11yo: What is soap on the hardness scale?
Me: maybe a one?
Kid: What is water? It must be less than zero. It’s like negative infinity: It goes on and on forever except in another direction like negative numbers do (motioning down w/ her hand)
Me: How can there be a negative infinity?
Kid: It’s like subtracting. But what *is* negative numbers? Does it represent an object? Does it represent the objects that aren’t there? Infinity is an idea of going on and on forever. And it could go on and on in the other direction. That way there are multiple infinities … but there are probably “equalitive numbers” too. Like they’re all equal to each other.
Me: Any other thoughts?