On August 25, 1609, Italian astronomer Galileo demonstrated his first refracting telescope at the Venetian Parliament.

Four hundred years ago, mankind forever changed its understanding of the universe. On August 25, 1609, an Italian mathematician named Galileo Galilei demonstrated his newly built telescope to Venetian merchants. Soon after, he turned his telescope towards the sky. He saw mountains casting shadows on the moon, and then realized that the moon, like the earth, is a world with complex terrain. He saw Jupiter's moons-orbiting another celestial body, contrary to what the church taught. He saw that Venus, like the moon, has a waxing phenomenon, indicating that Venus orbits the sun and not the earth, which is even more contrary to what the priest said. He saw sunspots, proving that the sun itself was not a perfect celestial body as stated in Greek cosmology accepted by the Church. But he also saw something else that is often forgotten today. He saw the Milky Way, a cloud-like strip across the sky, made of stars.

That observation was the first to suggest that not only was Earth not the center of everything, but that the vastness of the universe was far beyond the comprehension of people of that era. And the universe has been growing and getting older ever since. Astronomers' latest estimate is that the universe is about 13.70 billion years old, three times the age of Earth and 100,000 times the lifespan of modern humans as a species. Exactly how big the universe is is unknown. Its age and the finite speed of light mean that no astronomer can go beyond 13.70 billion light years. Yet the universe may be larger than that.

Reality is not necessarily limited to this universe. Physics, closely linked to astronomy, tells us that although the objects people call the universe are vast and vast, they may be just one of countless similar structures that each follow slightly different laws and are currently called the multiverse because of the lack of a better description.

Galileo's contemporaries believed that the crystal ball of the universe contained planets and stars, and these stars represented the edge of the universe. The rupture of this theory (together with Darwin's view of natural selection) became the greatest revolution in human understanding of oneself. Galileo lived in a world with limited levels of cognition. The Greeks had a clear understanding of the size of the earth and its distance to the moon, and medieval people who read Greek writings also inherited these views. Such a distance is exactly the level that human imagination has been able to reach for a long time. In the past, it was easy for people to believe that as big as the heart, the universe was as big as the universe. However, in the face of modern cosmology, it is even more difficult for people to debate whether this is based on human self-interest, let alone multiverse theory.

Four hundred years later, the heirs to Galileo's ideas are no longer regarded as dangerous revolutionaries. They will meet this week in Rio de Janeiro under the auspices of the International Astronomical Union. But their discoveries have changed the world as much as Galileo's, from planets around other stars that may harbor alien life to dark matter and energy of unknown properties that are important in real life. Modern humans may be more attuned to the idea of a sudden change in humanity's place in the universe than medieval humans were. But that should not blind people to the wonders of the cosmic conjecture.

Comment: Great inventions have changed human understanding of the universe.