I just created 100 pennies and I loaned them out to you + interest
How is it possible for you to pay me the 101 pennies you now legally owe me if only 100 pennies are in circulation?
Nice argument against non-inflationary currencies, which Bitcoin is hoping to become.
Let's try your problem, starting with this "sound money":
You have all of the gold in the world, and lend it to me @ .1% yearly interest.
"How is it possible for
you me to pay
me you etc., etc.?"