The workshop "From Dust to Terrestrial Planets" was initiated by a working group of planetary scientists invited to ISSI by Johannes Geiss in November 1997. The group split to focus on three topics, one of which was the history of the early solar system, including the formation of the terrestrial planets in the inner solar system. Willy Benz, Gunter Lugmair, and Frank Podosek were invited to convene planetary scientists, astrophysicists, and cosmochemists to synthesize the current knowledge on the origin and evolution of our inner planetary system. The convenors raised the interest of scientists from all over the world in the detailed assessment of the available astronomical, chronological, geochemical and dynamical constraints of the first period of inner solar system evolution. In partic ular, this included appraisal of the newest results from astronomical observations by the Hubble Space Telescope, the Infrared Space Observatory, and other space and ground-based facilities of solar-like systems and nebular disks, possibly repre senting early stages of the solar accretion disk and planet formation. At the same time, the current models of the origin, evolution, transport, and accretion processes of circum stellar disks were presented. This included the new insights provided by the recent discovery of extrasolar giant planets, which were considered insofar as they are relevant to the overall dynamics of the inner part of the solar system.

Recent results from high-energy scattering and theoretical developments of string theory require a change in our understanding of the basic structure of space-time. This book is about the advancement of ideas on the stochastic nature of space-time from the 1930s onward. In particular, the author promotes the concept of space as a set of hazy lumps, first introduced by Karl Menger, and constructs a novel framework for statistical behaviour at the microlevel. The various chapters address topics such as space-time fluctuation and random potential, non-local fields, and the origin of stochasticity. Implications in astro-particle physics and cosmology are also explored. Audience: This volume will be of interest to physicists, chemists and mathematicians involved in particle physics, astrophysics and cosmology.

This unique volume contains the proceedings of two "Non-Sleeping Universe" conferences: "Stars and the ISM" and "From Galaxies to the Horizon." The book provides an overview of recent developments in a variety of areas, covering a very wide range of spatial and temporal scales.

Over the past five de-:: ades researchers have sought to develop a new framework that would resolve the anomalies attributable to a patchwork formulation of relativistic quantum mechanics. This book chronicles the development of a new paradigm for describing relativistic quantum phenomena. What makes the new paradigm unique is its inclusion of a physically measurable, invariant evolution parameter. The resulting theory has been sufficiently well developed in the refereed literature that it is now possible to present a synthesis of its ideas and techniques. My synthesis is intended to encourage and enhance future research, and is presented in six parts. The environment within which the conventional paradigm exists is described in the Introduction. Part I eases the mainstream reader into the ideas of the new paradigm by providing the reader with a discussion that should look very familiar, but contains subtle nuances. Indeed, I try to provide the mainstream reader with familiar "landmarks" throughout the text. This is possible because the new paradigm contains the conventional paradigm as a subset. The foundation of the new paradigm is presented in Part II, fol owed by numerous applications in the remaining three parts. The reader should notice that the new paradigm handles not only the broad class of problems typically dealt with in conventional relativistic quantum theory, but also contains fertile research areas for both experimentalists and theorists. To avoid developing a theoretical framework without physical validity, numerous comparisons between theory and experiment are provided, and several predictions are made.

The symbiosis between particle physics and cosmology has virtually become a conjugal relationship. Hence the 9th biennial Course of the International School of Cosmic-Ray Astrophysics was designed to bridge these formerly dispa- rate disciplines. This NATO Advanced Study Institute (ASI) took place at the Ettore Majorana Centre in Erice, Italy, June 20-30, 1992. Seventy participants from 17 countries enjoyed the opportunities for lively interactions as much as they benefitted from the stimulating lectures. This volume is based on a selection of lectures and shorter talks presented at the sessions. Warm thanks are due to my co-director, Prof. J. P. Wefel and to co-editor Dr. Rein Silberberg for their co- operation. The support of NATO's Scientific Affairs Di- vision and of Dr. L. V. da Cunha, Director of its ASI Pro- gramme, was invaluable. We also acknowledge important con- tributions by the following: Prof. A. Zichichi, Director of the Majorana Centre and its dedicated staff; the Italian Ministry of Education; the Italian Ministry of Scientific Research; the Sicilian Regional Government; the National Science Foundation of the USA, the European Physical Soci- ety, and Mrs. Shirley Ratner of Bethesda, Maryland. The Scientific Advisory Committee consisted of Profs. P. V. Auger, G. P. S. Occhialini, B. Rossi, M. M. Shapiro, R. Silberberg, J. A. Simpson, J. A. Van Allen, J. P. Wefel, and A. Zichichi. All of the foregoing persons and agencies helped make this ASI a memorable experience for the parti- cipants.

