Does putting the concept of acceleration in SR make it equivalent to GR? I see a lot of sources (including many posts in this forum) which seem to say that SR can handle acceleration fine, but not gravity. However, an acceleration IS gravity by the equivalence principle, so what's the difference? (That historicallly EP was developed after SR does not matter, I think). In this context, I have seen a lot of explanations saying that the Twin Paradox can be resolved within SR framework and does not require GR. The main differentiator though is that one of the twins preferentially 'feels acceleration'. Isn't it ultimately then putting the explanation in GR territory without openly acknowledging it?