Vinaire's Blog

Reference: Disturbance Theory

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James Bradley’s (1729) explanation for aberration of light became unacceptable in 1804 because light was established to be a wave. It was no longer looked upon as corpuscular, which was assumed earlier by Newton. So, the medium of light (aether) became an issue.

The aberration of light is an astronomical phenomenon which produces an apparent motion of celestial objects about their true positions, dependent on the velocity of the observer.

Pre-1800 Corpuscular theory of light – Light was considered to be made up of particles that had inertia and they traveled in straight lines. Aberration of light was explained very simply by James Bradley using this model for light. It was shown that the telescope had to be tilted to capture a vertically descending light particle because earth moved. This created the angle of aberration.

1804 Thomas Young – He proved the wave nature of light through the famous double-slit experiment. This revived investigation into the nature of the medium through which light moved. This medium was viewed as aether that filled all space. It was completely elastic as it could transmit light over infinite distances.

1810 François Arago – He expected the speed of light to be different as corpuscles of light were supposed to be affected differently by the gravity of different stars. But light from different stars produced the same refractive index, and, therefore, had the same velocity. This negated Newton’s corpuscular theory of light, and supported a uniform medium of aether.

1816 Augustin-Jean Fresnel – Since the speed of light was constant in aether, he expected it to have different values relative to earth as earth changed its directions. However, Arago’s results negated that. Therefore, Fresnel postulated that earth’s velocity did account for the aberration of light, but aether was partially dragged at the point of measurement to maintain a constant velocity of light. Fresnel calculated an aether drag coefficient based on the refractive index that seemed to explain the inconsistency.

1887 Michelson & Morley – Earth was expected to have a velocity relative to aether in order to explain the aberration of light. However, the velocity of light was found to be constant regardless of the direction in which earth moved. This created the same inconsistency as the Arago’s experiment, but on a much larger scale.  This could not be explained by Fresnel’s partial ether drag hypothesis.

1905 Albert Einstein – He explained the inconsistency by dropping the aether model and returning to the corpuscular theory of light. This generates questions about the very nature of light. Light cannot be a wave. It cannot be a particle with significant inertia either. The questions now become,

1. If light is made up of particles that do not require a medium to travel, then how do these particles coordinate their motion?

2. Matter has relative speeds. Light seems to adjust its speed to ‘c’ relative to any matter. So, how does light and matter coordinate their motion?

3. Are light particles made up of electromagnetic fields? Do they exist within larger fields? If not, then what do we have?

The theory of relativity is too mathematical and does not seem to answer these questions

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