13.8 E-Book

John Gribbin

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 397

Veröffentlichungsjahr: 2015

Beschreibung

The 20th century gave us two great theories of physics: the general theory of relativity, which describes the behaviour of things on a very large scale, including the entire Universe; and quantum theory, which describes the behaviour of things on a very small scale, the sub-atomic world. The refusal of the Universe to reveal an equation that combines these two great ideas has caused some people to doubt our whole understanding of physics. In this landmark new book, popular science master John Gribbin tells the dramatic story of the quest that has led us to discover the true age of the Universe (13.8 billion years) and the stars (just a little bit younger). This discovery, Gribbin argues, is one of humankind's greatest achievements and shows us that physics is on the right track to finding the 'Theory of Everything'. 13.8 provides an eye-opening look at this cutting-edge area of modern cosmology and physics, and tells the compelling story of what modern science has achieved – and what it can still achieve.

Leseprobe

13.8

THE QUEST TO FIND THE TRUE AGE OF THE UNIVERSE AND THE THEORY OF EVERYTHING

JOHN GRIBBIN

Published in the UK in 2015 by Icon Books Ltd, Omnibus Business Centre, 39–41 North Road, London N7 9DP email: [email protected]

Sold in the UK, Europe and Asia by Faber & Faber Ltd, Bloomsbury House, 74–77 Great Russell Street, London WC1B 3DA or their agents

Distributed in the UK, Europe and Asia by TBS Ltd, TBS Distribution Centre, Colchester Road, Frating Green, Colchester CO7 7DW

Distributed in Australia and New Zealand by Allen & Unwin Pty Ltd, PO Box 8500, 83 Alexander Street, Crows Nest, NSW 2065

Distributed in South Africa by Jonathan Ball, Office B4, The District, 41 Sir Lowry Road, Woodstock 7925

Distributed in India by Penguin Books India, 7th Floor, Infinity Tower – C, DLF Cyber City, Gurgaon 122002, Haryana

ISBN: 978-184831-918-9

Text copyright © 2015 John and Mary Gribbin

No part of this book may be reproduced in any form, or by any means, without prior permission in writing from the publisher.

Typeset in Dante by Marie Doherty

Printed and bound in the UK by Clays Ltd, St Ives plc

Contents

About the Author

Acknowledgements

List of Illustrations

Introduction: The Most Important Fact

Part Zero: Prologue

2.712 – Taking the temperature of the Universe

Part One: How Do We Know the Ages of Stars?

1 2.898 – Prehistory: Spectra and the nature of stars

Locating lines

Hunting helium

Hunting hydrogen

The heat of the Sun

The heat of the stars

The heat inside

2 0.008 – At the heart of the Sun

A French connection

No free lunch

Seats of enormous energies

A hotter place?

A quantum of solace

3 7.65 – Making ‘metals’

Cycles and chains of fusion

Rocks of ages

From the Bomb to the stars

The last should be first

Stardust

4 13.2 – The ages of stars

Hertzsprung, Russell and the diagram

Ashes to ashes

Globular cluster ages

White dwarf ages

Radiometric ages and the oldest known star

Part Two: How Do We Know the Age of the Universe?

5 31.415 – Prehistory: Galaxies and the Universe at large

The power of pure reason

One step forward, two steps back

Nebular spectroscopy

First steps

The long and winding road

An unresolved debate

A universe destroyed

6 575 – The discovery of the expanding Universe

Surprising speeds

Taking the credit

A Russian revolution

A Priestly intercession

7 75 – Sizing up the cosmic soufflé

Einstein’s lost model

Keeping it simple

Across the Universe

Doubling the distances

Hubble’s heir

Another Great Debate

8 13.8 – Surveys and satellites

The culmination of a tradition

Too perfect?

The dark side

Supernovae and superexpansion

Sounding out the Universe

Ultimate truth

Glossary

Sources and Further Reading

End Notes

Index

About the Author

JOHN GRIBBIN was born in 1946 in Maidstone, Kent. He studied physics at the University of Sussex and went on to complete an MSc in astronomy at the same university before moving to the Institute of Astronomy in Cambridge, to work for his PhD.

After working for the journals Nature and New Scientist, he has concentrated chiefly on writing books on everything from the Universe and the Multiverse to the history of science. His books have received science-writing awards in the UK and the US. His biographical subjects include Albert Einstein, Erwin Schrodinger, Stephen Hawking, Richard Feynman, Galileo, Buddy Holly and James Lovelock.

Since 1993, Gribbin has been a Visiting Fellow in Astronomy at the University of Sussex.

