Our Origins. Chapter 1

Transcription

1 Part 1 Origins What is there beyond everything? Have you ever stayed out late, just to look at the stars? Long enough to make your head spin Not because you re bent back, But because you looked so far away The more the night is dark, the further you can see in the heavenly sky Have you ever thought what s behind the stars? Other stars of course, but what s behind them? Jostein Gaarder Allesia, 11 years old, a primary school student in Perugia, continues in such a way: There will be some angels, Or some meteors From the smallest galaxy There will be Jesus, there will be paradise There will be very small stars There will be our desires and Our dear animals who are dead, There will be my Grandfather and many other people There will be my past and my future.

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3 Our Origins Chapter The Ancient Questions On a moonless night we might find ourselves stretched out on a deserted beach or high up on a mountain, far away from the lights that have diminished our view of the sky. If the sky is clear and there are no obstructions on the horizon, the spectacle we see is truly extraordinary: surrounded by myriads of stars we are immersed in an enchanted world. Above us the great luminous stripe of the Milky Way sweeps across the sky from one side to the other. We recognize, depending on the season, the principal constellations: the great W of Cassiopeia, the sword of Orion high in the winter sky, the Scorpion low in the summer sky, the Swan and the Pleiades constellations with ancient Greek and Arabic names, invented by people who, in contrast to us while gazing at the sky, were fascinated by such beauty, and created stories and myths to explain the origins of stars. Wherever we look, there are luminous points: the brightest few are planets; the others, the majority, are stars. Farthest away, not quite visible to the naked eye, are galaxies which, like ours (the Milky Way), consist of hundreds of billions of stars. Then if we have a telescope, and point it to an apparently empty zone of the sky, we discover new luminous points, stars still fainter and farther away. Everywhere we look we see a great show that is only an infinitesimal part of our universe. At such moments, it is difficult not to ask ourselves, What is the origin of all that we see, of the stars, the planets, and of our own life? It is difficult not to ask ourselves whether we have our roots in the universe, or if there might Our Origins 3

4 exist other forms of life around stars. These are questions that humans have always asked, and for which they have offered answers drawn more from the realm of myth and fantasy than from science. Today, however, for the first time in human history, one can try to give some answers to the problems of our origins, thanks to the extraordinary progress made during the last century in the fields of physics, chemistry, astronomy, geology and biology. The techniques used are those of science. Perhaps they are cold, but the answers have the same fascination as did the ancient myths. The conviction that we could answer these questions is so strong that, in the 1990s, American scientists decided to give the name Origins to a series of investigations, space missions and large instruments on the Earth devoted to answering two simple questions: Where do we come from? What is the origin of the universe, of the stars, planets, of the elements that constitute our world and, finally, of life? How did life begin on the Earth? Are we alone in the universe? Are there observations that will enable us to determine if forms of life similar to ours exist on distant planets? The choice of the name Origins and of these two themes is an attempt to convince the greater American public of the importance of continuing this research and, above all, that it is worth the investment of the enormous financial resources required. Consider, for example, the Hubble Space Telescope (Figure 1.1), an orbiting observatory built by the United States with contributions from Europe, some of whose images we shall use in this book. The cost of the instrument and of managing the mission was more than 4 billion Euros, an amount similar to the estimated cost of the bridge over the Straits of Messina, just for this single space mission, although admittedly one of the costliest. Aside from political ends, there is, among the scientists who proposed the Origins program, the conviction that something extraordinary had happened. Science had begun responding to ancient questions like those of the origins of the universe and of man, and to understand the incredible sequence of events that had made possible the emergence of an extraordinary planet like ours on which life has been able to reproduce and to evolve. The awareness of what was going on, brought the past Director of the Origins Program of NASA to write : When the answers to these questions are known, our civilizations will evolve and we will have new visions of who we are and what our future might be. We have already learned enough to appreciate that the universe is enormous and ancient, but life tiny and transient is its precious jewel. In 2004, the European Space Agency (ESA) began a program similar to that of NASA, called Cosmic Visions (Section 12.1). The questions posed by European researchers are similar to those of the Origins program, and the need to find answers has by now involved scientists of all nations. 4 Beyond the Stars

5 Figure 1.1: The Hubble Space Telescope (HST) from which several of the images reported in this book were taken. On the bottom right is a picture of HST orbiting around the Earth, on the left is a schematic picture of the satellite. Despite the relatively small mirror (2.4 m), the quality of the optics and the fact that it operates outside the atmosphere made HST the most sensitive optical instrument ever built. Launched in 1990, HST, after the last maintenances of 2008 and 2009, should function until 2004, with no other intervention. Then HST will fall to Earth like all satellites inside a geosynchronous orbit (Section 10.1). ( STScI & NASA.) 1.2 You Can t Answer Everything By now, many results are known. We know, for example that the universe was born 13.7 billion years ago in a great explosion, the Big Bang, and that since then it has continued to expand and cool proportionately. 1 We know, therefore, that everything we can observe has a beginning in time and that at this beginning the universe was very hot and confined in a microscopic space. One could ask what was there before the Big Bang, but this is one of those questions for which science has no answer, at least not today. Galileo taught us that science must be based on facts, on measurements, and what cannot be measured does not belong in the kingdom of science. 2 Since what occurred before the Big Bang is not observable, science cannot say anything about it. One can form theories and hypotheses, but they will exist only in the world of 1 This is easy to understand: when a system expands, the energy it contains is distributed in an ever larger volume so it is diluted and diluting the energy means cooling or lowering the temperature. 2 In effect, the need of a greater rigor in science and to base it on measurement (also to separate science from magic) had been felt by Leonardo da Vinci a century before Galileo. In the Trattato della Pittura, he described science like this: No human investigation can be called science unless it has mathematical demonstrations; and if you say that science that begins and ends in the mind is true, this is not conceded and is negated for many reasons, first among them that in mental discourse there is no measurement, without which nothing can be known with certainty. Our Origins 5