orbit on crystalline spheres around us. So this retrograde motion stayed as an enigma in the Greek time and would eventually come back into prominence in the Carpenican revolution. The astronomical knowledge of the ancient world of the Greek world was codified by Ptolemy, a thinker from about 100 AD. He wrote up the astronomical knowledge of the ancient world in a 47 volume encyclopedia called the Alma Guest which is Arabic for the greatest. And this was the knowledge that went forth through the dark ages in medieval times that followed when scientific progress essentially ground to a halt. The Ptolemaic model is based on Geocentric Cosmology with the earth stationary at the center of the universe. And to explain what are actually non-uniform motions of the planets in the night sky, you can't do it with simply spherical objects. A reminder of why we're looking to explain this with spherical objects was the dominant influence not only of Aristotle but of Pythagoras. And for Pythagoras, the spear is the most perfect Shape, as a circle is the most perfect shape. And so it was natural, that celestial objects would follow circular trajectories, but they don't. And so to make that happen in a Ptolemaic or geocentric model, you have to add offset or retrograde spheres, spheres within spheres, if you like. And in the end, it took 47 spheres in the Ptolemaic model to explain the motions of only 7 objects. King Alfonso x of Spain in the 11th century, when presented this by the quote, astronomers of the time said, if his almighty had asked me I would have suggested something simpler. So this was considered a cluge, an inelegant solution for cosmology, but they are things wrested through the medieval times. An extraordinary set of ideas emerged from ancient Greek philosophers about 2,500 years ago including the notions of atoms, the idea of a heliocentric universe, the size of a universe that's far larger than the earth, and other concepts that would only be proven in the 20th century. The Greeks applied logic and mathematics to their understanding of nature. And they were the first culture to use mental models and abstraction as a way of understanding the world around them.
