Chapter Content
Okay, here's a podcast script based on the text you provided, keeping it conversational and adding some filler words, but without any dates or a host.
(Sound of gentle, inquisitive music fading in and then fading slightly to background)
So, um, yeah, we're gonna be going way back. Like, *way* back. All the way to Miletus, you know, twenty-six centuries ago. I know, I know, a book about quantum gravity…starting *there*? You might be thinking, "Come on, let's just get to the quantum stuff!" But honestly, understanding where these ideas *came* from is super helpful, because a lot of the really important stuff, the bedrock of how we see the world, well, it started over two thousand years ago. Just tracing those origins, it makes it all, like, clearer, and makes the later stuff easier and more... natural to understand.
And plus, some of the questions that were first asked, like, *way* back then? They're *still* relevant. Still totally crucial for how we understand things today. I mean, some of the newest ideas about the structure of space? They're actually borrowing from concepts and questions that were raised, get this, a *long* time ago. And when we talk about these old ideas, I'm also going to point out the ones that are, like, super key for quantum gravity.
So, with quantum gravity, we can kind of separate the ideas into two camps. One, those not-so-familiar concepts that actually have roots in the, uh, *very* beginning of scientific thought, and two, those totally brand new ideas. And you'll see, you'll see how shockingly close the questions asked by these ancient scientists are to the answers we're getting from, like, Einstein and quantum gravity. It's pretty wild.
(Slight pause)
So, let's talk about… particles.
(Sound of a gentle whoosh)
The story goes that there was this guy, around, oh, I don’t know… twenty-five hundred years ago, and he hopped on a boat from Miletus to Abdera. Which, believe it or not, was a pretty significant journey for knowledge, you know?
He was probably trying to escape some political turmoil in Miletus, where the elites were, like, fighting each other. Miletus was this *huge*, booming Greek city. Maybe the most important one before Athens and Sparta really took off. Big trading hub, controlling, like, a hundred settlements and trading posts, all the way from the Black Sea to Egypt. You had caravans from Mesopotamia and ships from all over the Mediterranean, and, of course, bringing all *sorts* of ideas with them.
Now, in the century before that, this absolutely *critical* intellectual revolution took place in Miletus. Some thinkers started, um, completely rethinking how we ask questions about the world and how we look for answers. And one of the *greatest* was Anaximander.
Because, look, from the beginning of recorded history, people have been asking how the world was formed, what it's made of, why it's so ordered, why natural phenomena happen. And for *thousands* of years, the answers were, well, pretty similar. These elaborate stories, you know? Gods, spirits, made-up creatures, all that stuff. From cuneiform to ancient Chinese characters, from hieroglyphs in pyramids to Sioux myths, from the oldest Indian texts to the Bible, from African legends to Aboriginal Australian stories… it all sounds cool, right? But it's all kinda… the same. You know? Like, a feathered serpent, an Indian sacred cow, grumpy or friendly gods who breathe and say "Let there be light" and BOOM, create the world. Or pull the world out of a stone egg.
But then, around, oh, I don’t know… twenty-five hundred years ago, in Miletus, Thales and his students, Anaximander, Hecataeus, their whole crew… they came up with a *different* way of finding answers. And this major shift… this really opened up a new way of understanding. It was like the first glimmer of scientific thought.
The Miletian school, they realized that, like, using observation and reasoning, instead of just relying on fantasy, ancient myths, or religion – and especially using, like, critical thinking, right? – *that’s* how you could constantly revise your worldview, discover new facets of reality hidden beneath common views, and, you know, discover new things.
And maybe even *more* important, they figured out this new *way* of thinking. Where students weren't, like, forced to just accept and agree with their teachers. They were actually free to *develop* those ideas, not afraid to abandon or criticize the parts that needed improvement. It was this, like, middle ground between blindly following a school and, like, totally rejecting everything it stood for. And that was super important for, like, the ongoing development of philosophy and scientific thought. From that point on, knowledge started growing at this crazy, dizzying rate, partly because of past knowledge, sure, but even *more* because people could, you know, *critique* and improve it. Hecataeus’ history book starts off with this awesome line that gets right to the heart of critical thinking. He recognized how easily we can all be wrong. "I write what seems to me to be true because the stories of the Greeks are full of contradictions and absurdities." Right?
