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For example, if money leaves my account (negative number) it doesn't disappear or go into a universal money vacuum somewhere, it just goes (positive number) to another account. Same for body temperature, photon emission, or anything else in the universe - don't the laws of conservation mean that negative numbers are just measurements for movement between systems but there's never an real "subtraction" of anything anywhere anytime?
And if negative numbers really are contrived to help us deal with systems in isolation, then have we hamstrung our fundamental mathematics by treating them as real numbers instead of imaginary?