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Auf Deutsch
Journal of the Royal Astronomical Society of Canada, Vol. 83, No. 4, p. 260, 1989
Enfin un livre excellent et à point, sur ce sujet brûlant d'actualité qui est la recherche des êtres vivants extraterrestres. Si l'Univers est vide d'intelligence extraterrestre, quel est notre rôle comme témoins et acteurs dans cet Univers silencieux? Si l'Univers est plein d'intelligence extraterrestre, quelle est notre place et notre part dans cet Univers? On y apprend que les questions existentielles (place de l'humain dans l'Univers) d'une telle recherche astronomique bousculent un peu les religions qui prétendent y apporter des réponses. Ainsi l'étude rapportée en page 177 dénombre une opposition religieuse à ces recherches astronomiques: seulement 38% des protestants approuvent ces recherches, contre 42% des juifs, contre 44% des catholiques, et contre 50% des gens sans religions (pas de pourcentage pour les musulmans).
Dans ce livre on a affaire à une vulgarisation scientifique de talent par un scientifique, et non pas par un journaliste en mal de sensations pour lequel il faudrait faire preuve de scepticisme (cf. page 137). L'auteur est né à Stockholm en Suède (en 1946), puis a étudié à l'Université de Toronto au Canada (maîtrise 1970), et a séjourné à l'Observatoire de Besançon en France (doctorat 1983), avant de prendre sa place d'astronome à Toulouse en France (depuis 1986).
Les 3 premiers chapitres traitent des comètes, de l'origine de la vie, de l'évolution, de la disparition des dinosaures il y a 65 millions d'années, des catastrophes venues du ciel. Puis il traite de la conquête spatiale, de la possibilité de vie sur les planètes voisines, des nuages interstellaires, des endroits où nous savons que des planètes sont en train de se former (chap. 4 à 6). La tranche des chapitres 7 à 9 traite des civilisations extraterrestres possibles: démographie, sociologie, et expansion dans notre Galaxie. Les chapitres 10 à 12 discutent des stratégies, des recherches, et des débats sur l'écoute des signaux intelligents extraterrestres. Enfin, le 13e chapitre traite du plan philosophique de ces recherches. Et une grande bibliographie de 13 pages est très utile à qui veut approfondir ce sujet d'avantage, grâce à l'aide de sa bibliothèque locale ou universitaire.
De nombreuses illustrations de toute sorte illustrent ce livre. Très peu de fautes d'orthographe sont à signaler. Une défaillance à signaler, corrigeable à la prochaine édition: il n'y a pas d'index des sujets traités. Le tableau 12 (page 156) donnent toutes les recherches observationnelles ayant utilisés des télescopes depuis les débuts en 1960, mais le tableau 12 s'arrête malheureusement en 1984. Pourtant plusieurs recherches ont eu lieu de 1984 à 1988. Mes propres recherches au Parc Algonquin en 1982 ont duré 200 heures, et non pas les 72 heures indiquées dans ce tableau.
Nombre de références dans ce livre sont tirées du ler symposium de l'Union Astronomique Internationale sur ce sujet tenu à Boston en 1984. J'ai dévoré ce livre, surtout la deuxième moitié que je n'ai pas pu m'arrêter de lire tant elle passionne! L'auteur nous donne rendez-vous dans 5 ans (page 87), quelque temps après le 2e symposium de l'Union Astronomique Internationale sur ce sujet (Paris, 1990). Cote finale: neuf étoiles sur dix à cette 1re édition du livre!
Jacques Vallée
Dr Vallée est membre de l'institut Herzberg d'astrophysique à Ottawa.
Revue des questions scientifiques (Namur), 1989
Ce livre présente une excellente synthèse de nombreuses informations concernant le problème de l'existence éventuelle d'une vie et même de civilisations extraterrestres. L'auteur est Astronome, à l'Observatoire Midi- Pyrénées. Il se préoccupe à la fois de recherche fondamentale et de la diffusion de l'astronomie. Ces deux aspects sont très bien perçus par le choix des thèmes abordés et par le fait que ce livre est d'une lecture agréable. Le titre, un peu énigmatique, provient du fait que les radioastronomes "écoutent" surtout à des fréquences comprises entre 1,4 et 1,8 GHz, où l'absorption de l'atmosphère terrestre présente un minimum. C'est ce qu'on appelle "le point d'eau". D'autre part, il y a eu et il y a encore une série de programmes d'écoute de signaux pouvant provenir de civilisations extraterrestres éventuelles. Elles se sont soldées jusqu'à présent par un grand "silence". L'auteur examine cependant cette hypothèse avec une certaine sympathie, me semble-t-il. Il insiste souvent, en tout cas, sur la nécessité d'une grande humilité face à ce problème, car "notre position dans l'univers n'a rien d'exceptionnel".
Il estime que "le point de départ et moteur de la recherche sont ici la conviction profonde que la question doit maintenant être abordée, et qu'il faut lui apporter une réponse sans tarder". Un travail de réflexion tous azimuths est donc "indispensable pour défricher le terrain". C'est l'objectif du livre. L'auteur examine l'origine et l'évolution de la vie sur Terre, en incluant des données sur des composants organiques trouvés dans l'espace et sur des catastrophes résultant d'impacts de gros météorites. Il envisage ensuite, avec un certain optimisme, la possibilité de voyages interstellaires. Il fait le point sur la recherche de la vie au voisinage du Soleil et l'écoute de messages radio provenant de civilisations extraterrestres. Comme Fermi l'avait déjà fait en 1946 et comme beaucoup d'astronomes le disent actuellement, il s'étonne "du grand silence cosmique", posant des questions "de plus en plus criantes". Il note d'autre part que "le soutien de l'opinion est important dans les sociétés démocratiques pour assurer le financement de cette recherche".
Il considère qu'elle doit être pluridisciplinaire, mais il insiste essentiellement sur les moyens astronomiques. C'est compréhensible, mais quand même problématique. Ceci apparaît clairement dans le chapitre consacré aux OVNI, qui contraste avec l'ensemble du livre par le fait que les informations présentées à ce sujet témoignent de connaissances étonnament rudimentaires. Cela reflète peut-être un choix personnel, ou la pression exercée par le milieu scientifique, spécialement en France. En tout cas, l'auteur semble (vouloir) ignorer les données existantes quant aux effets physiques produits par les OVNI, qui interpellent pourtant le monde scientifique. La bibliographie à la fin du livre est généralement bien mais on n'y cite même pas les livres de J. Allen Hynek (the UFO expérience, a scientific inquiry, 1972 et the Hynek UFO report, 1977), bien qu'il soit astronome. qu'il ait été le consultant officiel de l'US Air Force au sujet des OVNI, entre 1951 et 1968, et qu'il a créé ensuite le "Center for UFO Studies".
Cette partialité est sociologiquement très intéressante, mais quant au problème fondamental du livre, il faudrait peut-être envisager aussi l'hypothèse d'un "silence au point d'eau" parce que des civilisations extraterrestres avancées n'ont pas besoin de nous envoyer des signaux radio. Il se pourrait qu'ils nous visitent depuis longtemps, comme semblent l'indiquer de nombreux témoignages. Dans ce cas, ils doivent nous trouver très bornés, puisque nous ne voulons même pas examiner ce qui se passe sur notre Terre, si cela n'est pas conforme à ce que nous croyons. Pourquoi l'humanité est-elle encore toujours incapable de faire une étude objective du message enfoui dans des milliers de témoignages indépendants, faisant état d'effets physiques et physiologiques? Cette question là est également "de plus en plus criante".