Acknowledgements

The University of Sussex provided me with a base to work from, and the astronomy group there provided many stimulating discussions on various aspects of astronomy. Beyond Sussex, Virginia Trimble of the University of California, Irvine kept us straight on history, and François Boucher of the Institut d’Astrophysique Paris kept us up to date on the Planck satellite discoveries. I am also grateful to the Alfred C. Munger Foundation for continued financial support.

List of Illustrations

1. Robert Wilson (left) and Arno Penzias (right) in 1978 in front of the Crawford Hill Antenna, which revealed the existence of the cosmic background radiationAIP Emilio Segre Visual Archives, Physics Today Collection

2. George GamowAIP Emilio Segre Visual Archives

3. Georges LemaîtreAIP Emilio Segre Visual Archives, Locanthi Collection

4. Henrietta Swan and Annie Jump Canon outside Harvard ObservatoryAIP Emilio Segre Visual Archives, Shapley Collection

5. Ejnar HertzsprungPhoto by Hans Petersen, Novdisk Pressefoto A/S, courtesy AIP Emilio Segre Visual Archives, gift of Kaj Aage Strand

6. Cecilia Payne-GaposchkinAIP Emilio Segre Visual Archives, Physics Today Collection

7. Henry Norris RussellAIP Emilio Segre Visual Archives, W.F. Meggers Collection

8. Ernest Rutherford, 1926AIP Emilio Segre Visual Archives, William G. Myers Collection

9. Arthur EddingtonAIP Emilio Segre Visual Archives, Segre Collection

10. Fred HoylePhoto by Ramsey and Muspratt, courtesy AIP Emilio Segre Visual Archives, Physics Today Collection

11. Hermann BondiAIP Emilio Segre Visual Archives, Physics Today Collection

12. Solvay Conference, June 1958Seated l–r: W.H. McCrea, J.H. Oort, G. Lemaître, C.J. Gorter, W. Pauli, Sir W.L. Bragg, J.R. Oppenheimer, C. Moller, H. Shapley, O. Heckmann; Standing, l–r: O.B. Klein, W.W. Morgan, F. Hoyle(back), B.V. Kukaskin, V.A. Ambarzumian (front), H.C. van de Hulst (back), M. Fierz, A.R. Sandage (back), W. Baade, E. Schatzman (front), J.A. Wheeler (back), H. Bondi, T. Gold, H. Zanstra (back), L. Rosenfeld, P. Ledoux (back), A.C.B. Lovell, J. GeheniauPhotograph by G. Coopmans, Institut International de Physique Solvay, courtesy AIP Emilio Segre Visual Archives, Leon Brillouin

13. Alexander Friedmann, near MoscowLeningrad Physico-Technical Institute, courtesy AIP Emilio Segre Visual Archives

14. Willem de SitterScience Photo Library

15. Albert Einstein with Hendrik Lorentz, circa 1920Museum Boerhaave, Leiden

16. Vesto SlipherAIP Emilio Segre Visual Archives

17. Milton Humason, 1923Photograph by Margaret Harwood, courtesy AIP Emilio Segre Visual Archives

18. Mount Wilson Observatory under construction, 1904The Hale Observatories, courtesy AIP Emilio Segre Visual Archives

19. 100-inch Hooker telescope, Mount Wilson ObservatoryPhotograph by Edison R. Hoge, Hale Observatories, courtesy AIP Emilio Segre Visual Archives

20. Edwin Hubble (left) and James Jeans (right) at the 100-inch telescope at Mount Wilson ObservatoryAIP Emilio Segre Visual Archives, Physics Today Collection

21. 200-inch Hale telescope, Palomar ObservatoryMt. Wilson-Palomar Observatories photo, courtesy AIP Emilio Segre Visual Archives, Physics Today Collection

22. Hubble in the 200-inch observer cage, 1950HUB 1042 (7), Edwin Hubble Papers, The Huntington Library, San Marino, California

23. Allan SandageCourtesy of The Observatories of the Carnegie Institution of Washington

24. Fraunhofer lines

25. Flame emission spectrum of copperPhysics Department, Imperial College/Science Photo Library

26. Hertzsprung-Russell diagramESO (European Southern Observatory)

27. Leavitt’s plot of brightness vs period for Cepheids in Small Magellanic CloudBennett, Jeffrey O.; Donahue, Megan O.; Schneider, Nicholas; Voit, Mark, The Cosmic Perspective, 4th © 2006. Printed and electronically reproduced by permission of Pearson Education, Inc., New York, New York

28. Hubble’s law The ‘velocity’ of galaxies (v) is proportional to the distance to the galaxies (d). The two values are related by the Hubble constant (H).

