What is the role of the Earth's rotation in the Michelson-Morley experiment?

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Discussion Overview

The discussion centers on the role of the Earth's rotation in the Michelson-Morley experiment, particularly in relation to measuring the velocity of light and the ether wind. Participants explore the implications of Earth's motion, including its rotation and orbital velocity, on the experiment's outcomes.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that the Earth's rotation should be considered alongside its orbital velocity and the sun's velocity with respect to the ether when measuring ether wind velocity.
  • Others argue that the Earth's rotation can be neglected if the experiment is conducted quickly, as its speed is much smaller than that of light.
  • A participant clarifies that the Michelson-Morley experiment compared the speed of light in two perpendicular directions but did not measure the speed of light at different moments.
  • Some participants assert that the speed of the Earth around the sun is significantly larger than its rotational speed, which can be disregarded in the context of the experiment.
  • It is noted that the experiment was sensitive enough to potentially detect an ether wind due to Earth's rotation over a twelve-hour period, raising questions about the assumptions regarding the sun's rest in the ether.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of the Earth's rotation in the experiment, with no consensus reached on its significance or the implications of the measurements taken.

Contextual Notes

There are unresolved assumptions regarding the ether medium and the implications of the Earth's motion on the experiment's results. The discussion reflects varying interpretations of the experiment's design and sensitivity.

abhilash.s
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I understood that the basic idea of the Michelson-Morley experiment was to measure the velocity of light, as seen from a frame fixed relative to the earth, in two perpendicular directions. Assuming the existence of the ether medium (only for the purpose of understanding the rejection of the ether medium), while intending to measure the ether wind velocity, should not we also take into account the spinning motion of the Earth with respect to the ether in addition to its orbital velocity around the sun and the sun's velocity with respect to the ether?
 
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Not if the experiment is done quickly enough- like within a few minutes. The rate at which the Earth is spinning on its axis is very small compared to the speed of light. As far as the "orbital velocity around the sum" and the "sun's velocity with respect to the ether", those are being taken into account when you measure "the Earth's velocity with respect to the ether".
 
abhilash.s said:
I understood that the basic idea of the Michelson-Morley experiment was to measure the velocity of light, as seen from a frame fixed relative to the earth, in two perpendicular directions. Assuming the existence of the ether medium (only for the purpose of understanding the rejection of the ether medium), while intending to measure the ether wind velocity, should not we also take into account the spinning motion of the Earth with respect to the ether in addition to its orbital velocity around the sun and the sun's velocity with respect to the ether?
You probably already know this but the experiment was not measuring the speed of light in two perpendicular directions but rather merely comparing them for all orientations in a plane parallel to the surface of the earth. It had no ability, for example, to determine if the speed of light was constant from one moment to the next.
 
The speed of the Earth around the sun is much larger than the speed due to the rotation of the earth, which can be neglected.
 
Meir Achuz said:
The speed of the Earth around the sun is much larger than the speed due to the rotation of the earth, which can be neglected.
Nevertheless, the experiment was sensitive enough to detect an expected ether wind caused by the rotation of the Earth sometime over a twelve hour period. They didn't have to wait for several months. There was no guarantee that the sun was at rest in the ether.
 

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