All along, we have a misunderstanding, that the ancients were very stupid, even the earth is a ball can not see, but said that the earth is a flat disk, or that the earth is square, there is a big turtle riding the earth, under the big turtle there is a series of small turtles, the earth is surrounded by the sea, the sky is like a pot clasped overhead.
This idea lasted for thousands of years, until between 1519 and 1522, the famous HNA Magellan risked falling into the abyss to complete the first global voyage of mankind, which proved that the earth was a ball.
Yes, the story sounds perfect, highlighting both the heroism of navigators and the ingenuity of modern people. People knew that the earth was a ball more than 2,000 years ago, and on this basis, a good set of cosmic models were established.
If we still think that the earth is a ball discovered by modern people later, we can only say that we are too ignorant. Okay, let's start with today's topic and see how the ancient sages came to know the earth.
In fact, gaitian said, that is, a pot lid was buckled on the earth, which was not the saying of the ancient Greek philosophers, which was handed down from a long past, and the specific time can no longer be verified.
Since the rise of ancient Greek philosophy, the gods and men have quickly realized that the earth is a sphere, which has developed into a recognized standard in the industry, and no one disputes it, because the evidence is too strong.
It is said that the mathematician Pythagoras first said that the earth is a ball, he lived from 572 BC to 497 BC, Pythagoras believed that everything is numbered, everything is composed of numbers, of course, the laws behind all things can also be described in mathematics. Right.
In addition to his obsession with mathematics, Pythagoras believed that the universe created by God should be perfect and harmonious, without any flaws or irregularities, and it was clear that he was suffering from a disease called obsessive-compulsive disorder. So now let's think about what is flawless? Two-dimensional circles and three-dimensional ones, of course, right.
The ball
Any other geometry was imperfect in his eyes, uncomfortable to look at, and he did not dare to imagine that the earth was a triangle, so Pythagoras somehow chose the spherical shape, saying that the earth was a ball, so that he could sleep comfortably.
Logically, you say that the earth is a ball, you have to provide evidence for your claim, right, but Pythagoras said, I will not, I will play philosophical speculation with you, you have the ability to raise the bar with me, obviously no one can leverage the Pythagorean school at that time.
On the contrary, this perfect harmonious cosmology, this obsessive-compulsive disorder has been transmitted to later generations of philosophers, including Plato, Aristotle, and even to later generations of scientists, including Copernicus, Kepler. As you will see from the following columns, for thousands of years human beings have had a crazy pursuit of perfect circles and spherical shapes.
However, at that time, some people also raised such a question, and it was also coincidental that I had the same confusion when I was a child, you said that the earth is round, well, I believe it! But if the earth is round, won't the person standing on the edge slip down? Isn't the man standing under the earth upside down?
I couldn't figure this out when I was a kid, and the same ancients more than 2,000 years ago couldn't figure it out. If my IQ is the average of modern people, it means that my IQ is no different from that of the ancients, which means that the ancients are not dumber than our modern people, right. So we should not laugh at some of the views of the ancients with the eyes of modern people. Some of their insights into nature at that time were actually very great. You'll appreciate this in a series of articles that follow.
Well, let's get back to the point, and then say that there will actually be an answer to this question very quickly, and as to whether it is right or wrong, it doesn't matter, at least it solves the doubts in people's hearts, which is the most critical.
More than 100 years after Pythagoras' death, ancient Greece produced a cattle man, he was Aristotle, he received the true transmission from his teacher Plato, and he also believed that the earth was a ball.
Not only did he continue to carry forward this idea, but he also found solid and reliable evidence for it, so that even today it seems that there is no better evidence than this evidence. Unless the five hundred or so astronauts who have been in space, they have seen the Earth with their own eyes. Right.
The first proof is that the lunar eclipse knows, the shadow of the earth is cast on the moon, and it is obvious that the edge of the earth's shadow is an arc, right! Can you now say that the earth is a triangle, a square? This evidence is too direct, but it makes me feel sorry that you say, we Chinese see the moon less? At least Houyi didn't look at the moon less, but no one said that the earth might be a ball. What a shame.
This evidence can tell us firmly that the Earth is either a ball or a disk, and rightly, both geometries can cast a circular shadow. But Aristotle believed that no matter how the moon turns, no matter what time, the shadow of the earth is round, which shows that the possibility that the earth is spherical is very large, rather than a disk, the disk may cast other sexual rotations, right! That's understandable.
In addition to this evidence, there are other evidences that can confirm that the earth is a ball, for example: Aristotle found that when you say that a ship that is gradually going away, why did the hull disappear first, and then the mast disappear? A boat coming towards you is just the opposite, see the mast first, then see the hull? Right.
It is clear that the Earth is a ball. For example, if you keep sailing south on your boat, you will find that at night you will see constellations that are invisible in the north, as well as some vague nebulae. For example, the Magellan Nebula, which is exclusive to the southern night sky, cannot be seen in the north. Of course you sail south and see more southern constellations, then there will be northern constellations disappearing on the horizon. Right.