A. Meessen
La Recherche, n 209, avril 1989
Si la notion de "must" n'avait pas déjà existé, il aurait fallu l'inventer à propos de ce livre: une revue de qualité sur la recherche d'éventuelles civilisations extraterrestres. Le sujet passionne le grand public depuis longtemps, et les astronomes s'y sont attaqués, de plus en plus sérieusement, depuis une trentaine d'années. Il était donc grand temps de faire sérieusement le tour des nombreux problèmes de tous ordres - astrophysique, biologie, biochimie, philosophie - que ne manque pas de poser un sujet qui a déjà inspiré depuis longtemps nombre d'auteurs de science fiction.
On est tenté ici de paraphraser Camus car, mieux peut-être que le problème du suicide, la simple question "sommes-nous oui ou non les seuls à penser dans cet Univers" pourrait bien décrocher dans un référendum la palme du sujet le plus intéressant de la philosophie.
Emmanuel Davoust s'est donné la peine de retrouver les nombreux articles publiés sur ce sujet et a resitué dans leur contexte les diverses questions abordées. Un travail rigoureux et sérieux; peut-être même un peu trop sérieux ... Un reproche qu'on pourrait faire en effet à E. Davoust, c'est une timidité peut-être excessive devant son sujet. L'origine de la vie, l'avenir de l'humanité, la sociologie des civilisations extraterrestres ou la recherche de signaux d'origne artificielle, tels sont quelques-uns des sujets traités dans ce livre passionnant et bien documenté.
Ciel et Terre, vol. 104, p. 145, 1988
Voici un excellent ouvrage comme nous devrions en voir paraître plus souvent originellement en langue française. L'auteur, Emmanuel Davoust, est un astronome professionnel actuellement en poste à la branche de Toulouse de l'Observatoire Midi-Pyrénées. Sa mobilité (naissance à Stockholm, études d'astronomie à Toronto, assistant à l'Observatoire de Besançon, différents longs séjours à l'étranger), ses travaux et ses activités de vulgarisation l'ont amené à présenter remarquablement dans cet ouvrage un regard moderne et nouveau sur un problème d'actualité astronomique, mais également d'une importance capitale pour la conscience de l'humanité.
Le point d'eau est le surnom donné, non sans humour, par les astronomes à la fréquence où ils pensent avoir le plus de chances de détecter un signal radio "artificiel" d'origine extraterrestre. Mais jusqu'à présent, et malgré des recherches de plus en plus sophistiquées, ce point d'eau est resté silencieux...
Comme le souligne dans la préface Jean Heidmann, autre astronome professionnel et vulgarisateur francophone bien connu, supposer que la vie est le résultat de processus évolutifs naturels du cosmos semble maintenant une hypothèse de travail rentable.
Emmanuel Davoust passe en revue avec compétence les différentes questions relatives à l'intérèt et au silence du point d'eau. Voici, à titre d'indication, les différents intitulés des chapitres de l'ouvrage:
les comètes et l'origine de la vie,
la dimension temporelle de la vie,
évolution et catastrophes,
notre avenir est-il dans l'espace?,
recherche de la vie au voisinage du Soleil,
recherche de svstèmes planétaires,
démographie des civilisations extraterrestres,
sociologie des civilisations extraterrestres,
OVNI et paléovisites,
stratégies de recherche des civilisations extraterrestres,
recherche de signaux d'origine artificielle,
le débat dans la société,
la place de l'homme dans l'univers.
L'ouvrage se termine par une présentation sommaire de notre galaxie et une riche bibliographie (13 pages!). Diverses illustrations en noir et blanc parsèment le texte que j'ai trouvé très agréable à suivre. Quelques coquilles typographiques non expurgées ne gênent en rien la compréhension de l'ensemble.
En conclusion, je considère qu'il s'agit d'un ouvrage recommandable à tous.
A. Heck
Les Cahiers Clairaut, n 44, hiver 1988-89
Le problème de la vie dans l'Univers est traité par Emmanuel Davoust sous tous ses aspects. Le titre du livre s'explique : les radioastronomes ont surnommé "le point d'eau" la bande de fréquences où ils pensent avoir le plus de chances de détecter un signal artificiel d'origine extraterrestre. Or, pour le moment, "silence au point d'eau". Mais la recherche dans ce domaine n'en est que plus attrayante ...
Le sommaire du livre montre l'étendue de l'enquête 1. Les comètes et l'origine de la vie. 2. La dimension temporelle de la vie. 3. Evolution et catastrophes. 4. Notre avenir est-il dans l'espace. 5. Recherche de la vie au voisinage du Soleil. 6. Recherche de systèmes planétaires. 7. Démographie des civilisations extraterrestres. 8. Sociologie des civilisations extraterrestres. 9. Ovni et paléovisites. 10. Stratégie de recherche des civilisations extraterrestres.11. Recherche de signaux d'origine artificielle. 12. Le débat dans la société. 13. La place de l'homme dans l'Univers.
On comprend la portée philosophique du sujet. L'humanité a eu beaucoup de mal à se faire à l'idée que la Terre n'était pas le centre du monde et la conviction est loin d'être unanime. Découvrir la vie hors de la Terre nous éviterait cette rémanente tentation de nous croire uniques pour ne pas dire excellents, sublimes, etc ... Ce qui rend la lecture du livre de Davoust fort plaisante.
Arts et métiers, janvier-février 1989
L'actualité rejoint notre propos : les Soviétiques viennent de lancer une mission sur Mars et Phobos, l'un de ses satellites : étude du sol et du sous-sol à la recherche d'une eau probable.... et l'on pense aux futures colonies artificielles implantées dans l'espace. Où est l'utopie? En attendant avril 89 et les résultats de cette mission qui dévoileront peut-être quelques uns des nombreux mystères de notre univers, nous avons le temps de lire cet ouvrage et de nous interroger. A partir d'une importante compilation d'informations sur le thème de la recherche de la vie dans l'univers, ce spécialiste des galaxies qu'est Davoust (astronome-adjoint à l'Observatoire Midi-Pyrénées à Toulouse où il poursuit des recherches sur les galaxies en interaction à partir d'images obtenues au pic du Midi), applique la rigueur de sa démarche scientifique à cette étude. il ouvre le débat et éclaire des questions aussi passionnantes et fondamentales que sommes-nous seuls dans l'univers ? d'un regard moderne et prospectif. Vaste aventure à lire et peut- être à vivre par les générations à venir.
Ciel Et Espace, Octobre 1988, p. 14
Savez-vous ce qu'est "Point d'eau" ? Dans le jargon des radioastronomes, le point d'eau est la bande de fréquence où ils pensent avoir le plus de chances de détecter un signal artificiel d'origine extraterrestre ! C'est de cette image que s'est inspiré Emmanuel Davoust pour présenter ce livre exemplaire, synthèse des recherches et des questionnements sur l'existence de civilisations extraterrestres ou, au sens large, de la présence de vie dans l'Univers.