The past decade has seen a considerable surge of interest in historical and philo sophical studies of gravitation and relativity, due not only to the tremendous amount of world-wide research in general relativity and its theoretical and observational consequences, but also to an increasing awareness that a collaboration between working scientists, historians and philosophers of science is, in this field, partic ularly promising for all participants. The expanding activity in this field is well documented by recent volumes in this Einstein Studies series on the History of General Relativity as well as by a series of international conferences on this topic at Osgood Hill (1986), Luminy (1988), and Pittsburgh (1991). The fourth of these conferences, hosted by the Max Planck Institute for the History of Science, was held in Berlin from 31 July to 3 August 1995, with a record attendance of some 80 historians and philosophers of science, physicists, mathematicians, and as tronomers. Based on presentations at the Berlin conference, this volume provides an overview of the present state of research in this field, documenting not only the increasing scope of recent investigations in the history of relativity and gravitation but also the emergence of several key issues that will probably remain at the focus of debate in the near future. RELATIVITY IN THE MAKING The papers of this section deal with the origins and genesis of relativity theory."

This NATO Advanced Study Institute course provided an updated understanding, from a fundamental and deep point of view, of the progress and current problems in the early universe, cosmic microwave background radiation, large-scale struc ture, dark matter problem, and the interplay between them. Emphasis was placed on the mutual impact of fundamental physics and cosmology, both at the theo retical and experimental or observational levels, within a deep and well defined programme, and a global unifying view, which, in addition, provides of careful inter-disciplinarity. In addition, each course of this series introduced and promoted topics or sub jects which, although not of a purely astrophysical or cosmological nature, were of relevant physical interest for astrophysics and cosmology. Deep understanding, clarification, synthesis, and careful interdisciplinarity within a fundamental physics framework, were the main goals of the course. Lectures ranged from a motivation and pedagogical introduction for students and participants not directly working in the field to the latest developments and most recent results. All lectures were plenary, had the same duration, and were followed by a discus sion. The course brought together experimentalists and theoreticans physicists, astro physicists and astronomers from a wide variety of backgrounds, including young scientists at the post-doctoral level, senior scientists and advanced graduate stu dents as well.

The twenty-second Coral Gables conference "UNIFIED SYMMETRY: In the Small and In the Large" continued with the efforts to unify the small and the large. The information gathered with the Huble telescope has in part, in the absence of the SCC , provided a basis for the physicists to unify cosmology and elementary particle physics. The congressional cancellation of the biggest experimental project on the frontiers of physics should not be regarded as an insurmountable obstacle to progress in theoretical physics. The physicists' rise to prominence was mostly reached through their creation of the nuclear era. The post cold war era has somewhat reduced the political, military, and, in part, the social role of the physicist. Some in the administration and the Congress would like physicists to focus on the directly utilitarian aspects of science. Thus, some people do not realize that this regimentation of science would inhibit the creativity. The contributions of solid state physics research to the advancement of technology is the result of physics freely pursued independently of its applications. Modern Physics beginning with Newton's theory of gravity has enabled us to create the space age, to contribute to various technologies, and to impact on our technological modus vivendi.

