Like many other discoveries, humans have discovered that Earth is just a small planet. It was discovered in the ancient Near East, in what some call the third century BC, in the largest city of the time, Alexandria in Egypt. In this city lives a man named Eratosenes
One of the people who envied him the most at the time called him "β"—the second letter of the Greek language. This is because, he says, Eratosni was the first person in the world to know anything. But Eratosenes were apparently "α" (the first letter of the Greek language) in almost all fields. He was an astronomer, historian, geographer, philosopher, poet, theatrical critic and mathematician. His writings range from Astronomy to Analgesia. He is also the director of the Alexandria City Library.
One day, he read the following passage from a manuscript in the museum: At the western frontier outpost near the first great waterfall of the Nile, at noon on June 21, the upright pole cast no shadow on the ground. On the day of the summer solstice, the longest day of the year, near noon, the shadows of the church's columns grew shorter and shorter, and finally disappeared at noon. At this time, the sun was shining directly overhead, and the reflection of the sun could be seen in the water of a deep well.
The above observations are easy to ignore. Poles, shadows, reflections in wells, the position of the sun—what is the point of such a simple thing as everyday life? But Eratosni, a scientist, immediately thought of doing an experiment to see if Alexander's upright pole cast a shadow on the ground at noon on June 21. Their experiments confirmed that the pole cast a shadow on the ground.
Eratosni wondered to himself: Why didn't the pole in Siin cast a shadow, but at the same time the pole of Alexander in the north cast a clear shadow? Suppose there are two vertical rods of equal length on a map of ancient Egypt, one upright in Alexandria and the other upright in Sean. It is easy to understand to assume that neither pole casts a shadow on the ground at a given moment, as long as the earth is flat. At this time, the sun is shining directly overhead. If two long poles cast an equal-length shadow on the ground, it makes sense on a flat Earth: at this time the sun's rays are obliquely hitting the two poles at the same angle. But at the same moment, there was no shadow in Siin, but there was a clear shadow in Alexandria, what was going on?
He thinks the only possible answer is that the Earth's surface is curved, and the greater the arc, the greater the difference in shadow length.
Because the sun is so far away from us, the sunlight hits the Earth in parallel. Unlike the angles of the sun's rays, the poles cast shadows on the ground for different lengths. In terms of the difference in the length of the shadows cast on the ground, the distance between Alexander and Sean must be the angle of deviation between them on the ground — about 7°. That is, if the poles are inserted into the center of the earth, they will intersect there at an angle of 7°. 7° is equivalent to 1/50 of the entire Earth's circumference of 360°. Eratosni knew the distance between Alexander and Sean about 800 kilometers because he had hired someone to take a step test. 800 km multiplied by 50 equals 40,000 km: this is the circumference of the Earth (original note: if the distance between Alexander and Siin is about 500 miles instead of miles, then the circumference of the Earth is 500 miles× 50 = 25,000 miles).
The answer is correct. Eratosni's only tools were long rods, eyes, feet, and brains, plus an interest in experimentation. With these things, he deduced the circumference length of the Earth, with an error of only a few percent, which was an extraordinary achievement 2200 years ago. He was the first to correctly measure the size of a planet.
At that time, the Mediterranean Sea was famous for its navigation industry, and Alexander was the largest seaport on our planet at that time. When you know that Earth is a planet not too large in diameter, don't you want to go out to sea to explore? Don't you want to explore the undiscovered lands, or even go on a circumnavigation of the globe? 400 years before Eratosni, a Phoenician fleet was employed by the Egyptian pharaoh Nico and sailed around Africa. They set sail from the Red Sea (most likely in open ships without decks), headed south along the eastern coast of Africa, north from the Atlantic, and finally back from the Mediterranean. The epic journey took 3 years, the equivalent of the time it takes for the modern Voyager spacecraft to fly from Earth to Saturn.
After the discovery of Eratosni, brave and adventurous voyagers made many great seafaring attempts. Their ships are small. The nautical instruments were imperfect, and the position of the ship was calculated only from the range gauge and compass, and sailed as far along the coast as possible. In the long night, although they were able to determine the latitude of the ship by observing the relative position of the constellation and the horizon night after night, they could not determine the longitude of the ship. For navigators in the vast sea, the familiar constellations must be a great comfort to them. The stars were friends of the explorers, friends of the ocean voyagers of the Earth in those days, and friends of spaceships in modern times. Some people may have tried circumnavigating the globe after Eratosn had calculated the circumference length of the Earth, but no one succeeded before Magellan. Stories of bravery and adventure must have been told in the early days as sailors and navigators—the most pragmatic people in the world—betting their lives on the numbers of a scientist in Alexandria!