Un sujet difficile traité ave brio par cet astronome de l'Observatoire de Toulouse spécialiste des galaxies en interaction. Cette seule question " Sommes-nous seuls dans l'Univers ?" est chargée d'une telle connotation émotive qu'il est difficile pour un auteur de conserver le recul nécessaire, ici celui de l'analyse scientifique, de garder la tête froide pour passer en revue toutes les données du problème, examiner en détail les fantastiques horizons qu'entrouvre l'astrophysique moderne. Simplement, sans termes techniques, l'auteur passe en revue les différents stades d'évolution cosmique, organique, prébiotique, biologique primitive et enfin avancée où les astronomes ont un rôle majeur à jouer.
Ce simple tour d'horizon, cette promenade dans les comètes, à la surface de la Terre primitive, sur Mars, Titan, au sein des disques protoplanétaires et autres scènes du grand théâtre universel situent l'enjeu de la grande quête du vivant. Au fil des pages, comme défilent les visions des mondes, se réduit la question "Y a-t-il de la vie dans l'Univers ?", pour laisser place à la perspective du "contact", de la détection de signaux d'origine extraterrestre. Jean Heidmann, l'un des pionniers français de ces recherches, ne dissimule pas dans sa préface l'enthousiasme qui anime les auditeurs du "point d'eau". S'il reste silencieux, c'est que nous ne savons pas écouter !
Une seconde partie de l'ouvrage d'Emmanuel Davoust peut surprendre. Ces chapitres s'intitulent "Sociologie des civilisations extraterrestres", " Le débat dans la société", "La place de l'homme dans l'Univers". On est habitué depuis le fameux Patience dans l'azur d'Hubert Reeves (Atom of Silence dans sa version américaine !) à ce que les astrophysiciens posent aussi les termes de leurs recherches en choix de société. Et l'on comprend très rapidement que des discussions naissent ou disparaissent les crédits d'études, les temps de télescopes et tous ces moyens nécessaires à l'écoute de voix dans le silence. On comprend combien le soutien populaire est un facteur décisif dans le choix des voies de recherche. Avec talent et humour, dans un parfait style "d'accroches" journalistiques, fabuleusement documenté (la bibliographie mérite à elle seule l'achat de l'ouvrage), Emmanuel Davoust conduit son sujet avec la maîtrise du parfait vulgarisateur qu'il est. Son enthousiasme est contagieux : à quand le second livre ?
A. C.
Europe and Astronomy, Nov 88/Feb 89/May 89, p. 226
L'auteur de ce livre, Emmanuel Davoust, est astronome professionnel spécialiste en galaxies à l'Observatoire Midi-Pyrénées à Toulouse. Dans "Le point d'eau" des questions fondamentales sont posées: sommes-nous seuls dans l'univers ou est-ce qu'il existe quelque part la vie extraterrestre ou même des civilisations extraterrestres? En traitant ce thème, divers autres points intéressants sont abordés: le rôle des comètes et les météorites dans la propagation de la vie, l'évolution de l'univers et de la vie, la recherche spatiale et la colonisation de l'espace, d'autres systèmes solaires, les places où des civilisations extraterrestre pourraient être situées et comment détecter ces civilisations et quel signaux "ils" pourraient envoyer. Ce sont notamment ces fréquences qui sont restées silencieuses que les astronomes appellent "le point d'eau". Ce livre traite aussi les projets de recherche qui sont en cours, la question des OVNIS et l'attitude de la société à l'égard d'une éventuelle vie extraterrestre. L'auteur conclut avec des réflections sur la place de l'homme dans l'univers. Ce livre qui évite des approches trop techniques et qui éclaire aussi le coté plus philosophique du sujet est sans aucun doute une lecture passionnante pour un public très large.
Carl Vandaerle
Le Journal des Astronomes Français, n 34, janvier 1989, p. 4
Emmanuel Davoust a réussi le pari difficile d'écrire un livre passionnant et documenté sur un sujet qui dérange le plus les astronomes dans leurs rapports avec le public : la vie dans l'Univers. Silence au point d'eau est agréable à lire, clair et complet. Tous les aspects du problème sont abordés sans complaisance et l'on sent que l'auteur a été maintes fois confronté aux préoccupations et aux questions du public à travers son approche multiforme du problème de la vie terrestre et extraterrestre. Malgré quelques imprécisions scientifiques de détail facilement corrigeables lors d'une édition ultérieure, l'ouvrage devrait être lu par tous les professionnels de l'astronomie ; ils y trouveront une documentation remarquable et un grand nombre d'éléments de réponses aux grandes interrogations des hommes de l'ère spatiale. Il doit aussi être lu par tous les curieux des choses de la vie : à travers cette recherche de civilisations extérieures universelle, ne pose-t-on pas les vraies questions concernant l'avenir des espèces sur notre propre planète ? Souhaitons grand succès à cet excellent livre et espérons que, pour le prochain tirage, l'éditeur aura rectifié les quelques erreurs de pagination et de légendes qui atténuent un peu l'enthousiasme de la lecture.
Jean-Louis Heudier
Science et Avenir, 1988
Le "point d'eau" est une bande de fréquences que les astronomes se réservent pour leurs éventuelles communications avec les extra-terrestres. Cette fréquence-clé a été choisie dans le domaine des ondes radio car le bruit de fond galactique est minimum dans cette gamme. Pour le moment, à part des sursauts radio provoqués par l'entrée du satellite Io dans la magnétosphère de Jupiter, aucun signal exceptionnel n'a été enregistré. Le silence règne désespérément sur le "point d'eau". Mais les astronomes ne se découragent pas. Au contraire, ils multiplient et diversifient leurs tentatives pour communiquer avec d'éventuels extra-terrestres : des messages gravés sur des plaques d'aluminium sont déposés sur les planètes lors des expéditions spatiales; les astronomes essayent de mettre au point une langue cosmique universelle baptisée "Lincos"; des signaux codés comportant la formule de l'ADN, la position de la Terre dans notre galaxie ou le nombre d'êtres humains sont envoyés par des télescopes vers des amas globulaires ; "Big Ear", le radiotélescope de l'université de l'Etat de l'Ohio, se consacre entièrement à la recherche de signaux à la fréquence du "point d'eau". Il n'y a pas si longtemps, la recherche de la vie extra-terrestre relevait encore de la science-fiction. Aujourd'hui, cette préoccupation est reconnue comme légitime par l'Union astronomique internationale.
Silence au point d'eau est la première enquête scientifique sur le thème si controversé de la vie extraterrestre. Son auteur, Emmanuel Davoust, est astronome à l'observatoire Midi-Pyrénées à Toulouse. Ce livre est écrit dans un style clair et agréable cependant qu'il aborde des sujets aussi complexes que l'origine de la vie et la formation de l'Univers. Un ouvrage à conseiller vivement à tous ceux qui désirent parler des "petits hommes verts" en connaissance de cause.
