Two Light Speed Experiments

 

C. Kingston

 

That the speed of light is constant is generally accepted as almost a fact even though it is actually an assumption. It seems a reasonable assumption that no amount of theorizing is likely to alter that particular mind set on the part of the believers. On the other hand, it is perhaps possible that experimental results that indicate otherwise might at least open the matter up for further consideration. This note outlines two such experiments.

 

The proposed experiments are based on theoretical considerations that indicate the dependence of the speed of light on the gravitational environment through which the light is traveling. The closer the light (or electromagnetic radiation in general) is to the center of a gravitational source, the slower its speed. As the light travels away from that gravitational center, its speed increases. A discussion of this can currently be found in the web site  Light, the Enigma.

 

Experiment 1.

The Michelson-Morley experiment compared the speed of light in two horizontal directions (relative to the surface of the earth) using an interferometer arrangement. This experiment played an important role in the birth of the assumption that the speed of light is constant. The speed of light would not be expected to change significantly in different horizontal directions. The maximum change of speed would be between a horizontal and a vertical direction since the gravitational environment would change the most between those directions. Thus the experiment is simply to calibrate the interferometer with both arms in the horizontal direction, and then rotate the apparatus around one arm so that the other arm is vertical. The length of the arms would have to be sufficient to make the difference observable. A length of 20 meters for each arm should be adequate, since the experiment based on the Mossbauer effect using a gamma ray from iron-57 (‘Harvard Tower Experiment’ by Pound, Rebka, and Snyder) was able to show the difference in speed over a distance of about 22.6 meters, although the results were interpreted as a change of energy rather than speed.

 

Experiment 2.

This experiment has essentially been already done and it is now a matter of interpretation of the results. Consider a spacecraft heading away from the center of the solar system. As it travels outward, the gravitational environment is changing in such a manner that the average speed of an electromagnetic signal between the craft and earth is continuously increasing. If the signal were considered to be always traveling at the same speed, then any range calculations based on the timing of the signal would appear to place the craft continuously closer to the observer than the actual (or predicted) position of the craft. This could be interpreted as acceleration toward the observer. This is exactly the interpretation made using the reported data from the Pioneer 10 and 11 craft (the acceleration is characterized as being toward the sun, which is essentially toward the observer given the distance of the craft). The experiment is to remodel the collected data so that the value of c in the equations represents the average speed of each signal (or a reasonable estimate thereof) based upon its path through the gravitational field of the solar system rather than as a constant value. The signal speed at any particular position would be a function of the ‘clock rate’ at that position. If the signal speed varies as suggested above, the appearance of an anomalous acceleration should not be apparent with this modification of a properly designed model.