What does this mean? The earth is a ball! Not only that, Aristotle more than 2,000 years ago also explained to me after 2,000 years that I was troubled as a child.
Why don't people below the earth feel their heads down? Aristotle said that nature is not forced to move for two kinds of motion and natural motion, then natural motion is to say that all objects have the nature to return to the center of the universe, so where is the center of the universe? Yes, the center of the earth!
We wanted to go back to the center of the earth, but we were blocked by the ground, so we could stand firmly on the ground. Pretty! The explanation is really great. Wrong though!
This again illustrates the problem, that with my IQ compared to Aristotle's, it would be self-defeating, because I had the same problem, but I did not find an explanation for this problem, and finally learned Newton's set, and then I learned the truth. ay! This only shows that I am a common man! We can only do science popularization for everyone.
Don't worry, it's not over yet, the wisdom of the ancient Greeks is far more than that. At the same time as Aristotle, there was a man named Eratosenes, who was also about the 3rd century BC.
On the basis of geometry, this big brother proved that the earth is a ball using mathematical and logical thinking, and also calculated the circumference of the earth.
He was living in Alexandria, Egypt, but his ancestral home was Hillini in Greece, and it just so happened that the two cities were at the same latitude, so in Eratosenes' life, the trajectory of the sun seen in the sky was exactly the same every year, at least for him, he never saw the sun at the top of the dome at the summer solstice, that is, he had not seen the sun directly above his head, so at this time there was no shadow of any object, because the sun was vertically downward, right? It's not hard to understand if you think about the examples you get in life.
But one day Eratosenes received a letter from the city of Seni, which is south of Alexandria, well, now you pause, first of all, the relative positions of the three cities are clear, look down! The letter said that at the time of the summer solstice the sun was shining straight into the bottom of a deep well, and it was also said that a pile was laid on the ground, which had no shadow from the ground pile. This shows that the sun is at the top of the dome, and the sunlight and the ground are 90 degrees, right.
I just thought, are the people of Seni City so boring? It was strange that he lived there every day, the sun was overhead, and he wrote a letter to the master, but the content of the letter really shocked Eratosthenes.
He hadn't seen the sun overhead in any year, so he conducted an experiment in Alexandria on the day of the summer solstice the following year, hitting a ground pile perpendicular to the ground and measuring the length of the shadow with the ground pile at noon.
Next is the geometry that the ancient Greeks were best at, according to the length of the shadow and the height of the pile, you can calculate the angle between the sunlight and the pile, which is a simple right triangle, when the measured value was 1/50 of the circumference, that is, 7.2 degrees.
This angle is exactly equal to the position of the sun and the angle of the dome of the sky. Right. Then if what is said in the letter is true, then the angle between the sun and seni city at this time is 0.
First of all, Eratosenes pondered the question, why is there such a difference? The city in the north has an angle with the sun, but the city in the south does not, why? Because the earth is a ball. If it is flat, there is no such difference. Right.
Next is the focus of the whole experiment, it is not difficult to see that the angle between the two cities to the center of the earth is equal to 7.2 degrees, right. So if you know the distance between two cities, that is, the length of the arc, and then multiply by 50, is not the circumference of the earth!
In this historical event, the most important thing is the scientific thinking above, as for the calculated circumference, it is certainly inaccurate, the biggest reason is that there was no accurate means of ranging at that time, the only way was to rely on camels to walk a road, see how long it took, and then calculate how long the distance was.
This method is too crude, and there are two versions of the distance unit Stardia used at that time, 1 Statia is equal to 185 meters, and there is another, 1 Stateia equals 157.5 meters.
According to these two distance units, the earth circumference of Eratosenes has two values, 46620 km and 39375 km, so the current recognized value is 40041 km, the former is 16% larger, and the latter is only 2% smaller.
Right, it still looks pretty accurate. However, it does not matter whether it is accurate or not. Other people's scientific methods are correct and worth learning.
Therefore, the earth is a ball, this matter has long been figured out by the ancient Greeks, and it has become a recognized truth in academic circles. It was just that the information was blocked at that time, and there was no science popularization for the public like those of us, so most of the people at that time still did not know that the earth was a ball.
Even when magellan sailed, there were still a large number of sailors who thought that they might fall into the endless abyss, and when they left, they said goodbye to their families and cried a lot.
So you say that Magellan himself knew that the earth was a ball? He must have known, and was convinced, that in those days, hundreds of brothers could be ordered to sail, there was a big steamship, and it could get the support and financing of the royal family, and Magellan must have done great things, was in the upper class, not an idle person, and the insight and knowledge of others were certainly not comparable to those of us peasants. Right. At that time, a peasant boy's family may not even have a rack car, and he has seen some big ships. Right.
Finally, one more question, which has always caused me heartache, is when we Chinese know that the earth is a ball. At the beginning of the 20th century, when they were forced to learn advanced Western technology, only a small number of people knew this fact. Why wasn't science born in China? That is, the famous Needham problem, there is an opportunity to talk about this matter later.
Well, that's it for today.