This is the continuation of a discussion in https://www.physicsforums.com/showthread.php?t=431068". Where does SR end and GR begin, in today's textbooks (not internet forums)? Do accelerating frames (coordinate systems) belong to also to SR, or is GR needed? I say that they belong solely to GR, and find my view disputed with 4.5 : 4.5 people supporting each view. Granted, but I had more responses to that innocuous comment than to most of my disputed positions regarding real physics. So it seems people are interested. I'm not an expert in history/philosophy of science or wherever this question belongs, so maybe I'm simply wrong. I'll argue nevertheless until someone convinces me. Let me state also that in my opinion, if we want to separate theories, it makes sense to say flat spacetime->SR, curved spacetime->GR. I don't dispute that. But I say that this is not how it is actually handled, and that the other position (which I believe is still the "official" one) also makes sense. We had these quotes: where I fully agree with DaleSpam: It is undisputed that SR can handle accelerated motion, as long as it is described in an inertial coordinate system. I need to see a quote concerning accelerated frames, not accelerated motion. Now for the different objections: I don't think it's unnatural. An essential part of SR is what you must (or mustn't) read into its standard coordinates. You deal with inertial frames, and you use phrases like "the speed of light is constant". You teach Lorentz transformations, and you say you understood SR when you can handle them intuitively. The "accelerated frame" is a human made definition, not something you can establish by experiment. So I think it's ok to let humans define whether a theory can handle a certain human-made definition. If I did, that was not my intention. Yeah, general covariance (of all equations) the key principle of GR. Human made, agreed, but that's what defines GR. At least, that's my position. I'd say you almost have a point here. But there's one thing: Newton deals with accelerating systems by introducing fictitious forces, letting the meaning of coordinates unchanged. But in relativity, fictitious forces mean geometry. You can't have fictitious forces without all sorts of weird coordinate transformations, i.e. time dilation, horizons, problems in defining large scale distance and such. You're in the same mess then whether spacetime is flat or not, you need the generally covariant formulation. I say that SR excludes this kind of weird coordinates. You deal with it using general covariance and the mathematical apparatus of GR. This is GR. I know of no example where an accelerating frame is handled correctly in detail without using different line elements, as in GR. That's your position, but I haven't seen your evidence yet. I can certainly show that it all started with my position in 1915, and I've seen that there's a majority in internet forums for your position. But I've missed the change you proclaim in the literature, or even in Wikipedia. I still see GR and SR tied with the respective principles of covariance.