Michelson–Morley Experiment Questions
During the 19th century, most physicists believed that just as water waves must have a foundational substance (medium) to propagate from one point to another, light also must need a medium to transmit its waves (luminiferous aether). Another example is audible sound; it essentially needs a physical medium (such as water or air) to transfer its waves. As light can propagate through a vacuum, it was believed that even a vacuum space must be full of luminiferous aether. As the speed of light is so quick, and physical bodies go through the aether without any notable drag or friction, it was considered to possess an exotic combination of characteristics.
The Michelson–Morley test was one of the unsuccessful experiments that acted as the best proof against the validity of the luminiferous aether or ether theory. This was a controlled experiment to detect the presence of the aether, the hypothetical medium filled in space that was believed to be the carrier of electromagnetic waves (visible light, radio waves, etc.). This experiment was conducted by Edward W. Morley and Albert A. Michelson between April and July 1887. The research paper was released in November 1887. The two physicists Morley and Michelson were anticipating light to have varied speed when they move in different directions, but they got no major differentiating fringes that pointed to a different velocity in any orientation or any location of the Earth.
The experiment heavily relied on a device called the Michelson interferometer, a special optical apparatus that analyses the optical trajectory lengths for light propagating in two mutually perpendicular orientations. Michelson suggested that if the speed of light were stable with respect to the hypothetical aether through which the Earth was orbiting around the Sun, that movement could be found by comparing the speed of light in the direction of Earth’s movement and the speed of light at the right angles to the Earth’s movement. In fact, no variation was detected. This negative result discredited the aether theories and conclusively led to the concept by the theoretical physicist Albert Einstein (1905) that speed of light is a universal constant.
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Michelson–Morley Experiment Questions and Answers
1) Give a brief about the Michelson–Morley experiment.
This experiment was a controlled experiment to detect the presence of the aether, the hypothetical medium filled in space that was believed to be the carrier of electromagnetic waves (visible light, radio waves, etc.). This experiment was conducted by Albert Michelson and Edward Morley between April and July 1887. The research paper was released in November 1887.
2) The Michelson–Morley test was one of the unsuccessful experiments that acted as the best proof against the validity of the __________ theory.
Answer: luminiferous aether or ether
Explanation: The Michelson–Morley test was one of the unsuccessful experiments that acted as the best proof against the validity of the luminiferous aether or ether theory.
3) Give a brief about the comparison conducted by the Michelson–Morley experiment.
The Michelson–Morley experiment analysed the speed of light in perpendicular directions in order to find the relative movement of substances through the immobile luminiferous aether. The experiment gave a negative result in that Morley and Michelson derived no significant variation between the speed of light in the motion’s direction through the imagined aether (ether) and the speed at right angles. The end result is usually considered the first consistent evidence against the aether theory. It also initiated a new field of research that ultimately led to the modern concept of relativity (this rules out the existence of an immobile aether).
4) What were the main assumptions about aether before the Michelson–Morley experiment?
Earth revolves along the Sun’s orbit at a velocity of about 30 km/s. The Earth is always in motion; thus, two significant possibilities were assumed: (a) The aether is motionless and only partly dragged by the Earth, which was suggested by Augustin-Jean Fresnel (1818), or (b) this ether is entirely dragged by the Earth and therefore shares its movement at the surface of the Earth which was suggested by Sir George Stokes (1844). Later, James Clerk Maxwell recognised the electromagnetic property of light and constructed what we now call Maxwell’s equations. However, such mathematical relations were still defined as explaining the movement of waves through an ether (aether), whose motion state was not known. Finally, Augustin-Jean Fresnel’s concept of a stationary aether (almost) was preferred by the scientific community as it appeared to be validated through the Fizeau experiment and the aberration of light from stars (1851).
5) What was the aim of the Hoek experiment?
The Hoek experiment attempted to observe interferometric fringe shifts that were caused by speed variations of oppositely travelling light waves through water (at rest). The outcomes of similar tests were all negative.
6) What was the exact experimental result of the Michelson–Morley experiment?
The two physicists Morley and Michelson were anticipating light to have varied speed when they move in different directions, but they got no major differentiating fringes that pointed to a different velocity in any orientation or any location of the Earth.
7) Who developed the interferometer?
To calculate the speed of the Earth with the aid of ether and to find the varying pattern of the light, Albert Michelson constructed a device known as an interferometer.
8) What are the components of an interferometer?
The interferometer has the following elements:
- Coherent light source
- Screen
- Movable mirror
- Beam splitter
- Beam splitter reference mirror
9) Which are the other experiments similar to the Michelson–Morley experiment?
Michelson–Morley-type experiments have been attempted numerous times with gradually increasing sensitivity. Such experiments include the ones that were conducted between 1902 and 1905, and a chain of experiments attempted during the 1920s. Recently in 2009, experiments with optical resonators validated the absence of any type of aether wind at the level between 10 to 17. Along with Kennedy–Thorndike and Ives–Stilwell experiments, Michelson–Morley-type tests form the primary tests of special relativity.
10) What is meant by aether in physics?
In physics, aether or luminiferous ether is a theoretical universal material considered during the 19th century as the supporting medium for the propagation of electromagnetic waves or waves (e.g., X-rays and light), just like sound waves are propagated through elastic media such as air.
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Practice Questions
1) What is meant by an interferometer?
2) What is meant by aether?
3) When was the Michelson–Morley experiment conducted?
4) What were the main conclusions of the Michelson–Morley experiment?
5) What is the relationship between the speed of light and the propagation medium?
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