# The Nature of Space and Time

Publication Year: 2010

Einstein said that the most incomprehensible thing about the universe is that it is comprehensible. But was he right? Can the quantum theory of fields and Einstein’s general theory of relativity, the two most accurate and successful theories in all of physics, be united into a single quantum theory of gravity? Can quantum and cosmos ever be combined? In *The Nature of Space and Time*, two of the world’s most famous physicists—Stephen Hawking (*A Brief History of Time*) and Roger Penrose (*The Road to Reality*)—debate these questions.

The authors outline how their positions have further diverged on a number of key issues, including the spatial geometry of the universe, inflationary versus cyclic theories of the cosmos, and the black-hole information-loss paradox. Though much progress has been made, Hawking and Penrose stress that physicists still have further to go in their quest for a quantum theory of gravity.

Published by: Princeton University Press

Series: Princeton Science Library

#### Cover

#### Title Page, Copyright Page

#### Foreword

THE DEBATE between Roger Penrose and Stephen Hawking recorded in this book was the high point of a six-month program held in 1994 at the Isaac Newton Institute for Mathematical Sciences at the University of Cambridge. It represents a serious discussion of some of the most fundamental ideas about the nature of the universe. Needless to say, we are not yet...

#### CHAPTER ONE: Classical Theory

s. W. Hawking

IN THESE LECTURES, Roger Penrose and I will put forward our related but rather different viewpoints on the nature of space and time. We shall speak alternately and shall give three lectures each, followed by a discussion on our different approaches. I should emphasize that these will be...

#### CHAPTER TWO: Structure of Spacetime Singularities

R. Penrose

IN THE FIRST LECTURE by Stephen Hawking, singularity theorems were discussed. The essential content of these theorems is that under reasonable (global) physical conditions, singularities must be expected. They do not say anything about the nature of the singularities, or where the singularities are to be found. On the other hand, the theorems are very...

#### CHAPTER THREE: Quantum Black Holes

S. W. Hawking

IN MY SECOND LECTURE, I'm going to talk about the quantum theory ofblack holes. It seems to lead to a new level of unpredictability in physics over and above the usual uncertainty associated with quantum mechanics. This is because black holes appear to have intrinsic entropy and to lose information from our region of the universe. I should say that these claims...

#### CHAPTER FOUR: Quantum Theory and Spacetime

R. Penrose

THE GREAT PHYSICAL THEORIES of the twentieth century have been quantum theory (QT), special relativity (SR), general relativity (GR), and quantum field theory (QFf). 'These theories are not independent of each other: general relativity was built on special relativity, and quantum field...

#### CHAPTER FIVE: Quantum Cosmology

S. W. Hawking

IN MY THIRD LECTURE, I shall turn to cosmology. Cosmology used to be considered a pseudoscience and the preserve of physicists who might have done useful work in their earlier years, but who had gone mystic in their dotage. There were two reasons for this. The first was that there was an almost...

#### CHAPTER SIX: The Twistor View of Spacetime

R. Penrose

LET ME START with some remarks about Stephen's last lecture. • Classicality of Cats. Stephen argued that because a certain region of spacetime is inaccessible we are forced into the density matrix description. However, this is not sufficient to explain the classical nature of observations in our region. The density matrix that corresponds to finding...

#### CHAPTER SEVEN: The Debate

S. W. Hawking and R. Penrose

THESE LECTURES HAVE SHOWN very clearly the difference between Roger and me. He's a Platonist and I'm a positivist. He's worried that Schrodinger's cat is in a quantum state, where it is half alive and half dead. He feels that can't correspond to reality. But that doesn't bother me. I don't demand that a theory correspond to reality because I don't know what...

#### AFTERWORD TO THE 2010 EDITION: The Debate Continues

s. W. Hawking and R. Penrose

IN THE YEARS FOLLOWING the original publication of *The Nature
of Space and Time*, there have been many important developments,
both on the observational and theoretical sides. Yet, despite this increased
knowledge, our two points of view appear to have diverged
even further, rather than come together to a clear, common understanding.
This is, no doubt, indicative...

E-ISBN-13: 9781400834747

E-ISBN-10: 1400834740

Print-ISBN-13: 9780691145709

Print-ISBN-10: 0691145709

Page Count: 160

Publication Year: 2010

Edition: With a New afterword by the authors

Series Title: Princeton Science Library

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