Let’s imagine a world where time machines are invented.
Hypothetically, what’s stopping anyone from travelling to the past, where the dollar is much more valuable, and buying things at a much lower price? What if you then go back to the present, sell those things at a higher price and repeat the cycle? And wtf would happen if everyone there started doing that?
I don’t follow. If you took the coin from the past, it no longer exists in the present. You still have 1 coin. You are duplicated, however, and now two of you exist in the present timeline. You could do the duplication glitch by taking the present timeline coin back to the past and giving it to past self, who now has two coins.
If I steal a gold coin from the year 2000, then, with that coin in hand, travel to 1999 and steal the same coin, I now have two copies. I then travel to 1998, 1997, et cetera, et cetera, on down the line, each time I gain an additional copy of the same coin. I then take all these coins with me to the present and spend them. Now just swap out the years for 2 minute intervals and you’ve got an infinite number of coins, or nearly so, anyway.