Long ago, modern humans died off. Only a few people remained, and they made all sorts of GMO plants, like moss that grows extremely quickly and can be dried into flour. Houses are made out of wood...but instead of the wood being harvested from trees, it is grown in place by using GMO trees that are shaped like houses. In this world, fire is very rare. Flint is hard to come across, and very few people are allowed to have knowledge beyond how to do their job. As currency, I would like them to use fire. They would transport it in small glass jars, with some sort of ultra-fast-growing but very slow burning plant growing inside (also GMO). Eventually, money would "burn out". In order to use the fire, you must destroy the glass jar (which makes it no longer usable as currency). My question is, how would this affect the economy? Note that a steady supply of currency is grown daily.

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Aug 28, 2018 at 3:32
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    $\begingroup$ It appears that no one has as yet made a "he has money to burn" joke $\endgroup$
    – Mawg
    Aug 28, 2018 at 13:55

9 Answers 9


1) Business and commerce would be nearly impossible for three reasons: It's incredibly cumbersome, you can't make change, and you can't save.

If the going rate is three loaves of bread for one jar of fire, but I only want one loaf of bread, the baker and I are stuck - we can't reach a fair agreement because a jar of fire cannot be easily divided.

If I want to purchase a wagon that costs two hundred jars of fire, equivalent to weeks of labor, early jars of fire will burn out before I have saved enough to make the purchase. Similarly, what is the wagon seller going to do with two hundred jars while they still have value? She can't purchase and eat 600 loaves of bread before they mold. (And how will either of us transport 200 jars of fire without the wagon?)

2) Anyone who can grow the plant in their yard (or attic) suddenly becomes quite rich. A poorly-regulated money supply leads quickly to all kinds of unnecessary economic horrors -- runaway inflation, depressions, panics, bubbles, etc...and their corresponding social and political impacts.

As a side effect, even if you managed to have a banking system to save money (addressing Problem #1), those panics, bubbles, and inflation would wipe out the value of those paper savings.

3) Floods will be doubly terrible because not only were your lands and homes and livelihoods destroyed, but everybody's money is gone also. Now nobody can hire help to rebuild...and customers (whose money is also gone) can't buy your products to help themselves rebuild.

4) Some folks will burn down their houses because a jar of fire fell off a table in their wooden house. Hard to see how they will buy another, since we still have Problem #1.

The upshot is that most of your economic activity will shift to some other safer and more useful currency that will quickly supplant jars of fire.

Note that current currencies avoid Problem #1 by providing multiple denominations, and avoid Problem #2 by layered protections to prevent counterfeiting (among other regulations)

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    $\begingroup$ If the money would eventually burn out and become worthless, thats another reason people won't use it. Why would I trade my stuff, for a fire thats going to be nearly extinguished? If you have a fixed money, whose value depreciates quickly with time, people are going to try move onto a new and more stable currency. $\endgroup$
    – Shadowzee
    Aug 27, 2018 at 2:09
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    $\begingroup$ @Shadowzee yes, we talked about that in #1. Even gave an example of precisely that problem. $\endgroup$
    – user535733
    Aug 27, 2018 at 2:09
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    $\begingroup$ This is an excellent answer. I’ll add that it’s good to keep in mind, objects used as currency have three properties: they are durable (good store of value), they are interchangeable (my dollar bill is the same as your dollar bill) they have limited supply. Even in places with no official currency, people will find an object with those properties and start trading with that. Famous example: cigarettes used as currency in jails. $\endgroup$
    – Andrea
    Aug 27, 2018 at 13:49
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    $\begingroup$ Hold on, if you want to buy one loaf of bread, use a fire glass that's 2/3 burned! $\endgroup$ Aug 27, 2018 at 15:56
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    $\begingroup$ @RedwolfPrograms that means everybody must carry a ruler to measure the amount of fire - it's open to disagreement and fraud "Hey, you said it was half-burned, this is three-quarters!". Each jar must be examined carefully and it's value negotiated. You'll need a whole cupboard to make simple change. I think we just made the system even more cumbersome and inconvenient. We just went from 200 jars for a wagon to 350 fractional jars for that wagon. $\endgroup$
    – user535733
    Aug 27, 2018 at 19:01

tl;dr: Fire is a chemical reaction, and in a closed system would die out

Fire is the reaction of organic matter with oxygen to form water and carbon dioxide (or monoxide)