Services Documentaires Multimédia
Ce livre, sur la question passionnante de la vie dans l'univers, se distingue par la richesse de sa documentation et la rigueur de sa démarche scientifique. La simplicité du langage le rend cependant accessible à un large public.
www.amazon.fr/exec/obidos/ASIN/2877170020/artvisitwww-f-livres-21/402-6896062-1841765
Choice (Middletown, CT, USA, november 1991)
Davoust, an astrophysicist at the French Midi Pyrenees Observatory, originally wrote in French; this version has been well translated by his wife. He has placed philosophical quotes at the start of each of his 13 chapters. He is a thinker who sets forth here the many facts and conclusions linked to the question "Is there extraterrestrial life in the universe?" As he shows, this is an increasingly popular topic among layman and scientists, who will meet in a conference on "Frontiers of Life" in France in October, 1991. After an interesting foreword by astronomer Harlan Smith, Davoust discusses observational facts from comets and life on Earth, through space probes, to radio surveys for possible extraterrestrial signals, and covers clearly the Gaia theory, formation of planetary systems, UFOS, and NASA's SETI Program, all with a total of 26 good illustrations and no formal math. He concludes that the basic question cannot yet be answered, but bioastronomy is worth further study. The demonstration of scientific reasoning is as good a in David Layzer's Cosmogenesis (CH, May'90). A 16-page bibliography but no index. Highly recommended for all readers.
T. Page
NASA Johnson Space Center
Space science reviews, 62, p. 210, 1993
A nicely readable and well-written book on the problems of extraterrestrial intelligence (the only science without a subject matter, according to Harlan Smith's lucid foreword), The book describes in three chapters problems of life on Earth, Life in the Universe, and Intelligent life in the Universe. It centers on the possibilities of the existence and detection of extraterrestial intelligent life. The title refers to the window in the water spectrum used for detecting signals from outside. Many books have been written on this topic, but the mild humour of this one and the good scientific level of its contents give it a special flavour.
Cornelis de Jager
Laboratory for Space Research at Utrecht
Astronomy, January 1993, p. 94
Davoust, an astronomer at France's Observatoire Midi-Pyrénées, asks one of the biggest questions in the whole field of astronomy: Are we alone? He provides no definitive answer, of course, to the extraterrestrial life question. But besides writing an interesting book that reviews the requirements for life in the universe and the chances we'll find it elsewhere, he also explores what this search for life means to us on Earth. Unlike the bland rehashes often served up on the subject, this book has a personal tone that gives it interest for anyone who has already delved into the field. lt finishes with a 14-page bibliography (yay!) but lacks an index (boo!).
The Observatory, vol. 112, p. 131, 1992
This book is concerned with the usual pre-Copernican view of the origin of life and with the possibility of space travel and space communication between intelligences at a distance apart. I cannot assert that every page contains a serious error, but those which caught my eye do. Page 5 is a noteworthy beginning. It starts at its top by being three orders of magnitude in error for the distance to which an interstellar particle of bacterial size and density can be driven by radiation pressure over the age of the Galaxy. It continues with an elementary calculation of the rate at which the Earth acquires meteoritic carbon that is internally inconsistent to four orders of magnitude. And, still on the same page, we are told that largish meteorites are ablated only to a shallow depth of a millimetre, which I will leave to those who understand such things to comment on.
On page 8 the author fails to cross successfully over the pons asinorum which awaits all those who seek to play in the 'origin of life' game. The pons asinorum concerns the claim, itself of dubious provenance, that amino acids found in meteorites are racemic, not the L-type in biological systerns. Therefore, the tyros who fall off the bridge say, the amino acids in meteorites are not of biological origin. The trap is that amino acids of L-type tend, when fossilized, to go racemic. This fact, well-known to anthropologiste, is used to date fossilized bones on time-scales of a few hundred thousand years.
With these elementary mistakes in the bag as it were, one would not expect the author to succeed in calculating the relativistic clock paradox successfully. Nor does he. Although giving numbers purportedly to three-decimal accuracy, Table 5 on page 63 is ludicrously wrong, the numbers in the last row of the table being three to four orders of magnitude in deficit of the correct values, a margin of error which appears to be par for the course.
The situation would surely have been improved, at least in a first approximation, by employing some impecunious graduate student to remove the grosser mistakes. And there must surely be professors at the prestigious institution which published this book who could manage the clock paradox correctly. As Shakespeare might have said: This book, and the death of a dear friend, would go near to make a man look sad.
Fred Hoyle
I did not send a letter of protest to this nasty reviewer, who obviously has an axe to grind (see the New Scientist review). Table 5 is correct (see my paper in American Journal of Physics, 63, 221, 1995). I might be wrong on the question of racemic amino acids in meteorites (admittedly not my field), but the other alleged errors are disputable on the ground of the underlying assumptions.
Physics Today, March 1992, p. 70
Contemplation of life elsewhere in the universe is common to almost all cultures and ages. In ours, discussion of extraterrestrial life involves much more than scientific issues, and for better or worse, opinions are shaped by everything from supermarket tabloids, science fiction, the global economy, religions and intellectuel orientation and attitudes about technology, not to mention ambition and turf protection in the sciences.
The Cosmic Water Hole, a translation from the French, is a book for lay audiences concerning the existence and search for extraterrestrial life. Emmanuel Davoust, an astronomer who studies galaxies at the Observatoire du Midi-Pyrénées, surveys current views of the origins of life on Earth and extrapolates to future times and other worlds. Following conventional wisdom, which asserts that evolution and Copernicanism require the ubiquity of life, the author discusses panspermia, the idea that life on Earth began extraterrestrially, and the prospects for our eventual colonisation of space, whether driven by curiosity or catastrophe.
Important themes thread the work. First is the connection between life on Earth and geologic and cosmic activity: that life itself has modified the atmosphere significantly, subsequent to the subsidence of volcanic activity. As a counterpoint, the precariousness of life brings up topical issues, such as global warming and the runaway greenhouse effect, along with the near consensus view that an astronomical catastrophe played a key role in the demise of dinosaurs and the subsequent hegemony of mammals.
A second theme is the punctuated manner of scientific progress, discussed through examples of both the misadventures of science (claims of canals on Mars and other spurious discoveries, problems with science in the US space program, debate over SETI) and the successes (understanding of stellar evolution, the general context of big-bang cosmology, studies of Antarctic meteorites, existence of protoplanetary disks, prospects for discovering extrasolar planets). The politics of science is illustrated through the debate over whether searches for signals or other manifestations of extraterrestrial intelligence are worth pursuing. This latter discussion, which reveals the difficulties of communication and concensus among ourselves, is a sobering antedote for heady conjectures about two-way communication with other civilizations.
The book discusses past and current attempts at detecting signals from extraterrestrial sources, beginning with Frank Drake's OZMA in 1960. Detection of and contact with extraterrestrial life require a hierarchy of conditions to be satisfied, the book-keeping for which is contained in the venerable Drake equation. A short description of the largest SETI project under development, NASA's Microwave Observing Project, to commence in the mid-1990s and proceed into the next century, helps introduce the notion of the waterhole, a microwave band containing spectral lines from atomic hydrogen and hydroxyl molecules. The book finishes with a brief discussion of what it means that human beings exist on this planet, given the physical requirements for our existence, and the likelihood that Earth-like conditions may be produced elsewhere. The impact for us of searches outward is posed in terms of the possible shock of contact and contrasted with the inner glow we might feel if we knew that the universe was generally inhabited rather than empty.
The style of The Cosmic Water Hole is broadbrush. As such, the author leaves out details that would be of interest to more technically inclined readers. The author compensates for this lack of depth by weaving into the discussion much of the conventional wisdom about the physical universel including big- bang cosmology and the arrow of time. The reference list serves as a reasonable gateway to the literature, but the book suffers from the absence of an index. A glossary of terms would have been helpful, particularly for lay readers. In places the translation is coarse, and some of the quantitative aspects are inconsistent in different parts of the book.
