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"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.

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.

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.

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.

> 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.

QM posits that fields which constitute matter and fields which constitute EM are both manifestations of an underlying phenomenon — that’s the whole idea behind unification. (And we’ve already successfully unified such fields.) My comment is just applying that theory to interpreting the Michelson-Morley experiment.

Please don’t reply with such trite anti-scientific comments, which conflate actual scientific claims with nonsense.

If you have an actual objection, then you should present it. But argument by mockery because you fail to understand modern physics lowers the quality of the discussion.

> My comment is just applying that theory to interpreting the Michelson-Morley experiment.

Really? Where in the Standard Model do I find the luminiferous aether that you suggest the apparatus is made of?

Field theories are aether theories; as is GR. (Wilczek says as much.) You’re fixated on a particular model of aether, rather than addressing the broader concept. But that’s as illogical as me insisting atoms aren’t real because the Bohr model of electron shells was wrong.

The current aether for light is called “EM field”; matter is made of other fields demonstrated to unify at high energies by the LHC and similar experiments, within the standard model. But you knew all that.

You’re just pretending ignorance to avoid addressing my central thesis: fields are aethers.

> You’re fixated on a particular model of aether

Well, yes, of course. This is a discussion of Michelson-Morley interferometers. In that context the word "aether" has a very specific and well-established meaning, and it is not at all the same as a quantum field.

> fields are aethers

You are free to employ the Humpty Dumpty theory of language and redefine the word "aether" if you like. But in the context of Michelson-Morley interferometers, no, quantum fields are not "aethers". The whole notion of making the word "aether" plural in that context is non-sensical. In the context of Michelson-Morley interferometers there is only one aether: the luminiferous aether, a hypothetical physical substance that exists in three-dimensional space. Quantum fields are not even remotely like that. They are not physical. They do not exist in 3-D space. They cannot be directly measured. Physical objects are emergent properties of fields, but they are not "made of" fields. The constituents of a piece of lab equipment are particles, not fields.

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.

> 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.

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

> 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.