$C_xH_yO_z + O_2 \rightarrow H_2O + CO_2$ (I know it's not balanced, but that's not the point)

This reaction occurs in heat, which would have to be provided somehow. The reverse reaction is basically photosynthesis. However, there is a problem: photosynthesis, even with GMO like blue-green algae, takes a long time, fire takes a short time (needs to burn fuel or die out), so either your jar is massive, with obvious implications for money worth (if you can't easily move it, you can't use it), or your money lasts a very short time (also bad: who uses money if it will go out of circulation shortly?). Also, the system would have to be kept in constant sunlight or other light/heat, with the fire burning out the plants if taken out of it. So, with a civilization that can make this, why not use good ol' gold or silver?

EDIT: Although plain ol' fire might not work, here's a workaround: Bioluminescence. Mixing chemicals to make light is pretty hard, and your GMO algae or whatever could always produce light as a byproduct of the photosynthesis.

  • $\begingroup$ Or, it isn't a flame, it could just be a sort of glowing ember that burns very slowly $\endgroup$ Aug 27, 2018 at 15:57
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    $\begingroup$ In fact, you might want to see something like bioluminescence: that might help you with what you need $\endgroup$ Aug 27, 2018 at 16:24

Well, while your idea of using fire as currency is interesting, why not make a small change. It's not fire that is valuable but rather flammable goods/items which have value. It can be made to fit in with the idea that the GMO plants that are used are made to be fire resistant.

This also solves the problem of having smaller denominations as well as introduces an idea of various tiers of currency. I.e some fuel is better than and thus worth more than other fuel.

Given that you want to ensure that the currency dies out make it so that people in your world need to burn this currency every so often to survive (basically winter happens) this would allow those who are in control of growing the trees for this to remain in power.

You could also prevent other people from growing their own currency by simply using a knowledge blackout - people have no idea the shaped/carved currency they are using is actually growable and given that it's needed to survive no one is going to bother to experiment with it.

If you implement it in this manner you should have a stable economy with the tree growers in power.

  • $\begingroup$ It doesn't even need to be a knowledge blackout - if the burnable substance is processed, it cannot just be regrown (you cannot regrow wheat with a pack of flour) $\endgroup$
    – Falco
    Aug 27, 2018 at 13:17
  • $\begingroup$ Just like US money is heavily processed cotton and linen. Maybe make the way it burns (color, shape of flame, temperature, etc) the desireability. $\endgroup$ Aug 27, 2018 at 21:16

Currency must have a few properties: - it must be hard to create. (therefore banknotes and gold work. Rocks do not). - Currency must make it easy to store and transport value. So I can catch fish at the sea, capture their value with currency, and save that value, or take it somewhere else. Therefore something that decays is not very useful.

Fire is a tool, it's a chemical reaction. It's easy to duplicate no matter how hard you want to contain this knowledge. Heck, a fire service is needed because fire tends to spread by accident. It can also not be stored. Currency that loses its value is simply not attractive to use. This means that you will find it hard to convince me to part with my nice grain or bread for something that will peter out in a few days.