The Fourth HEIDELBERG International Conference on Dark Matter in Astro and Particle Physics, DARK2002, was held in Cape Town, South Africa, in the period 4-9 February 2002. This majestic natural area was the site of the first conference of this series (hosted since 1996 in Heidelberg) to be held outside of Germany. Dark Matter has become one of the most exciting and central fields of as trophysics, particle physics and cosmology. The conference covered, as usual for this series, a large range of topics, theoretical and experimental. Topics included Astronomical Evidence for Dark Matter, the Cosmic Microwave Background, Supersymmetry, Inflation and Dark Energy, Structure Formation, Hot and Cold Dark Matter, and Ultrahigh Energy Cosmic Rays all of which were represented by experts in the field. It was very nice to see again many of our 'old' friends in Dark Matter here in South Africa. The organizers were very glad to see, in addition to world experts, the new generation here. Many young participants gave very nice professional talks during the conference. We are grateful to John Ellis for doing an incredible job preparing his excellent summary talk during the sessions. Some special interest and intensive discussions were naturally raised by the first announcement of terrestrial evidence for hot dark matter, obtained from neutrino less double beta decay. This now adds to the evidence for cold dark matter which we have from DAM A for several years already, and which remained unchallenged up to now by other experiments.

The aim of this book is to present the theory and applications of the relativistic Boltzmann equation in a self-contained manner, even for those readers who have no familiarity with special and general relativity. Though an attempt is made to present the basic concepts in a complete fashion, the style of presentation is chosen to be appealing to readers who want to understand how kinetic theory is used for explicit calculations. The book will be helpful not only as a textbook for an advanced course on relativistic kinetic theory but also as a reference for physicists, astrophysicists and applied mathematicians who are interested in the theory and applications of the relativistic Boltzmann equation.

Quantum gravity has developed into a fast-growing subject in physics and it is expected that probing the high-energy and high-curvature regimes of gravitating systems will shed some light on how to eventually achieve an ultraviolet complete quantum theory of gravity. Such a theory would provide the much needed information about fundamental problems of classical gravity, such as the initial big-bang singularity, the cosmological constant problem, Planck scale physics and the early-time inflationary evolution of our Universe. While in the first part of this book concepts of quantum gravity are introduced and approached from different angles, the second part discusses these theories in connection with cosmological models and observations, thereby exploring which types of signatures of modern and mathematically rigorous frameworks can be detected by experiments. The third and final part briefly reviews the observational status of dark matter and dark energy, and introduces alternative cosmological models. Edited and authored by leading researchers in the field and cast into the form of a multi-author textbook at postgraduate level, this volume will be of benefit to all postgraduate students and newcomers from neighboring disciplines wishing to find a comprehensive guide for their future research.

It has often been noted that a kind of double dynamics char- terizes the development of science. On the one hand the progress in every discipline appears as the consequence of an increasing specialization, implying the restriction of the inquiry to very partial fields or aspects of a given domain. On the other hand, an opposite (but one might better say a complementary) trend points towards the construction of theoretical frameworks of great ge- rality, the aim of which seems to correspond not so much to the need of providing "explanations" for the details accumulated through partial investigation, as to the desire of attaining an - rizon of global comprehension of the whole field. This intell- tual dialectics is perceivable in every discipline, from mathe- tics, to physics, to biology, to history, to economics, to sociology, and it is not difficult to recognize there the presence of the two main attitudes according to which human beings try to make "intelligible" the world surrounding them (including themselves), attitudes which are sometimes called analysis and synthesis. They correspond respectively to the spontaneous inclination which pushes us to try to understand things by seeing "how they are made", in the sense of "looking into them" and breaking them into their constitutive parts, or rather to encompass things in a global picture, where they are accounted for as occupying a place, or playing a role, which are understandable from the point of view of the whole.

