[SCR]

Feynman lectures on gravitation - Richard P. Feynman;
Fernando B. Morinigo, William G. Wagner [editors], California Institute of Technology; edited by Brian Hatfield;
foreword by John Preskill and Kip S. Thorne; Addison-Wesley Publishing Company; 1995

(auf den linken Button "Download kostenlos" gehen; nach ca. 45 Sekunden kann man ein RAR-Archiv herunterladen; nach dem Entpacken des Archivs hat man eine Datei mit Endung .djvu vorliegen; es wird hierfür ein geeigneter Betrachter benötigt; ich verwende dazu das kostenfreie Programm WinDjView; es handelt sich um eine unter Windows direkt ausführbare EXE, die keine Installation benötigt; WinDjView ist erhältlich unter http://windjview.sourceforge.net)

Exemplarische Aussagen:

Zitat von Feynman

I am not getting anything out of the meeting. I am learning nothing. Because there are no experiments this field is not an active one, so few of the best men are doing work in it. The result is that there are hosts of dopes here and it is not good for my blood pressure: such insane things are said and seriously discussed that I get into arguments outside the formal sessions (say, at lunch) whenever anyone asks me a question or starts to tell me about his "work." The "work" is always:
(1) completely un-understandable,
(2) vague and indefinite,
(3) something correct that is obvious and self-evident, but worked out by a long and difficult analysis, and presented as an important discovery, or
(4) a claim based on the stupidity of the author that some obvious and correct fact, accepted and checked for years, is, in fact, false (these are the worst: no argument will convince the idiot),
(5) an attempt to do something probably impossible, but certainly of no utility, which, it is finally revealed at the end, fails, or
(6) just plain wrong.
There is a great deal of "activity in the field" these days, but this "activity" is mainly in showing that the previous "activity" of somebody else resulted in an error or in nothing useful or in something promising. It is like a lot of worms trying to get out of a bottle by crawling all over each other. It is not that the subject is hard; it is that the good men are occupied elsewhere. Remind me not to come to any more gravity conferences!

Zitat von Feynman

We live in a world which is in general not Euclidean, which has a curvature which is measurable by doing suitable experiments.

Zitat von Feynman

It is easy to visualize the notion of curvature when we are considering a two-dimensional space: a flat, uncurved space is a plane, and a curved space is a curved surface.
Although in our later work we shall need to work analytically with curvatures, it is appropriate to work a little with the two-dimensional geometry that we can easily visualize; the notions of curvature in higher dimensions are precise analogs of the curvatures of surfaces.

Zitat von Feynman

It is hard enough to think of the four dimensional space of Special Relativity with good intuition — I find it very difficult to visualize what is close to what, because of the minus signs. And to visualize this thing with a curvature will be harder yet.

Dazu Baez/Bunn aus http://math.ucr.edu/home/baez/einstein/node20.html:

The Meaning of Einstein's Equation
Feynman gives a quite different approach to this in:
The Feynman Lectures on Gravitation, R. P. Feynman et al. (Westview Press, Boulder, Colorado, 2002).
His approach focuses on the curvature of space rather than the curvature of spacetime.

Baez/Bunn selbst sehen das "etwas anders":

Zitat von Baez/Bunn

Again, all this is easier to visualize in 2d space rather than 4d spacetime. A person walking on a sphere 'following their nose' will trace out a geodesic -- that is, a great circle. Suppose two people stand side-by-side on the equator and start walking north, both following geodesics. Though they start out walking parallel to each other, the distance between them will gradually start to shrink, until finally they bump into each other at the north pole. If they didn't understand the curved geometry of the sphere, they might think a 'force' was pulling them together.

Similarly, in general relativity gravity is not really a 'force', but just a manifestation of the curvature of spacetime. Note: not the curvature of space, but of spacetime. The distinction is crucial. If you toss a ball, it follows a parabolic path. This is far from being a geodesic in space: space is curved by the Earth's gravitational field, but it is certainly not so curved as all that! The point is that while the ball moves a short distance in space, it moves an enormous distance in time, since one second equals about 300,000 kilometers in units where c=1. This allows a slight amount of spacetime curvature to have a noticeable effect.

In linearized gravity, you interpret the gravitational field as just a tensor field on flat spacetime. Nevertheless, you can recover position-dependent (i.e., gravitational) time dilation; in the linearized approximation, we calculate it as ordinary velocity-dependent SR time dilation, but because the motions of bodies in this flat spacetime are influenced by the gravitational field, so are their relative velocities, and you end up observing the same dilation you would get in a curved spacetime.

The details of this are worked out in section 3.6 of Ohanian and Ruffini, and sections 5.2 of the Feynman Lectures on Gravitation.

Diese deutsche Seite von Jörg Resag kann ich diesbezüglich sehr empfehlen: http://www.joerg-resag.de/mybk2htm/start2.htm
(Alleine schon die Herleitungen auf dieser Seite http://www.joergresag.privat.t-onlin...htm/chap53.htm und dann die abschließende Visualisierung ganz unten, was Ricci-Tensor bzw. Weyl-Tensor bewirken / wie sie zusammenspielen - Das finde ich schon erstklassig dargestellt).