Why did Michleson assumed that ether is moving ?

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Discussion Overview

The discussion centers around Michelson's assumptions regarding the ether and its movement in relation to the speed of light. Participants explore the implications of these assumptions for the Michelson-Morley experiment, considering the nature of the ether and its relationship to the Earth’s motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions why Michelson assumed the ether was moving, suggesting that if the ether were stationary, the speed of light would remain constant regardless of the Earth's motion.
  • Another participant explains that the ether was presumed to be fixed relative to the background stars, not to the Earth, indicating a belief in multiple frames of reference.
  • A later reply clarifies that Michelson initially thought the ether was stationary but that the Earth moved through it, leading to the expectation of measuring an ether wind.
  • Some participants discuss the geometric interpretation of light speed in relation to the ether, comparing it to a boat crossing a river, which illustrates how light would travel at an angle if the ether moved perpendicular to its path.
  • There is mention of the ether theory being defunct, but participants acknowledge that it was the prevailing thought during the time of the experiment.
  • One participant expresses confusion about the mathematical implications of measuring light speed in different directions relative to the ether and the Earth’s motion.

Areas of Agreement / Disagreement

Participants express various interpretations of Michelson's assumptions and the implications for the experiment. There is no consensus on the clarity of the ether's properties or the mathematical reasoning behind the measurements.

Contextual Notes

Some participants note the limitations of the ether theory and the assumptions made during the time of the experiment, highlighting the complexity of the mathematical relationships involved without resolving them.

Dark_knight90
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Why did Michelson assume that ether is moving ?

I mean why didn't he assume that Ether doesn't move and that is why speed of light doesn't change ? .. If Earth is moving in a direction, speed of light is "c".. if it is moving in the other direction, speed of light is "c" too .. because the ether is standing still so there is nothing that the beam of light go with or against ?

Thank you
 
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They assumes the medium would be fixed with respect to background stars, or the galaxy, or whatever, but not fixed in the frame of reference of the Earth.

That is, they did not presume the frame of reference of the Earth was unique above all others.
 
Phrak said:
They assumes the medium would be fixed with respect to background stars, or the galaxy, or whatever, but not fixed in the frame of reference of the Earth.

Thank you
 
Dark_knight90 said:
Why did Michelson assume that ether is moving ?

I mean why didn't he assume that Ether doesn't move and that is why speed of light doesn't change ? .. If Earth is moving in a direction, speed of light is "c".. if it is moving in the other direction, speed of light is "c" too .. because the ether is standing still so there is nothing that the beam of light go with or against ?

Thank you
Your question is confusing to me. Before Michelson did his experiment, he assumed that the ether was not moving but that his location on the surface of the Earth was moving through it at different speeds in different directions at different times of the day and at different seasons of the year. He also assumed that the speed of light was c relative to the ether and that he could measure an ether wind as his apparatus moved through the ether.

When he failed to measure any ether wind no matter when he did his experiment, he concluded that the Earth must be dragging the ether with it just like it drags the air with it as it rotates and so there is not a 1000 mile per hour wind caused by the rotation of the Earth at the equator. He concluded his paper with the suggestion that maybe if the experiment were performed again at the top of a high mountain, it might be able to detect some ether wind where presummably the Earth would be dragging the ether less.

When you said "because the ether is standing still", did you mean it is standing still with respect to the Earth or standing still with respect to the sun or other stars?
 
Regarding Michelson Morley Experiment

The speed of light (relative to the ether) is the hypotenuse of a right triangle with sides of length (speed of light on Earth) and (Earth's velocity relative to Ether)

Can anyone clarify that point ?
 
Dark_knight90 said:
Regarding Michelson Morley Experiment

The speed of light (relative to the ether) is the hypotenuse of a right triangle with sides of length (speed of light on Earth) and (Earth's velocity relative to Ether)

Can anyone clarify that point ?

You realize that the ether of light is a defunct theory, right?
 
yes I do know that .. but that is what they thought about when they were doing the experiment .. it seems to be a simple idea but i can't get it ..

They thought that if they would measure the speed of light (with the Earth motion) and (against the Earth motion) and (perpendicular to the Earth motion) .. The first two are simple addition and subtraction but the third one is not understandable to me
 
If light travels at a constant speed through the ether and the ether moves perpendicular to it, then the light moves at an angle. Consider a boat traveling straight across a river: it has to angle upriver in order to move straight across and as a result takes longer to get across the river than if the river wasn't moving.
 
Have a look at http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/lightclock.swf" .
I think it's more understandable if you see how the length of the light path changes with velocity.
 
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  • #10
russ_watters said:
If light travels at a constant speed through the ether and the ether moves perpendicular to it, then the light moves at an angle. Consider a boat traveling straight across a river: it has to angle upriver in order to move straight across and as a result takes longer to get across the river than if the river wasn't moving.

Got it .. Thank you :)
 

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