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The Riddle of Gravitation
In this thought-provoking book, written for the layman, a noted physicist offers a fresh, nonmathematical introduction to the conceptual foundations of both Newton's and Einstein's theories of gravitation. Since Einstein's general relativity theory, which deals with gravitation, requires some acquaintance with the ideas of the special theory of relativity (not in itself concerned with gravitation), the first part of the book is devoted primarily to the special theory. This section ranges from Newtonian physics through Einstein's discovery of the relativity of time and space, to the fusion of time and space into a four-dimensional whole by Hermann Minkowski.
Part Two is concerned with the general theory of relativity proper. General relativity is based on the hypothesis that, under the influence of gravity, space and time are curved, rather than flat, and that all aspects of gravity can be understood in terms of geometry. Part Three is devoted to recent developments, including the search for gravitational waves, the quantum theory of gravitation, particle motion, and other topics. Five appendixes contain mathematical derivations for the reader who desires a more technical treatment of the subject.
For this new edition, Professor Bergmann has also added updated material on gravitational radiation detectors, current problems in cosmology, the significance of singularities of the gravitational field, and more. The result is a fascinating excursion into the rarefied world of theoretical physics, yet one that is well within the grasp of the nonphysicist. Indeed, any intelligent layman, curious about relativity theory and its relation to current astronomical knowledge, will welcome this eloquent and cogent presentation of the subject.
Part Two is concerned with the general theory of relativity proper. General relativity is based on the hypothesis that, under the influence of gravity, space and time are curved, rather than flat, and that all aspects of gravity can be understood in terms of geometry. Part Three is devoted to recent developments, including the search for gravitational waves, the quantum theory of gravitation, particle motion, and other topics. Five appendixes contain mathematical derivations for the reader who desires a more technical treatment of the subject.
For this new edition, Professor Bergmann has also added updated material on gravitational radiation detectors, current problems in cosmology, the significance of singularities of the gravitational field, and more. The result is a fascinating excursion into the rarefied world of theoretical physics, yet one that is well within the grasp of the nonphysicist. Indeed, any intelligent layman, curious about relativity theory and its relation to current astronomical knowledge, will welcome this eloquent and cogent presentation of the subject.
- GenresPhysicsScienceNonfiction
234 pages, Paperback
First published October 1, 1977
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Displaying 1 - 4 of 4 reviews
July 26, 2024
Bergmann was an associate of Einstein and who wrote about Einstein’s theory of relativity. The book was on the thick side. A few things, though, struck me as interesting.
Bergmann writes that “in Newton’s time, only two kinds of force were available for quantitative investigation: “One was the force of gravity; the other the forces of push and pull in everyday life, pushing a baby carriage, say, or pulling a dog by its leash.” Separating gravity from push and pull like this (two separate forces) is confusing as gravity’s so-called attractive force is a “pulling” inward. Gravity and pulling are not, in other words, two separate forces. And, when a larger mass collides with a smaller mass, isn’t there a “pushing” effect as well, which is not attraction? In both cases - pulling and pushing - there are accelerating effects of one body pulling or pushing another, with the respective masses of the bodies determining which pulls or pushes the other and to what degree.
There’s this commonly stated understanding of gravity as “mutual” attraction between two bodies. How does attraction work “mutually” when a larger mass is dominant relative to a lesser mass? While there is some mutual tugging, it’s a losing dynamic vis-a-vis a larger mass. More importantly, as the lesser mass wants to remain at rest, if at rest, or to continue its straight-line motion, if in motion, isn’t such inertial resistance a counter to “attraction?”
While Newton’s focus was on the accelerating effects on such inertial bodies, in looking at external, accelerating impacts, he set inertia aside to look only at gravitational effects. Understanding gravity within the Newton paradigm, we see orbiting systems as gravitational systems: a smaller body is pulled into orbit by a larger mass. What gets lost in that formulation is inertial movement - the “desire of a body to not get pulled into orbit but to stay at rest or to continue in its straight line movement. Isn’t only half of the orbiting effect ignored: one body wants to go straight, and another body wants the lesser body to move, perpendicular to the gravitational center. The compromise between the inertial and gravitational movement is roughly a 45 degrees angle and there’s curvature as a result, i.e. an orbit. (Bergmann writes: “Gravity acts at right angles in the direction of the flight of a particle, thereby resulting in a curved trajectory.”)
