TÉLÉCHARGER METEORITE 0.11

TÉLÉCHARGER METEORITE 0.11

TÉLÉCHARGER METEORITE 0.11

Désolé, il n'y a aucun circuit ni aucune activité disponible à la réservation en ligne à la date que vous avez sélectionnée. Choisissez une autre date. Associez-vous cet endroit ou cette activité à l'histoire?

Nom: meteorite 0.11
Format:Fichier D’archive
Version:Nouvelle
Licence:Libre (*Pour usage personnel)
Système d’exploitation: iOS. Android. Windows XP/7/10. MacOS.
Taille:60.45 MB

Choisissez une autre date. Associez-vous cet endroit ou cette activité à l'histoire? Oui Non Je ne sais pas Cette attraction est-elle un joyau caché ou hors des sentiers battus? Oui Non Je ne sais pas Faut-il fournir des efforts physiques marche, présence d'escaliers, escalade dans ce lieu ou cette activité? Oui Non Je ne sais pas Est-ce que ce lieu ou cette activité convient à tous les âges? Oui Non Je ne sais pas Ce lieu ou cette activité dispose-t-il d'un parking?

Oui Non Je ne sais pas Recommanderiez-vous ce lieu ou cette activité à des familles avec enfants?

télécharger la présentation (pdf) - Cerfav

And there is a well-established remedy: assemble recollections from those who were involved in the work. We follow that path, but in more detail in a more limited line of research. Early studies of the fossil radiation involved a relatively small number of people in what has proved to be a considerable advance in establishing the physical nature of the universe.

This means we could aim for complete coverage of recollections from everyone involved in the early work who is still with us. We did not reach completeness: we suppose it is inevitable that a few colleagues would have reasons not to want to take part. We are fortunate, however, that almost everyone we could contact was willing to xi xii Preface contribute recollections.

All are well along in life now, but they have not slowed down; all had to break away from other commitments to complete their assignments.

We are deeply indebted to the contributors for taking the time and trouble to make this collection possible, and for their patience in enduring the lengthy assembly of the book. Their stories are important, but to keep the numbers manageable in the style of this book we had to impose a limit to recollections from people who were involved in this subject before That is when activity started gathering strength for the next leaps of technology and theory in increasingly large research groups.

Rashid Sunyaev was an invaluable guide to contacting contributors in Russia. We have descriptions of the origins of the critical radiation energy spectrum measurements from Mark Halpern, Michael Hauser, and Ed Wishnow, and of the development of ideas on the distortion of the radiation spectrum from Ray Weymann.

Some steps toward the organization of this project ought to be recorded. But we all returned to other interests. This led to a proposal that was circulated to some 12 proposed contributors. The number is uncertain because we did not keep records. It yielded three essays — they are in this collection — but attention again drifted to other things.

That discussion led to a blunt actuarial assessment: if the story were to be told in a close to complete way it would have to be done before too many more years had passed. That generated the momentum that led to completion of the project. We sent a proposed outline of the book with an invitation to contribute to 28 people on 7 December As one might expect, the outline for the book continued to change after that as we better understood what we were attempting to do.

A more unsettling change is that although we had given the list of contributors careful thought, we continued to identify people who ought to contribute: we have in this book some dozen additions to the December list. A simple extrapolation suggests we have forgotten still others: we likely have not been as complete as we ought to have been.

We hope all who did contribute to this book, in many ways, are aware of our gratitude. We apologize in advance for any omissions in this procedure. List of contributors J.

Shakeshaft St. Stokes Versa Power Systems, Inc. The properties of this radiation which we describe beginning on page 16 show that it is a fossil, a remnant from a time when our universe was denser and hotter and vastly simpler, a very nearly uniform sea of matter and radiation.

The discovery of the radiation left from this early time is memorable because, as is often true of fossils, measurements of its properties give insights into the past.

The study of this fossil radiation has proved to be exceedingly informative for cosmology, the study of how our universe expanded, cooled, and evolved to its present complicated condition. The discovery of the fossil radiation grew out of a mix of lines of evidence that were sometimes misinterpreted or overlooked, and of ideas that were in some cases perceptive but ignored and in other cases misleading but entrenched.

We introduce the accounts of how this happened by explaining the lines of research that led up to the situation then. The story of what happened when the pieces were put together in the s is told through the recollections of the people in the best position to know — those involved in the research.

We have essays by most who took part in the recognition that this fossil exists, its properties may be measured, and what is measured may inform us about the nature of the physical universe. This did not happen all at once; nor was it done by a single person; nor was it always done knowingly. The collection of essays tell what happened in all the richness and complexity we suppose is typical of any activity that people take seriously.

The last part of this book describes how the developments in the s led to the search and discovery of methods of accurate measurement of the properties of the fossil radiation and of methods of interpreting what 1 2 Introduction is measured. This part of the story is told in a more orderly way — it is concerned with research directed to the solution of relatively well-posed problems — but it is no less rich.

It shows how advances in technology and in the strategies of its application can dramatically increase our understanding of the world around us. And because cosmology still is a relatively new science, it has not yet become exceedingly technical: we can explain the developments in words accessible to a nonspecialist who is willing to read carefully. As a practical matter this is about the best scientists generally can do.

But it is important to have some examples that take the opposite tack: explore what happened in detail.

The more specialized mathematics and comments in footnotes and the Glossary are intended for specialists. Introduction 3 variety of careers. Some continued in this line of work after , but many have gone on to other things. Others were reluctant to get involved because the data one could bring to bear on such questions were so exceedingly limited.