(Slight chuckle)
There's this story, see, that Heracles went down to the underworld from Cape Tenaro. Hecataeus visits Cape Tenaro and says, “Nah, there's actually no underground passage here or any way to get to the underworld." And that's how he judged the story to be false. It marked the dawn of a new era.
And this new way of getting knowledge? It worked. I mean, in just a few years, Anaximander had figured out that the Earth floats in the air, that the sky extends *below* the Earth, that rainwater comes from the evaporation of surface water, that the different kinds of materials in the world should be understood as a simple, unified component, which he called "apeiron," meaning "unlimited." He figured out that animals and plants evolve and adapt to changes in their environment. And that humans must have evolved from other animals. Like, *boom*. The basic, fundamental rules of understanding the world were being laid out, and they're still, generally speaking, applicable today.
Miletus was kinda at the crossroads of the new Greek civilization and the older Mesopotamian and Egyptian empires. It was fed by their knowledge and, at the same time, immersed in Greek-style political freedom. Its social space didn't have any royal families or strong priestly classes. Citizens were free to discuss their destinies in the marketplace. Miletus became one of the *first* places where people could create laws together. The first *official* meeting in world history took place in Panionium, where the Ionian delegations gathered. And, at the same time, people first started doubting whether *only* gods could explain the mysteries of the world. Through discussion, you could come to the best decisions for the group. Through discussion, it became possible to understand the world. That’s the *priceless* legacy of Miletus: the cradle of philosophy, natural science, geography, history. And it’s not a stretch to say that the *entire* scientific and philosophical tradition, from the Mediterranean to the modern day, has important roots in the speculations of those sixth-century BC thinkers in Miletus.
(Slight pause)
But, sadly, Miletus's time in the sun didn't last forever. In around, oh, I don’t know… twenty-five hundred years ago, the Persian Empire invaded, the revolt failed, and the city was ruthlessly destroyed. A lot of its residents were enslaved. In Athens, the poet Phrynichus wrote this tragedy called "The Taking of Miletus." It was, like, so powerful that it was banned because it just brought up too much pain. But, like, twenty years later, the Greeks beat back the Persian invaders, and Miletus was, like, reborn. People moved back, and it became a center for commerce and ideas again, spreading its, uh, thoughts and spirit.
(Slight pause)
So, yeah. That guy I mentioned at the start of this chapter, he must've been inspired by that spirit because, legend has it, that around, oh, I don’t know… twenty-four hundred years ago, he set off from Miletus to Abdera. His name was Leucippus. We don't know a whole lot about his life. He wrote a book called "The Great Cosmology." As soon as he got to Abdera, he started a school to teach science and philosophy. And soon after, he took on this young student named Democritus, who'd go on to have a *massive* impact on later thought.
These two thinkers together built up this, like, magnificent edifice of classical atomism. Leucippus, the teacher, and Democritus, his great student, who wrote all these books in every area of knowledge. People looked at Democritus and revered him. Seneca called him "the wisest of the ancients." Cicero asked, "How can he be compared to anyone, not only for his genius, but for his spirit?"
So, what did Leucippus and Democritus figure out? The Milesians knew that you could understand the world using reason. They were convinced that all these different natural phenomena had to be reducible to something simple, and they tried to figure out what that something *was*. They imagined this basic substance that everything was made of. Anaximenes of the Milesian school thought this substance could condense and rarefy, so one element could turn into another. That was, like, the beginnings of physics, even though it was rough and primitive. But now what was needed was a *big* idea, a broader view to understand the secret order of the world. And that's what Leucippus and Democritus came up with.
The core idea of Democritus’ system is super simple: The whole universe is made up of infinite space, in which countless atoms are moving. Space has no limits. There's no up or down. No center, no boundary. And atoms have no properties except their shape. They have no weight, no color, no taste. “Sweet is by convention, bitter is by convention, hot is by convention, cold is by convention, color is by convention; in truth there are only atoms and the void.”
(Slight pause)
Atoms are indivisible. They're the basic particles of reality. You can't break them down any further. And *everything* is made up of them. They move freely in space, crashing into each other. They hook together, they push and pull. Similar atoms attract each other.