James M. Cordes
Cornell University
Journal of the British Astronomical Association, vol. 101, n 6, p. 361, 1991
Is there anybody out there? Or is planet Earth a lone oasis of life surrounded by a vast, uninhabited universe? Emmanuel Davoust does not pretend to know the answer to these fondamental questions, but he leaves the reader in little doubt that we humans should endeavour to find out.
Davoust is an astronomer at the observatoire Midi-Pyrénées and, throughout the book, he concentrates on the astronomical aspects of the subject rather than the more sensationalist approaches of certain popular authors. Indeed, Davoust dismisses all such 'revelations' about extraterrestrial visitors as nonsense, apart from a brief look at the surprising knowledge of the Sirius system possessed by the nomadic Dogons of Mali.
Although the author admits the possibility that we are the only intelligent life form in the universe, he justifies his optimism in the existence of extraterrestrial civilisations by suggesting that the evolution of life is a normal stage in the evolution of the universe. As the author says, 'each step in the development of our knowledge has been a lesson in modesty' since the days when humans thought earth lay at the centre of the universe.
The book seems to be aimed at a general readership, and any complex technical terms are usually clarified in brief footnotes, although some of the sentences are not easy to understand. There are also 27 black-and-white illustrations, though these add little to the text.
The book follows a logical pattem of analysis by starting with chapters on the origin and evolution of life on Earth. After examining the question 'Is our future in space?', Davoust goes on to examine the possibilities of life elsewhere in our solar system and in other nearby planetary systems.
The second half of the book deals with the scientific debate over the presence of other intelligent life in the universe and is necessarily more speculative since there is very little hard information to go on. If there is intelligent life out there, how can we detect it? And why haven't they contacted us? Davoust summarises past efforts to search for signs of extraterrestrial life and examins the scientific debate surrounding these questions, though he does not mention the \$ 100 million search to be initiated by NASA next year using its Deep Space Network of radio telescopes.
Indeed, this is one of the problems with the book. It was originally published in 1988 and, although some effort bas been made to update this translation, it still struck this reviewer as sometimes being too French orientated and rather showing its age. A few minor errors surfaced, such as a reference to Apollos 11 to 16, and an emphasis on hydrochloric rather than sulphuric acid in the atmosphere of Venus, but these were rare.
On the plus side, having covered a complex subject with a broad brush, the author has provided a comprehensive bibliography to enable follow-up research, though most references predate 1985. Despite these minor reservations, I would recommend this book as a useful, thought-provoking introduction to the subject of the search for extraterrestrial life.
Peter Bond
Peter Bond is a freelance writer who specializes
in astronomy and space exploration.
American Journal of Physics, 60, n 7, p.670, July 1992
Consider a scenario for research at the frontiers of a scientific discipline, particle physics, for example: A new particle is predicted by an elegant (or not-so-elegant) mathematical scheme. Its observable properties are specific within reasonable limits. Experimenters propose an ensemble of experiments for its discovery, run simulations of the experiments, and assess the probabilities of success with a given technique. If detection seems feasible, equipment is constructed, experiments are run, and observations are made. The particle is either discovered or more rigorous constraints are put on its properties. While admittedly a gross idealization, this scenario does convey some of the character of what most of us consider hard science.
Contrast this scenario with the Search for Extraterrestrial Intelligence, or SETI: The specifications of what we are looking for are far more elusive. We have no idea what form alien life might take and no universally agreed-upon formula for intelligence. Because the interstellar distance scale makes field exobiology impossible, we resign ourselves to listening for radio messages from other civilizations, assuming that TV and radio broadcasting is the hallmark of an intelligent race. Even so, we have little more than the barest idea of what the signature of an artificiel signal will be. What frequency? What modulation scheme? What signal strength? To confound matters, since we have no firm confirmation of any planetary systems besides our own, we do not even know in which direction to look.
No wonder that the science of SETI, which dates at least as far back as the seminal paper by Coconi and Morrison in 1959 (Nature 184, 844), is long on ideas and short on facts. SETI literature consists mostly of articles on what to look for and how to look, along with a host of argumentative papers on the question of whether SETI has any scientific program worth pursuing at all. Empirically, the skeptics seem to have a point. Over the past 30 years, more than three dozen radio searches have been undertaken, none with any success so far. But even the skeptics admit that the search space is enormous and only a small portion of it has been monitored with any care.
Emmanuel Davoust's slim volume, translated from the French, attempts to provide a review of this contentions field, up-to-date as of the late 1980s. For the nonspecialist or the educated layperson, it should provide a reasonable guide to some of the conventional wisdom and burning issues of contemporary SETI research. While its approach is as balanced as any in this field could be, it also reflects Davoust's own personal preferences, as well as his regional perspective as a European astronomer.
The book tackles the SETI problem in three sections. The first four chapters on the origin and evolution of life aim at establishing a motivation for the search. Life, we are assured, is a natural phenomenon, and is likely to arise spontaneously wherever conditions are right. The problem is defining what those right conditions are, and where to look for them. Surely one of the conditions is that, at least for carbon-based life, water must exist in liquid form. Thus the search for life involves the search for cosmic water holes (one of two meanings inherent in the title), oases like planet earth itself.
Davoust's second section illustrates how difficult it is to find such oases. The last two decades of planetary exploration have turned up only two sites where liquid water may exist in our solar system: Europa, a moon of Jupiter, and Titan, a moon of Neptune. In both cases, our reasons for suspecting liquid water are primarily theoretical, not empirical, and the Galileo and Cassini missions to the gaint planets may eliminate even these last outposts. Beyond our solar system there is only marginal evidence that other planetary systems exist. The difficulties are many. First, modern detection equipment is pushed to the edge trying to detect the presence of small reflecting bodies near large luminous stars. Second, habitable planets around solar-type stars are likely to take at least a year or two to orbit. Dedicated planetary detection programs thus need long time-baselines to produce results, while the lifetimes of astronomers are relatively short and their careers even shorter. Finally, though planets seem to be a likely outcome of star formation, the theory and observation of protoplanetary systems is in such a rudimentary form that savvy estimates of how many habitable planets there are in the galaxy vary by at least ten orders of magnitude.
Despite this, the question of whether we are alone compels many to undertake the search. Davoust's final section centers on the techniques of that search, including a useful discussion of how best to conduct it. While an intelligent society might leave traces of its existence all across the electromagnetic spectrum, the most likely place to look for a broadcast seems to be in a band of frequencies between 1400 and 1800 MHz. Here, other sources of natural noise are at a minimum, and since these frequencies lie between those emitted by interstellar hydrogen atoms and interstellar hydroxyl radicals, which combined make water molecules, astronomers call this region the "water hole." Davoust includes a brief review of the extent to which past SETI projects have explored the radio water hole, and what the prospects are for future exploration.
What can one conclude, if one is to come to any conclusion at all? It seems that not much has changed substantively since Shklovskii and Sagan's compendious overview of the field, Intelligent Life in the Universe, in 1966. There are more entries in Davoust's bibliography, of course, and his text describes new hopeful techniques in the search for extraterrestrial planets and vastly improved multichannel receivers to carry on SETI itself. But the evidence is as scanty and as ambiguous as ever.
