> Is it? I'd say empty space is empty space whether it can be filled or not.
Though technically correct when sticking to matter, it feels so wrong because of how it encourages inapplicable intuitions from the macroscopic world.
"We are mostly empty space" is used as trivia, with an implicit exclamation mark suggesting it is astonishing and significant, but it is intentionally incomplete and lacks context - the whole picture shows something far more substantial that has nothing to do with our macroscopic intuitions.
Is it? I'd say empty space is empty space whether it can be filled or not.
If the universe was just 2 plates N meters apart that was impossible to move any closer (e.g. because of opposite forces, like with magnets which work fine in a vacuum), the space between them would still make sense to call empty...