Does zero exist?
As always, it depends on what you use the word "zero" to mean.
If we mean the mathematical concept, then it certainly exists, otherwise I don't know how mathematicians could even understand each other when they talk about zero.
If we use the word "zero" to mean a particular number of things, as presumably mathematicians do, and in these very enlightened times as most people seem to do as well, then it is a matter of conventions between willing adults. Whenever we think that there is no elephant in the room, we say that the number of elephants in the room is zero. This seems to make perfect sense, not only to mathematicians and philosophers, but to most people as well.
The impression that zero is problematic may come from the idea that it seems that we cannot count things when there is no thing there to count. This is true! Yet, whenever there are not too many things to count, we don't actually need to count things, and zero thing cannot be too many. If we see four cookies, we somehow immediately think that there are four cookies. When there is no cookies left, it is the convention that we may say either that there is no cookie in the box, or equivalently that there is zero cookie in the box.
If this is a crutch, then it is an inordinately convenient crutch, as it is probably one of the smartest innovations ever introduced in the way we conceive of numbers, and accordingly one which has been adopted in all cultures. Even the most conservative of zealots think nothing of using the zero.
This would resonate with the idea that mathematics is a human construct, designed to help us make sense of the world. In this context, zero serves as a tool to facilitate our understanding, rather than an inherent aspect of reality.
Exactly! The key word is "understanding", which really just means that the concept of zero helps us make sense of the world. No, there is no zero out there, but there is no 143,566,847 either and nobody thinks there is.
I suspect that this question is motivated by the idea that mathematics somehow contains some implicit claim that zero exists as an entity out there in the world! I don't think this is the case at all. Mathematicians presumably all believe that there is a concept of zero, but this is a true belief as far as I can tell, and that there is a concept of zero does not imply that there is a zero out there in the physical universe, in between quarks and leptons somehow. To say that zero lepton is a quark just means that no lepton is a quark.
You can relax, zero has no metaphysical significance.
This also raises questions about the limits of language and cognition. If we rely on zero as a crutch, what does that reveal about our capacity to understand the world without quantification?
Nothing further from the truth! The concept of zero on the contrary shows how versatile language is and how intuitive most humans are. It is simply a marvel that we should be able to discuss Black Holes, the Holy Trinity, quantitative easing and what not as if it was just the sort of things we do every morning when we brush our teeth! Just consider how incredibly far our nearest cousins in the animal kingdom are of achieving the same sort of things.
Can we truly grasp the concept of absence without resorting to a symbol or concept like zero?
Yes, of course. The notion that the things that counts the most for us may disappear and therefore be absent is probably one of the most important humans have to understand if they are to feel at ease in this world. Zero is just a name and we seldom use it outside actual calculations.
It is perhaps interesting to signal that mathematicians themselves see 0 as standing appart from natural numbers. Perhaps to fit with the historical genesis of numbers, the set ℕ is sometimes said to be the union of ℕ*, the historical (or perhaps actual) set of natural numbers, i.e. {1, 2, 3, ...}, and {0}, making 0 itself not a natural number.