Davoust's book can be recommended, then, not for its newness, but for its completeness and conciseness. For those preparing to teach a SETI course, it hits all the high points. As a text, however, its pace is a bit too hurried, and its lack of an index a fatal and inexcusable flaw. For classroom use, Goldsmith and Owen's excellent The Search for Life in the Universe, which will soon be published in a second edition, remains the textbook of choice. As for SETI itself, the last word --- or rather the first word -- has not yet been received.
Laurence A. Marschall
Laurence A. Marschall is Professor of physics at Gettysburg College, where he
does research on young stars in clusters and in binary systems. He is the
author of The Supernova Story and a contributing editor of The Sciences.
Science books and films, August/september 1991, p. 167
Among the most fascinating topics to space explorers specifically and the scientifically curious in general are the important questions concerning the origin of life and the possible existence of extraterrestrial life. Even though, as the author quotes others, "Exobiology is the only science without a subject matter," the ideas presented in this book are worth thinking about, as the magnitude of their potential importance warrants such examination. The various chapters cover a wide variety of subjects, including the origin of life on Earth, the search for other planets, and how to detect signals from extraterrestrial civilizations -- if they exist. The author also discusses plans for future space exploration and colonisation by our species and the philosophy of why the existence or nonexistence of extraterrestrial life will profoundly affect our planet. This book includes a few technical errors and sometimes promotes conjecture as fact. It is also heavily oriented toward the European viewpoint of the subject, which is fine, as it highlights lesser known efforts, but it does tend to overlook other important American studies. Generally, the text is a good examination of a complex subject. It is readable, interesting, and thought provoking and should be considered by all those interested in the question of life on or off the Earth.
Gary W. Finiol
Colorado Department of Health, Denver, CO
New Scientist, 28 March 1992, p. 48
By a strange irony, the subject most guaranteed to raise passions among astronomers today concerns something that may not exist at all: extraterrestrial life.
The planetary researcher Carl Sagan, for example, passionately believes in this quest to answer "one of the most basic questions there is". On the other hand, the mathematician Frank Tipler is so convinced that aliens cannot exist that he questions the motives of those who are trying to seek out alien life: Sir Martin Ryle, a former Astronomer Royal, was so worried that contact with a superior intelligence would destroy the Earth's culture that he argued for an international ban on scientists sending out deliberate messages to the stars.
As a result, it is difficult to find a book that gives a balanced account of the case both for and against ET's existence. Some authors have clearly nailed their colours to the mast, setting out to convince readers that theirs is the only sensible point of view. But many other supposedly even-handed accounts have reflected -- subconsciously, no doubt -- their author's beliefs.
That is why I welcome Emmanuel Davoust's contribution. It breaks little new ground because there have been no important developments in the field for several years. What is important to me is that by the time I reached the last page of the appendix, I still had no idea whether Davoust believes in extraterrestrial life or not. From this book, you can soak up both sides of the argument without worrying that the subconscious persuaders are at work.
Along the way, Davoust enjoys setting out all the main contributions to the debate, backed up by a bibliography so full that it would be useful even to the most professed expert on extraterrestrial life. (But why, oh why, is there no index?)
The origin of life is still a mystery, even on Earth where we can study living organisme. Most scientists believe that gases in the planet's early atmosphere were welded together to form simple organic molecules, and that these formed into cells in the "primeval soup" of the first oceans. But some researchers have suggested that comets may have had a crucial role. They may have dumped organic molecules onto the young Earth, or possibly even delivered living cells te our planet. So we do not know whether life would arise spontaneously on another planet like the Earth.
Even if some simple cells do appear, would they naturally evolve into multicellular and then self-styled intelligent beings? It is over to the evolutionists here, another hot area of debate among the specialists.
Astronomers bring in their own uncertainty when we start asking how many stars have planets like the Earth. They cannot detect any with today's equipment but that does not stop them from stating just how common Earth-like planets are in our Galaxy.
In 1946, Enrico Fermi put forward the strongest argument against extraterrestrials: "If they exist, where are they?" Our Sun is a latecomer in the Galaxy as a whole so, if other civilisations are common, there must be many that are older than ours, and could undoubtedly master the problems of interstellar travel.
Davoust takes the trouble to dismiss briefly UFOs and other supposed signs of visitors from space, and entertains us with a selection of the possible reasons why extraterrestrials, if they exist, might be avoiding us. They might, perhaps, be galacto-greens and not want to pollute their environment by launching spacecraft. Or perhaps they are so superior to us that they are already here, and exist in a form that we do not recognise. My favourite suggestion is that the aliens are watching the primitive human race from a distance, for education and entertainment: "They do not enter for the same reason that we keep out of nature preserves on the Earth."
More fascinating than the sociology of a putative extraterrestrial race are the sociological effects of the search for ET on human civilisation. It has been undertaken mainly by highly motivated individuals with little funding. As the debate bas ebbed and flowed in the US, Congress has twice cut off NASAs modest funding of the search for radio waves from alien civilisations and twice restored it. These radio searches have given the book its title: according to 20th-century Earthlings, the best frequency for communicating with other planets is near those emitted by water, which defines a meeting- place analogous to the water hole in the savannah.
In 1966, 34 per cent of the American public believed in extraterrestrial life. A poll of college students in 1981 showed that 90 per cent believed Earth was not the only place where intelligent life exists. Forty-two per cent thought we should try to communicate with intelligent beings on other planets. This figure dropped to 38 per cent for Protestants in the sample, as compared to 50 per cent for students with no religious beliefs.
While we wait patiently for the first contact with ET, the search for extraterrestrial intelligent beings is certainly proving to have something to tell us about own race.
Nigel Henbest
Science Reporter April 1992
Astronomers often find it hard to believe that of the billions and billions of stars in the universe only our sun should possess a planet endowed with life. They have reasons to be skeptic, for if the appeareance of life on earth was a chance event, it is unlikely that it would be confined to our planet only. Some believe there could be several million stars with planets having the right conditions for life to appear and evolve. Does it mean that we are not alone in the universe? Can we find out if life exists elsewhere in the cosmos ? In this delightfully written book, Emmanuel Davoust, an intemationally known specialist on galaxies, explores these provocative questions in the light of our existing knowledge of prebiotic chemistry, palaeontology, and astrophysics.
The subject of extraterrestrial life, which until recently seemed to be reserved for philosophers and writers of science fiction, has been opening up to astronomers in the past 20 years or so. One of the first questions astronomers have been trying to sort out was whether life on earth itself had an extraterrestrial origin, as suggested by some, like the British astronomer Fred Hoyle. Could it be that primitive life appeared first in the cold depths of space and carried to earth by extraterrestrial visitors like comets and meteorites?
"Far from giving any conclusive answers, research in prebiotic chemistry only poses more questions about life and its origin. Life is not ready to give up its mystery. Analyses of meteorites and dust which have landed on Earth have turned up no obvious traces of extraterrestrial life. Knowing that the interstellar medium is hostile to life, I tend to prefer spontaneous generation to the panspermia hypothesis."
Despite current uncertainties about life's origin, says Davoust, we must not rush into explanations "that depend on extraordinary interventions." Whatever its temporal or spiritual nature. We will find the answer at the telescope, he asserts.
