Michelson-Morley experiment (1 Viewer)

[Zero Infinite]

Although I get the basics of what the experiment was about, there are some aspects of it I don't understand completely. Like, why the light was made to travel across ether, with and against ether, and what the interference pattern was meant to show. Different sources seem to explain different things, and I need some clarification. Can someone simply explain the main points of the experiment, because I don't think I'd be able to explain it properly in an exam.

 

[BrotherBread]

The experiment made light travell perpendicular to, and against the aether. The idea being that if aether exists, being a medium of light, and it was moving, then it would make the light move too. almost like a leaf in a steam, if the stream is moving the leaf will move in the same direction as it but not always at the same speed.

The easiest way to grasp the concept of the interference I think is that, if the aether were to exist than the light at one point in the set up would be moved, and therefore at the point where the light terminates and is observed would be less luminous.

My issue with the experiment is that we were taught, (bodgy teacher I think so most of what I say could be wrong) that aether has no properties. If that is so then regardless of aether existing or not it should have no effect on lights direction of travel.

I'm not sure if that helps. Someone will probably come and explain it better or even more correct.

 

[chousta]

Although I get the basics of what the experiment was about, there are some aspects of it I don't understand completely. Like, why the light was made to travel across ether, with and against ether, and what the interference pattern was meant to show. Different sources seem to explain different things, and I need some clarification. Can someone simply explain the main points of the experiment, because I don't think I'd be able to explain it properly in an exam.

Hi hopefully i can help you with your understanding, because i found the posters analogy wasn't too clear (sorry to say).

Ill run through the experiment quickly:

The Michelson & Morley experiement was designed specifically in order to test for the existence of an Aether / Ether, which was believed to be a medium in which it filled all space and was stationary in space, it completely permeates all matter, has a low density and is also able to propagatate light waves easily. Basically they believed that light being a waveform required such a medium.

-What was the aim of the Mich-Mor Experiment???
The experiment attempted to measure the relative velocity of the earth through the aether.

Thus why would u make the light travel at different directions????
Consider the existence of such an aether(as they did back then), then according to their logic it would take different amounts of time, or reflect different patterns in their apparatus, if there was such a thing as the aether.

BUT!!! there was no difference in patterns when they changed directions, it was always the SAME!!

-why???
Later showed by Einstein the speed of light(c) is a constant!!!

Also to rememeber........people had their own theories and according to the syllabus one needs to know more than just the 3 people aforementioned.

Lorentz was another scientist who tried to show the exist of the aether, and explain the 'NULL' result of the experiment (meaning it did/didnt disprove the aether). He stated that the lengths of the sides of the apparatus used by Mich-Mor (known as the interferometer) were contracting. However we now know this is the case but irrelevant, however Einstein later used his ideas of length contraction to explain his own theories.



MAIN POINT: LIGHT IS A CONSTANT!!!


hope this helps, if u need any more help pm me.

 

[airie]

Basically, the experiment aims to firstly verify the existence of aether, then find the earth's velocity relative to the aether, proposed to be the absolute frame of reference. An interferometer was used so that a light beam is split into travelling two paths perpendicular to each other, and create an interference pattern. As the interferometer is rotated through a 90 degree angle, it is proposed that this interference pattern should shift as the apparatus is rotated, due to the different directions in which the light beams are travelling relative to aether. However, no such change is detected (or rather, nowhere near as much as the aether theory postulated - but the apparatus is not 100% precise); they then improved the accuracy of the apparatus, and still, a null result was ontained. This therefore means that the aether theory cannot be verified, thus discredited it, which means that when Einstein's theory comes around (that EM waves do not need the medium of aether to propagate, thus the existence of aether is totally unnecessary), there's no competing theory.

Note however, this experiment did NOT prove that aether does not exist, as you cannot simply argue that something does not exist, just cos you can't detect its presence.

 

[elseany]

wow chousta, that was an awesome explanation, dunno why airie even bothered... geez.

 

[Zero Infinite]

I finally get it now, after reading about a speedboat race analogy. Basically, in a river, the aether wind would act like the current, so by comparing light rays heading across the aether and into the aether, they could calculate a value for the aether wind as the wind would attribute to the difference in their speeds. But, there was no detectable shift in the interference pattern, so apparently there is no detectable motion of the Earth relative to the aether.

Maybe I wasn't thinking properly before... It seems reasonably easy to understand now. Anyway, thanks everyone who responded.

 

[dr baby beanie]

Gotta love that speed boat analogy.

 

[Zero Infinite]

I think the reason why it's complicated is that they didn't know which direction the aether wind was in. And, that interference stuff was confusing if you didn't get the whole picture. Add to that the fact they had no idea that the speed of light is constant and a whole lot of mess follows.

 

[angmor]

the interference pattern would imply that the rays of light arrived at different points of time, and therefore that the rays would have different speed due to their movement through the aether.

but regardless of that, it was einstein who used this result to show that regardless of the existence of the aether or not, the speed of light is a constant.

hope that explains some things that the above posters havent.

 

[ianc]

it is highly probable that einstein didn't use the result of the m-m experiment to come up with his assumption of the speed of light being constant, because he made no reference to it in his original papers on special relativity in 1905

but i spose an hsc marker wouldnt care and would just be happy to know you understand why the m-m experiment didnt work.

 

[vizman]

Basically, the experiment aims to firstly verify the existence of aether

the experiment was never to verify the existence of an aether, but rather to measure the velocity of earth to the aether, which is why the result was a "null" result. the experiment was known more for starting debate into the aether, which was later proved not to be necessary.

 

[fwong]

the experiment was never to verify the existence of an aether, but rather to measure the velocity of earth to the aether, which is why the result was a "null" result. the experiment was known more for starting debate into the aether, which was later proved not to be necessary.

No, if the MM experiment could measure the Earth's velcioty in ether, it means ether existed. In other words, the existence of ether is tied closely with the relative velocity of Earth in the MM experiment.