*That's* what the world is. That's reality. Everything else is just a byproduct of this motion and the combining of atoms. Random and accidental. The infinite number of materials that make up the world just come from the combinations of atoms.
When atoms come together, the only things that matter at the fundamental level are their shape, their arrangement, and the order in which they combine. Democritus used this analogy: Just like we can get comedies or tragedies, farces or epics, by rearranging letters, the basic atoms can change the world infinitely through their arrangement.
(Slight pause)
This eternal dance of atoms, it has no end, no purpose. We, just like the rest of the natural world, we're just one of the many byproducts of this endless dance. We're all, you know, products of random combinations. Nature is constantly experimenting with forms and structures. We, like animals, are the product of random chance. Our lives are just the combining of atoms. Our thoughts are made up of sparser atoms. Dreams are made of atoms, too. Hope and emotions are written in the language of combined atoms. The visible light that lets us see is made of atoms. The ocean's made of atoms. Cities, stars, *everything*. It’s a view that's so incredibly simple, and yet it's *incredibly* powerful. And later civilizations, much of what they knew would be built on it.
(Slight pause)
Building on this, Democritus wrote a ton of books, explaining this vast system, dealing with problems in physics, philosophy, ethics, cosmology, politics. He talked about the nature of language, religion, the origins of human society. His book "Little Cosmology" starts off impressively, like, "In this work I discuss everything." Unfortunately, those works are all lost. We only know about Democritus's ideas through quotes from other ancient writers and their summaries of his thoughts. His thoughts show a strong humanism, rationalism, and materialism. Once you clear away the remnants of mythological thinking, Democritus was inspired by a naturalism, a love of nature, a concern for humanity, a deep ethical concern for life that was, like, two thousand years ahead of the similar ideas in the 18th-century Enlightenment. Democritus’ moral ideal was to reach peace of mind through moderation and balance, by trusting reason and not letting yourself be ruled by emotions.
Plato and Aristotle, they were *very* familiar with Democritus's views, but they disagreed. They stuck to other ideas. Some of which actually really slowed down the growth of knowledge for future generations. They firmly rejected Democritus's naturalistic explanations, and they favored a teleological way of understanding the world. Which means they believed everything happens for a purpose. But this way of thinking about nature is *super* misleading because, you know, you're thinking about things with an end goal in mind, and that just confuses human affairs with the natural world.
Aristotle discussed Democritus's views at length and with respect. Plato, on the other hand, *never* quoted Democritus. Scholars think that's not because Plato didn't know his work, but because he deliberately *avoided* it. Plato’s criticism of Democritus is sort of subtle. Like his criticism of physicists in general. In the *Phaedo*, Plato puts this criticism of all physicists in the mouth of Socrates, and it had a lasting impact. He complained that physicists explained the Earth as round, but he objects because he can't think of what good a round Earth would do. Plato's Socrates tells about how he was initially full of hope for physics, but he eventually lost all faith in it.
"I hoped that he would tell me whether the earth is flat or round. And after that he would go on to explain the reason and the necessity of it, and tell me what was best, and why it was best for the earth to be as it is. If he said that the earth was in the center of the universe, he would explain that its being in the center was best."
(Slight chuckle)
Plato was, like, totally lost!
So, what about splitting things up? Does it ever *stop*? Is there a limit?
(Slight pause)
Richard Feynman, one of the greatest physicists of the 20th century, he wrote at the beginning of his physics lectures:
"If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms – little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world."
(Slight pause)
Without *any* knowledge of modern physics, Democritus had figured out that everything's made up of indivisible particles. How did he do it?
Well, part of his argument came from observation. He guessed, for example, that the wearing down of a wheel or the drying of clothes could be explained by the slow flying away of particles of wood or water. He also had philosophical arguments. And that's what we're going to focus on because that kind of thinking can be used all the way up to quantum gravity.
Democritus realized that matter *couldn't* be a continuous whole, because the very idea that "matter is a continuous whole" has a contradiction. We know about Democritus's reasoning because Aristotle passed it down to us. Democritus said that if matter is infinitely divisible, then it means it can be divided an *infinite* number of times. So, imagine you're dividing a piece of matter, like, *forever*. What's left at the end?
