Several decades ago, when I looked at the sky and dreamed of being able to move through the Universe, I was guided by imagination and saw a future similar to what films such as Star Trek show: interstellar or intergalactic travel at speeds much greater than the speed of light. In recent decades, this has not been realized, but from a scientific point of view, many changes have occurred. We know much more about our Universe, about the planets that populate it, which at the time we did not even know if they existed. We found planets around stars similar to our sun but mostly planets around red dwarfs, which are by far the most numerous stars. The approximately 5000 planets discovered are only a handful of objects, the discovery of which made us understand that planets are not rare objects in space but rather common objects and that every star has planets. The universe is full of planets. In our galaxy alone, there are hundreds of billions, and as we have seen, an estimated 6 billion are similar to Earth, which revolves around stars similar to the Sun. If we move on to red dwarfs, half of this population of stars should have a habitable terrestrial planet and an average of one habitable terrestrial planet every 5–6 light years. It is no coincidence that the closest star to us, Proxima Centauri, has a habitable planet, Proxima Centauri b. With the billions of terrestrial-type planets that exist, for statistical reasons, many of them must be in the habitable zone. What about life in the Universe? If things go as in the case of Earth, on which life appeared a few hundred million years after its formation, it must be present on many habitable planets in our galaxy and in the Universe. It probably will not be the life we would like to find, the strange humanoids of Star Wars or similar films; it will be bacteria or who knows what else, but it is still life. The most interesting thing is that if we had visited our planet a few billion years ago, we would not have found cows, horses, or men but rather simple bacteria and that simple life has evolved over billions of years to give rise to increasingly complex and more intelligent beings. Why could this not happen on other habitable planets, especially those that revolve around orange dwarfs that can have a lifetime of 20–40 billion years instead of the 10 billion of our Sun? As we have seen, starting from statistical studies based on knowledge of the astrophysical parameters of extrasolar planets, we conclude that in the life of the Universe, technological civilizations have existed until today. From the knowledge we have gained, it is easier to say that we are not alone than the opposite. This almost certainly clashes with the great silence that has been given to us by decades of research with electromagnetic waves of signals from advanced civilizations. Fermi’s idea inherent in his paradox that there are no intelligent extraterrestrial life forms can no longer be accepted as lightly as in the 1950s and, similarly, the Rare Earth hypothesis. The nonreception of signals from extraterrestrial civilizations can be due to many reasons, first, the enormity of space, the lack of knowledge of the place where these civilizations may be located, or the duration of these civilizations. On the other hand, if someone had tried to contact us by sending us electromagnetic signals in the last approximately 4.5 billion years, they would certainly not have found us. We have only been sending and receiving signals for a hundred years. Therefore, in addition to the enormous space between the stars, which makes contact difficult, we must add a time factor. Extraterrestrial civilizations may not be interested in communicating, or they may use other technologies. Another thing to add is that we talk about life but not only have we not been able to find the mechanisms by which it was born on Earth, but we also have difficulty defining it. Even if we do not have a good definition of life, most likely in the next decade, the study of the atmospheres of habitable planets with the space telescopes we have, and those we will have, will allow us to identify planets in which life releases gases that testify to its existence. Primitive life, such as that which existed on Earth long ago, changed the Earth and transformed it into Gaia, a sort of superorganism capable of self-regulating and generating conditions suitable for the development of life, owing to the activity of living things themselves. This discovery, however, would also lead us to a real paradigm shift and would make us understand that we are not unique in the Universe in this context either. As Arthur C. Clarke noted, there are two possibilities: “We are alone in the Universe or we are not. Both are shocking. However, I am convinced that if life managed to make its way onto a planet such as Earth, to become extinct and reborn, to evolve and achieve self-awareness, there is no reason why this has not happened, is not happening and will not happen in other places in the Universe.

Epilogue

章节
发表日期：

2025年

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Antonino Del Popolo

摘要

Several decades ago, when I looked at the sky and dreamed of being able to move through the Universe, I was guided by imagination and saw a future similar to what films such as Star Trek show: interstellar or intergalactic travel at speeds much greater than the speed of light. In recent decades, this has not been realized, but from a scientific point of view, many changes have occurred. We know much more about our Universe, about the planets that populate it, which at the time we did not even know if they existed. We found planets around stars similar to our sun but mostly planets around red dwarfs, which are by far the most numerous stars. The approximately 5000 planets discovered are only a handful of objects, the discovery of which made us understand that planets are not rare objects in space but rather common objects and that every star has planets. The universe is full of planets. In our galaxy alone, there are hundreds of billions, and as we have seen, an estimated 6 billion are similar to Earth, which revolves around stars similar to the Sun. If we move on to red dwarfs, half of this population of stars should have a habitable terrestrial planet and an average of one habitable terrestrial planet every 5–6 light years. It is no coincidence that the closest star to us, Proxima Centauri, has a habitable planet, Proxima Centauri b. With the billions of terrestrial-type planets that exist, for statistical reasons, many of them must be in the habitable zone. What about life in the Universe? If things go as in the case of Earth, on which life appeared a few hundred million years after its formation, it must be present on many habitable planets in our galaxy and in the Universe. It probably will not be the life we would like to find, the strange humanoids of Star Wars or similar films; it will be bacteria or who knows what else, but it is still life. The most interesting thing is that if we had visited our planet a few billion years ago, we would not have found cows, horses, or men but rather simple bacteria and that simple life has evolved over billions of years to give rise to increasingly complex and more intelligent beings. Why could this not happen on other habitable planets, especially those that revolve around orange dwarfs that can have a lifetime of 20–40 billion years instead of the 10 billion of our Sun? As we have seen, starting from statistical studies based on knowledge of the astrophysical parameters of extrasolar planets, we conclude that in the life of the Universe, technological civilizations have existed until today. From the knowledge we have gained, it is easier to say that we are not alone than the opposite. This almost certainly clashes with the great silence that has been given to us by decades of research with electromagnetic waves of signals from advanced civilizations. Fermi’s idea inherent in his paradox that there are no intelligent extraterrestrial life forms can no longer be accepted as lightly as in the 1950s and, similarly, the Rare Earth hypothesis. The nonreception of signals from extraterrestrial civilizations can be due to many reasons, first, the enormity of space, the lack of knowledge of the place where these civilizations may be located, or the duration of these civilizations. On the other hand, if someone had tried to contact us by sending us electromagnetic signals in the last approximately 4.5 billion years, they would certainly not have found us. We have only been sending and receiving signals for a hundred years. Therefore, in addition to the enormous space between the stars, which makes contact difficult, we must add a time factor. Extraterrestrial civilizations may not be interested in communicating, or they may use other technologies. Another thing to add is that we talk about life but not only have we not been able to find the mechanisms by which it was born on Earth, but we also have difficulty defining it. Even if we do not have a good definition of life, most likely in the next decade, the study of the atmospheres of habitable planets with the space telescopes we have, and those we will have, will allow us to identify planets in which life releases gases that testify to its existence. Primitive life, such as that which existed on Earth long ago, changed the Earth and transformed it into Gaia, a sort of superorganism capable of self-regulating and generating conditions suitable for the development of life, owing to the activity of living things themselves. This discovery, however, would also lead us to a real paradigm shift and would make us understand that we are not unique in the Universe in this context either. As Arthur C. Clarke noted, there are two possibilities: “We are alone in the Universe or we are not. Both are shocking. However, I am convinced that if life managed to make its way onto a planet such as Earth, to become extinct and reborn, to evolve and achieve self-awareness, there is no reason why this has not happened, is not happening and will not happen in other places in the Universe.