“It is worth noting that a wrong folkoric definition of an Inertial Frame in the Popular Science literature (even in text books) reads that 'it is a frame in uniform motion'. We know very well by now that the idea of motion requires a frame of reference, so that such a definition of an Inertial Frame has no meaning whatsoever, confusing the reader because it tacitly reaffirms the idea of absolute motion -- when the goal of every didactic exposition of Relativity Theory should be precisely the opposite.”

“As we already pointed out, 'special' means 'restricted to Inertial Frames of Reference', i.e. this theory cannot describe the Universe from an arbitrary reference frame. This restricted scope is not to be ignored, though not overemphasized either. ...Ironically, and precisely because of the great success of this simple version of Relativity Theory, most of its detractors have chosen to ignore (out of ignorance or malice -- you judge case by case) its philosophical foundation and restriction to Inertial Frames, so as to declare it invalid.”

“The notion of Local Inertial Frame is crucial to understanding Nature and, in particular, General Relativity. Notwithstanding, very few popular science books (not even textbooks) emphasize enough its fundamental character.”

“The objective and merit of Einstein's theory is to identify those physical magnitudes which are absolute, i.e. common for all Inertial Frames, distinguishing them from those which are a mere perspective, only shared by those observers in repose within a given Inertial Frame.”

“The universal character of the centrifugal forces leaves us impotent as to discern whether what is going on inside the carrousel is because we are rotating with respect to terra firma (remember my eyes are closed), or because – for some unknown reason unrelated to motion – radial gravitational field has temporarily emerged while the carrousel is as in repose as it was before the given impulse. The latter would have certainly been the interpretation adopted by an intelligent being, had s/he been born and grown up inside the carrousel, without any access whatsoever to the exterior world.”

“Both space and time are metrically amorphous, i.e. they do not have - despite how strongly we believe so - an inherent metric which would allow us to measure them without any definitions. In this sense, thus, neither space nor time is absolute.”

“Why is it so difficult for us to think in relative terms? Well, for the good reason that human nature loves absoluteness, and erroneously considers it as a state of higher knowledge.”