This volume contains the lectures and contributions presented at the NATO Advanced Study Institute (ASI) on "Frontier Topics in Nuclear Physics", held at Predeal in Romania from 24 August to 4 September 1993. The ASI stands in a row of 23 Predeal Summer Schools organized by the Institute of Atomic Physics (Bucharest) in Predeal or Poiana-Brasov during the last 25 years. The main topics of the ASI were cluster radioactivity, fission and fusion. the production of very heavy elements, nuclear structure described with microscopic and collective models, weak: interaction and double beta decay, nuclear astrophysics, and heavy ion reactions from low to ultrarelativistic energies. The content of this book is ordered according to these topics. The ASI started with a lecture by Professor Greiner on the "Present and future of nuclear physics", showing the most important new directions of research and the interdisciplinary relations of nuclear physics with other fields of physics. This lecture is printed in the first chapter of the book.

ROSAT Observations G. HASINGER Max-Planck-Institut flir extraterrestrische Physik, D-85740 Garching, Germany Abstract. This review describes the most recent advances in the study of the extragalactic soft X-ray background and what we can learn about its constituents. The deepest pointed observations with the ROSAT PSPC are discussed. The logN-logS relation is presented, which reaches to the faintest X-ray fluxes and to the highest AGN surface densities ever achieved. The N(>S) relation shows a 2 density in excess of 400 deg- at the faintest fluxes and a flattening below the Einstein Deep Survey limit. About 60% of the extragalactic background has been resolved in the deepest field. Detailed source spectra and first optical and radio identifications will be discussed. The results are put into perspective of the higher energy X -ray background. Key words: X-rays, background radiations, active galactic nuclei. 1. Introduction The extragalactic X-ray background (XRB), discovered about 30 years ago, has been studied extensively with many X-ray experiments, in particular with the satel lites HEAO I and II (see ego Boldt 1987) and with ROSAT (e. g. Hasinger et aI. , 1993). Figure 1 shows a compilation of some of the most recent spectral measure ments for the X-ray background. Over the energy range from 3 to about 100 keY its spectrum can be well approximated by an optically thin thermal bremsstrahlung model with kT ~ 40 keY, while at lower X-ray energies a steepening into a new component has been observed observed (e. g.

