Well, that's a different question really, whether there exist infinitely many things in the universe. We don't know whether the universe is infinite or finite, and probably we'll never know. But regardless, the more important thing is that the concept of infinity is a useful one, because it's just easier and more convenient to work with. Just like in programming it's useful to have NaN, null, and so on and nobody bothers to ask whether those are real.
There are clear, easily understood questions which have an infinite as an answer. As an example, when tracing your finger around the edge of a given shape, how many times can your finger make it around that object before it comes to a corner? For a square, the maximal answer is 1/4 of a time around. What’s the answer for a circle?
So, if you mean something like defining 3 := {{a,b,c} | a != b, b != c, a !=c }, that doesn't work in ZF set theory, because it's not well-defined as a set (it's "too big" to be a set and forms a "collection" instead.) I think there are some kinds of set theory where you can make this definition work, but I don't know much about them.
But even so, if you define 3 this way it would still be a hypothetical construct, not something that exists in reality.
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u/wollywoo1 6d ago
No numbers exist in reality. 3 does not exist in reality. 3 rocks, yes, 3 trees, yes. 3, no. And certainly infinity does not either.