I think this gets back to the question of what you mean by “there”. Because if I have, say, water in a tank, and I move around a stick I placed in that water, then the ‘water field’ (or whatever I want to call the positions of the water molecules) will update based on that, and it will update at a finite speed because the information is carried by traveling water molecules. So the water field is there because water molecules are there- if you put something in their way, they’ll run into it.
But electromagnetic waves are carried by photons, which are really weird. Water molecules have a rest mass- if you managed to slow one down to no speed at all, it would exert about as much gravitational pull as normal, and it would still get in the way of other things you tried to push through it. A photon has no rest mass, and a way of thinking about that is to say that if the photon isn’t moving, it isn’t there.
And so if by “thereness” you mean “if I shoot a neutron at a stationary one, is the neutron sometimes deflected?” then water molecules are there and photons aren’t.
But there’s another sense that we can talk about thereness- what happens when we (or they) speed up. If I had the aforementioned water tank on a train moving near the speed of light, things would look the same inside the train- but really weird from outside. To observers, the ability of the ‘water field’ to update depends on how fast the water field is moving relative to the observer- but that isn’t true for the electromagnetic field. All observers see it ‘updating’ at the same rate.
So, what do we mean by “aether”? Here, I think we might be getting in a linguistic/historical issue, which is what you originally asked about. I was fascinated, watching a talk between PZ Myers and Dawkins (one of those, might not be the first one), where for Dawkins the phrase “group selection” seemed to be irretrievably connected with Wynne-Edwards, despite there being several defensible things that also have a connection with that name. Each time it came up, he had to check- “you’re not talking about Wynne-Edwards group selection, right?”
I believe (but haven’t extensively researched the physics in question) that the luminiferous aether was tied to the idea that there is one correct reference frame, and so when that disagreed with experiments that idea got tossed out. That means we don’t have a visual answer to the question “what wiggles when there’s an electromagnetic wave?”, and as far as I can tell it doesn’t make a difference what you visualize wiggling, but calling it ‘aether’ makes people ask questions to make sure you’re not an adherent of a dead theory.
I think this gets back to the question of what you mean by “there”. Because if I have, say, water in a tank, and I move around a stick I placed in that water, then the ‘water field’ (or whatever I want to call the positions of the water molecules) will update based on that, and it will update at a finite speed because the information is carried by traveling water molecules. So the water field is there because water molecules are there- if you put something in their way, they’ll run into it.
But electromagnetic waves are carried by photons, which are really weird. Water molecules have a rest mass- if you managed to slow one down to no speed at all, it would exert about as much gravitational pull as normal, and it would still get in the way of other things you tried to push through it. A photon has no rest mass, and a way of thinking about that is to say that if the photon isn’t moving, it isn’t there.
And so if by “thereness” you mean “if I shoot a neutron at a stationary one, is the neutron sometimes deflected?” then water molecules are there and photons aren’t.
But there’s another sense that we can talk about thereness- what happens when we (or they) speed up. If I had the aforementioned water tank on a train moving near the speed of light, things would look the same inside the train- but really weird from outside. To observers, the ability of the ‘water field’ to update depends on how fast the water field is moving relative to the observer- but that isn’t true for the electromagnetic field. All observers see it ‘updating’ at the same rate.
So, what do we mean by “aether”? Here, I think we might be getting in a linguistic/historical issue, which is what you originally asked about. I was fascinated, watching a talk between PZ Myers and Dawkins (one of those, might not be the first one), where for Dawkins the phrase “group selection” seemed to be irretrievably connected with Wynne-Edwards, despite there being several defensible things that also have a connection with that name. Each time it came up, he had to check- “you’re not talking about Wynne-Edwards group selection, right?”
I believe (but haven’t extensively researched the physics in question) that the luminiferous aether was tied to the idea that there is one correct reference frame, and so when that disagreed with experiments that idea got tossed out. That means we don’t have a visual answer to the question “what wiggles when there’s an electromagnetic wave?”, and as far as I can tell it doesn’t make a difference what you visualize wiggling, but calling it ‘aether’ makes people ask questions to make sure you’re not an adherent of a dead theory.