### From Publishers Weekly

Starred Review. If it's possible to write a literary treatment of cutting-edge cosmology, groundbreaking physicist Bojowald has done it, complete with illustrations of abstract sculpture and quotes from thinkers as diverse as Nietzsche, Schopenhauer, Charles Dickens, and Joseph Heller. Bojowald, a professor of physics at Penn State, explores loop quantum theory, an idea he developed as a postdoctoral student in 2000, to fill in the gaps left by 20th-century physics. Despite advances like relativity theory, curved space, and quantum theory, physics falters when it comes to explaining what happened before the Big Bang, when time, space, matter, and energy were all shrunk into a bizarre entity called a singularity, where math and logic as we know them failed. Later, string theory, with its extra dimensions and elegant equations, offered promise, but only with loop quantum cosmology were physicists able to see the universe be born, expand, shrink, and be reborn, over and over again. Bojowald largely avoids mathematics for accessibility, but that can leave his writing dense with rigor as he strives to cover "the Whole Story." Readers willing to meet his challenge will find a fascinating new universe revealed by his enthusiastic firsthand approach. 37 illus. (Nov.) (c)

Copyright © PWxyz, LLC. All rights reserved.

Copyright © PWxyz, LLC. All rights reserved.

### From Booklist

In theoretical physics, gravity can be an intractable problem. At extreme values prevalent near the big bang or black holes, general relativity can’t accommodate it. String theory purports to be a solution, but not all physicists are on the string bandwagon. One such recalcitrant, Bojowald champions a rival theory called loop quantum gravity, which he here valiantly presents to the nonmathematical. If his explanation daunts some science readers, its implications will be sufficiently clear and exciting to pull them through his text, because those involve the start of the big bang and the interior of a black hole. Notionally, each one is a singularity as Bojowald describes the failure of mathematics when energy density goes to infinity and space collapses to zero volume. Loop quantum gravity offers an escape from these terrifying places by acting like a quantum-mechanical Atlas who holds space open just enough so that physics—the universe—can continue to exist. Complex but comprehensible, Bojowald’s treatment of loop quantum gravity should compete with popular string-theory titles such as Endless Universe (2007), by Paul Steinhardt and Neil Turok. --Gilbert Taylor

### Review

“Readers will find undoubted insights into one possible explanation of the universe at its most fundamental and will experience the work of top-level science.”

—

“

—

“Bojowald argues precisely and meticulously.”

—

“Bojowald manages to describe these complicated ideas without bogging down in mathematical notation. And like Stephen Hawking, he manages to help readers over the difficult spots with entertaining and literate prose.”

—

“Bojowald’s explanations are thorough and logical, and his ideas and metaphors [have] panache.”

—

—

*The Wall Street Journal*“

*Once Before Time*tells the story of Bojowald’s discovery and its implications in fascinating, eloquent, even literary prose.”—

*New Scientist*“Bojowald argues precisely and meticulously.”

—

*Providence Journal*“Bojowald manages to describe these complicated ideas without bogging down in mathematical notation. And like Stephen Hawking, he manages to help readers over the difficult spots with entertaining and literate prose.”

—

*Pittsburgh Post-Gazette*“Bojowald’s explanations are thorough and logical, and his ideas and metaphors [have] panache.”

—

*The Columbus Dispatch**--This text refers to the Paperback edition.*### About the Author

Martin Bojowald is an associate professor of physics at Pennsylvania State University’s Institute for Gravitation and the Cosmos. Originally from Germany, he now resides in Pennsylvania.

### Excerpt. © Reprinted by permission. All rights reserved.

1. Gravitation

Mass Attraction

Should something from the window fall

(and if it just the smallest be)

how jumps the law of gravity

as mighty as wind from the sea

at every ball or blueberry

and takes them to the core of all.

-Rainer Maria Rilke,

Over large distances, the universe is governed by the gravitational force. In physics, the action of a force is the cause of motion or of any form of change. Complete rest is possible only if no net forces are acting. One scenario in which this can happen is the absence of any matter whatsoever-a state called vacuum. But matter quite obviously does exist, and just by its mass it causes gravitational forces on other masses. To realize motionless states of rest, at least approximately, all acting forces must compensate each other. In addition to gravity, there are the electric and magnetic forces to be considered, as well as two kinds of forces called weak and strong interactions, reigning in the realm of elementary particles.

