That's a defensible perspective, I guess, but the fact remains that you don't fall through your chair, and that's all we really want from a description of "solid" matter. Turns out your chair behaves weirdly when you shoot alpha particles through it, but your bottom isn't made of alpha particles, so what does that prove as far as solidity goes? I suppose it proves that solidity is a non-fundamental property of matter, and that is profound, but that doesn't mean we need to change the name. It just seems like a semantic cul-de-sac to me.

I think of it more like a pincushion. A needle will go right into it with very little resistance. One’s hand or fingertip — not so much.

Right. And no one confuses a pincushion for empty space. They just also don't confuse it with adamantium.

You can sit on a pincushion filled very densely with needles equally well as a solid wooden chair. Yet the needles clearly have more space between them than a solid block of wood. Your personal inability to penetrate or see into that space doesn’t mean the space isn’t there. Indeed, how do you know if there’s a microscopic crack? You look at photons reflecting and amplify them into your optical range. How do we know whether or not there’s space in the atom range? We use an electron microscope. It’s still a microscope - a tool to objectively pierce the physical realm in ways that you can’t with your own sense.

None of that, even to the extent it's true, makes a lick of difference to my point. You definitely don't need to lecture me about how scientific instruments supply info my biological senses can't. I know how subatomic particles work. I'm trying to make a point about obfuscatory terminology.

> Ye olde Rutherford experiment nicely illustrates the points of 'yes it is all empty space'

No, it does not. It illustrates that the portion of an atom that strongly scatters alpha particles occupies a small fraction of the atom's volume. Asserting that alpha particle scattering is the only correct definition of the threshold between emptiness and non-emptiness is an awfully strange position to take.

When interacting with other electrons at energy scales relevant to human life, i.e. maybe ten electron volts and down, an electron cloud is somewhere between solid (core electrons especially in heavy atoms) and squishy (valence electrons). Give a rock the ol' "I refute it thus!" and your toes will report that that rock's electrons are quite competently occupying their space.

Ask an alpha particle at nuclear energy scales a million times greater, and that electron cloud is like a swarm of gnats to a speeding car. The electrons only interact with the alpha electromagnetically, and it takes another object that interacts through the strong nuclear force to really bother a nucleus (most of the time).

Ask a neutrino, and it will tell you that all the nuclei in the Sun are but a wisp of fog.

This is a good example of how approximations valid in one regime fail in another but are not therefore useless. Rutherford's experiment reveals that there is more going on with matter than what can be probed by fingers and microscopes and chemical reactions, but it in no way invalidates those other observations.