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    $\begingroup$ No, a currency must not be "hard to create". It must be stable. Being hard to create makes it stable but that is not the only way to keep something stable. $\endgroup$
    – MichaelK
    Aug 27, 2018 at 12:40
  • $\begingroup$ What I mean is that it must be hard to create on your own, i.e. hard to duplicate. Gold is a good currency because it is hard to aquire. Modern paper money is good because it is hard to forge. Leaves are a bad currency because they - litereally - grow on trees. Pebbles are a bad currency because they are all around. If you agree that a certain currency represents some wealth or effort, it must be difficult to duplicate or else everyone will duplicate the currency and get extremely rich. $\endgroup$
    – user24119
    Sep 16, 2018 at 17:43
  • $\begingroup$ It is hard to keep something you can create yourself stable, yes. But it is the stability that is the main point, not that it must impossible to make yourself. Compare for instance crypto-currencies. $\endgroup$
    – MichaelK
    Sep 16, 2018 at 18:05
  • $\begingroup$ therefore banknotes and gold work. Rocks do not — false: en.wikipedia.org/wiki/Rai_stones $\endgroup$
    – user28434
    Aug 24, 2020 at 13:04

Not ordinary fire. But maybe...

As others have pointed out: forget about plain old fire of the fuel + oxidiser + heat + chain reaction sort. You cannot make that work in any possible way.


You said that there has been extensive genetic engineering taking place before the collapse of civilisation. What if there came about some kind of plants that are of very special genetic strains, strains that have fantastic qualities, qualities that make them valuable and/or rare.

The problem with these plants is that that require extremely pure conditions to grow. The outside world is too full of nasty fungi and spores and other kind of genetic "dust" that just blows around... and this will attack these fragile valuable plants and quickly kill them.

These plants do not burn as a flame per se, but they do glow in wonderful colours as they take in sunlight and clean air and water, and then — in a special, superb kind of photosynthesis — create all sorts of wonderful things.

You can work this plot hook in many different ways. Things like filters, air and water purifiers, containments and similar become important in this society. Crossbreeding of different types of plants might become a thing. Just milk the fact that genetic engineering was used extensively.

To put things into perspective: compared to computers, the genetic engineering we do today is pretty much like this.. the first very primitive and limited computers. We are only just getting started with genetic modification and engineering. Compare the development of computers and their amazing capacity today, what genetic engineering could have done before the collapse, and then you have lots of freedom as an author to invent things.


You could enact some system of harvesting solar fusion elements such as plasma from local stars. Using this plasma as a resource may be a form of fire that is both rare and-- for the most part-- renewable?


While it does make for an interesting effect, especially if your world and story is told visually (i.e. movie, comic, game etc.) it doesn't sound feasible as currency (as others pointed out).

Unless fire is not the actual currency, only the "design" element of the currency it represents.

Why not make it into something that is revered or a symbol of high status instead ?

I also see a problem with fire being rare.

Provided you don't change nature and physics from ours, fire will be plentyful. Granted, a very moist or cold climate will minimize its appearance considerably.

However, hot weather, lightning strikes and plain old friction cause fires quite often just to name a few.

I also have a problem with a society capable of gene manipulation without tools that require electricity (if fire is rare, this method of creating fire can't exist either), metallurgy and other products made in processes involving heat (i.e. glass, plastic etc.)

How is food prepared in this world if there is no fire / heat? Is everything eaten raw, dried (ah, needs dry and above room temperature air, known to potentially facilitate fire) or frozen ? Are only plants that can be consumed raw considered food?

Sounds like a raw vegan diet, potentially causing malnourishment issues and could require a more developed civilization capable of creating nutritional supplements.

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    $\begingroup$ Those magical ancients may have made a small glowing fruit that carries an artificial enzyme that converts some artificial dietary fibers that are embedded in a fairly common weed into digestible proteins and vitamins. The two parts could make both more resistant to pests. The specific nutritional requirements for that fruit can limit production. The glowing core looks a lot like a candle, marking the viability of the plant. That would sorta hit the same notes as requested and address some concerns. $\endgroup$
    – The Nate
    Aug 27, 2018 at 6:26
  • $\begingroup$ I like it. Very convenient but I could buy its existence. $\endgroup$ Aug 27, 2018 at 12:37

As others have pointed out, the way you describe fire means it's going to be a pretty rough option. However, we can solve your problem science magic science!

Fire is actually a chemical reaction that requires:

  1. Heat
  2. Fuel
  3. Oxygen

Flame and light are actually byproducts of this reaction. The neat thing is that if you remove any of these legs you no longer have fire, but if you reintroduce them, hooray, fire! Like an Apache match.

