General relativity theory began in the early twentieth century in the borderland
between physics and mathematics. After the initial confrontation of the theory with
the three classic tests (red shift, Mercury perihelion shift, deflection of starlight),
there was little contact between theory and observation until the last half of the
century. But then the discovery of the cosmic microwave background radiation
made it clear that the theory had much to offer for describing the evolving universe.
Since then the field of observational cosmology has blossomed, using many different approaches to measuring the properties of the universe on a large scale.
Theoretical cosmology has naturally blossomed with it and the combination of
observation and theory has resulted in the present standard model of cosmology, the
lambda cold dark matter or LCDM model. It is fair to say that there is now no more
active area in fundamental physics than cosmology.
But we must not underestimate the progress in relativity theory and observation
for other basic systems, notably neutron stars and black holes. The agreement
between black hole theory based on the Kerr metric and diverse observations is one
of the most impressive successes in physics. This is most relevant now that it has
become apparent how important supermassive black holes are for the structure and
evolution of the universe.
Another truly extraordinary prediction of general relativity has been verified
with the observation of gravitational waves. The first waves detected were generated by binary black hole and neutron star mergers, using the LIGO and Virgo
detectors. The detection required a century of thought and decades of experimental
effort. Certainly, the connection of the two extraordinary predictions of relativity
theory, black holes and gravitational waves, is most impressive and gratifying. The
future promises to be even more interesting since gravitational waves are an entirely
new observational window on the cosmos, and there is no way to predict what they
might reveal.
Clearly, the frontier of fundamental physics research has now shifted to the large
end of the distance scale, the universe. But our understanding of the universe
requires also an understanding of the small end of the distance scale, most notably
in our study of the early universe. The thriving field now called particle astrophysics and cosmology (PAC) did not even exist until almost the twenty-first
century but is now the center of much frontier research.
A remarkable fact concerning the detection of neutron star mergers and the
gravitational waves they emit is worth noting here; the kilonovas that are the end
result of the mergers are the source of much of the heavier elements we observe in
the universe, including the matter that makes up our planet and notably—ourselves.
The purpose of this book is to introduce the reader to general relativity theory
and all that it can tell us about the universe. It is intended to be as clear, simple, and
brief as possible, and as rigorous as reasonable. It is divided into four somewhat
independent parts that might be considered separate volumes.
Part I is a brief review of special relativity; most physics students will have
studied special relativity in other courses and may skim easily over this part, but it
can serve as a brief introduction for others.
viii
Preface
between physics and mathematics. After the initial confrontation of the theory with
the three classic tests (red shift, Mercury perihelion shift, deflection of starlight),
there was little contact between theory and observation until the last half of the
century. But then the discovery of the cosmic microwave background radiation
made it clear that the theory had much to offer for describing the evolving universe.
Since then the field of observational cosmology has blossomed, using many different approaches to measuring the properties of the universe on a large scale.
Theoretical cosmology has naturally blossomed with it and the combination of
observation and theory has resulted in the present standard model of cosmology, the
lambda cold dark matter or LCDM model. It is fair to say that there is now no more
active area in fundamental physics than cosmology.
But we must not underestimate the progress in relativity theory and observation
for other basic systems, notably neutron stars and black holes. The agreement
between black hole theory based on the Kerr metric and diverse observations is one
of the most impressive successes in physics. This is most relevant now that it has
become apparent how important supermassive black holes are for the structure and
evolution of the universe.
Another truly extraordinary prediction of general relativity has been verified
with the observation of gravitational waves. The first waves detected were generated by binary black hole and neutron star mergers, using the LIGO and Virgo
detectors. The detection required a century of thought and decades of experimental
effort. Certainly, the connection of the two extraordinary predictions of relativity
theory, black holes and gravitational waves, is most impressive and gratifying. The
future promises to be even more interesting since gravitational waves are an entirely
new observational window on the cosmos, and there is no way to predict what they
might reveal.
Clearly, the frontier of fundamental physics research has now shifted to the large
end of the distance scale, the universe. But our understanding of the universe
requires also an understanding of the small end of the distance scale, most notably
in our study of the early universe. The thriving field now called particle astrophysics and cosmology (PAC) did not even exist until almost the twenty-first
century but is now the center of much frontier research.
A remarkable fact concerning the detection of neutron star mergers and the
gravitational waves they emit is worth noting here; the kilonovas that are the end
result of the mergers are the source of much of the heavier elements we observe in
the universe, including the matter that makes up our planet and notably—ourselves.
The purpose of this book is to introduce the reader to general relativity theory
and all that it can tell us about the universe. It is intended to be as clear, simple, and
brief as possible, and as rigorous as reasonable. It is divided into four somewhat
independent parts that might be considered separate volumes.
Part I is a brief review of special relativity; most physics students will have
studied special relativity in other courses and may skim easily over this part, but it
can serve as a brief introduction for others.
viii
Preface