Are tiny particles with dimensions left? No way, because then the matter hasn't been infinitely divided. So, what's left is just points, with *no* dimensions. Okay, now let's put those points together. You can't get something with dimensions by putting two points with no dimensions together. Or three, or four. No matter how many points you put together, you're *never* going to get dimensions because the points themselves don't *have* any. So, we can’t get matter from points.
Democritus concluded that the *only* possibility is that anything and everything is made of a finite number of discontinuous objects, that are finite in size. *Indivisible* atoms.
This kind of, you know, elaborate, precise argument? It came from Cilento in Southern Italy, a town now called Velia. Back around, oh, I don’t know… twenty-five hundred years ago, it was a thriving Greek settlement called Elea. And that's where Parmenides lived. As a philosopher, he totally continued the rationalism of Miletus and the ideas that came out of there: that reason can show us what things are *really* like, not just how they *appear*. Parmenides found a way to get to the truth using *only* reason, and by declaring that all appearances are just illusions. He revealed a way of thinking that went slowly towards metaphysics, moving away from what would later be known as "natural science." His student Zeno, who was also from Elea, he came up with these clever arguments to prove this rationalism and to strongly disagree with the believability of appearances. And among those arguments was this series of paradoxes that are now known as "Zeno's Paradoxes." And they tried to show that appearances are *not* real, claiming that the usual idea of motion is completely ridiculous.
(Slight pause)
The most famous of Zeno's Paradoxes is told as a fable. Achilles, right? He challenges a tortoise to a race, and the tortoise gets a head start of ten meters. Can Achilles catch the tortoise? Zeno claimed that strict logic shows that he could *never* catch the tortoise. Before he can catch the tortoise, Achilles has to cover those ten meters. And to do that, he has to spend *some* time. During that time, the tortoise is going to move forward a little bit. To cover *that* distance, Achilles is going to have to spend *more* time. But, at the same time, the tortoise is going to keep moving. On and on and on. So Achilles needs an *infinite* number of time periods to catch the tortoise. And Zeno said that an infinite number of time periods is an infinite amount of time. So, based on strict logic, Achilles needs an infinite amount of time to catch the tortoise. We will *never* see him do it. And yet, we *can* see Achilles catch the tortoise, and he can pass as many tortoises as he wants. So what we’re seeing is irrational. It's an illusion.
(Slight chuckle)
Frankly, it's kinda hard to believe, right? So, where's the problem? One possible answer is that Zeno's wrong. It’s wrong to assume that adding up an infinite number of things always gets you infinity. Imagine you take a rope, right? You cut it in half, then you cut it in half again, and again and again and again. You keep cutting it in half an *infinite* number of times. You'll end up with an infinite number of little rope pieces. And yet, the sum of these infinite numbers is actually *finite* because they can only add up to the length of the original rope. So infinite numbers of ropes become a rope with a finite length. Infinite numbers of shrinking time periods become a finite time. Our hero, although he has to run an infinite number of distances, he can do it in a finite amount of time and, therefore, catch the tortoise.
(Slight pause)
Paradox, solved, right? The solution is found in the idea of a continuous object: An arbitrarily short time period can exist. Aristotle was the first one who instinctively realized this, and later the math of ancient and modern times, well, they developed it.
But in the *real* world, is that *really* the answer? Does a rope of any length exist? Can we really cut a rope as many times as we want? Does an infinitesimally small time exist? And *that’s* the problem that quantum gravity has to face.
According to legend, Zeno met Leucippus and became his teacher. Leucippus knew Zeno's puzzles *very* well, but he came up with a different solution. Leucippus suggested that maybe things that are *arbitrarily* small *don't* exist. There's a lower limit to divisibility.
The universe is discrete, not continuous. If there are infinitesimally small points, you can't create dimensions because, as Democritus argued, and as Aristotle told us, there is no way to get dimensions from points. And therefore, a rope has to be made of a finite number of objects of finite size. We can't cut the rope as many times as we want. Matter isn't continuous. It's made of individual atoms with a finite size.
