This question about the twin paradox(twins A,B). I hope everyone knows the statement. I have read explanations for this but they differ. Some authors say twin(say B) who takes the trip accelerates so he cant be an inertial frame of reference. Some say it has nothing to do with acceleration and it can be solved by time dilation,length contraction and relativity of simultaneity. Okay this brings me a lot of doubts a)Which explanation is correct?(it doesnt have to be practically possible) b)those who say acceleration is the culprit, if you can blame the other guy as moving when in constant velocity why cant you do the same for acceleration? c)are there any frames in universe which can be validated as inertial?for example if you say earth is one it is certainly not because it revolves around itself,sun,galaxy etc. Like wise if you take a point in space(or any where else) how can you be sure its not accelerating or revolving etc?