Some were drawn to cosmology by the challenge of making a particular measurement or calculation. Others became involved by accident, not realizing that their work would become important to the study of the expanding universe. We have descriptions of what it was like to be a student then, or to be further along into a career in science, along with accounts of how the contact with this subject shaped careers and lives.

Liste de bolides

Our set of recollections cannot be complete because some of the actors are no longer with us. We have also lost Francesco Melchiorri, a pioneer in the use of bolometers to measure the radiation.

Their pioneering work in the s and s on the thermal properties of the early universe is central to the history related in Chapter 3. Bob Dicke suggested that Wilkinson and Peter Roll search for this fossil radiation, using technology he had invented two decades earlier. Dave Wilkinson, his colleagues and students, and in turn their students, have played a leading part in the measurements of the properties of the radiation, from the time of its discovery and continuing through to the two spectacularly successful satellite missions, Cosmic Background Explorer COBE and WMAP, which have given us precision measures that imply demanding constraints on the large-scale nature of the universe.

In the late s Sciama became persuaded by the evidence for a hot big bang, while Hoyle continued to lead the spirited exploration of alternatives to the relativistic big bang cosmology. We do have recollections by close associates; they are a valuable part of the story. We are saddened by the loss of two contributors to the collection of essays. Our explanation of his thinking commences on page 59; his recollections start on page Ron Bracewell at Stanford University took an early lead in the development of the strategy for the measurements of the small departures from an exactly smooth sea of radiation.

These measurements have proved to be exceedingly useful guides to how the concentrations of matter in galaxies and clusters of galaxies grew, in the process disturbing the radiation.

His recollections begin on page The technique he and his student Ned Conklin pioneered reappears in later generations of experiments.

That is illustrated in Figure 5. The recollections by our colleagues Don Osterbrock and Ron Bracewell, along with the other contributors to this volume, will edify generations to come. What did you know then about cosmology and what did you think of it as a branch of physical science?

La page que vous souhaitez afficher est introuvable.

We have made no attempt at documentation in these recollections, which we suspect would have been sparse compared to the density and complexity of the set of essays. They had the advantage of being able to ask a series of questions. An analog of the follow-up question in an interview is the sharing of recollections of dates and events by some of our contributors. Apart from gentle hints, and a few corrections of well-documented points, we have not contributed to this interaction, or otherwise attempted to enhance the content or coherence of the essays.

The essays are informed by a considerable variety of philosophies of the theory and practice of science. To this must be added the variety of what the contributors happened to be doing in the s, what they later considered worth recording in this volume, and what they happen to remember Introduction 5 or are able to recover from fragmentary records. But in our opinion these recollections are the best feasible basis for an understanding of what actually happened and why.

We hope the reader will enjoy the opportunity of applying this tradition to the set of essays.

The research in the s on fossils from the big bang grew out of what had happened earlier. In Chapter 3 we trace the histories of ideas and methods of measurement from early developments in the s up to the general recognition in the s that one may put these ideas and methods together.

Examine le système solaire

Our account of the science before is selective: we pay particular attention to those developments in cosmology that have proved to be relevant to the interpretation of a fossil from the early hot stages of expansion of the universe, the sea of radiation, along with a related fossil, the lightest of the chemical elements.

This chapter concludes with a broader assessment of the state of the theory and practice of cosmology in the early s: the observations and ideas that were more widely discussed and those that might have merited closer attention. That is not the whole story by any means: we have omitted wrong steps that no longer seem relevant and all the other rough places that the essays are meant to illustrate.

And because cosmology up to the s was a small science, and only a small portion of that was concerned with fossils from the early universe, we have the space to explore the more interesting of the steps we now see were in wrong directions. This is important: mistakes are an inevitable part of advances in the enterprise of science.

But the scant observational basis allowed considerable and perhaps even unhealthy room for speculation undisciplined by observation.

Even in the s it was not at all unreasonable to doubt the progress toward checking ideas by piecing together an empirically based theory of the physical universe from our limited view in space and time. An example is in the foreword to the book General Relativity and Cosmology by Robertson and Noonan In the foreword the physicist W.

Informations des mises à jour

Whether this be true of general relativity remains to be seen. Cosmology is mostly a dream of zealots who would oversimplify at the expense of deep understanding. Much remains to be done — experimentally, observationally and theoretically. But in the mids Fowler was skeptical of the proposal that the radiation is a fossil from the past rather than something produced by processes operating in the universe as it is now.

At the time, experimental tests of general relativity were not very demanding, even on the length scale of the Solar System. If the observational and experimental basis for cosmology were as schematic now as it was in the s, the discovery of the sea of radiation still would be an interesting development, but perhaps much less important to science than it has proved to be.

That is because the measured properties of this radiation are a considerable part of the suite of evidence that now tightly constrains ideas about the large-scale nature of the universe, including stringent tests of aspects of general relativity theory applied on the enormous scales of cosmology.

Fowler gave an accurate prediction of the present situation: much has been done, and it has yielded a rich harvest. Research in physical science has made enormous progress by operating under the assumption that there is an objective physical reality that operates by rules we can discover, in successively improved approximations. The great advances of science reinforce the assumption: this is not an issue scientists generally consider worth discussing. Here the older notion of reality is abandoned; we have a better approximation.

Introduction 7 experience and teach us new things about the world around us. As experimentalists learned how to overcome the many obstacles to the spectacular precision of later measurements of the fossil radiation, they in turn drove theorists along their own learning curves on how to characterize the universe the measurements were revealing.