# Feynman Lectures On Gravitation

## Richard Feynman

- 280 pages
- English
- ePUB (mobile friendly)
- Available on iOS & Android

# Feynman Lectures On Gravitation

## Richard Feynman

## About This Book

The Feynman Lectures on Gravitation are based on notes prepared during a course on gravitational physics that Richard Feynman taught at Caltech during the 1962-63 academic year. For several years prior to these lectures, Feynman thought long and hard about the fundamental problems in gravitational physics, yet he published very little. These lectures represent a useful record of his viewpoints and some of his insights into gravity and its application to cosmology, superstars, wormholes, and gravitational waves at that particular time. The lectures also contain a number of fascinating digressions and asides on the foundations of physics and other issues.Characteristically, Feynman took an untraditional non-geometric approach to gravitation and general relativity based on the underlying quantum aspects of gravity. Hence, these lectures contain a unique pedagogical account of the development of Einstein's general theory of relativity as the inevitable result of the demand for a self-consistent theory of a massless spin-2 field (the graviton) coupled to the energy-momentum tensor of matter. This approach also demonstrates the intimate and fundamental connection between gauge invariance and the principle of equivalence.

## Frequently asked questions

^{8}, which was first done by EĆ¶tvĆ¶s. One can do this by comparing the gravitational force of the earth with the centrifugal force due to the earthās rotation, which is a purely inertial effect. In principle, a plumb bob which is at some latitude, not 0Ā° nor 90Ā°, does not point to the center of the earth. Actually it does not point to the center also because of the earthās bulges, but all this can be taken into account in making the comparison. In any case, at some intermediate angle such as the following: (Figure 1.1) the plumb bob points in a direction which is the resultant of the gravitational force and the centrifugal force. If we now make a plumb bob out of some other material, which has a different ratio of inertial to gravitational mass, it would hang at a slightly different angle. We can thus compare different substances; for example, if we could make the first bob out of copper, and a second one of hydrogenācome to think of it, it would be difficult to make it out of pure hydrogenā(maybe polyethylene would do), we can check the constancy of the ratio of the inertial mass to the gravitational mass

^{8}, for many substances, from oxygen to lead.

^{8}. This accuracy of one part in 10

^{8}is already telling us many important things; for example, the binding energy of nuclei is typically of the order of 6 MeV per nucleon, and the nucleon mass is like 940 MeV; in short the binding energy is of the order of one percent of the total energy. Now, an accuracy of 10

^{8}tells us that the ratio of the inertial and gravitational mass of the

*binding energy*is constant to within 1 part in 10

^{6}. We even have a check on the ratio of the electronic binding energies for electrons in the lower shells, since 10

^{ā8}of a nucleon mass is something like 9 electron volts. If the experiment can be pushed to an accuracy of one in 10

^{10}, as it may be in the near future, we would have a five percent check on the ratio for even chemical binding energies, which are of the order of two volts.

^{8}we can check on the gravitational behavior of corrections to electronic binding energies of the K-electrons in lead due to the vacuum polarization, which involve virtual pairs and thus antimatter. It may be said at this point that there is absolutely no evidence that would require us to assume that matter and antimatter differ in their gravitational behavior. All the evidence, experimental and even a little theoretical, seems to indicate that it is the energy content which is involved in gravitation, and therefore, since matter and antimatter both represent positive energies, gravitation makes no distinction.

*K*

_{0}and done at M.I.T. The experiment itself is not without its flaws, but perhaps we may use the results to kill the theory of unequal behavior. These arguments are due to M. Good [Good 61].

*K*

_{0}and are affected by gravity, otherwise the argument does not work. These two are antiparticles of each other, so we will see what happens if one is attracted, and the other is repelled by gravity. These particles have two decay modes which are describable as

*m*to the mass difference, such that sec. This value is inconsistent with the idea that matter is attracted but antimatter repelled, because of the fact that the experiment was carried out in the gravitational field of the earth; if the gravitational potential is

*Ļ*, then there is an increase or decrease in mass by

*mĻ*for one, and ā

*mĻ*for the other; the expected mass difference is larger than the limit set by the M.I.T. experiment. If we consider not the earthās gravitational potential, but the sunās, which is larger, or even the Galaxyās, we get better and better limits on the degree to which the equality of gravitational interaction holds. The whole argument can be brushed aside by those who cling to the antimatter-repels theory; all that is needed is that

*K*

_{0}and should not be gravitating particles, but this requires a new special assumption. It is evident that any single experimental fact can be disregarded if we are willing to think up a special reason why the experiment should show the result that it does.

*Ī²*-decay interactions the āWeakā interactions, the discovery of gravitation would be a tremendous embarrassment. Evidently, gravitation...