I wish that humans were not so easily duped into believing that things for which someone else uses the same name are really the same and things for which someone else uses different names are really different.

The Michelson–Morley experiment was indeed very important, but it has not proved in any way the non-existence of ether. It has just proved that the ether does not behave as it was previously supposed, i.e. like the materials with which humans are familiar.

It does not matter at all what names are used for it, one may choose to name it "ether", "vacuum", "electromagnetic field", "force field" or anything else, but all the modern physics, since James Clerk Maxwell and William Thomson, is built on the assumption that the space is not empty, but it is completely filled with something that mediates all the interactions between things.

Only before the middle of the 19th century, the dominant theories of physics assumed the existence of true vacuum. The existence of true vacuum is possible only in the theories based on action at a distance, like the Newtonian theory of gravity or the electromagnetic theory of Wilhelm Eduard Weber, but not in field-based theories, like the electromagnetic theory of Maxwell or the gravitational theory of Einstein.

It is rather shameful for physics that the main result of the Michelson-Morley experiment has been the replacement of the word "ether" by "vacuum", as if a change of name would change the thing to which the name is applied, instead of focusing on a better understanding of the properties of the thing for which the name is used.

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SAI_Peregrinus a day ago | parent | next [-]

"Ether" is a hypothetical substance with certain properties. The Michelson-Morley experiment proved that no substance with those properties existed. There's something else with different properties, so it makes perfect sense to use a different name.

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TeMPOraL a day ago | parent [-]

In context of approximately everyone's education, the history goes like this: in the past people believe there's something in empty space, and used the name "ether" for that. You learn that, then you learn that MM showed there's no "something", no "ether", but that empty space is, in fact, empty, which is what "vacuum" means. And then if you pay attention or any interest to the topic, you learn that there in fact is no pure vacuum, there's always "something" in empty space.

The obvious question to ask at this point is, "so ether is back on the table?".

Turns out the mistake is, as GP said, thinking MM proved space is empty; it only disproved a particular class of substances with particular properties. But that's not how they tell you about it in school.

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lisper a day ago | parent | next [-]

More specifically MM showed that earth is not moving relative to a hypothetical medium through which electromagnetic waves propagate. So either the universe is geocentric or there is no such medium.

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zmgsabst a day ago | parent [-]

Another interpretation is that the apparatus and not just light is made from ether — and so the signal is lost because the measuring apparatus is also subject to the local distortion.

That interpretation is also consistent with LIGO: we can detect those ether disturbances because the distortion of our motion on the apparatus doesn’t cancel the signal in the same way.

	▲	lisper 11 hours ago \| parent [-]
		> Another interpretation is that the apparatus ... is made from ether Or maybe an invisible pink unicorn is sneaking into the lab at night and tweaking things.

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jfengel a day ago | parent | prev [-]

It's more than just the lack of material. It demonstrates that light propagates in a specific way that is different from any ordinary material. Light moving in a vacuum is different from a baseball moving in a vacuum. The speed of light is independent of your own motion, which is not true of anything with mass.

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lisper 11 hours ago | parent | prev | next [-]

> The Michelson–Morley experiment was indeed very important, but it has not proved in any way the non-existence of ether. It has just proved that the ether does not behave as it was previously supposed, i.e. like the materials with which humans are familiar.

That's kind of like saying that our failure to observe invisible pink unicorns does not prove the non-existence of invisible pink unicorns, it just proves that invisible pink unicorns don't behave the way you expect them to.

Luminiferous ether was a specific hypothesis about how light works. It made a prediction, which turned out to be wrong, which falsified the theory. Whether you want to attach the description "proves the ether does not exist" or "proves the ether does not have the properties ascribed to it by the theory" is completely irrelevant.

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ge96 a day ago | parent | prev [-]

I thought the whole point was if it did exist the motion goes faster in one direction than the other.

edit: not sure if you're referring to dark matter

yeah I gotta read your comment more thoroughly

	▲	lutusp a day ago \| parent [-]
		> I thought the whole point was if it did exist the motion goes faster in one direction than the other. No, the idea was that, in a space filled with the hypothetical ether, Earth's velocity through the ether should have been detectable by comparing light beams traveling in different directions. The null result was very important -- it didn't prove the absence of an ether, it only showed that it wasn't a factor in light propagation.