Moving from solar systems to galaxies, many refer to the latter as orbiting systems. But is that accurate? When a large gravitational mass attracts a smaller body, the attraction of gravitational pull overcomes the lesser force and its inertial, resisting motion. Rather than the formation of an orbiting galaxy, might this be a large-scale example of Einstein's theory of relativity in which space-time is drawn toward the gravitational center. This, in turn, increases the density of gas and dust. It’s not pulling per se. It’s the propelling, inertial, force that cannot withstand the movement, shaped by geometry, toward the center. Seen that way, Bergmann speculates that there might very well be a sequence to galactic formation, beginning with dispersed gas and dust, which solidifies, forms spirals as it gathers and moves to the gravitational center, and then forms a bulge and eventually, a black hole at the center, which governs the galaxy (the inward movement, and its direction).
By not giving inertia its scientific due, the “pushing” part of the push-pull dynamic gets lost. Pushing, in effect, takes on another meaning as inertia becomes a counter-force that pushes (resists, per its relative mass) itself away from gravity’s pulling force. That “pushing away” is a resisting force (Unfortunately, inertia’s connotation of stasis suggests inactivity, not a force of movement per se). Also, as Bergman makes clear, inertia, as a fixed state, does not exist because everything is in motion in Einstein’s universe and, for measurement purposes, a frame of reference must be identified and stipulated. “In general relativity,” he says, “no straight-line coordinates exist, nor any other rigidly fixed coordinating systems.”
Under Einstein’s theory, Bergmann notes that kinematic mass is separate from gravitational mass. From him, I understand the former to mean that when velocity is added to a body - via gravitational (accelerating effects, pulling) or via a large body pushing a lesser body, the mass of the larger body is transferred, via the speed of motion, to a lesser body (per Newton).
Bergmann writes of gravity and electromagnetic fields that interconnect all mass-energy phenomena. When there’s movement toward a gravitational center, what is it that moves? With gravitational lensing, what is it that bends? This suggests that the so-called “fabric” of spacetime is constituted by something. What is it? Is it dark matter and energy? Is it neutrinos and cosmic rays?
As a last point, if everything is curvature in the Einstein cosmos, how can it be flat? Bergmann seems to make the point that even Hubble’s findings on galactic movement (moving farther away, with increasing speed) can be seen in terms of cosmic curvature, with movement arriving back at its beginning point.
Bergmann writes that “in Newton’s time, only two kinds of force were available for quantitative investigation: “One was the force of gravity; the other the forces of push and pull in everyday life, pushing a baby carriage, say, or pulling a dog by its leash.” Separating gravity from push and pull like this (two separate forces) is confusing as gravity’s so-called attractive force is a “pulling” inward. Gravity and pulling are not, in other words, two separate forces. And, when a larger mass collides with a smaller mass, isn’t there a “pushing” effect as well, which is not attraction? In both cases - pulling and pushing - there are accelerating effects of one body pulling or pushing another, with the respective masses of the bodies determining which pulls or pushes the other and to what degree.
There’s this commonly stated understanding of gravity as “mutual” attraction between two bodies. How does attraction work “mutually” when a larger mass is dominant relative to a lesser mass? While there is some mutual tugging, it’s a losing dynamic vis-a-vis a larger mass. More importantly, as the lesser mass wants to remain at rest, if at rest, or to continue its straight-line motion, if in motion, isn’t such inertial resistance a counter to “attraction?”
While Newton’s focus was on the accelerating effects on such inertial bodies, in looking at external, accelerating impacts, he set inertia aside to look only at gravitational effects. Understanding gravity within the Newton paradigm, we see orbiting systems as gravitational systems: a smaller body is pulled into orbit by a larger mass. What gets lost in that formulation is inertial movement - the “desire of a body to not get pulled into orbit but to stay at rest or to continue in its straight line movement. Isn’t only half of the orbiting effect ignored: one body wants to go straight, and another body wants the lesser body to move, perpendicular to the gravitational center. The compromise between the inertial and gravitational movement is roughly a 45 degrees angle and there’s curvature as a result, i.e. an orbit. (Bergmann writes: “Gravity acts at right angles in the direction of the flight of a particle, thereby resulting in a curved trajectory.”)