(Slight pause)
Whether or not that abstract argument is correct, its conclusion—as far as we know today—contains a lot of truth. Matter *does* have an atomic structure. If I split a drop of water in two, I get two drops of water. I can keep splitting those drops. But I can't split it forever. At some point, there's just one molecule left. And that's it. There's no drop of water smaller than a single water molecule.
And how do we know this? We've gathered centuries of evidence, and a lot of that evidence comes from chemistry. Chemical substances are made of a few elements combined together. Chemists came up with a way of thinking about matter, thinking that it was made of molecules and that a molecule was made of atoms in a fixed ratio. Water, for example – H2O – is made of two parts hydrogen and one part oxygen.
But these were just clues. At the beginning of the 20th century, there were *still* a lot of scientists and philosophers who didn't think the atomic hypothesis was true. That included the famous physicist and philosopher Ernst Mach, whose ideas about space had a big influence on Einstein. Ludwig Boltzmann was giving a talk at the Royal Academy in Vienna. Near the end, Mach publicly declared, "I don't believe that atoms exist!" This was around the turn of the century. And scientists like Mach just understood chemical symbols to be useful ways to summarize the laws of chemical reactions. And not, like, evidence that the water molecule, made of two hydrogen atoms and one oxygen atom, really existed. They'd say you can't *see* the atoms. Atoms can *never* be seen. And then they'd ask, how big would an atom *be* anyway? Democritus never measured the size of an atom.
(Slight pause)
But someone could. The definitive proof of the "atomic hypothesis" had to wait until not so long ago, when it was discovered by this rebellious, young man, a mere twenty-five years old, who studied physics, but hadn’t been able to get a job as a scientist. And was just stuck working as an employee in the patent office in Bern. Later in this book, I'll talk a *lot* more about this young man and the three articles he sent to the most authoritative journal of physics at the time, *Annalen der Physik*. The first of these articles contained the *definitive* proof of the existence of atoms and even calculated their size, solving the problem that Leucippus and Democritus had raised twenty-three centuries earlier.
That twenty-five-year-old's name, as you all know, was Albert Einstein.
How did he do it? His idea was shockingly simple. Anyone since the time of Democritus could have done it, if he'd been as smart as Einstein and had the mathematical skills to do the complex calculations. Here's what he thought: If we watch really small particles, like dust or pollen grains floating in the air or in a liquid, we'll see them vibrate and jump. Because of the vibrations, they move randomly, drifting slowly, gradually moving away from their starting position. The movement of these particles in liquid is called Brownian motion, named after the biologist Robert Brown, who described the phenomenon in detail in the 19th century. The typical trajectory of this particle movement looks like just randomness. It's as if the particle is being disturbed in random directions. Actually, it's not "as if" it's being disturbed, it *is* being disturbed. The particle is vibrating because it's being disturbed by the air molecules, colliding with the particle from left to right.
(Slight pause)
The clever part comes next. There are *tons* of gas molecules in the air. Roughly as many molecules hit the tiny particle from the left as hit it from the right. If the gas molecules were infinitesimally small and infinitely numerous, the pushes from the left and right would balance out, canceling each other out in every instant, and the particle wouldn't move. But the molecules are a *finite* size and a *finite* number, not infinite, and that causes…fluctuations (that’s the key word). So, the pushes are never *perfectly* canceled out, just mostly canceled out. Imagine that at any given moment, when there are a finite number of molecules and the molecules are very large, the particle is pushed randomly a significant amount. Sometimes from the left, sometimes from the right. Between two pushes, it moves back and forth significantly, just like a soccer ball that kids are kicking around on the playground. The molecules are smaller, and the intervals between the pushes will get smaller. The pushes from different directions will be more easily balanced out and cancel each other out, and the particle will move less.
With a little math, you can calculate this, and you can estimate the size of the molecules from the observable movement of particles. Like I mentioned before, Einstein did that when he was twenty-five years old. By watching particles drift in liquid, by measuring how much they "drift"– how far they move from a particular position – he calculated the size of Democritus's atoms, the basic particles that make up matter. After twenty-three hundred years, he provided the proof of Democritus's insight: Matter is made of particles.
(Slight pause)
(Sound of gentle, reflective music)
(Sound of pages turning)
And now... On to the nature of things.
