The Paradox of Aging in Relativity: Resolving the Twin Paradox with a Twist

[PAllen]

Now, MTW doesn't even mention Dolby & Gull's coordinate system, while they do mention momentarily comoving inertial (MCMI) coordinate system. I would tend to agree that in terms of popularity, MCMI is more popular than Dolby & Gull. I would even say that I personally like it better than Doby & Gull. MTW also mentions in later sections a specific extension of the MCMI idea, called "Fermi Normal Coordinates", that I feel are very important. I tend to think of Fermi Normal coordinates as being "natural", but that's just my personal bias. People seem to have different ideas of what is "natural", and I don't believe it's too productive to argue about this.

It is interesting to note that in the GR context (rather than SR), radar coordinates have a long history. Synge, in the 1950s and 60s proved many interesting facts about them, in particular that they are experimentally indistinguishable from FN coordinates at the scale of wildly moving rocket (within the rocket), and that at the distance they become distinguishable from FN, each has nasty tradeoffs, so a preference is hard to justify.