29. Infrared view of the Orion NebulaESO/J. Emerson/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit

30. The Lowell Observatory at Anderson Mesa, ArizonaTony and Daphne Hallas/Science Photo Library

31. Spiral galaxy NGC 1232ESO

32. The echo of the Big Bang John C. Mather shows some of the earliest data from the COBE spacecraft (the COBE blackbody curve) on 6 Oct. 2006 at NASA Headquarters in Washington, DC.NASA/Bill Ingalls

33. Flat, closed and open universe diagramMark Garlick/Science Photo Library

34. Cosmic microwave background seen by Planck The map shows tiny temperature fluctuations that correspond to regions of slightly different densities at very early times, representing the seeds of all future structure, including the galaxies of today.ESA and the Planck Collaboration

35. Planck power spectrum of the cosmic microwave background The dots are measurements made by Planck. The wiggly line represents the predictions of the ‘Lambda–CDM’ model of the Universe.ESA and the Planck Collaboration

Introduction

The Most Important Fact

The Universe began. The origin of everything we see about us – stars, planets, galaxies, people – can be traced back to a definite moment in time, 13.8 billion years ago. The ‘ultimate’ question that baffled philosophers, theologians and scientists for millennia has been answered in our lifetime. It has taken almost exactly half a century, starting in the mid-1960s with the discovery of the cosmic microwave background radiation,1 for the idea of a Universe of finite age to go from being a plausible hypothesis – but no more plausible than the idea of an eternal, infinite Universe – to being established as fact. The age of the Universe has been measured with exquisite precision using data from space observatories such as Planck. But accounts of this scientific triumph often overlook the fact that there is a second leg to the journey. The existence of this second leg is what makes the discovery of the beginning so compelling.

The most important thing we know in science is that our theory of the very small – quantum theory – agrees precisely with our theory of the very large – cosmology, aka the general theory of relativity. This is in spite of the fact that the two theories were developed entirely independently and that nobody has been able to unify these two great theories into one package, quantum gravity. But the fact that they separately give the ‘right’ answers to the same question tells us that there is something fundamentally correct about the whole of physics and, indeed, the whole scientific enterprise. It works.

What is that profound question? How do we know they agree? Because the age of the Universe calculated by cosmologists, 13.8 billion years, is just a tiny bit older than the ages of the stars it contains, as calculated by astrophysicists. This is such a profound insight that it ought to be shouted from the rooftops; instead, it is taken for granted. I intend to redress the balance.

Recent events have highlighted the way in which the significance of this agreement has slipped under the radar. I was provoked into writing this book when, in the spring of 2013, data from the Planck satellite made headlines. The story trumpeted by the media was that ‘the Universe is older than we thought’. This caused wry amusement amongst cosmologists. Although true, what the data told us is that the estimated age of the Universe had increased from 13.77 billion years to 13.82 billion years, an increase of less than half of one per cent (later revised down to 13.80 billion years). What is more astonishing about these data is that we know the age of the Universe to such a degree of accuracy. A generation ago (although even then we knew that there had been a beginning), we could only say that the Universe was somewhere between 10 and 20 billion years old. The precision of the new measurement is half of the most important fact – both in physics, which is the focus of this book, as well as in the wider world of thought. The philosophical and religious implications I leave for others to debate.

The ages of the oldest stars show that they are just a little bit younger than the Universe. If that doesn’t sound impressive, imagine how scientists would feel if it were the other way round – if stars were measured as being older than the Universe! It would tell them that at least one of their two most cherished theories, quantum physics and the general theory of relativity, must be wrong.

In fact, we don’t have to imagine how scientists would feel if stars were measured as being older than the Universe. The consensus I have just described has emerged since the end of the Second World War, which coincidentally means that it has emerged precisely during my lifetime and that I was not only a member of one of the teams that measured the age of the Universe but knew personally many of the people involved in this story. When I was a child, astronomers did indeed find that their estimates of the ages of stars came out bigger than their estimate of the age of the Universe. This was one of the underpinnings of the ‘steady-state’ model, which perceived the Universe as infinite in time and space, and essentially unchanging. I will explain how we got from the apparent conflict of the 1940s to the modern consensus, including the significance of the Planck results, and will make the importance of this consensus clear. But I will also set the scene by looking at the ‘prehistory’ of the subjects, cosmology and astrophysics, going back to the 19th century discoveries that pointed the way to an understanding of the nature of stars and the Universe – to the most important fact.

John Gribbin 1 June 2015

PART ZERO

Prologue

PART ONE

How Do We Know the Ages of Stars?

12.898

Prehistory: Spectra and the nature of stars

The positivist philosopher Auguste Comte wrote in 1835 that: ‘there is no conceivable means by which we shall one day determine the chemical composition of the stars’. Unknown to him, the first step towards that understanding had, in fact, already been taken, and the process would be completed not long after his death in 1857.

Locating lines