What we consider basic or obvious was not always so. For it to be, we had to learn it first. Now it seems clear to us that a ball falls after being thrown due to gravity, that a magnet sticks to the fridge due to electromagnetism or that a piece of cork floats due to the push of water. But these phenomena had to be discovered and understood one day. In the same way, it seems clear to us that the Earth describes an orbit around the Sun and not the other way around , that our planet is, in essence, the same as the rest of the planets and that the universe is an inconceivably large place full of stars and galaxies separated by huge distances. But although this has “always” been so, it has not always seemed obvious to us, we have had to learn it .
If we take a look at the mythologies of ancient cultures we will see how the human imagination tried to answer questions about the origin of the world and the universe in as many different ways as there were cultures. Some refer to divine beings who, through their words, their dreams or even their vomit, created everything that exists. In others, a creature sent by this divine being makes the earth emerge from the original infinite ocean. There are also those in which the Earth is nothing more than the body, or a part of the body, of said divine being. Thanks to the discoveries accumulated during the last millennia, these stories have become mythological stories , which tell us more about the human being and his fears and concerns than about the universe we inhabit.
For example, many of these myths consider that we live on a flat Earth, but it has been more than 2000 years since we began to discard that possibility. In ancient Greece, specifically, and thanks in part to the philosopher Eratosthenes , who from Alexandria tried to measure the radius of the Earth . Eratosthenes knew that to the south of Alexandria was Siena, a city where on the summer solstice, at noon, objects did not cast shadows. This only happened in that city and on that day of the year. Knowing the distance between the two cities, and the angle formed by the shadows of Alexandria on that particular day, he was able to determine the size of the Earth. However, this Earth continued to have a privileged place as the center of the universe.
Also around this time Anaxagoras proposed that the Sun must be a fiery, glowing rock and that the thousands of stars in the night sky must be similar rocks but so distant that they are barely visible as dots. Aristarchus of Samos even tried to measure the distance to the Sun and the size of the star . He was wrong by a good margin, but the important thing is that he deduced that the Sun was very far away and that it was much larger than the Earth.
These ideas did not catch on and the central position of the Earth resisted some 16 more centuries until the heliocentrism of Copernicus , which took the planet out of its central position, the observations of the moons of Jupiter and the details of the lunar surface of Galileo , which indicated that the Earth was not the only object with detail and interest, and Kepler’s deduction that it must be the Sun that caused the celestial movement of the planets . With this our universe grew, it went from being a spherical Earth surrounded by crystalline spheres that contained the objects of the firmament to occupying the size of the solar system.
Over the decades, these little points of light called stars have aroused more and more interest and even attempts have been made to measure our distance from them. In the 19th century, scientists like Bessel did just that. Using the apparent change in position of the nearest stars, caused by the Earth’s motion around the Sun (think of how your finger changes position if you alternately close and open your eyes, and imagine separating your eyes until they are at points opposite sides of Earth’s orbit), we discovered that some of the closest stars were millions of times farther from Earth than the Sun , which was already incredibly far away.
With technical and theoretical advances we were able to measure the distance to more and more distant stars, until we began to configure a map of the galaxy, thousands of light years in size. Once again our concept of the universe had been expanded thousands of times. Shortly after, at the beginning of the 20th century, thanks to the work of Leavitt, Hubble and others , we began to detect stars that were ten, one hundred and one thousand times one thousand light years away. This is how we realized that our galaxy was just one among dozens (which eventually became billions) of other galaxies that populated the cosmos.
In just 3 centuries we had gone from occupying the center of a tiny universe, barely larger than planet Earth, to being an imperceptible speck of dust among countless dust specks that formed one of countless galaxies . We came to inhabit a universe in which our collective history was but a fleeting moment in an eternity. And perhaps in the future we will finally get off the natural and imaginary podium that we believe we occupy. At the latest the day we discover extraterrestrial life (which is not guaranteed although it does seem feasible) but, hopefully, sooner.
