The Michelson and Morley Experiment (1 Viewer)

[Omegalomaniac]

hey!
Could anyone please tell me a quick overview on the purpose of this experiment? I'm trying to research it right now but i don't understand :/

Thank you

 

[annabackwards]

Ah i remember looking this up because i of my dodgy teacher XD

The purpose was to detect the velocity of the aether wind AKA to detect the velocity of the Earth traveling through the station aether.

They expected a difference in interference patterns of light traveling in different directions through the aether and were going to use the difference to calculate the velocity of the aether wind

 

[biopia]

The purpose of the MM experiment was to measure he velocity of the earth through the aether, which was the proposed medium for light waves to propagate through. The aether was devised because physicists postulated that since light is a wave, it needed a medium to travel through, e.g. water for water waves, air for sound waves.
MM devised an experiment to measure the velocity of the earth through the aether, but they did not seek to prove or disprove it's existence. They were firm believers in the aether until their experiment yielded a null result. Actually, I am pretty sure it took even more convincing.
The experiment involved having two light beams fired at right angles to each other while colliding with a half silvered mirror which allowed half of the light to pass through, and the other half to be deflected. Since the beams were fired at right angles to one another, it was thought that one beam would be traveling with the aether and one would be travelling across it. Think about a river. If you a swimming against the current, and then with the current, it is hard initially, but is very easy on the way back because you would pick up the velocity of the water, while swimming across the river would be equally hard both forward and back. This idea was the premise for the MM experiment.
After they conducted the experiment the first time, they did a second time after rotating the apparatus through 90 degrees ideally switching the two beams positions. Because the beams of light cannot be perfectly placed an equal distance from the half silvered mirror, they expected the interference pattern to change after rotating the apparatus. This did not occur. Absolutely no change in the interference pattern was observed. This provided experimental evidence for the idea that light did not need a medium to travel through.

Hope that helps!

 

[youngminii]

Purpose:

• It was thought that light required a medium to propagate through, based on the Physics of that time
• This theroetical medium was called the 'aether'
• The aether was thought to exist everywhere
• Since it's a medium, Earth must be travelling against/with it
• Just as you would feel a wind through the window of a moving car, an 'aether wind' should be created from the relative velocities of Earth and the aether
• That meant (from the pre-Einstein definition of light) light's velocity should be affected by this aether wind
• Michelson-Morley's experiment aimed to find this aether wind (relative velocitiy of aether against Earth)
• See above post for the actual experiment
• Nothing was found: A null result (well, technically something was found, but that was due to experimental error)
• Experiment was repeated using much larger apparatus, same result
• This does not disprove the aether's existence, it only proves that the current aether model needed revision
• A number of revisions were proposed: 'the Earth 'pulls' the aether with it so no relative velocity is created' was a popular one
• Einstein came in (apparently unaware of this experiment) and postulated that light in invariant in all inertial frames of references, meaning that aether's existence became redundant

 

[Omegalomaniac]

So the null result of the MM experiment came from the fact that both beams of light were at the same velocity, therefore disproving the existence of the aether?

Thank you for helping so far!! I think i'm actually understanding something here

 

[Omegalomaniac]

Purpose:

• It was thought that light required a medium to propagate through, based on the Physics of that time
• This theroetical medium was called the 'aether'
• The aether was thought to exist everywhere
• Since it's a medium, Earth must be travelling against/with it
• Just as you would feel a wind through the window of a moving car, an 'aether wind' should be created from the relative velocities of Earth and the aether
• That meant (from the pre-Einstein definition of light) light's velocity should be affected by this aether wind
• Michelson-Morley's experiment aimed to find this aether wind (relative velocitiy of aether against Earth)
• See above post for the actual experiment
• Nothing was found: A null result (well, technically something was found, but that was due to experimental error)
• Experiment was repeated using much larger apparatus, same result
• This does not disprove the aether's existence, it only proves that the current aether model needed revision
• A number of revisions were proposed: 'the Earth 'pulls' the aether with it so no relative velocity is created' was a popular one
• Einstein came in (apparently unaware of this experiment) and postulated that light in invariant in all inertial frames of references, meaning that aether's existence became redundant

what is the current model of the aether?

 

[Aerath]

what is the current model of the aether?

There is none. It doesn't exist?

 

[annabackwards]

There is none. It doesn't exist?

+1 lol

 

[youngminii]

So the null result of the MM experiment came from the fact that both beams of light were at the same velocity, therefore disproving the existence of the aether?

Thank you for helping so far!! I think i'm actually understanding something here

Yeah but remember that it did not disprove the existence of the aether. The experiment proved that the aether model was wrong and needed revision.

The point is they want you to realise that it's impossible to disprove something. If I said there was a huge spaghetti monster flying around earth, you wouldn't be able to disprove it.

what is the current model of the aether?

By current model I meant the current model at the time.

 

[Dx_God]

well basically the purpose of the experiment is to prove the existence of aether. it was said to be the "Absolute frame of reference". because earth is said to be moving, the relative motion of earth and aether should generate wind similar to the wind u would feel when a car passes u at high velocities relative to u. this wind generated should have an impact on the motion of different objects depending upon the direction of the object which is traveling. for principle of relativity to be said true, light must also be affected by this wind. the main part of the experiment was actually the rotation of the experimental set up which most people tend to miss out. if aether wind truly existed then as u rotate the equipment, the speed of light should vary and results in different diffraction patterns. but however the result showed same diffraction patterns. this result gave rise to einstein's hypothesis of the constancy of the speed of light as the existence of aether was not important. u can also relate this to the creation of special relativity if u were answering a question like this in the hsc. (i already tried to simplify my response so the actual experiment is not included. but i can tell u the actual experiment if u want)

 

[Dx_God]

Yeah but remember that it did not disprove the existence of the aether. The experiment proved that the aether model was wrong and needed revision.

lol the scientists at the time basically left it as its existence was not important as it basically had no effects to matter (its just like blank space and discussing something like that is stupid). and as youngminii had said, the experiment never proved aether didn't exist as only its properties needed to changed.

 

[Omegalomaniac]

Yeah but remember that it did not disprove the existence of the aether. The experiment proved that the aether model was wrong and needed revision.

The point is they want you to realise that it's impossible to disprove something. If I said there was a huge spaghetti monster flying around earth, you wouldn't be able to disprove it.


By current model I meant the current model at the time.

thanks for that analogy
Thank you all for the help!! (& putting up with my stupidity )