(Sound of gentle, reflective music fades slightly)
"Only when the world is destroyed will the verses of Lucretius perish." That’s what Ovid said, anyway.
I've always thought that the loss of all of Democritus's works? That's one of the most tragic intellectual losses in the collapse of classical civilization. Just look at the list of his works. And try to imagine what we missed out on when this vast body of scientific thought was lost. It's hard not to feel, you know, frustrated.
Aristotle's works were all preserved. Western thought was rebuilt from Aristotle, not from Democritus. Maybe if *all* of Democritus’s work had survived and Aristotle’s works had been lost, the intellectual history of our civilization might have been better.
But the centuries of monotheism wouldn't have allowed Democritus’ naturalism to survive. Around, oh, I don’t know… sixteen hundred years ago, Emperor Theodosius declared Christianity the only legal religion and brutally repressed other beliefs. The ancient schools of Athens and Alexandria were closed, and all the texts that didn't agree with Christian teachings were destroyed. Heathens like Plato and Aristotle, who believed in the immortality of the soul or the existence of a prime mover, those guys could be tolerated by the victorious Christians. But not Democritus.
(Slight pause)
However, one work survived the catastrophe in its entirety. Thanks to it, we know a little bit about classical atomism, and more importantly, we know about that scientific spirit. That work is *On the Nature of Things*, the magnificent poem by the Roman poet Lucretius.
Lucretius followed the philosophy of Epicurus, who was a student of Democritus's student. Epicurus was more interested in ethics than in scientific questions. He didn't reach the depths of Democritus. Sometimes he gave sort of superficial explanations of Democritus's atomism, but he generally agreed with the great philosopher of Abdera on his view of the natural world. Lucretius expressed the atomism of Epicurus and Democritus in his poetry. And that’s how a philosophy as profoundly meaningful as that could survive the intellectual destruction of the Dark Ages. Lucretius sang about the atoms, the seas, and the skies of nature. He expressed philosophical problems, scientific ideas, and elaborate arguments in witty verses.
(Slight pause)
"I will also reveal what force guides the sun in its journey and the moon in its travels, lest we think that they travel year after year on their courses out of free will... or lest we think that they are turned according to a divine plan."
(Slight pause)
The beauty of the poem lies in the feeling of wonder at the grand vision of atomism. That recognition that everything is profoundly unified because we all – the stars, the sea – are made of the same stuff.
"We all come from the same seed, have the same father, the Earth that nurses us like a mother, receives the clear raindrops, produces the bright ears of wheat, the green trees, and also humans, and all kinds of beasts, to give us food, nourish living beings, live a happy life, and propagate offspring..."
(Slight pause)
The poem brings a sense of peace from realizing that there aren't any fickle gods demanding that we do extremely difficult things and punishing us. For Lucretius, religion is ignorance, and reason is the torch that brings light.
(Slight pause)
Lucretius's work, after being forgotten for centuries, was rediscovered by the humanist Poggio Bracciolini in the library of a German monastery. Poggio had been the secretary of several Popes. He became a fanatic collector of ancient books, following the famous rediscovery of Petrarch. The essay by Quintilian he found completed the law courses in colleges throughout Europe. The treatise on architecture by Vitruvius that he discovered improved the way buildings were designed and constructed, but his greatest achievement was rediscovering Lucretius. The ancient manuscript that Poggio found has been lost. But a copy made by his friend Niccolo Niccoli is still preserved in its entirety in the Laurentian Library in Florence.
(Slight pause)
When Poggio brought Lucretius's book back into the light, the soil was ready for new ideas. It was like someone could already hear a distinctly different voice, since the time of Dante.
"Your eyes pierced my heart, awakening my sleeping thoughts. See, love divides my life, and I am so desperate and mad."
The rediscovery of *On the Nature of Things* had a big impact on the Italian and European Renaissance. And it directly or indirectly appears in the writings of a lot of authors, from Galileo to Kepler, from Bacon to Machiavelli. Even over a century after Poggio discovered *On the Nature of Things*, atoms are still shining in Shakespeare's plays.
"Mercutio: O, then, I see Queen Mab hath been with you. She is the fairies' midwife, and she comes in shape no bigger than an agate-stone on the forefinger of an alderman, drawn with a team of little atomies over men's noses as they lie asleep..."
