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# What is Ether theory? (I think the book I read is misinterpreting Ether)

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I was reading about Ether, Maxwell and Young-double-slit experiment. I got a question about Ether law. Let me say what I read about Ether Law.

Suppose, a boat is traveling with Adverse of Water flow. Suppose, that boat is traveling $1 \ km/m$. So if the boat travels with favorable than if I push the boat with same "speed" than it will travel more faster than earlier cause the water flow is pushing it also.
They didn't finish the text here. So I am not going to say that it is Ether law.
They also said; If we think a train and that is traveling $200 \ km/h$ through west and another train is traveling through east with $100 \ km/h$. Then observer from second train will see that the first train is traveling backward with $100 \ km/h$ but if an observer (who isn't traveling) will see that the first train is traveling with $200 \ km/h$ through west.
That's what I had read in Relativity but I had read it in Ether theorem also. That's why I was confused too much.
If we think of two bus. And both bus are traveling. Suppose, first is coming from west and another bus is coming from east. So, at initial point the if someone shout from first bus then they will hear that sound "lately". The closer the bus gets the faster the sound will be. So it's like "speed" of sound is increasing.
I am saying that it doesn't make sense to me. Cause we had came closer to that sound the sound's velocity didn't increase or decrease at any time.
The author wrote that just like speed of sound is increasing so speed of light should increase also (They wrote it after the next line). They said,"earth is revolving the sun. It isn't moving circularly but just like oval. So if we think that the earth is too far away from sun at point A and it's closer to sun at point B". So the light from sun should reach to the earth more faster at point B rather than point A. Which proves that the speed of light is increasing.
I said earlier that it doesn't make sense to me.

I had asked one of my teacher today that, "What's the difference between Relativity and Ether?" He replied,"Ether is a part of Relativity". I had read in that Maxwell said Ether isn't true. Light travels at constant speed. I believe Maxwell's theory is true. But I am not saying that Ether is false. I am saying that the explanation of Ether is false. If Ether is false than Relativity is also. But I believe in Relativity.

At Maxwell's time average physicists had believed that Ether is true but Maxwell said it isn't. After Maxwell died, Michelson (Did I spell it wrong?) had proved that Ether is false but he didn't say what's happening with light (wave) (by his experiment).

Did Maxwell really said that Ether is false?

I was reading the Wiki (Aether) after writing the whole text. What I understood from the Wiki that is Ether actually says light (everything) needs medium to travel (or Ether provides such a medium). But Michelson had proved that light can travel in vacuum. What actually Ether is? It's like Ether doesn't have anything to do with Relativity. I had found another Wiki (Luminiferous aether).

it (Ether) required the existence of an invisible and infinite material with no interaction with physical objects.

After reading these Wiki, I think Ether is something like "medium" or "space" which have no interactions between any physical materials. I can't understand the Ether further. From the question, I understood that GR is related to Aether. I can't understand where the roadmap is going. I think the book had gave me huge confusion in my head.

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Throw that book out? (1 comment)

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Back when what light is and how it propagates was poorly understood, people naturally related it to sound. Sound propagates thru a medium, like air. Light was therefore assumed to propagate thru a medium too. This hypothetical medium was referred to as the ether.

While this line of reasoning is understandable, it turned out to be wrong. Light isn't carried by stuff. This may not sound like much, but is actually quite profound. Since light isn't carried by some stuff, unlike with sound, propagation isn't dependent on the sender's and receiver's movement thru any stuff. The experiments you describe seem to be intended to result in an observable difference whether sound or light propagates thru stuff.

For example, lets say you hold a sound transmitter and receiver 1 m apart. In normal still air, there will be a delay of about 3 ms between the transmitter sending something, and the receiver receiving it. If you take the same setup and mount it on the roof of a moving car, then that value decreases when the air is moving from the transmitter to the receiver, and increases when in the other direction. If you do this on a rocket in space (vaccuum), then you won't receive anything at all because there was no medium to carry the sound.

If you do the same thing with a light transmitter and receiver on a rocket in space, you first notice that you do receive the transmission at the receiver. That either means light travels without requiring a medium, or that some mythical medium exists anyway in what we think is the vacuum of space. The latter is what this "ether" was assumed to be.

However, if you make the rocket go fast, then try the test again, you don't find any difference in the propagation time. If you flip the transmitter and receiver with the rocket going the same speed as before, you still observe the same propagation delay. If light was carried by some ether, then there should have been a difference.

This not only shows that light doesn't propagate thru a medium, but that there is no such thing as an absolute "going fast". There is no ether sea that you can measure speed relative to. That's what relativity is all about.

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Modern physics has pretty much dismissed the concept of the ether. Any modern claim that something like the luminiferous aether exists would be up against mountains of experimental results indicating that it doesn't, and mountains of experimental results indicating that theories based on the very concept of it not existing being correct.

The luminiferous aether was a way to explain how, for example, EM radiation (such as light and magnetism) could propagate. However, not only did it suffer from inconsistencies and generally resulted in undesirable effects; when experiments were conducted, those were unable to demonstrate the existence of such a medium. By now, we have experimental results at least down to the 10-17 level.

The results of the Michelson-Morley experiments was part of what motivated what later became the special theory of relativity, which does not rely on the existence of any particular all-encompassing medium and which specifically postulates that the speed of light in vacuum is the same for all observers regardless of motion (which, at a minimum, would be very difficult to reconcile with the existence of such a medium).

Maxwell lived between 1831 and 1879, while the Michelson-Morley experiment was conducted and published in 1887, so while I don't have an absolute answer to whether Maxwell stated that the ether did not exist, he would not have had any experimental result that would support such a statement. (He may or may not have realized the difficulty of reconciling his own results with the existence of such a medium.) Wikipedia notes, though, that "Einstein developed special and general relativity to accommodate the invariant speed of light, a consequence of Maxwell's equations" (my emphasis). Keep in mind that Einstein was born in 1879, the same year that Maxwell died, and published his paper on special relativity in 1905, a full quarter century after Maxwell's death.

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