InMay1988,theFirstInternationalConferenceonDissociativeRecombination:Theory, ExperimentandApplicationswasheldatChateauLakeLouise,Alberta,Canada. Thismeeting gaveaconsiderableimpetustothissubject,whichisofparticularinterestforalargevarietyof fieldsincludinginterstellarclouds,planetaryatmospheres,gaslasers,plasmaprocessing,ion sourcesandthermonuclearplasmas. Sincethen,indeed,severalcollaborationswereinitiated betweenexperimentalistsworkingwithdifferenttechniques,betweentheoreticiansdealingwith molecularstructureononehandanddynamicsontheotherhandandalsobetween experimentalistsandtheoreticians. Duringthelastfouryears,therefore,alargenumberof studieswerecarriedoutandraisedanewsetofquestions. Moreparticularly,theresultsthat wereobtainedconcerningcontroversialspeciessuchasH!andHeir,castingsomedoubton theverymechanismsbywhichdissociativerecombinationproceeds. The Second International Conference on Dissociative Recombination: Theory, ExperimentandApplications heldat"I'AbbayedeSaintJacutdelaMer",Brittany,France, May3-8,1992,camethereforeattherighttimetosurveythecurrentstateofthesubject. The symposiumbroughttogetherleadinginvestigatorsinthefieldsofmolecularionrecombination research,atomicandmoleculartheoryandexperiment,plasmasphysics,astrochemistryand aeronomy. Speakerspresentedtalksreviewingtheirownworkandthesewerefollowedby livelydiscussionsessions. Freetimeperiodsallowedparticipantstodiscoveranenchanting peninsulaofNorthBrittanywhilepursuingstimulatingscientificdiscussions. Thepapersinthis volumearebasedonthesetalksandfurtherdiscussions,withtheexceptionofcontributions fromT. AmanoandB. M. McLaughlinwhowereunabletoattend. Alistofparticipantsas wellasasouvenirgroupphotoisgivenattheendofthebook. WeareindebtedtoNATOforitsfinancialsupportwhichcontributedtothegreat successofthissecondmeeting. TheUniversityofRennesIandtheBalzerscompanyarealso acknowledgedfortheiradditionalsupportManythankstothewholestaffoftheabbeyforits kindnessandeffortsinprovidinguswithapropitiousenvironmentforsuchaworkshop. We arealsogratefultoL. Caubetforhervaluableadministrativeassistanceduringthepreparation ofthemeeting. Finallyaspecialmentionmustbegiventoallthesessionchairpersonsfortheir skillinorchestratingthediscussions. Lookingforwardtoattendingthethirdmeeting. TheEditors Bertrand R. Rowe J. Bria/l A. Mitchell Andre Callosa DepartementdePhysique DepartmentofPhysics DepartementdePhysique AtomiqueetMoleculaire TheUniversityofWesternOntario AtomiqueetMoleculaire UniversitedeRennesI London,Canada,N6A3K7 UniversitedeRennesI CampusdeBeaulieu CampusdeBeaulieu 35042RennesCedex, 35042RennesCedex, France France v CONTENTS ORALCONTRIBUTIONS PolyatomicIonDissociativeRecombination . 1 D. R. Bates RecentDevelopmentsandPerspectivesintheTreatmentofDissociative RecombinationandRelatedProcesses...11 A. Giusti-Suzor, I. F Schneider, and 0. Dulieu CharacteristicsofSuperexcitedStatesofMoleculesandMQDTStudiesofNO+ DissociativeRecombination...25 H. Sun, K. Nakashima, and H. Nakamura CalculationsforAr +Xe*andArXe+ +e 35 A. P. Hickman, DL Huestis, and R. P. Saxon Electron-IonContinuum-ContinuumMixinginDissociativeRecombination 47 s. L. Guberman ATheoreticalStudyoftheHCO+andHCS+ElectronicDissociativeRecombinations. . 59 D. Talbi, and Y Ellinger DissociativeRecombinationofCH;:SomeBasicInformationfromElectronic 2 StructureCalculations. 67 WP. Kraemer TheoreticalProblemsintheDissociativeRecombinationofH~ +e...75 H. Takagi RecentMergedBeamsInvestigationsofHydrogenMolecularIonRecombination...87 J B. A. Mitchell, F B. Yousif, P. Van der Donk, and T. J Morgan vii FlowingAfterglowStudiesofElectron-IonRecombinationusingLangmuirProbesand OpticalSpectroscopy...99 NG. Adams RecentFlowingAfterglowMeasurements . 113 B. R. Rowe InfraredSpectroscopicStudiesoftheDissociativeRecombinationProcessesofH...127 3 T. Amano RecombinationofClusterIons . 135 R. Johnsen PredissociationofExcitedStatesofH . . 145 3 H. Helm AStudyofHe e,3I,;)BoundandContinuumStates...155 2 CJ Gillan, B. M McLaughlin. and P. G. Burke ElectronCollisionInducedExcitationsandDissociationofHeH+usingthe R-MatrixMethod . . 163 BK Sarpal, J Tennyson, and L. A. Morgan AssociativeIonisationofHydrogen:ExperimentswithFastMergedBeams...173 F Brouillard, andX Urbain TheoryoftheAsssociativeIonisationReactionbetweenTwoLaser-Excited . 187 SodiumAtoms 0. Du!ieu, A. Giusti-Suzor, andF Masnou-Seeuws ResonantTheoryofDissociativeAttachment...195 J. J. Fabrikant MicroscopicandMacroscopicTheoriesofTermolecularRecombinationbetween AtomicIons...205 MR. Flannery DissociativeRecombinationinPlanetaryIonospheres . . 219 JL. Fox ChemistryofSupernova1987a . 243 A. Dalgarno DissociativeRecombinationinInterstellarClouds . .