While the electric force is easily compensated over large distances by the existence of positive and negative charges, mutually neutralizing each other, the forces that come into play in the interior of nuclei act only at extremely short range. What remains over long distances is gravity alone. It rules the general attraction of masses and energy distributions in space, and thus dictates the behavior of the universe itself. In contrast to electricity, there are no negative masses: Gravitational attraction cannot be fully compensated. Once massive objects such as stars or entire galaxies form, the resulting gravitational interaction dominates all that happens. The facets of this commonplace force, often ignored in recent research and yet-in cosmology and black holes-giving rise to a rich variety of exotic phenomena, are the topic of this book.

Newton's law of gravity:

Distant action and a fatal flaw

The first general law of gravity was formulated by Isaac Newton. As is typical for many important steps in gravitational research, this theoretical development required a unified view on well-known phenomena on Earth with a long list of intricate observations of objects in space: the moon and some planets. The latter was accomplished thanks to technologies that, for those times, were highly sophisticated; conversely, such research has spawned the development of new instruments. Combining fundamental questions and technological applications, in many areas of science and in gravitational research in particular, is a success story that continues into the present day.

Even before Newton, the initial untidy flood of data, as it was accumulated by astronomers such as Tycho Brahe, Johannes Kepler, and many others, was ordered into a model of the solar system. Since Nicolaus Copernicus and Kepler, this model has largely held the form we know today: Planets orbit around the sun along trajectories that, by a good approximation, can be considered as ellipses, or slightly oblong circles. But what is propelling the planets along their curved tracks? From common observations we know that a force is necessary to keep a body from moving stubbornly along a straight line. How can one describe or even explain the required force in the case of the planets?

Newton's groundbreaking insight-the existence of a universal force of gravity causing not only the motion of all planets around the sun, and of the moon around the earth, but also the everyday phenomena of falling objects-is impressive. It is an excellent example of the origin of scientific explanation: not an answer to a "why" question in the sense of an anthropomorphic motivation, but a plethora of complicated phenomena, unrelated at first sight, reduced to a single mechanism: a law of nature. Newton's mathematical description of the situation is very compact and highly efficient for predictions of new phenomena described by the same law. In the case of Newton's law of gravity, the unfathomable power of theoretical prediction has repeatedly been employed-for instance, to find new planets via small deviations imposed by their gravitational pull on the trajectories of other planets, or in planning modern satellite missions.

Such success stories, in which an elegant mathematical description explains and predicts a multitude of phenomena, can be found throughout physics; they are indeed the landmarks of its progress. Reliving such insights is often so gratifying that scientists employ the term "beauty"-a pragmatic kind of beauty whose core, the mathematical formulation, can be seen only by the initiated, but which in its concrete successes can also be appreciated by outsiders.1

Concretely, Newton's law of gravity describes the attractive force between two bodies caused by their masses. The force increases proportionally with the amounts of the masses: The attraction between two heavy bodies is larger than that between two light ones. It is also inversely proportional to the squared distance between the bodies; it weakens considerably when the bodies are farther apart. In addition to these proportionalities, the exact quantitative strength of the force is determined by a mathematical parameter, now called Newton's gravitational constant. In this value one can see the unification of earthly and heavenly phenomena. The gravitational constant can be derived from the tiny attraction of two masses on Earth, as was first accomplished in Henry Cavendish's laboratory in 1797 and '98; using the same value to calculate the force exerted by the sun on the planets shows exactly the right nudge required to hold the planets on their observed orbits.

In contrast to its clear dependence on distance, Newton's gravitational force is completely independent of time. Time independence sounds plausible, for a fundamental law of nature should, after all, be valid at all times in the same way. It is also consistent with the dominant understanding of space and time in Newton's age and long thereafter, not to mention our everyday conceptions of them. Although one can easily change the positions and distances of objects in space, space itself appears unchangeable. Also, time seems to pass simply and uniformly, without being influenced by physical processes or technical instruments. Since gravity, according to Newton, acts instantaneously-independently of how far apart the masses are-the force need be formulated only for the case of two masses not at the same place, but at the same time.

Despite its plausible form and celebrated successes, Newton's theory did have a flaw in its beauty. Like the beauty of the theory itself, this flaw, too, can be understood completely only with a sufficient amount of background knowledge. But even on the surface, it is a good example of the progress of theoretical physics. Newton himself had reportedly been uneasy about the "animalistic" tendencies of his law of gravitation: As an animal is attracted from far away by the expectation of food or companionship, a massive body appeared to move toward another one from a distance. This action at a distance, apparently without the more intuitive type of local interactions as realized for bodies pushing each other at close contact, was considered a serious conceptual weakness in spite of all concrete successes.