Montaigne quotes Lucretius at least a hundred times in his essays. And Lucretius's direct influence extended to Newton, Dalton, Spinoza, Darwin, all the way to Einstein. Einstein's idea about Brownian motion of small particles in liquid revealing the existence of atoms might have come from Lucretius. Here's a passage from Lucretius offering a vivid "proof" of the concept of the atom:
"Concerning the fact that I am describing here, there is a similar thing that often appears before our eyes. Look, whenever the rays of the sun are projected, slanting through the dark hallways of a house, you'll see lots of tiny particles mingling in lots of ways. In the space illuminated by light, they ceaselessly strike each other like in an eternal war, and they grapple together in groups, without any stopping, sometimes meeting, sometimes separating, being pushed up and down. From this spectacle, you can guess what eternal, ceaseless movement there is in that wider emptiness. At least to the extent that a small thing can indicate great things, this example can lead you to look for the path to knowledge. It's precisely for this reason that you should pay closer attention to these objects. They dance in the sunlight, pushing and hitting each other, and these pushes are enough to indicate that there is a secret and invisible movement of matter hidden below and behind them. Because here you will see lots of tiny particles retreat and strike under the power of invisible forces, thereby changing its small route and being forced to return backward again, now here, now there, scattered in all directions. Know that all of their shifting movements begin from the original atoms because it is the atoms of things that move themselves first, and then those objects made of atoms' small combinations and are closest to the atoms are also stirred up by those invisible collisions, and then these things stimulate bigger things: in this way, the movement begins to gradually rise from the atoms, finally appearing in our senses, until those particles that can be seen in sunlight also begin to move, although we can't see what is pushing them."
(Slight pause)
Einstein re-created the "vivid evidence" that was first imagined by Democritus and then presented by Lucretius, and he translated it into mathematical language, making it possible to calculate the size of atoms.
The Catholic Church tried to suppress Lucretius. But it was too late. The worldview that had been rejected by medieval Christian fundamentalism was reborn in Europe, opening up people's minds. There was not just rationalism, atheism, and Lucretius's materialism spreading across Europe, and not just quiet reflection on the beauty of the world, but there was more: a new way of thinking, a clear and complex structure for thinking about reality, a structure that was very different from the medieval thought of previous centuries.
The marvelously crafted universe that Dante had fervently praised in the Middle Ages was now understood according to a hierarchical structure, which also mirrored the hierarchical structure of European society: A spherical universe centered on the Earth. Unbreakable divisions between the celestial and the terrestrial. Teleological and metaphorical explanations of natural phenomena. A fear of God and death. A neglect of nature. A structure of the world that was determined by forms that preceded things. A source of knowledge that only came from the past, from Revelation, and from tradition.
All those things do not exist in the world of Democritus that Lucretius sings about. There is no fear of God. There is no teleology in the world. There's no hierarchy to the universe. There is no division between heaven and earth. There is a profound love of nature. We are immersed in nature, recognizing that we are an important part of it. Men, women, animals, plants, it's all an organic whole without a hierarchy. Democritus's beautiful language makes you feel a deep sense of universalism: "For the wise, the whole world is open. The homeland of a noble soul is the whole world."
People wanted to think about the world in a simple way. To study and understand the mysteries of nature. And to know more than our ancestors had. Galileo, Kepler, Newton would establish incredible conceptual tools. Straight-line movement in space. The fundamental elements that make up the world and how they interact. Space as the container of the world.
The idea that the division of matter is finite, that the world is discrete, that infinity ends at our fingertips. This idea finally emerges. It’s the core of the atomic hypothesis. And it returns in an even more remarkable way in quantum mechanics, and today it once again proves its importance as the foundation of quantum gravity.
The first person who integrated the naturalistic ideas that emerged during the Renaissance and who resurrected Democritus's ideas, lifting them to the core of modern thought, was an Englishman. He's one of the greatest scientists in history, and he's the first protagonist of the next chapter.
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Okay, on to the "Classic" stuff!
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So, in the last chapter, I might have given you the impression that Plato and Aristotle only had a negative effect