Why did Michleson assumed that ether is moving ?

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In summary, the ether was a defunct theory that was used by Michelson when he did his experiment to try to disprove the theory of the speed of light being c. He failed and concluded that the Earth must be dragging the ether with it.
  • #1
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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  • #2
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.
 
  • #3
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
 
  • #4
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?
 
  • #5
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 ?
 
  • #6
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?
 
  • #7
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
 
  • #8
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.
 
  • #9
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 :)
 

1. Why did Michelson assume that ether is moving?

Michelson assumed that ether was moving because it was believed to be the medium through which light waves traveled. At the time, scientists thought that light waves were like sound waves and needed a medium to propagate through. Therefore, Michelson believed that if he could measure the speed of light in different directions, he could determine the speed of the Earth's movement through the stationary ether.

2. What evidence did Michelson have to support his assumption?

Michelson's assumption was based on the prevailing scientific belief at the time and the results of previous experiments that suggested the existence of ether. He also had observations of the Doppler effect, which showed that the speed of light was constant in all directions, supporting the idea that light waves traveled through a medium.

3. Did Michelson's experiment prove the existence of ether?

No, Michelson's experiment did not prove the existence of ether. His results showed that the speed of light was the same in all directions, which was unexpected if light waves were traveling through a stationary medium. This led to the development of Albert Einstein's theory of special relativity, which did away with the concept of ether and explained the results of Michelson's experiment.

4. What impact did Michelson's experiment have on the scientific community?

Michelson's experiment had a significant impact on the scientific community. It challenged the prevailing belief in the existence of ether and led to the development of a new theory of space and time. It also paved the way for further experiments and advancements in the understanding of the fundamental laws of physics.

5. Why is Michelson's experiment still important today?

Michelson's experiment is still important today because it marked a significant shift in the understanding of space and time. It also played a crucial role in the development of Einstein's theory of relativity, which has had a profound impact on modern physics and our understanding of the universe. Furthermore, the experiment continues to be a cornerstone in the study of the fundamental principles of physics and is still referenced in current scientific research.

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