According to the principle of the constancy of the speed of light in SR, if an observer chases after a flash of light, the light will keep moving away from the observer at the universal speed c no matter how much the observer speeds up. Likewise, if an observer runs into a flash of light, the light will keep moving towards the observer at c no matter how much the observer speeds up.
As I mentioned in a previous post, another consequence of the constancy of c is the possibility of causality paradoxes if hypothetical superluminal signals are considered. But at low speeds, too, there are some surprising effects. For example, if two observers A and B at rest relative to each other at opposite ends of the observable universe started to walk in the same direction A--> B--> at the same time, then, in accordance with the transformations of SR, A would suddenly have to consider that B set out 300 years earlier than A and is now long dead. If both stopped after a few metres, however, B would promptly come back to life as far as A is concerned since A would now consider that A and B set out at the same time, after all, and also stopped at the same time.
All this strangeness is at least partly the making of physicists because, as explained in previous posts, the notions of "simultaneity" and "one-way speed" as defined in SR crucially depend on Einstein's choice of clock adjustment procedure. It is now time to look at the literature on SR to see how physicists have justified such a clock adjustment procedure, and how they have defended the idea that it represents a synchronization procedure that may serve to define simultaneity and one-way speed.
Let me begin with a little survey of the texts I would like to examine. The first two are Albert Einstein's famous 1905 article "On the Electrodynamics of Moving Bodies" and his subsequent account of the main features of SR intended for a wider audience, first published in 1916. In my opinion, these two publications are much clearer regarding the foundations of special relativity than many other texts published on the subject since. In particular, Einstein is perfectly lucid on the role of convention, definition or stipulation in his theory. On the other hand, there is very little in these texts to motivate or justify his clock adjustment procedure, let alone the idea that it may serve as a synchronization procedure.
This is perhaps unsurprising since, as far as I know, Einstein was addressing an audience whose main concern was to reconcile recent experimental results with the erroneous idea of an essentially static, all-pervasive medium for light, or "ether". He was not writing for future generations of students of physics who had never had any reason to believe in such an "ether" in the first place and were much more interested in the issue of meaningful synchronization procedures.
This is where modern textbooks and other publications focusing on the foundations of special relativity come in. Two which I would like to consider are an online article by Allen Janis wholly dedicated to the issue of the "Conventionality of Simultaneity" in SR, and a 1977 article by Reza Mansouri and Roman U. Sexl on "A Test Theory of Special Relativity: I. Simultaneity and Clock Synchronization". In addition, I have identified four books which are of particular interest to me because of their explicit emphasis on the concepts underlying SR: Leo Sartori's Understanding Relativity (1996); Wolfgang Rindler's Relativity: Special, General, Cosmological (2001); Vesselin Petkov's Relativity and the Nature of Spacetime (2005); and above all Kevin Brown's Reflections on Relativity (2010).
Kevin Brown's book is particularly relevant to my project because it explicitly addresses some of the very same issues I am grappling with in this blog. What is more, it gives a clear, coherent and erudite account of the foundations of SR unrivalled by any of the other texts I have mentioned. If there is hope for my understanding of the principle of the constancy of c, it lies in Kevin Brown's book!
But first things first, so let me start with Brown's illustrious precursor, Albert Einstein - in my next post.
