On Mechanical Structure of FOMMX

The apparatus of a Michelson-Morley eXperiment measures the difference in the speed of light in two perpendicular directions and repeats this measurement over a variety of orientations. These results are combined to show the velocity of a (6D) continuum (previously 3D called aether) through the solar system.

The general approach is to direct light along two perpendicular arms  and interferometrically measure the difference in speeds between the light-paths in the arms. The arms are horizontal and rotate about a vertical axis a few times a minute. The horizontal plane of rotation sweeps through a large portion of the sky each sidereal day. These rotations provide the requisite variety of orientations.

The sense element of the arms is an optical fiber which lies in a tray, which in turn lies in a clear plexiglass tube of 3" diameter. The straight length, end to end, of the fiber is 14', a bit longer than the light path of Dayton Miller's apparatus. The arm is two 7' lengths of tube joined to a 3D printed hub. The tube and hub cannot support the weight of the tube or the starting torque. Therefore, two mechanically strong bars, the same length and orientation as the tubes, are used to support the tube from above via guy wires, and to apply torque to the arms.

The rotation of the arms is driven by a servo-motor attached to the ceiling of the lab. The motor-shaft is connected to a 2' vertical shaft, the bottom of which is rigidly connected to the crossed bars. The bars are connected by guy wires to the arms directly below them. This provides support against gravity and torque indirectly to the arms.

Between the bars above and the arms below is the hub. This is a frame holding DFB diode laser, photodetector, data logging computer, etc. These components that produce heat and are placed above fiber components to avoid potential thermal variations in the fiber that might affect the interferometric signal.  The optical components are connected to the arms via optical fiber and the hub is rigidly connected to the arms to avoid flexure of this fiber that might also affect the signal. The top of the hub is attached to the bars with a bearing to prevent applying torque from the motor to the frame of the hub, again to avoid potential deformation of optical fiber.


  1. Looking forward to the FOMMX producing data, Steven.


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