Michelson Morley experiment (1 Viewer)

[killua_3]

Just a quick question. why did they have to turn the apparatus 90 degrees? If they've already split the light into 2 waves, one going across and one going against aether, wouldn't that give them the interference they needed? What good does turning it do? Wouldnt it mean that still 1 light in going across and 1 light is going against?

 

[darkchild69]

Just a quick question. why did they have to turn the apparatus 90 degrees? If they've already split the light into 2 waves, one going across and one going against aether, wouldn't that give them the interference they needed? What good does turning it do? Wouldnt it mean that still 1 light in going across and 1 light is going against?

They had no idea which direction the ether was oriented. The whole idea was to get one wave travel "across" the ether and the other wave travel "with and against" the ether.

They rotated it by 90 degrees, cuz at some point during the 90 degree rotation the waves would be oriented exactly right, and the interference pattern should maximise.

 

[killua_3]

They had no idea which direction the ether was oriented. The whole idea was to get one wave travel "across" the ether and the other wave travel "with and against" the ether.

They rotated it by 90 degrees, cuz at some point during the 90 degree rotation the waves would be oriented exactly right, and the interference pattern should maximise.

oh. so they didnt only test angels of 0 and 90, but they tested everything in between as well because they didnt know which way the aether wind blew?

 

[darkchild69]

I believe so

I have seen different textbooks say different things, but my basic understanding of it, is if you were to rotate the device through 90 degrees, then you should observe variations in brightness due to the interference of the waves, if the luminiferous ether is present. When you rotate it by 90 degrees, the wave which hit the viewing scope first previously, should now hit it second.

 

[killua_3]

I believe so

I have seen different textbooks say different things, but my basic understanding of it, is if you were to rotate the device through 90 degrees, then you should observe variations in brightness due to the interference of the waves, if the luminiferous ether is present. When you rotate it by 90 degrees, the wave which hit the viewing scope first previously, should now hit it second.

ta. i suppose its a mystery how these scientists operate

 

[JasonNg1025]

Yeah when they rotate it 90 degrees they're 'changing' the relative direction of both light rays relative to the ether. They predicted them to go at different velocities because of the constant ether wind direction, and then produce a different interference pattern. That's what I heard

But what I'm wondering is, if the ether didn't exist at all, why did they get an interference pattern in the first place? Maybe because they didn't really bother making the light paths the same length cause they knew they'd rotate it anyway?

 

[youngminii]

Waves interfere with each other no matter what. It can be constructive or destructive. If the light rays were moving at the same speed the whole time, then the interference pattern would show purely constructive interference.
That's what happened, there was only constructive interference (barring the experimental errors). It's just that you don't need to write in that detail, since it's assumed that you know what interference is when you say 'interference pattern'.