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Forum: The Classroom
Topic: michelson morley experiment
started by: KL1NK

Posted by KL1NK on May 29 2001,00:58

Does anyone know about the Michelson Morley experiment? I have to give a presentation on it tomorrow in physics and I'm kind of confused on some of the concepts of it. Any help is greatly appreciated.

Posted by CatKnight on May 29 2001,01:03

they were the two guys that tried to prove that the ether existed, but failed miserably

in fact they ended up proving it didn't exist!

Anyway, before we knew about photons and electroweak stuff, physicists thought that al types of waves had to propogate through a medium, e.g. sound through air, they thought light traveled through an ether, that existed everywhere.

they designed an experiment that consisted of some sort of cart with mirrors pointing in perpendicular directions. if the ether existed, then the speed of light measured going in the direction of travel should be different from the perpendicular direction, due to "ether drag" i guess. anyway they turned out to be the same.

*note: i typed this from memory and it might be slightly innaccurate. so don't quote me.

Posted by KL1NK on May 29 2001,01:21

Thanks. Does the earth's velocity fit in there anywhere? Most of the stuff I'm reading seems to say the experiment was to determine the earth's velocity with respect to ether. (is that basically the same thing?)

Posted by CatKnight on May 29 2001,01:29

uh...

they may have done something like that... ?

Posted by Non on May 29 2001,02:00

Man you are way off.

Posted by KL1NK on May 29 2001,02:25

I figured it out. Luckily I had a copy of Stephen Hawking's A Brief History of Time laying around.

Posted by DuSTman on May 29 2001,07:33

Yeah.. the experiment was actually designed to measure the "aether wind" - or the velocity we happened to be going relative to this magical medium of light, and in this respect it was an abject failure..

But it's failure proved the speed of light was the same in any inertial frame, which suprised everyone..

This shows the apparatus used. (yeah, fear my poor graphics skills etc)

The partially silvered mirror splitted the beam into two which were then reflected back by the respective fully silvered mirrors. and the partially silvered mirror again lets through some radiation but reflects the rest.. this results in two beams going towards the telescope from the partially silvered mirror, which had taken different paths. As a result, interference patterns are observed through the telescope.

The entire apparatus is then rotated 90 degrees to see the change in the interference pattern. This is then repeated 6 months later (when the earth is on the other side of the sun, so would be going in a different direction relative to the "aether wind".)

No change in the interference fringes was in fact observed either while rotating it 90 degrees or observing 6 months later..

This message has been edited by DuSTman on May 30, 2001 at 06:30 AM

Posted by CatKnight on May 29 2001,10:58

eh close enough

Posted by KL1NK on May 29 2001,12:20

Thanks DuSTman

Posted by Dark Knight Bob on May 29 2001,12:53

its surprising how such a simple and strangely enuff boring eexperiment can be used to prove that the ether dont exist. i mean our physics teacher one lecture just set it up and said "today i'm gonna show you how the ehter dont exist" and it took like 10 seconds

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