Lets say I have a way to buy goods (say gold) from the past (say 30 years ago). I would like to take my new 100$ bill and buy the stuff, and then bring them back to the future (any movie references unintended). Sell the stuff for a profit because obviously its worth more here. Would the dollar bills I am using to pay for the goods be considered counterfeit in the past?
I am thinking this would be the case because the treasurer who signed it and serial numbers don't exist as yet or the serial number is duplicate.