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?
You’d have to find the oldest bills you can find, time travel to the year they were issued, trade for older currency, time travel further back, and repeat until you’re at the point in time where the currency’s relative value is sufficient for your goals. So there’s that; it would be inefficient. I suppose you could travel with gold…
And rather than buying stuff, just put it in a bank you know would survive until present day and let it collect interest (or invest based on future knowledge, etc).
Ok…but wouldn’t some red flags be raised when you go to withdraw and they say “YOU are the person who opened this account?” “Yes.” “In 1824?” “Yes.”
“Oh it was my grandfather, I got the same name and here is his will.”