iBook The Future of the Universe - Rejuvenating the Sun and Avoiding Other Global Catastrophes

iBook The Future of the Universe - Rejuvenating the Sun and Avoiding Other Global Catastrophes

This book is about an audacious idea: asteroengineering—literally, the physical engineering of a star, especially the star we call our Sun. It is an idea on the grandest of scales. Part science fiction, part science fact, asteroengineering is a response to a very definite and a very real problem, a problem that our distant descendants will one day have to face. It is also a universal problem that will be experienced – at some stage or other – by every extraterrestrial civilization that has or will exist. Indeed, the problem to be addressed resides within the parent stars of each and every lifesupporting planetary system within our galaxy. In short, stars puff up to become luminous red giants as they age, and by doing this they vaporize those planets previously situated in the habitability zone where life can otherwise thrive. As their parent star ages and approaches the red giant phase, a civilization has two options open to it: stay at home, or pack up and leave. The latter option would require the hapless civilization to cocoon itself within giant spaceships and then set itself adrift in the uncharted depths of space. If a civilization chooses to stay put, however, then all life will end—unless, that is, something is done about the demise of its parent star. The idea of star engineering was possibly first discussed in the mid-1980s in the book Atoms of Silence: An Exploration of Cosmic Evolution by Hubert Reeves (MIT Press, 1984). The blatant defiance of the idea was inspiring. That we might engineer the Sun – the hub of the solar system and steadfast provider of warmth for life on Earth – now that’s an ambitious goal! It is a brazen and challenging notion, and one that sets the mind both searching and reeling. This book provides a preliminary examination of the solar rejuvenation options that may be realized and put into practice by our descendants in the deep future. 1 2 Rejuvenating the Sun and Avoiding Other Global Catastrophes It is often said that science fiction is just pre-science fact. There are few, if any, science fiction stories about engineering stars to save a planetary system, but this is essentially the aim of asteroengineering. If nothing is done about the future evolution of our Sun, then it will destroy all life on Earth. This fiery destruction of Earth won’t happen within our lifetime, however, and we are still many hundreds of millions of years away from potential destruction. Indeed, our distant descendants will have many long years of preparation time before even the first steps towards solar rejuvenation must be taken. Some of our galactic companions – assuming that they exist – will not, however, be as lucky as us. They may, in the here and now, be involved in the very process of altering their parent stars. As we shall argue in Chapters 1 and 6, asteroengineering may, in fact, be in common practice throughout the Milky Way galaxy (and other galaxies), and if so, this can be offered as a potential solution to the famous paradox, posed by physicist Enrico Fermi, which asks why are there no alien life forms in our solar system at the present time. Our suggested answer is that they are not here – that is, in the solar system – because they have had no reason to leave their home worlds. Indeed, it is our contention that advanced galactic civilizations will most likely choose to rejuvenate their parent stars into longlived, non-giant forming states, than adopt a galactic colonization program. Before our descendants have to worry about the effects of an aging and more luminous Sun, there are a multitude of terrestrial and astronomical disasters that they will have to guard themselves against first. Not just earthquakes, landslides, tornadoes, and tsunamis; our descendants will have to contend with comet and asteroid impacts, the explosion of nearby supernovae, and the close passages of wayward stars. All of these problems, however, just like the increase in size of the aging Sun, are potentially fixable by strategic planning and, in some cases, direct intervention. Asteroengineering is one of the direct intervention cases. We cannot possibly perform the required engineering at the present time— nor indeed, do we need to. But we can determine what must be done in principle, and that is half the battle. In the meantime, by learning how to tame and nullify the dangers posed to life on Earth by the heavens around us, humanity can begin to acquire Introduction 3 the engineering skills that will eventually be needed to save the entire planet and all the life that resides on, in, and around it from the raging gigantism of an aging Sun. Although you will find technical arguments and a good number of equations written in this book it is hoped and intended that the material presented is accessible to the non-specialist. The mathematics presented is no more advanced than that of a firstyear university-level science course, and no detailed knowledge of physics is assumed. The general reader, though, need not worry about the mathematical and technical details too much; if you can’t follow the equations then skip to the conclusions, where all should be made clear in words. Chapter 3 is by far the most difficult chapter with respect to its weight of mathematics and physics, but please don’t be put off; have a go at trying to follow the arguments. Stars are indeed wonderful objects, whether described in the flowing lyrics of iambic pentameter or precisely described in an intricate web of mathematical detail. Comments on Units and Notation Astronomers are notoriously bad for their inconsistent use of physical units. Although we will ostensibly use the SI units of meters, kilograms, and seconds, there are times when other (i.e., non-SI) units are more conveniently adopted. Distances, for example, will typically be expressed in either astronomical units (AU) or in parsecs (pc), and occasionally as light-years (ly). Accordingly: 1 AU = 1496 x 1011 m 1pc = 206265 AU = 3261 ly We will also use solar units (designated by the symbol ) where mass, size and energy output per unit time (luminosity) are expressed according to the measured quantities: 1 M = 19891 x 1030 kg 1 R = 696265 x 107 m 1 L = 385 x 1026 Watts 4 Rejuvenating the Sun and Avoiding Other Global Catastrophes Temperatures will be expressed in Kelvins (K), where zero Kelvins (the convention is to say Kevins rather than degrees Kelvin) corresponds to the absolute zero point temperature. In the more commonly used Centigrade (°C) scale, absolute zero falls at −273 °C. Among the mathematical symbols that you will commonly see: ‘∼,’ meaning to order of magnitude, and ‘≈,’ meaning approximately equal to. The symbols ‘<’ and ‘>’ are used to indicate the ‘less than’ and ‘greater than’ inequalities. In this manner, for example, a > b means quantity ‘a’ is greater in magnitude than quantity ‘b.’