You just need to take advantage of this fact, so maybe your plant inside this jar has been GMO'd to produce an incredible amount of heat as part of photosynthesis. And when the jar breaks, the introduction of O2 creates fire, and that fire has some purpose otherwise why bother breaking the jar? Perhaps burning the plant allows it to produce a new seed that requires planting in a new jar? And the amount of air in the jar is the amount required for germination & growth.

Perhaps the ash from the burning plant is like the spice, but it's extremely volatile - if you don't consume it within $SHORT_TIME then it loses efficacy/becomes toxic.

Oooh, and if you make the plant corrosive to anything besides glass (and/or temperamental to being in the dark too long), then that gives a reason to use the glass jars.

So to sum up, you've got a plant that absorbs O2 to germinate/grow. Once it passes a particular threshold, it ignites, leaving behind a single seed and an extremely valuable, but short-lived byproduct. It's also hostile to anything but clear glass - the additives to color other glasses green/brown/red/etc. either kill it or it kills.

Now you have:

  • A reason to keep stuff in a jar (so you can harvest the spice on demand)
  • A reason to use glass (everything else is a bad idea)
  • Fire
  • A reason it's valuable

If you wanted to have alternate denominations of money, maybe you flip the impurities thing around and by introducing whatever makes green or red or blue or brown glass at the time of combustion, you can produce multiple seeds that produce the products with less valuable effects - so instead of seeing 10 minutes into the future you only see 5, or whatever.

Great. Now I really want to read a story about this stuff!


Practical aspects: It seems to be agreed that the jar + Burning Plant idea is really difficult to be set up.

Why not separate the combustible from the activator? I will take a few concrete examples, but feel free to replace them with items from your world:

  • Matches are the activators (could be a chemical product stored in glass)
  • Coal is the combustible (could be an GMO)

This could help you to have a system of coins and bills or something, since the two products are used together to burn things With this principle you also ease trades (matches are lights, and it is easy to spare them, and to give change)

Market aspect:

A currency has a value, this value is based on another product: for example € with gold (If you have several countries and currencies it’s more based on the exchange rate and interest rate) So your currency should have a reference, something valuable which should not fluctuate too much.

But here you want to use a consumable as currency which means that its value will depend on the value of your chosen “valuable product” and the amount of your currency available (remaining matches in your country for example).

How do people earn these matches ? Is it an universal income ? How many matches are consumed by people per year? How many matches do you need for survive per year? How many matches are you earning each year? How much is it fluctuating during the year? (consuming/earning rate)

Those questions will help you determine your currency fluctuation, but also to determine the real impact on the market (inflation and deflation)

You can imagine that the value of coal will decrease in summer, and dramatically increase in winter. I would suggest to have durable matches to always have a stable amount of matches on the market: the amount of matches/coal should drop significantly in winter, if a match has a short lifetime then in spring there will be no resources left.

This is a real problem: if one match is worth one bread in summer, one match could equal ten breads in winter. How do you really determine the value of your currency ? Keeping that in mind people will probably prefer to sell in summer and to buy in summer.

Separating the activator from the combustible (and maybe the combustive?) could introduce some new concepts: - You waste matches when failing the strike, and as matches are your daily money and the value is evolving, wasting a match in winter means losing a lot - People always want to optimize things, they will develop techniques intending to limit the waste of coal/match; - People will take risk in selling all their matches during winter and buying a lot in summer. - Poor people will buy the bare necessities of life selling there last remaining matches.

Have you read the stormlight archive by Brandon Sanderson? There are some similarities as they use glowing spheres as main currency, meaning they use it for light as well as money. These aren’t really combustible as they are rechargeable but the Wkipage could give you ideas https://en.wikipedia.org/wiki/The_Way_of_Kings

EDIT: Hope this is better

  • $\begingroup$ I don't get what you are trying to say with your answer. Can you try to rephrase it? $\endgroup$
    – L.Dutch
    Aug 28, 2018 at 11:30

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