A Michelson-Morley Experiment for the Advanced Lab
Charles Rogers and Richard Selv aggi
Texas A&M Univ ersity - Commerce
Abstract
The famous 1887 Michelson-Morley experiment measured the propagation of light in a rotating interferometer in the physics department at Case Western Reserve University.
For more than one hundred and twenty years, the data obtained from this experiment have been examined by many professionals interested in this experiment. These
investigations have raised numerous questions concerning the analysis and interpretation of the originally published data. With interest in replicating this experiment, we have
designed a new rotating interferometer of the same scale as the original experiment. This apparatus is composed on a standard four foot by six foot optical breadboard
supported on a cylindrical float inside a concentric cylindrical tank. The interferometer consist of sixteen adjustable front surface mirrors, an aluminized beamsplitter, and a
compensation plate arranged in the same geometry as used in the original experiment. The interferometer is rotated smoothly by the equivalent of a 2-meter diameter brushless
motor. The light source is a helium-neon laser and a wireless optical sensor. Our students learn to align the optics, collect realtime data using a LabVIEW vi, and analyze their
data using both original and current theories of operation of this instrument. We will present the details of this experiment and preliminary data collected.
Michelson and
Morley's 1887
Experiment 2
Introduction
The Michelson-Morley experiment was designed to measure relative motion between the experimental apparatus and the “Luminiferous
Ether”. The failure to measure the relative motion of the orbital or larger velocities has since perplexed the world’s scientific community. The
reasons for replicating this experiment include confirmation of the original results with more accurate monitoring and measuring tools, to
develop a easy to replicate experimental apparatus that can be produced in other advanced physics labs, to use new techniques such as a
stepper motor to rotate the apparatus at different rotational velocities, to perform additional experimental applications including those
recommended by Michelson and Morley, to confirm theoretical explanations of the measured results, to develop a better understanding of the
factors affecting the oscillation of the interference pattern and the unidirectional drift of the interference fringes.
Description of the replica M-M Interferometer
Photographs taken during the assembly of the Michelson-Morley interferometer are shown in the lower left corner of this poster. An optical
breadboard is supported on a wooden table within concentric cylindrical tanks. The optical components for the interferometer are positioned on
the breadboard with a 12 meter path length for each arm. A stabilized HeNe laser is used for the light source and a CCD sensor is used to
detect the interference pattern. Estimated mass of the final rotating platform is 800 kilograms. Fringe movement data is recorded as a timelapse video file and is currently analyzed using Matlab scripts. A microcontroller with 10-bit ADC are used to digitize output from the temperature
and pressure sensors and communicate these data. Another microcontroller provides timing and control of the platform rotation. We also
record the air temperature on each arm of the interferometer and the ambient air temperature and atmospheric pressure. We plan to replace the
temperature sensors with 14-bit temperature and relative humidity sensors.
Data Collection
The following figures show initial data collected from the stationary interferometer to survey environmental conditions within the
laboratory.
Concentric water tanks and optical support
Optical breadboard balanced on the support
HeNe laser Light source
Beam splitter and one set of mirrors
CCD light sensor
One set of mirrors with temperature sensor
Date
Time
Temp1
Temp2 Temp3
Temp4
Temp5
Pressure
Additional images of this apparatus and videos of the rotating MM interferometer replica and recorded fringe pattern movement will be
shown at the conference.
Thermal shroud and half of the enclosure
Adjusting the CCD position
Fringe pattern at the CCD
Rotor magnets, two drive coils, and Hall sensor
Aligning the magnetic drive
Data acquisition display
Summary and Conclusion
Changes in atmospheric pressure appears to be the most important environmental variable affecting the interference pattern for this
interferometer. Turning off the air conditioning fans within the laboratory reduced pressure fluctuations and improved the stability of the fringe
pattern. Temperature of the air within the interferometer remained constant. The unidirectional drift is present in all previously described one-way
and two-way light experiments. In both Michelson-Morley and Miller experiments the fringe drift was removed before analyzing the data. The drift
of the interference fringes has been observed by others with considerable speculation as to their cause. We believe that corrections for
environmental variations can be applied to the data to accurately remove this effect.
Further experimental scenarios include the apparatus remaining stationary for twenty-four hours or rotating at one-quarter, one-half, one, and
two revolutions per minute. The accuracy of the apparatus can be increased by lengthening the light’s pathway and by increasing the number of
pixels per fringe. Reduction in the baseline oscillation artifacts can be achieved by placing the apparatus in a sealed remote subterranean room
without heating or cooling needs.
The Michelson-Morley experiment is one of the most important experiment in physics. It should be taught in the advanced laboratory. This
experiment offers an excellent hands on experience with optical interferometers and various signal processing and laboratory instrumentation
and automation techniques.
References
Calibration Methods
B
B
L
L
V = c/n
1. Michelson and Morley 2
 t= L n3
v
2. Miller 3
V = c/n
A
CCD
L
C
A1
v
3
c
A2
CCD
2
L∣v p  ∣
C
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2
 t=2 k
L
2
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c
3
cos−
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2
v
 t=2 L n n −1 3 cos 2
c
2
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