# How could an inter-temporal banking system work?

(This question is meant to be an improvement and/or replacement for How would you bring wealth back to the past?, which some users have argued is off-topic for this group.)

Imagine a future world in which time travel is not uncommon. (Think of it as being like intercontinental travel today -- something that lots of people do, but it's pretty expensive, so most people can't afford to do it more than a few times in their lives, if ever.) In such a world, an entire infrastructure would eventually grow up around time travel: for example there might be temporal travel agents who would book your entire trip, complete with false identification papers and lodgings at your destination time. There would also presumably be some kind of inter-temporal law enforcement.

And, of course, there would probably need to be some kind of banking system. After all, the main users of time travel are the wealthy, and the wealthy are not going to want to travel back in time without access to their funds. An inter-temporal banking system would have to function as a bureau de change, exchanging currency from one point in time for currency from another. Such a system would have to cope with the "exchange rate" produced by the effects of inflation over many years, and would have to grapple with the fundamental problem of transferring wealth across time without it losing value. How could such a system function?

In posing this question I am specifically not looking for "get rich by betting on sports or buying stocks" answers -- that kind of personal enrichment would, I assume, be prohibited by the inter-temporal law enforcement as a form of fraud. The question here is not "How could you make a lot of money in the past?", but rather "How could a banking system move money from future to past?"

Moving money from past to future is of course simple: you just deposit it in an account in the past and retrieve it when you return to your point of origin. Presumably the legal system would have to figure out some way of preventing everyone from enriching themselves via a long-term interest scheme -- it would be pretty disruptive to the economy if everyone who could afford a ticket to the past just invested their money in a savings account and came back to their point of departure a billionaire! -- but the basic problem of moving money forward in time seems easy to solve. How would a banking system handle the problem of moving money backward in time without disrupting the economy at either the point of origin or their destination, and without screwing up the timeline along the way?

• Don't confuse wealth (goods and services that are valuable to you) with money (exchange medium to trade those goods and services). Banking handles only money, not wealth. This is important - when there's a big imbalance between money and wealth, you get all kinds of terrible problems (like depressions or bubbles) and the corresponding knock-on effects. If the main point of your idea is to deliberately transport large amounts of only money (as opposed to, say, boxes of shoes or jewelry or machine tools) from one period to another, you may destabilize both periods if you send too much. – user535733 Jun 5 '18 at 18:15
• Any important consideration on the 'wealth to the past' question was that travel was a one-way trip. Does that apply here too or are we treating time as weebly-wobbly-timey-whimey-stuff? You may also want to be explicit about how time travel works, ie, branching, closed loop, etc. – Green Jun 5 '18 at 18:16
• What is the precise rules of time travel for your world? Many things which we consider to be simple cease to be simple with time travel, and the exact rules are going to be important to prevent a lot of common feedback patterns. – Cort Ammon Jun 7 '18 at 0:51
• This is a much better and interesting question than the original – Devon M Jun 7 '18 at 1:17
• Question about your world: can the people travel back before the time travel was created ? For example during MiddleAge ? It can change the bank system according to your choice – Ted Pwyll Jun 7 '18 at 11:22

I’m about to hand wave a whole bunch of time travel paradoxes, tropes, and mechanics away.

This question is thinking about temporal monetary transfer the wrong way. Why would a bank want to move present day funds into the past in the first place? There seems to be one obvious reason: people want to access their money during their time traveling adventures. But why would a bank try to actively manage currency across geography and time? That seems tedious — depending on time and location the items and currencies that hold value could fluctuate wildly, not to mention that you’d need to reliably hide it from citizens of the time. And in the question you linked, we’ve found that knowledge is truly the best way to gain wealth in the past. So how do we combine these two?

The “bank” functions as a guardian of historical knowledge surrounding past funding events.

Using knowledge to gain wealth in the past sounds great until you want to visit some small town in Africa in the year 854. Knowing the Super Bowl winners or lottery numbers isn’t going to help you there. And Google (or your futuristic search engine of choice, probably Google) is unlikely to help you get much further. Sure, you could go back and try to sell some modern technological knowledge or invention, but who wants to go through all that work just to be able to eat and sleep at your destination?

This is where your “temporal bank” steps in. You see, they have employees and contractors who scour geographical locations throughout history for accessible events that, with the right knowledge, you could utilize to acquire money in that time and place. Events like that local horse race outside a small Asian village in the early 300s BC for which no written record still exists. Over time they build a vast archive of these events — most of which would only have value to such a “bank” and its customers. When the excited time traveler comes knocking with hopes to transfer some money to the past, the bank looks up suitable events at times and locations near your destination that most closely match the money you want to acquire in that time period. And then they sell you the knowledge you need to access it. The bank takes possession of your modern currency and you can now easily acquire your currency in the past at a time, place, and type that is of use to you.

• Hordes of foreigners suddenly descend upon Mengke Khan's horse race to bet on the underdog and win? They'd just get killed. Beyond which, their involvement in these events—even where they don't start a riot—is going to affect odds and have other knock-on effects in at minimum the local economies, which we were trying to avoid. At that point, just tell them 'Go rob that noble over there. We'll teleport to the next county over when you're done.' – lly Jun 9 '18 at 6:49
• Beyond which, they'd all need sth locally valuable to begin with to act as their initial stake/investment. If we're an agency dedicated to responsible time travel, just use that in the first place and ban any past-altering get-rich-quick schemes in toto. – lly Jun 9 '18 at 6:52

# Moonlight as... a bank

There are a million ways to make this work if you own a bank. Banks don't typically have all of their money tied up in actual physical cash, so value can and has been assigned and moved around in many other ways. Use any of these 'back channels' to move money from the future version of the bank to the past. If you continue to move value from the future to the past, the future runs out of money, so you need to use a small portion of the money going into the past as investments, so that the future doesn't lose value.