In the era of Eratosni, globes were created to represent the Earth as seen from space. Such globes are basically practical in the Mediterranean region, where they know it all. But the farther away from their homeland, the more unrealistic the globe becomes. Our current understanding of the universe is also inevitable to encounter such unpleasant situations. In the first century, the geographer Strabo of Alexandria wrote:
Those who tried to sail the globe did not return to say that they had been hindered by the mainland, because the sea was always open. They returned because of lack of confidence, lack of food... Eratosni said that if the vast Atlantic Ocean were not an obstacle, we could easily reach India from Iberia by sea... In temperate zones it is entirely possible to have one or two habitable lands... Of course, if [the other part of our planet] were inhabited, the people who lived there would be different from us, so we would see it as another world.
That's how humanity began to explore other worlds in every possible way.
Later explorations of the Earth were global, going to China and Polynesia, and some from China and Polynesia. Of course, Christopher Columbus's discovery of the Americas and the centuries that followed was the culmination of the earth's geographical exploration mission, when the earth's geographical exploration mission was over. Columbus's first voyage was most directly related to Eratosni's calculations. Fascinated by his "Indo-Island Adventure," Columbus had intended to sail along the coast of Africa and then eastward to Japan, China, and India, determined to break into the unfamiliar western ocean—that is, "by sea to India," as Eratosni had boldly foreseen.
Columbus was once a merchant of old maps and an avid reader of the writings of ancient geographers, including Eratosni, Strabo, and Putulimi. But in order to pursue the Indies Adventure Program, in order for ships and crews to survive long voyages, the Earth must be smaller than Eratosni said, so. Columbus played a trick in his calculations. As the researchers at the University of Sararoca accurately pointed out, from all the books available to Columbus, he used the smallest circumference length of the Earth and the largest eastward extension of Asia, and even exaggerated it. If Columbus had not encountered America during his journey, his expedition would have failed utterly.
Now that the Earth has been thoroughly explored, it is no longer possible to discover any new continents or lost lands. But the technology we used to explore and settle in the most distant parts of the planet can now be used to help us fly away from Earth. Go on a cosmic expedition and discover the secrets of other planets. Flying off Earth we were able to condescend to observe it, to see the entire sphere of the Earth and the outlines of its continents as measured by Eratosni, thus confirming the remarkable talent of many cartographers of antiquity. How happy Elatosni and the other geographers of Alexandria would have been to see this!
In a sense, humanity began an intellectual adventure in the city of Alexandria, about 600 years after 300 BC, that led us to the shores of the universe. However, there is no record of the shape of this glorious marble city and the feelings of the people, and the repression and fear have almost forgotten the ancient city of Alexandria. Its inhabitants were incredibly diverse, ranging from Macedonian and later Roman soldiers, Egyptian priests, Greek nobles, Phoenician sailors, Jewish merchants, and visitors from India and southern Saharan Africa. For most of Alexander's prosperity, people lived in harmony and respected each other, except for a large number of slaves.
The city was founded by Alexander the Great and built by one of his former bodyguards. Alexander encouraged and valued foreign cultures and advocated an open mind for knowledge. According to legends —and it doesn't matter whether or not this legend is true—he was born in the world's first bell-shaped submersible in the Red Sea. He encouraged his soldiers to intermarry with Persian and Indian women. He respected the gods worshipped by other nations. He collected exotic creatures (including an elephant for his teacher Aristotle).
In order to make his city the center of world trade, culture and knowledge, he spared no expense. The city is glamorous because of its 30-metre-wide boulevards, elegant buildings and statues, Alexander's Mausoleum, and the Great Lighthouse, one of the Seven Wonders of the Ancient World.
However, the greatest marvel of Alexandria is the library and its attached museum (which is actually a public place dedicated to the 9 goddesses of literature and art). In this legendary library, the most surviving to this day is the once forgotten wet basement in the library's outbuilding "Seripine". Its only remnant may be a few decaying bookshelves, but this place was once the brainstorm and honor of the greatest city on our planet, and it was the first true scientific institute in the history of the world. Scholars have studied the entire universe in the library. The word "cosmos" comes from the Greek word meaning "heaven and earth and all things, in order," and in a sense, the universe is the opposite of "chaos." It hints at the interconnectedness of everything in heaven and earth, and shows humanity's reverence for the intricate mechanisms of the universe. It is a place where scholars gather to study physics, literature, medicine, astronomy, geography, philosophy, mathematics, biology and engineering.
