At different points in history, commodities have been at different levels of supply, and therefore have been at different prices. One good might be valuable in the present while another is nearly worthless; a century ago, this could have been switched. Therefore, any time traveler with an eye for making a profit could realize that there's an easy way to become rich:
- Buy a cheap commodity in the present.
- Sell said commodity in the past, when it was more valuable.
- In that same time, but a cheap commodity that is valuable in the present.
- Return to the present to sell that commodity.
If this is done on a large enough scale by enough time travelers, it could wreak havoc on global economies throughout time. This could lead to shortages of goods in time periods when they could be needed desperately - or in the years after trading begins, when prices would have risen.
Assuming that the trading does not happen at what the Doctor in Doctor Who calls "fixed points in time" - in other words, assuming that this trading can change the past, present and future - then I have a few questions:
- Is this strategy for getting rich feasible?
- What would be the large-scale economic effects?
- Time travel first arose around the present-day.
- Due to the nature of the mechanism, you can transport about one person and a suitcase at a time. One time travel machine is not great as a mass-transit device.
- I'm interested in how the economies of different eras would be affected as people slowly gain access to time travel after its invention. Growth is limited.
- Time travel was a government invention originally, but the secret was leaked pretty quickly. It was soon legalized for the public, but heavily regulated by most major governments. Certain companies - in the same vein as airlines or train companies - rent out machines for short trips, although there is a little bit of monitoring on their part. In other words, most people can use it - if you can afford a ticket of roughly \$10,000, for enough fuel to jump a total of perhaps 200 years (round-trip).
- These same companies will monitor their customers, to try to make sure they don't lead to the end of the world. Minor changes to history might be allowed to slide.
- In theory, you can travel as far back in time as possible, but you need more energy to do so, and more energy means higher costs. Very few people will be able to travel before 1,000 AD.
- In response to some comments/answers regarding paradoxes: I think that if you take a suitcase's worth of a good that's cheap - and likely in good supply - the market will essentially damp any ripple or butterfly effects it could cause. It's the equivalent of a drop in a bucket.
Because this isn't just an issue in one world - although I've described the specifications arising in the particular world I'm working on - I'm a bit wary of getting overly specific, but I hope the above constrains the question enough.