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.