Whatever its origin, the history of life on earth is now fairly well understood thanks to biology and palaeontology. But natural selection is still not accepted by many as the driving force of evolution, although there is almost unanimous agreement that physical conditions played an important role in the maintenance and evolution of life.
"If the Earth were smaller, its gravity, would be weaker. But Earth could not be much lighter. If its mass were less than 70 percent of what it is, Earth would no longer retain its atmosphere. However, if Earth were more massive, gravity would force animals to the ground and they would have to crawl. To pull their heavy bodies, they would need a large skeleton, very solid limbs, a thick neck, and a powerful heart. But such superficial differences should not breed life fundamentally different from what we know. We can imagine that strong gravity would reduce the activities of life forms, especially their creativity. The development of intelligence and the evolution of culture would slow down."
These are at the moment mere speculations. But they also point to the fact that if life exists elsewhere, its form will certainly not be the same as on our planet. Once it is accepted that life may exist elsewhere, the next question would be: Where to look for it?
"The first place for us to search for life in the universe is, of course, our own solar system. However, despite all that has been written about Selenites, Martians, Venusians, and Saturnians, the blue planet -- Earth -- seems to be the only one to harbor evolved life. No geometric structure has ever been detected on the surface of another planet. No exceptional radio signal has ever been received by our radio telescopes, other than the radio bursts produced by the Io when it enters Jupiter's magnetosphere. We must therefore look for elementary forms of life in the solar system. We shall see that, although most of the planets offer little hope, some of their natural satellites could contain some life forms similar to those on the primitive Earth."
Outside our solar system the search for other planetary systems in our Galaxy can contribute important data to our search for life in the universe. "If planets are very rare, the exceptional character of life on Earth will be emphasized. If on the other hand, all stars are surrounded by planets, asteroids, comets, or disks of dust, we will be encouraged to pursue our quest. Statistical information on the number of planets around stars of different kinds would allow us to better target our search for life in the universe."
But discovering planets does not mean that we have found life. Even if we soon discover planets around other stars, the detection of signs of life may be out of reach for another decade or more. The search for life outside the solar system remains an apparently utopian undertaking.
The many uncertainties notwithstanding, there still remains a feasible course of action for astronomers looking for extraterrestrial life to start listening to the universe in the hope of detecting radio signals of artificial origin.
"Radio waves offer a number of advantages. The background noise in the Galaxy is minimal in the domain of radio waves. Since we will have to detect a signal whose power will be attenuated by the distance it travels, this is an important advantage. There are "key" ranges of radio frequencies in which radio astronomers often observe for astrophysical purposes. They have nicknamed "the water hole" a frequency band between 1,400 and 1,800 megahertz (i.e., a wavelength of 18 to 21 centimetres) of natural emissions of the components of water: hydrogen and the hydroxyl radical (OH). Hydrogen is the most abundant element in the universe, and neutral hydrogen atoms radiate spontaneously at the wavelength of 21 centimetres. Any civilisation that has started exploring the universe must have detected this universal radiation."
Astronomers have been using these frequencies to search the skies for more than two decades in the hope of detecting a signal from some alien civilization, without any success. But that's not surprising, for the number of possible targets is large, and so far we have hardly listened at all. If success ever comes, it will usher in the last stage of the Copernican revolution, in which Earth lost its privileged status as the centre of the universe. Discovery of life elsewhere will dispossess Earth of its only other remaining distinction -- it will no longer be the only abode of life in the universe.
While many readers may not agree with Davoust's conclusions and projections for the future, this very well-written and highly informative book will provide them enough food for thought.
Biman Basu
Astrophysics and Space Science, 201, 161, 1993
The author considers life in the Universe from a number of angles and brings together numerous researches and speculations on a range of topics: Part 1: Comets and the Origin of Life, Evolution and Catastrophes and is our future in space. Part 2: Considers the search for life in our solar system and the search for other planetary systems. Part 3: Consists of a series of speculations about intelligent life in the Universe and their implications for our search strategies.
The book is itself a review of many hypotheses and speculations so the depth of coverage is limited. However the author brings together a greater range of speculations in one place than in any other book I have read on this area. I was pleased to see the credit given to amateur researches on SETI. I was also impressed that the author took on the thorny subjects of UFO's and Paeleovisits logically rather than dismissing them offhand.
I had few criticisms of the book, the only significant one being that the author does not always indicate the relative strengths of the hypotheses under review. This makes it a little difficult to see the wilder speculations among the established hypotheses.
Overall I would recommend this book to any amateur astronomer or students who need a readable, quick overview of the range of researches and speculations on life in the Universe. The bibliography provides plenty of avenues into more detailed reading for those who wish to follow up specific topics. The book provided me with many hours of stimulating thought and much material for entertaining arguments with friends.
Chris Jordan
Nature, 354, 28 November 1991
Next year, on Columbus Day, US researchers will begin a ten-year, $100-million programme to search for extraterrestrial intelligence. Davoust, a French astronomer, provides a very readable popular description of this and other efforts to detect radio transmissions made by extraterrestrial intelligence. But this book marks an important change from the vast numbers previously published in this genre: he admits that the search will probably fail because such intelligence probably does not exist. It is refreshing to see an astronomer join the biologists, who, according to the distinguished biologist Ernst Mayr are "... almost uniformly skeptical of the probability of extraterrestrial intelligence".
Davoust accurately expresses the force of the Fermi paradox: if extraterrestrial intelligences exist, why are they not already here? Even our primitive rockets can reach the stars in 105 years. Computer experts (such as Hans Morovec in Mind Children, Harvard University Press, 1988) tell us that within 50 years we should be able to make an intelligent computer capable of self-reproduction. The combination of our primitive rockets with a payload of self-reproducing robots would be sufficient to explore and colonize the Galaxy. With such a probe, this would take only a few hundred million years to accomplish. We know that if our own evolution is typical, then most civilisations in our Galaxy must have arisen billions of years ago. Thus most experts now admit that civilisations so advanced would be here if they wished to come.
Davoust devotes an entire chapter to possible sociological mechanisms that might prevent interstellar travel. But I think he neglects the crucial point: virtually any motivation we can imagine that would lead extraterrestrials to engage in interstellar radio communication with us would also motivate them to engage in interstellar travel. The above-mentioned radio search is for civilizations wanting to contact us, for our equipment is not powerful enough to eavesdrop. Although we do not know the motivations of all advanced civilizations, we thus do know the motivation of the civilisations we search for. But robot probes would achieve the aims of these civilisations much better than radio signals. For example, probes can contact civilizations that are not listening, that is, those that do not have radio technology. Probes can be used to explore and colonize uninhabited systems.
Carl Sagan has argued that "perhaps [extraterrestrial intelligences] just don't care to strip-mine every site in the Galaxy". In his books, Sagan himself shows that all communication has costs; as he repeatedly says, the bare fact of a received signal from an alien civilisation would change ours drastically. But the purpose of any communication is to change the knowledge of the person to whom the message is directed: to colonize a mind with memes (complexes of ideas). There is no fundamental distinction between colonisation with memes and colonisation with genes. But in the case of genes, it is at least possible to limit colonisation to uninhabited systems. Meme colonisation necessarily occurs in inhabited systems, and necessarily extinguishes other memes. It is necessarily imperialistic.