Science and knowledge developed, and genius thrived here. The Library of Alexandria was the first place where we humans systematically and conscientiously collected the knowledge of the world.
In addition to Eratosni, there was the astronomer Hipparchus, who charted constellations and estimated the brightness of stars; Euclid, who systematically classified geometry with his remarkable talents. To the king, who was struggling to solve a mathematical problem, he said: "There is no royal road on the road to geometry"; Dionys of Thrace, who defined the class of words, his contribution to linguistics, as Euclid's contribution to geometry; Herophilus, the physiologist, who confirmed that the center of intellectual activity was in the brain and not in the heart; Heron of Alexandria, inventor of the cogwheel train and steam engine, author of The Automatic Device, the first monograph on robots Apollonius of Perga, the mathematician, who demonstrated various forms of conical curves—ellipsoids, parabolas, and hyperbolic curves—(as we now know) the trajectories of planets, comets, and stars; archimedes, Leonardo, and leonardo da Vinci, the greatest mechanical geniuses before Archimedes, Leonardo da Vinci; and the astronomer and geographer Ptolemy, who compiled what we today call pseudoscience; and his geocentrism reigned for 1500 years. This fact shows that wisdom does not guarantee that great mistakes will not be made.
In addition to those great men, there was a great woman, Hypahir, a mathematician and astronomer, the last celebrity of the library, whose martyrdom was closely linked to the destruction of the museum seven centuries after its construction. We'll talk about this story later.
The Greek kings who ruled Egypt after Alexander the Great attached great importance to learning, and for centuries they fostered scientific work and maintained a good working environment for the elite of the times in the library. The museum has 10 research buildings – one for different disciplines of research, many fountains and colonnades, several botanical gardens, a zoo, several anatomy rooms, an observatory, and a large dining room where people discuss issues in their spare time.
At the heart of this library is its collection of books. Librarians scoured the culture and writing of countries around the world, and they sent people abroad to buy as many books and materials as possible. Merchant ships moored in Alexandria were searched by the police— not smuggled goods, but books. They borrowed ancient scrolls, copied them, and then returned them to their masters. Although the exact number of books in the museum is difficult to estimate, it is entirely possible that the collection of 500,000 volumes, all of which are papyrus manuscripts. Where did all these books go? The classical civilization that created these scrolls collapsed. Even the library was deliberately destroyed.
Only a small fraction of the work survived, and all that remained were some poor scattered fragments. How exciting are these unattainable fragments! For example, we know that the shelves of this library contain a book by the Samos astronomer Aristachas, who argued that the Earth is one of the planets and orbits the Sun, and that stars are extremely far away from us. These conclusions are entirely true, but we waited until nearly 2,000 years later to rediscover these truths. We need to raise our awareness of Aristachas's loss by 100,000 times in order to understand the great achievements of classical civilization and the tragic nature of its destruction.
Our science today has far surpassed that of ancient science, but there are still irreparable flaws in our understanding of history. Think about how many historical mysteries can be answered with a library card from the Library of Alexandria. We know that there is a three-volume set of world histories that have been lost, written by a Babylonian priest named Perrosas. The first volume of the book deals with the history from the "Creation" to the "Great Flood", which he considers to be 43. 20,000 years, which is 100 times longer than the chronology of the Old Testament. I'd love to know exactly what's written in the book.
The ancients understood the history of the universe for a long time, and they tried to understand the distant past of the universe. We now know that the universe is far older than we thought, and we've examined cosmic space to know that we live in the farthest corners of a fuzzy galaxy, on a grain of dust surrounding an ordinary star. If we are a small point in infinite space, we occupy a moment in infinite time. We now know that our universe — or at least its most recent incarnation — is about 15 billion or 20 billion years old. This is the time since the so-called "Big Bang". During the chaotic period of Hongmeng, there were no galaxies, stars or planets in the universe, and there was no life or civilization. The universe at that time was nothing more than a uniform, radiant fireball that filled the entire space. The transition from the chaos of the Big Bang to the universe we are now beginning to know is the most terrifying transformation of matter and energy that we have had the privilege of glimpsed. Before we discovered other, smarter intelligent creatures, our present humans were the most compelling transformational results—the distant descendants of the Big Bang. Our mission is to understand and further transform the universe that gave birth to us.