It is extremely difficult to correct this weak spot by constructing a theory only of local interactions that, of course, should otherwise remain compatible with the astronomical successes of Newton's theory. To start with, one will have to consider the time dimension, too, for such a local interaction must take some time to propagate from one body to the other. As it turned out, a consistent reformulation is possible only by radically changing Newton's-and our-intuitive conceptions of space and time. It requires much more highly sophisticated mathematical machineries and substantial efforts, but these efforts are rewarded by a theory of unprecedented beauty in the sense described above. All this required dedicated physical research and, not least, a strong mathematical grounding. The flaw in Newton's theory was to be corrected only long after Newton-by Albert Einstein.

Relativity of space and time:

Space-time transformers

All this took a long time, or a short time: for, strictly speaking, no time on earth exists for such things.

-friedrich nietzsche, Thus Spoke Zarathustra

In physics, as in all of science, it is important to distinguish between properties that depend on the person making an observation and properties independent of an observer. The mass of a particle refers only to the particle itself and will, if the particle remains unchanged, always be measured as the same value. Except for unavoidable experimental inaccuracies, it does not matter who is doing the measurement. A particle's velocity, on the other hand, appears different, and sometimes drastically so, depending on whether an observer is moving with respect to the particle. An observer moving along with the particle at exactly the same speed would perceive the particle as being at rest, well known from two cars cruising side by side along a straight stretch of highway. To the driver of one car, the other one seems not to be moving. Any other observer would see the car (or the particle) move and attribute to it a nonzero velocity. Relativity in general terms is the mathematical analysis of such relationships; it ultimately tells us what we can learn about nature in a fully objective, observer-independent way.

For many centuries, space and time were thought of as observer- independent. Distances between points and durations of temporal periods appeared absolute, no matter how an observer would be positioned or move. But the first fault lines in this worldview opened up toward the end of the nineteenth century, eventually leading to special relativity. In this new view, space and time cannot be seen in s...

Mass Attraction

Should something from the window fall

(and if it just the smallest be)

how jumps the law of gravity

as mighty as wind from the sea

at every ball or blueberry

and takes them to the core of all.

-Rainer Maria Rilke,

*The Book of Hours*Over large distances, the universe is governed by the gravitational force. In physics, the action of a force is the cause of motion or of any form of change. Complete rest is possible only if no net forces are acting. One scenario in which this can happen is the absence of any matter whatsoever-a state called vacuum. But matter quite obviously does exist, and just by its mass it causes gravitational forces on other masses. To realize motionless states of rest, at least approximately, all acting forces must compensate each other. In addition to gravity, there are the electric and magnetic forces to be considered, as well as two kinds of forces called weak and strong interactions, reigning in the realm of elementary particles.

While the electric force is easily compensated over large distances by the existence of positive and negative charges, mutually neutralizing each other, the forces that come into play in the interior of nuclei act only at extremely short range. What remains over long distances is gravity alone. It rules the general attraction of masses and energy distributions in space, and thus dictates the behavior of the universe itself. In contrast to electricity, there are no negative masses: Gravitational attraction cannot be fully compensated. Once massive objects such as stars or entire galaxies form, the resulting gravitational interaction dominates all that happens. The facets of this commonplace force, often ignored in recent research and yet-in cosmology and black holes-giving rise to a rich variety of exotic phenomena, are the topic of this book.

Newton's law of gravity:

Distant action and a fatal flaw

The first general law of gravity was formulated by Isaac Newton. As is typical for many important steps in gravitational research, this theoretical development required a unified view on well-known phenomena on Earth with a long list of intricate observations of objects in space: the moon and some planets. The latter was accomplished thanks to technologies that, for those times, were highly sophisticated; conversely, such research has spawned the development of new instruments. Combining fundamental questions and technological applications, in many areas of science and in gravitational research in particular, is a success story that continues into the present day.

Even before Newton, the initial untidy flood of data, as it was accumulated by astronomers such as Tycho Brahe, Johannes Kepler, and many others, was ordered into a model of the solar system. Since Nicolaus Copernicus and Kepler, this model has largely held the form we know today: Planets orbit around the sun along trajectories that, by a good approximation, can be considered as ellipses, or slightly oblong circles. But what is propelling the planets along their curved tracks? From common observations we know that a force is necessary to keep a body from moving stubbornly along a straight line. How can one describe or even explain the required force in the case of the planets?

Newton's groundbreaking insight-the existence of a universal force of gravity causing not only the motion of all planets around the sun, and of the moon around the earth, but also the everyday phenomena of falling objects-is impressive. It is an excellent example of the origin of scientific explanation: not an answer to a "why" question in the sense of an anthropomorphic motivation, but a plethora of complicated phenomena, unrelated at first sight, reduced to a single mechanism: a law of nature. Newton's mathematical description of the situation is very compact and highly efficient for predictions of new phenomena described by the same law. In the case of Newton's law of gravity, the unfathomable power of theoretical prediction has repeatedly been employed-for instance, to find new planets via small deviations imposed by their gravitational pull on the trajectories of other planets, or in planning modern satellite missions.