Davoust discusses at length the anthropologist Ben Finney's comparison of interstellar colonisation with historical human migrations. Finney claims: "No specific migration has ever gone unchecked. Ecological barriers, the slowing or cessation of innovation, flagging motivation, or the opposition of those in the way of expansion have ... stopped every ...colonisation movement so far."Finney infers that interstellar colonisation would stop short of the entire Galaxy.
But Finney's own data indicate the opposite.The analogue of the ecological-innovation barrier is the lack of a suitable robot probe, and our own civilisation is near to overcoming this. With a probe, there is no natural barrier to stop a colonizing species short of the entire Galaxy.By definition, there is no opposition of those in the way for the first intelligent species to evolve.Finney's data indicate that motivation flagged once the other three barriers made further expansion difficult.Finney's picture of the evolution of Polynesian society is exactly what John Barrow and I predicted (The Anthropic cosmological Principle, Oxford University Press, 1986) would be the behaviour of a colonizing extraterrestrial intelligence: an r-strategy characterized by rapid expansion in numbers would be typical of those at the frontier, whereas a K-strategy characterized by fluctuations in numbers around an equilibrium would be typical of those in the interior.
Those engaging in radio searches like to argue that absence of evidence is not evidence of absence. (Davoust repeats this slogan at least twice.) I totally agree, but we have evidence: extraterrestrial intelligences are not here. We just have to interpret this fact. Most astronomers cling to a belief in extraterrestrial intelligence against the evidence because of a philosophical principle: the copernican idea that our place in the cosmos must be completely typical. But we know this idea is false. The Universe is evolving: the cosmic radiation shows that there was once a time when no life existed because it was too hot. Thus, our place is atypical in time. In particular there must be a first civilisation, and it happens to be ours.
Davoust does not mention Brandon Carter's argument, based on the weak anthropic principle, for the nonexistence of extraterrestrial intelligence. This is unfortunate, because some of the most interesting new developments in particle physics use Carter's argument, which is derived from the fact that the time it took to evolve intelligence on Earth is within a factor of two of the lifetime of the Sun. Carter explains this approximate equality by assuming that the average time needed to evolve intelligence on an Earth-like planet is actually much longer than the lifetime of Sunlike stars. Biological evolution will cease when the star of an Earth-like planet dies, because the dying star destroys its planet. But the longer evolution can proceed, the more likely it is that intelligence will evolve. Thus the most probable time for the appearance of intelligence would be near the end of the time that evolution has had to operate on an Earth-like planet; that is, we expect approximate equality between the Sun's lifetime and the time needed to evolve intelligence.By making Carter's argument quantitative, S. Weinberg obtained an upper bound to the cosmological constant, whereas M. Shaposhnikov (Modern Physics Letters 59, 2607; 1987) made a prediction of the Higgs boson mass.This prediction failed, but it is a fascinating thought that there may be a connection between the Higgs mass and the rarity of intelligent life in the Universe.Pursuing this idea would be far more scientifically productive than doomed-to-fail radio searches. The original French title of Davoust's book was Silence au point d'eau. Silence there will be.
Frank J. Tipler is in the Department of Physics, Tulane University, New Orleans, Louisana 70118, USA.
Sterne Und Weltraum, 1/1994, p. 74
Mit der Gründung der Kommission "Search for Extraterrestrial Life" durch die Internationale Astronomische Union im Jahre 1982 entstand aus der jahrhundertealten Frage nach der Existenz ausserirdischen Lebens einer der populärsten
Zweige moderner astronomischer Forschung. Einzelne radioastronomische Such-projekte gibt es bereits seit dem Beginn der sechziger Jahre; in der davorliegenden Zeit war das Thema eher eine Domäne von Science Fiction- Autoren. Das vorliegende, von einem in der Galaxienforschung tätigen Astronomen geschriebene Buch zeigt aber, dass nichts so spannend sein kann wie die Realität. Es entstand nicht nur aus einer gründlichen Auswertung astronomischer Publikationen. Der Verfasser bemüht sich vielmehr um eine breitgefacherte Diskussion, die auch neuere Erkenntnisse aus Biologie, Paläontologie und aus anderen Bereichen, die hier durch interdisziplinäre Arbeit etwas beitragen können, aufgreift.
Der erste Teil des Buches widmet sich dem Leben auf der Erde. Es wird u. a. beschrieben, welche Hinweise die in Kernen antarktischer Meteorite gefundenen Aminosäuren auf dessen möglicherweise extraterrestrischen Ursprung geben. Der Autor versucht, den Werdegang von der Urzelle bis zur Entstehung höheren Lebens nachzuzeichnen und erläutert die Grundvorstellungen verschiedener Evolutionstheorien. Seine Strategie besteht also darin, aus den Umständen die nach heutiger Vorstellung an der Entstehung und Entwicklung des irdischen Lebens beteiligt waren, etwas über die Möglichkeit von Leben im interstellaren Raum zu lernen. Er macht damit deutlich, wie eng die Suche nach den erforderlichen Randbedingungen mit der Frage nach unserer eigenen Herkunft verknüpft ist.
Im zweiten Teil geht es zunächst um eine realistische Einschätzung der Anssichten, in unserer unmittelbaren kosmischen Umgebung, auf den Planeten des Sonnensystems, einfache Lebensformen zu finden. Nachdem die Raumsonden der NASA gezeigt haben, dass die benachbarten Planeten eher lebensfeindliche Orte sind, könnten einige der groben Monde von Jupiter und Saturn immer noch lohnende Ziele für eine Suche sein. Danach werden die Beobachtungsmethoden beschrieben, mit denen man bei benachbarten Sternen nach Planeten und dunklen Begleitern sucht, und es werden die Bemühungen der vergangenen Jahre geschildert. Die darauffolgenden Kapitel gehen der Frage nach, wie wahrscheinlich es ist, jemals ein Lebenszeichen von ausserirdischen Zivilisationen zu erhalten und was wir überhaupt zu finden hoffen dürfen, wenn wir danach suchen. Der Autor erläutert die dabei verwendeten Strategien und gibt einen Überblick über die bisherigen, hauptsächlich auf radioastronomischen Messungen beruhenden Projekte. Anschliegend beschreibt er die kontroverse Diskussion des Themas innerhalb der Gesellschaft und zeigt damit, welch zermürbender Kritik sich die Forschungsvorhaben oft sowohl von seiten der Politik als auch innerhalb der Wissenschaft ansgesetzt sehen.
Ein besonderes Kapitel ist dem UFO-Phänomen gewidmet. Davoust glaubt zwar, dass es auf diesem Gebiet eine Reihe unverstandener Beobachtungen gibt, die wissenschaftlich untersucht werden sollten. Hypothetische Besuche Ausserirdischer lehnt er jedoch ab, da andere Erklärungsmöglichkeiten, wie z. B. bisher unbekannte astronomische oder meteorologische Erscheinungen, zu wenig beachtet worden seien.
Insgesamt ist das Buch in einem Stil verfasst, der auch Lesem ohne astronomische Vorkenntnisse eine verständliche und interessant geschriebene Einführung in das Thema gibt. Alle benötigten Fachbegriffe werden durch Fussnoten kurz und prägnant erklärt. Besonders demjenigen, der Zugang zur intemationalen astronomischen Fachpresse hat, wird die im Anhang gegebene ausführliche Bibliographie nützlich sein.
Martin Neumann
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