Go back in time and acquire a bank somehow. As people use the bank (in the past), grab as much old cash as you can, and send it back in time to yourself. With regular shipments, you should have plenty of actual cash for use as spending money. If this isn't enough you can write a check you your past self, and make your past past self cook the books so its untraceable.

• Common sense, really. +1 – Joe Bloggs Jun 5 '18 at 19:29
• Good general idea for periods having banks; it make sense for the agency to operate one. Still suffers from the general confusion between money being currency and money being worth anything. The future can never run out of fiat money, any more than present-day states can. Today's fiat money is also not worth anything in the past, except as toilet paper. The bank will only operate like Green suggests: as a currency exchange keeping track of present-day deposits (in present-day currency) and past withdrawals (in various local ones). – lly Jun 9 '18 at 11:04

## No different than a modern bank or currency exchange

There are going to be two groups of currency, the our-future/their-present currency (designated as F\$) and the our-present/their-past currency (\C$). C\$currency can be any currency from any time/place but for simplicity sake, I'm just going to refer to it as US\$.

## Functional Equivalents

• Time Travel = Jet Travel. You get in a box or a tube, wait a little while and arrive at your destination. There will be customs/border patrol when you go and come back. Probably medical quarantines too if the traveler is going someplace sufficiently interesting.
• Time Travel Agency = Travel Agency. You traveler will need someone to make arrangements when you arrive. Someone will need to map out the places that rich people would want to go.
• Currency Exchange = Currency Exchange. Whenever a traveler goes to a new country not denominated in the traveler's native currency, some funds will need to be traded into the local currency. That the traveler is going backwards or forwards in time is irrelevant to the transaction.

As the owner of the bank, you will keep a single ledger of your customer's transactions in F\$. You don't know, nor care if they are going to Earth:Europe:10,000BC or Magrathea:North:10,000,000 AD. The traveler's transactions with you must be strictly linear. If these interactions can't be made strictly linear then you need to invent new ways of doing accounting. Government regulation of the currency will help a lot with this. ## Currency Exchange Operations If you run a currency exchange for these time travelers, you'll need to keep on-hand sufficient quantities of currency to sell to time travelers. Just as on Earth in 2018, currency is a commodity that can be traded. Buying from the Exchange The traveler will purchase the required amount of destination C\$ for some price denominated in F\$. Depending on the market, this will be either really cheap, or really expensive depending on supply and liquidity. The dynamics here will be very similar to modern currency exchanges on Earth. Selling to the Exchange This is the really tricky part. If travelers can go back to arbitrary points in time, as many times as they like, then they have the chance to create arbitrary amounts of wealth. The schemes to make money using time travel are innumerable. ...Although, maybe that just means that the price of C\$ approaches zero when trading with the currency exchange in F\$because the supply of C\$ is so great.

So, someone creates a ton of cash by investing in Nintendo in the 1990s then cashing out at the top of the Wii craze. First, they would need to get that currency in a form that will survive time travel, so physical bills. Hauling it back to the future will carry some cost thus preventing the sell price of C\$from reaching zero. My assumption is that wealthy people trying to make an extra buck from their travels will bring back unique artifacts that are not currency at all. These artifacts can be sold for F\$ to collectors.

## Government Regulation

Enabling this kind of time travel would require a currency that knows where and when it is in time. There will also need to be strict laws and sufficient safeguards to prevent the F\$from being doublespent and devalued. Some kind of forensics to detect if the F\$ has done any time travel will be essential.

# You can't flood the past with wealth or cash

...the wealthy are not going to want to travel back in time without access to their funds.

Whether you're talking about wrecking the local currency with inflation or making the past legitimately wealthier by providing them with usable commodities and supplies, you're absolutely going to shift the past all over the place if you allow the present-day rich to carry over large chunks of their present-day wealth to the past. By most measures, minimum-wage laborers in the present-day United States have higher standards of living than medieval kings; the actual rich have ridiculously more stuff and, at least early on, knowledge allowing vast manipulation of the past's economy.

The two options are to (a) have a hard-sf Bill-&-Ted's style of time travel wherein nothing you do in the past will change the future because it's already baked in—the past and future are the way they are because all time travel has already happened and already created what we already see—or (b) to have the company protect the timeline as much as possible, including by limiting visitors' involvement in the local economy. Chinese tourists already mostly deal with traveling in Europe by cooking for themselves; there's no reason time travelers who enter the past with more clothes than a Terminator couldn't have some sandwiches or a box lunch in their backpack.

# Stable institutions are the key

"How could a banking system move money from future to past?"

Ok, if you can't accept that and just absolutely want to have a semiplausible hands-off tourism service? Well, the butterflies are going to start flapping so fiercely that everything will soon be unrecognizable and unexploitable (cf. my answer in the other thread) but you'd be looking for stable institutions that provide protection and access to period wealth in exchange for payment in the present-day.

What would make sense in a historical context is if all or several of the main religions turn out to have been money laundering operations for the time travelers. These things obviously have ups and downs (just ask the poor Templars) but the major financial institutions of the West since the dawn of civilization have been the Mesopotamian, Egyptian, and Roman churches. Tithes and income from their real-estate holdings could be easily redirected and, at a minor level, cause only minor deviation from what originally occurred. Obviously every adherent couldn't be in on it, but representatives of the firm could maintain a steady inner core within the organizations that facilitate all of the logistics for visitors. There's almost nothing similarly sacrosanct and long-lived in the Sinosphere but the the direct heirs of Confucius have always done pretty well for themselves, all things considered, and a Korean immigrant family ran Japan's Kongo Gumi temple construction company continuously from AD 578 to 2006.