Such success stories, in which an elegant mathematical description explains and predicts a multitude of phenomena, can be found throughout physics; they are indeed the landmarks of its progress. Reliving such insights is often so gratifying that scientists employ the term "beauty"-a pragmatic kind of beauty whose core, the mathematical formulation, can be seen only by the initiated, but which in its concrete successes can also be appreciated by outsiders.1

Concretely, Newton's law of gravity describes the attractive force between two bodies caused by their masses. The force increases proportionally with the amounts of the masses: The attraction between two heavy bodies is larger than that between two light ones. It is also inversely proportional to the squared distance between the bodies; it weakens considerably when the bodies are farther apart. In addition to these proportionalities, the exact quantitative strength of the force is determined by a mathematical parameter, now called Newton's gravitational constant. In this value one can see the unification of earthly and heavenly phenomena. The gravitational constant can be derived from the tiny attraction of two masses on Earth, as was first accomplished in Henry Cavendish's laboratory in 1797 and '98; using the same value to calculate the force exerted by the sun on the planets shows exactly the right nudge required to hold the planets on their observed orbits.

In contrast to its clear dependence on distance, Newton's gravitational force is completely independent of time. Time independence sounds plausible, for a fundamental law of nature should, after all, be valid at all times in the same way. It is also consistent with the dominant understanding of space and time in Newton's age and long thereafter, not to mention our everyday conceptions of them. Although one can easily change the positions and distances of objects in space, space itself appears unchangeable. Also, time seems to pass simply and uniformly, without being influenced by physical processes or technical instruments. Since gravity, according to Newton, acts instantaneously-independently of how far apart the masses are-the force need be formulated only for the case of two masses not at the same place, but at the same time.

Despite its plausible form and celebrated successes, Newton's theory did have a flaw in its beauty. Like the beauty of the theory itself, this flaw, too, can be understood completely only with a sufficient amount of background knowledge. But even on the surface, it is a good example of the progress of theoretical physics. Newton himself had reportedly been uneasy about the "animalistic" tendencies of his law of gravitation: As an animal is attracted from far away by the expectation of food or companionship, a massive body appeared to move toward another one from a distance. This action at a distance, apparently without the more intuitive type of local interactions as realized for bodies pushing each other at close contact, was considered a serious conceptual weakness in spite of all concrete successes.

It is extremely difficult to correct this weak spot by constructing a theory only of local interactions that, of course, should otherwise remain compatible with the astronomical successes of Newton's theory. To start with, one will have to consider the time dimension, too, for such a local interaction must take some time to propagate from one body to the other. As it turned out, a consistent reformulation is possible only by radically changing Newton's-and our-intuitive conceptions of space and time. It requires much more highly sophisticated mathematical machineries and substantial efforts, but these efforts are rewarded by a theory of unprecedented beauty in the sense described above. All this required dedicated physical research and, not least, a strong mathematical grounding. The flaw in Newton's theory was to be corrected only long after Newton-by Albert Einstein.

Relativity of space and time:

Space-time transformers

All this took a long time, or a short time: for, strictly speaking, no time on earth exists for such things.

-friedrich nietzsche, Thus Spoke Zarathustra

In physics, as in all of science, it is important to distinguish between properties that depend on the person making an observation and properties independent of an observer. The mass of a particle refers only to the particle itself and will, if the particle remains unchanged, always be measured as the same value. Except for unavoidable experimental inaccuracies, it does not matter who is doing the measurement. A particle's velocity, on the other hand, appears different, and sometimes drastically so, depending on whether an observer is moving with respect to the particle. An observer moving along with the particle at exactly the same speed would perceive the particle as being at rest, well known from two cars cruising side by side along a straight stretch of highway. To the driver of one car, the other one seems not to be moving. Any other observer would see the car (or the particle) move and attribute to it a nonzero velocity. Relativity in general terms is the mathematical analysis of such relationships; it ultimately tells us what we can learn about nature in a fully objective, observer-independent way.

For many centuries, space and time were thought of as observer- independent. Distances between points and durations of temporal periods appeared absolute, no matter how an observer would be positioned or move. But the first fault lines in this worldview opened up toward the end of the nineteenth century, eventually leading to special relativity. In this new view, space and time cannot be seen in s...

*--This text refers to the Paperback edition.*