In Controversy, Trevor Palmer fully documents how traditional gradualistic views of biological and geographic evolution are giving way to a catastrophism that credits cataclysmic events, such as meteorite impacts, for the rapid bursts and abrupt transitions observed in the fossil record. According to the catastrophists, new species do not evolve gradually; they proliferate following sudden mass extinctions. Placing this major change of perspective within the context of a range of ancient debates, Palmer discusses such topics as the history of the solar system, present-day extraterrestrial threats to earth, hominid evolution, and the fossil record.

The book presents state-of-the-art results on the analysis of the Einstein equations and the large scale structure of their solutions. It combines in a unique way introductory chapters and surveys of various aspects of the analysis of the Einstein equations in the large. It discusses applications of the Einstein equations in geometrical studies and the physical interpretation of their solutions. Open problems concerning analytical and numerical aspects of the Einstein equations are pointed out.

Background material on techniques in PDE theory, differential geometry, and causal theory is provided.

A history of the attempts to test the predictions of Newtonian Gravity, describing in detail recent experimental efforts to verify both the inverse-square law and the Equivalence Principle. Interest in these questions has increased in recent years, as it has become recognised that deviations from Newtonian gravity could be a signal for a new fundamental force in nature. This is the first book devoted entirely to this subject, and will thus be useful to both graduate students and researchers interested in this field. It describes the ideas that underlie searches for such deviations, focusing on macroscopic tests. A comprehensive bibliography of some 450 entries supplements the text.

This symposium was organized at the B.M. Birla Science Centre, Hyderabad, India, and provided a platform for frontier physicists to exchange ideas and review the latest work and developments on a variety of interrelated topics. A feature of the symposium, as well as the proceedings, is the B.M. Birla Memorial Lecture by Nobel Laureate Professor Gerard 't Hooft. There were participants from the USA, several European countries, Russia and CIS countries, South Africa, Japan, India and elsewhere, of whom some forty scientists presented papers. Spanning a wide range of contemporary issues in fundamental physics from string theory to cosmology, the proceedings present many of these talks and contributions.

Stellar astrophysics still provides the basic framework for deciphering the imprints left over by the evolving universe on all scales. Advances or shortcomings in the former field have direct consequences in our ability to understand the global properties of the latter.

This volume contains the most recent updates on a variety of topics that, though independent by themselves, are inevitably connected on a cosmological scale. These include comprehensive articles by leaders in fields extending from stellar atmospheres through properties of the stellar component in the Milky Way up to the stellar environment in high redshift galaxies.

The wide coverage of astrophysical themes makes this volume very valuable for researchers and Ph.D. students in astrophysics.

Electroweak Phase Transition and the Early Universe, a NATO Advanced Re- search Workshop, was held March 23-25, 1994, at the Hotel Tivoli in Sintra, Portugal. The meeting was co-sponsored by three other Lisbon-based institutions: the Fundac;ao Gulbenkian, J. N.!. C. T. (Junta Nacional para Investigac;ao Cientifica e Tecnologica) and G. T. A. E. (Grupo Teorico de Alta Energias). The workshop brought together a large number of theoretical physicists who are actively researching topics relevant to the understanding of the standard model of electroweak interactions in the early universe. We were pleased and overwhelmed by the positive, and sometimes instan- taneous response that our enterprise raised right from its inception. The old town of Sintra provided a serene and pleasant environment for the par- ticipants. Some heated and controversial discussions on many unanswered questions in the standard model took place throughout the three days of the workshop. If one consensus emerged from the meeting, it was the imperative need for non-perturbative techniques for the understanding of the electroweak phase transition.

