Proper explanation for the MMX null result:

1. The null result of the MMX is due to that the speed of light is isotropic
HORIZONTALLY.
2. If the plane of the light rays (the right angled arms of the MMX) is
oriented vertically then non-null result will be observed. This means that
the speed of light is not isotropic in the vertical direction. This
interpretation is supported by the Pound and Rebka experiments and the
predicted gravitational red shift in the vertical direction by GRT.

Proposed Experiments designed to support the above interpretations is in the
paper entitled "Proposed Experiments to Detect Absolute Motion" in my
website:
http://www.geocities.com/kn_seto/index.htm

Ken Seto