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?
If you are standing in your shower (shower thoughts) and try to travel 200 years back, your location in space is not where the solar system, nor the earth was 200 years ago. So there’s that…
Physics-wise, the only conceived ways to time travel to the past is either FTL travel or wormholes, with the latter requiring “exotic matter” to stabilize, and even then, you can’t go back to any arbitrary time. Nobody knows if exotic matter actually exists. FTL seems off the board.
There are mechanisms in place to keep history and the past safe for historians.
I think our global economy is safe.
Maybe space is somewhat relative to time?
Of course THOSE theories don’t work, we haven’t yet figured out the one that will.