B Michelson's experiment surprise

1. Mar 5, 2017

Paulo Figueiredo

Hello!
Why the surprise in the result of the Michelson-Morley experiment?
If the mirrors were in earth, i think that the system is a galileu system. If the earth is moving or if the earth was not moving the result, in my opinion, were the same.

2. Mar 5, 2017

Ibix

Think of doing the experiment using sound. Do it on the platform. Then do it on the roof of a train. Would you be surprised if the wind had no effect on the sound? In an extreme case you could do the experiment on the back of a supersonic jet - travel faster than sound and the sound could never even reach the front mirror, let alone reflect off it.

That's why Michelson and Morley were surprised by the null result. They expected the different motion of the Earth through the ether to have an effect on their experiment. But it didn't.

3. Mar 5, 2017

Paulo Figueiredo

Hello Ibix. Thanks for your answer. I understand what you have said, but are you sure that in the experiment of the supersonic jet, if the sound came of the interior of the supersonic jet, the sound never reach the front mirror? I think that the result will be that if the sound came out of the jet.
What i want to mean is that if the sound came in the interior of the jet it will be indiferent if the jet were moving (with a uniform velocity) or not.
I think that the system is a "closed" , is a galileu system....
Am i wrong?

4. Mar 5, 2017

ZapperZ

Staff Emeritus
In a supersonic jet, the "medium", which is the air, travels WITH the jet. So the air inside the jet is considered to be at rest with the interior of the jet.

This is NOT the hypothesis of the classical ether, which was thought to be the medium that light travels in. It was thought that the ether pervades the universe, and that the earth and everything else move through the ether medium. So how fast and in what direction the earth travels through the ether should make a difference in the speed of light that is being measured even on earth.

So the two scenarios are completely different.

Zz.

5. Mar 5, 2017

DrGreg

I think you are referring to the aether drag hypothesis, the possibility that aether could be dragged along with the Earth's surface so that the speed of the aether "wind" would be zero at ground level. But if that were true, it would cause refractive effects, when viewing the stars, that have not been detected. See the blue link above for more details.

6. Mar 5, 2017

Ibix

The Michelson Morley experiment wasn't expected to be analogous to being inside the aircraft. Ether (if it existed) clearly wasn't bothered by walls - radio waves could penetrate. And Fizeau's experiments with light in flowing water weren't consistent with ordinary matter being the medium for light. Ether had to penetrate matter.

In fact, the first thought people had to explain the null result was that ether was "entrained" by matter. That is, it was dragged along with matter somehow. So then, yes, the Michelson-Morley experiment would be analogous to working inside the jet. But that's inconsistent with astronomical observations - starlight would be aberrated by parts of the ether being dragged and other parts not being.

So, no. Ether doesn't work and Newton has to be abandoned.

Edit: Beaten to it by Zz and DrGreg, I see.

7. Mar 5, 2017

8. Mar 5, 2017

Paulo Figueiredo

Thanks. I think i had understand the difference.

9. Mar 5, 2017

Paulo Figueiredo

Thanks Ibix. I think that now i understand the difference.