"Nothing" is about as slippery a concept as you can — or rather can't — imagine. Try to picture absolutely nothing at all. Is your nothing black, empty, soundless? Sorry, that's something. Those are all qualities, that is, you're imagining a something, located, perhaps, in space and time (something!) that happens to be black, empty and absent sound. Nothing is not even nothingness! Just thinking about nothing gets you something.
Following a long line of eminent thinkers, philosophers Robert Kuhn and John Leslie tackled the weirdness of nothing in their book The Mystery of Existence, coming up with a useful taxonomy that they call a "deconstruction." The idea (formally known as the "subtraction argument") is to peel away successive conceptions of nothing, starting off with the simple (pre-scientific) notion — possibly the one you just pictured — as space and time absent all visible objects. That's their level one nothing. Level two subtracts invisible particles (like electrons) but leaves energy; level three takes out all matter and energy; level four adds "forever." All we're left with is "naked" space and time. (You could get pedantic at this point and complain that space and time are, respectively, systems of spatial and temporal relations between things, thus an entirely empty universe is conceptually impossible.)
Level five, nothing gets more interesting as we subtract space and time. This is the "nothing" that got physicist Lawrence Krause into trouble with his 2012 book, A Universe from Nothing. His "Nothing" was thick with pre-existing laws, such as those governing quantum mechanics: It was a physicist's nothing. Quantum mechannics tells us that don't need space and time — or anything else — for universes to spontaneously pop into existence, all you need are laws of physics. But, as his skeptical reviewers delighted in pointing out, laws are something; Krause was offering a proximal cause, not a reason, for the existence of the universe. Which logically brings us to level six, which has no pre-existing laws, along with no everything else.
But, you might say, what about God? Couldn't God or cosmic consciousness or some sort of "immaterial yearning" (as it were) outside of time and space, create a universe ex nihilo, that is, out of a level six nothing? On the off-chance that's the case, level seven nothing removes God, gods, consciousness, anything that might not be covered in the above sequence of subtractions. Kuhn and Leslie manage to keep going for another couple of levels (no universals or Platonic forms, no possibilities of any kind that we haven't thought of), but you get the picture. By taking increasingly arcane elements out of the running, you might, if your imagination permits, arrive at some nebulous concept of nothing — Nothing, perhaps? But it's all pretty weird, sort of like conceiving of "you" before you were, um, conceived.
(Actually that last one is a bit easier to deal with, since you've been here, in your constituent particles, for nearly 14 billion years. Just not in the handy person-size package in which you now find yourself.)
So there's nothing for you. Except it isn't, it's something — a lot of words discussing concepts — about nothing. Dictionary compilers use the phrase negative definition — "silence is the absence of sound," for example — and it seems that with nothing, we're faced with the ultimate negative definition. Which (sigh) is something.
Barry Evans (firstname.lastname@example.org) gets pretty angsty when worrying about nothing