This is a spin-off of a parallel discussion, starting from: https://www.physicsforums.com/showthread.php?p=4281037#post4281037 The question is what SR predicts that an accelerometer in free-fall will read. This issue may be simply due to different people using a different meaning of "SR", but it could have a deeper cause. A basic reference for this discussion: Einstein 1905, http://www.fourmilab.ch/etexts/einstein/specrel/www/ and another one for context: Langevin 1911, http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time SR uses the inertial frames of classical mechanics; in my opinion it's obvious that SR doesn't predict that an accelerometer in free fall will indicate a large acceleration. That conflicts with the known laws of physics, even of classical mechanics. Arguments in favor of both opinions may help to clarify this issue.