Some help with the rotation of arms!
Frank Russo - March 04 2009.
In my vast experience with the Michelson-Morley, I've found that most persons have a lot of difficulty visualizing the two arms at the point of rotation... so I just thought I'd mention a few explanatory points.
The two arms should theoretically be equal in 'blank' straight distance to travel when a couple of photons are starting out at the origin, simply by having defined the two straight-line spatial lengths as 10.83079918 m... so we are okay with the start... all we now need to consider is where things are at, as the perpendicular photon reaches the perpendicular mirror so that it's ready for rotation! In what 'shape' would the orbital arm be at a simultaneous time? Well of course the perpendicular photon has travelled 11m along the hypotenuse instead of the spatial straight 10.83079918m, and this means that the orbital photon has advanced by 11m minus the origin equivalent motion of 1.921923284m which equals about 9.078076718 m... however one must of course realize that the mirror has also moved forward by the 1.921923284 m! But one must become aware of the fact that the orbital photon has travelled a linear 11m, so that it has gone beyond the original position of the orbital mirror by about 0.169200818m, hence at the completion of its orbital 11m, the orbital mirror will only be further forward by about 1.752722466 m!
To now see how long the corresponding orbital spatial overall equivalent straight length is when the perpendicular photon is at the mirror, we have to add the 9.078076718 m and the 1.752722466 m to still give us an orbital overall length of 10.83079918 m.
In conclusion then, the two arms are the same length at the start of the 'away leg', and they are the same length at the end of the away perpendicular leg... so obviously you should be able to rotate the two arms with them just changing identity... remember you are rotating the away leg rather than the return leg, (as the latter's starting points are asynchronous and is therefore impractical to do!). See my earlier paper about "the truth about aberrant simultaneity".
I hope that I've rendered the 'waters' crystal clear, rather than the muddied mess that Einstein caused!