Complex numbers, for example: they don't exist, but they're really useful to define and explain electrical experiments At risk of turning this into a discussio

Complex numbers, for example: they don't exist, but they're really useful to define and explain electrical experiments At risk of turning this into a discussion of what "exist" means, I reckon they do exist :p If they didn't exist, how could we possibly use them, and use them so effectively and consistently? Of course, if a number "existing" means "I can see this many number of apples" then sure, it doesn't "exist". Yes, this is definitely becoming a discussion of what the word "exist" means applied to number. I'll stop. :)