Observational and experimental data pertaining to gravity and cosmology are changing our view of the Universe. General relativity is a fundamental key for the understanding of these observations and its theory is undergoing a continuing enhancement of its intersection with observational and experimental data. These data include direct observations and experiments carried out in our solar system, among which there are direct gravitational wave astronomy, frame dragging and tests of gravitational theories from solar system and spacecraft observations. This book explores John Archibald Wheeler's seminal and enduring contributions in relativistic astrophysics and includes: the General Theory of Relativity and Wheeler's influence; recent developments in the confrontation of relativity with experiments; the theory describing gravitational radiation, and its detection in Earth-based and space-based interferometer detectors as well as in Earth-based bar detectors; the mathematical description of the initial value problem in relativity and applications to modeling gravitational wave sources via computational relativity; the phenomenon of frame dragging and its measurement by satellite observations. All of these areas were of direct interest to Professor John A. Wheeler and were seminally influenced by his ideas.

The reader will find in this volume the Proceedings of the NATO Advanced Study Institute held in Cortina d' Ampezzo, Italy, between July 25 and August 6, 1993, under the title From Newton to Chaos: Modem Techniques for Understanding and Coping With Chaos inN-Body Dynamical Systems. This institute was the latest in a series of meetings held every three years from 1972 to 1990 in dynamical astronomy, theoretical mechanics and celestial mechanics. The proceedings from these institutes have been well-received in the international community of research workers in these disciplines. The present institute was well attended with 15 series of lectures being given by invited speakers: in addition some 40 presentations were made by the other participants. The majority of these contributions are included in these proceedings. The all-pervading influence of chaos in dynamical systems (of even a few variables) has now been universally recognised by researchers, a recognition forced on us by our ability, using powerful computer hardware and software, to tackle dynamical problems that until twenty-five years ago were intractable. Doubtless it was felt by many that these new techniques provided a break-through in celestial mechanics and its related disciplines. And so they were.

The International Conference, Orbis Scientiae 1996, focused on the topics: The Neutrino Mass, Light Cone Quantization, Monopole Condensation, Dark Matter, and Gravitational Waves which we have adopted as the title of these proceedings. Was there any exciting news at the conference? Maybe, it depends on who answers the question. There was an almost unanimous agreement on the overall success of the conference as was evidenced by the fact that in the after-dinner remarks by one of us (BNK) the suggestion of organizing the conference on a biannual basis was presented but not accepted: the participants wanted the continuation of the tradition to convene annually. We shall, of course, comply. The expected observation of gravitational waves will constitute the most exciting vindication of Einstein's general relativity. This subject is attracting the attention of the experimentalists and theorists alike. We hope that by the first decade of the third millennium or earlier, gravitational waves will be detected, opening the way for a search for gravitons somewhere in the universe, presumably through the observations in the CMBR. The theoretical basis of the graviton search will take us to quantum gravity and eventually to the modification of general relativity to include the Planck scale behavior of gravity -at energies 19 of the order of 10 Ge V.

Observing our Universe and its evolution with ever increasing sensitivity from ground-based or space-borne telescopes is posing great challenges to Fundamental Physics and Astronomy. The remnant cosmic microwave background, as beautifully measured by successive space missions COBE, WMAP, and now PLANCK, provides a unique probe of the very early stages of our Universe. The red-shift of atomic lines in distant galaxies, the dynamics of pulsars, the large scale structure of galaxies, and black holes are a few manifestations of the theory of General Relativity. Yet, today, we understand only 4% of the mass of our Universe, the rest being called dark energy and dark matter, both of unknown origin! A second family of space missions is currently emerging; rather than designing ever more re nedobservationalinstruments,physicistsandengineersseekalsotousethespaceenvironment to perform high-precision tests of the fundamental laws of physics. The technology required for such tests has become available only over the course of the last decades. Clocks of high accuracy are an example. They are based on advances in atomic and laser physics, such as cold atoms, enabling a new generation of highly sensitive quantum sensors for ground and space experiments. Two experiments in space have now tested Einstein's relativity theory: * Several decades ago, Gravity Probe A con rmed the accuracy of the gravitational red-shift ?5 according to general relativity to a level of 7x 10 [R. F. C. Vessot et al. , Test of Relativistic Gravitation with a Space-Borne Hydrogen Maser, Phys. Rev. Lett. 45, 2081-2084 (1980)].