Springer & Praxis Publishing, 2009. — 167 p.In writing this book, I set out to educate, entertain, and stimulate public support for intelligent efforts by humankind to search for alien signals from space. As the book explains the primary facts and concepts in layman's terms, the reader will need only elementary mathematics to grasp the major issues. Whilst some oversimplification has been inevitable, the coverage is scientifically accurate. I hope the reasoning will resonate with the public. Once readers have grasped the fundamentals, I believe they will agree with me that the SETI effort to-date has been extremely limited in scope; in particular, it has not really explored the electromagnetic spectrum outside the very narrow radio-frequency region. In fact, not even 1 per cent of the spectrum has been explored! The people involved in SETI are trying to achieve a technically challenging task in a manner consistent with the laws of physics. It has absolutely nothing to do with the "I was kidnapped by aliens" reporting of the tabloid press. Unfortunately, in the public mind UFOs and alien signals tend to get lumped together, with the result that SETI work is often portrayed as being on the fringe of science. Certainly, in the past, many engineering and scientific academics risked SETI tarnishing their careers. The low probability of success is a barrier to academics interested in furthering their careers. Some members of the public may believe a massive effort to detect alien signals is underway, but this is far from being the case. In fact, no US government funding currently exists for SETI. The limited efforts that are in progress rely on charitable funding. SETI has been mainly the work of academics well versed in a particular discipline. However, as I show in the text, the detection of extraterrestrial signals is a systems engineering problem whose solution - constrained by limited resources - both minimizes the chance of failure and maximizes the chance of success. SETI efforts to-date have been marked by basic deficiencies which make it unlikely they will succeed. Section 4 of this book offers some suggestions for how a systems engineering approach might be developed. There has been a great deal of speculation in the literature about why we have had no success, with the inference being that this is because there is nobody to signal to us. This is known as the Fermi Paradox, but it is far too early to conclude that we are alone. Little has been done, especially at laser wavelengths. This book explains what has been done, what is being done, what can be done, and what may have to be done before we can in good conscience acknowledge the Fermi Paradox. A related effort is that underway to identify Earth-like planets orbiting other stars. This was initially done using terrestrial telescopes, but recently satellites have joined the hunt. After years of frustration, in excess of 300 extrasolar planets have been detected in the last decade, in some cases with a single star having several planets. The early methods were best suited to finding gas giants even larger than Jupiter, but the latest systems are designed to find Earth-like planets. The latest addition to this effort is the Kepler spacecraft launched by NASA in March 2009. When it does find a planet with a mass comparable to Earth that is orbiting a solar-type star at just the right distance for the surface to be conducive to life, NASA will certainly hail it as a major discovery. And indeed it will be, but a dozen or so further requirements must be satisfied before a star system can produce an intelligence capable of attempting to communicate across interstellar distances. This book seeks to inform the public of what has been done, what is being done, what can be done and what needs to be done, much of it at little cost and potentially great benefit to mankind. The obstacles to success are discussed in detail. There is a long way to go. SETI is limited to, at best, several million dollars per year globally. If we are serious, then we should do better than this. With public support, money can be forthcoming or the challenge may be taken up by a wealthy foundation. SETI has been of interest to me personally since 1965, soon after the birth of the laser. In 1961 Robert Schwartz and Charles Townes wrote a scientific paper which explained the potential for lasers in extraterrestrial communications. However, little was done while attempts to detect signals concentrated on radio frequencies. Interest in optical SETI was kept alive by a few people, notably myself, Stuart Kingsley and Ragbir Bhathal, until the lack of success at radio frequencies forced reconsideration. I pointed out in 1965 that laser signals would be best sent by short pulses, since this would allow a modest transmitter to readily overcome the brightness of the host star. Today, there is a serious effort at Harvard devoted to pulsed laser signals, but all the efforts at all wavelengths are still quite limited in relation to what can be done. Thus, this book is in four sections. The first section discusses the likelihood of intelligent life, taking into account the many constraints which could conceivably mean that we are the only intelligence in the galaxy. The second section discusses the basics of space communication and the technical approaches and issues. The third section describes the SETI efforts that have been attempted and are currently underway. The final section explains how we might proceed further. The bibliography should assist anyone seeking a guide to the literature on the subject. In my career, lasers have gone from being a new subject of interest, to finding use in a wide range of applications. I addressed laser communication in my 1965 book Laser Receivers, and spent my career helping to develop laser communication. It is gratifying that the advances in power and efficiency of lasers have facilitated such varied applications, and in my role as technical editor of a Laser Applications series by the Academic Press I kept up to date with the myriad uses of lasers in industry, defense, medicine and entertainment. I participated in these advances, being the first to patent a semiconductor diode pumped crystal laser that is ubiquitous today from a green laser pointer for public speakers, to a satellite-to-satellite communication link. As Director of Laser Space Systems for McDonnell Douglas for many years, and in working with both NASA and the United States Air Force, I was intimately involved with the development of space communication. In 1975 the IEEE gave me a Fellow Award, as did McDonnell Douglas in 1985, both for "Leadership and Contributions to laser communications". I believe there are excellent reasons for lasers being the best choice for SETI. I leave it to the reader to form a judgement on which part of the spectrum we are more likely to intercept a signal from space: radio-frequency, optical, infrared, ultraviolet, or something else. I discuss a variety of considerations, including information that makes it clear how difficult it is for interception to occur. The material on communication is based explicitly on my background and expertise. That on the likelihood of a planet giving rise to intelligence derives from the rapidly increasing body of knowledge of planetary science. Overall, I hope that this book provides a firm base for those who might wish to further the search for alien signals. Finally, it should be borne in mind that signals may be being sent to us right now, but we will not know it unless we are looking in the right part of the spectrum at the right time, with the right equipment pointing in the right direction. Success may be tomorrow, or a millennium away.Part 1: The likelihood of extraterrestrial intelligence Vast distances and long travel times Stars, their evolution and types Planets and our Sun The many constraints on life Why would anyone transmit to us? The Drake Equation and habitable planets Part 2: The basics of space communication Where to look in the electromagnetic spectrum? Receiver basics and how big is big? Noise and limitations on sensitivity Part 3: Programs in SETI A brief history of SETI Radio-frequency and microwave SETI, including the Allen Telescope Array Early optical SETI and the all-sky Harvard system Part 4: Possibilities in SETI The PhotonStar project Key issues for SETI Other parts of the spectrum, decoding the data and forming pictures Future systems for intercepting alien lasers
Чтобы скачать этот файл зарегистрируйтесь и/или войдите на сайт используя форму сверху.