Moving from solar systems to galaxies, many refer to the latter as orbiting systems. But is that accurate? When a large gravitational mass attracts a smaller body, the attraction of gravitational pull overcomes the lesser force and its inertial, resisting motion. Rather than the formation of an orbiting galaxy, might this be a large-scale example of Einstein's theory of relativity in which space-time is drawn toward the gravitational center. This, in turn, increases the density of gas and dust. It’s not pulling per se. It’s the propelling, inertial, force that cannot withstand the movement, shaped by geometry, toward the center. Seen that way, Bergmann speculates that there might very well be a sequence to galactic formation, beginning with dispersed gas and dust, which solidifies, forms spirals as it gathers and moves to the gravitational center, and then forms a bulge and eventually, a black hole at the center, which governs the galaxy (the inward movement, and its direction).
By not giving inertia its scientific due, the “pushing” part of the push-pull dynamic gets lost. Pushing, in effect, takes on another meaning as inertia becomes a counter-force that pushes (resists, per its relative mass) itself away from gravity’s pulling force. That “pushing away” is a resisting force (Unfortunately, inertia’s connotation of stasis suggests inactivity, not a force of movement per se). Also, as Bergman makes clear, inertia, as a fixed state, does not exist because everything is in motion in Einstein’s universe and, for measurement purposes, a frame of reference must be identified and stipulated. “In general relativity,” he says, “no straight-line coordinates exist, nor any other rigidly fixed coordinating systems.”
Under Einstein’s theory, Bergmann notes that kinematic mass is separate from gravitational mass. From him, I understand the former to mean that when velocity is added to a body - via gravitational (accelerating effects, pulling) or via a large body pushing a lesser body, the mass of the larger body is transferred, via the speed of motion, to a lesser body (per Newton).
Bergmann writes of gravity and electromagnetic fields that interconnect all mass-energy phenomena. When there’s movement toward a gravitational center, what is it that moves? With gravitational lensing, what is it that bends? This suggests that the so-called “fabric” of spacetime is constituted by something. What is it? Is it dark matter and energy? Is it neutrinos and cosmic rays?
As a last point, if everything is curvature in the Einstein cosmos, how can it be flat? Bergmann seems to make the point that even Hubble’s findings on galactic movement (moving farther away, with increasing speed) can be seen in terms of cosmic curvature, with movement arriving back at its beginning point.
January 10, 2018
While I did learn a few things from reading this book, overall it cannot be recommended. There are some sections where the author explains things clearly and comprehensively. But more often than not, it seems like the ramblings of a scientist that has too many thoughts on the subject to order them. Two or three sentences on a topic, and then suddenly a complete sidetrack on something mildly related, which leads to a brief mention of a scientist that might be relevant, which goes to another sentence about some other work that is completely different from the first two sentences of the paragraph. Basically, there is no structure to the writing.
The diagrams and figures used to demonstrate concepts are atrocious. They basically try to take really complex theoretical concepts and reduce them to a kindergarten level chart. The result is that the charts demonstrate absolutely nothing, make no sense, and consequently the concept is never really explained because instead of explaining it, there is a reference to the chart.
The diagrams and figures used to demonstrate concepts are atrocious. They basically try to take really complex theoretical concepts and reduce them to a kindergarten level chart. The result is that the charts demonstrate absolutely nothing, make no sense, and consequently the concept is never really explained because instead of explaining it, there is a reference to the chart.
June 18, 2008
This was one of my first reads on relativity and it was really fascinating. It covers Newtonian gravity, special and general relativity, and quantum gravity. Yes, it's from 1968, but still (mostly) correct and fairly accessible.
October 31, 2015
OK book, a few interesting things on gravitation I didn't know. Good, not great.
Displaying 1 - 4 of 4 reviews