In Andy Weir’s Artemis, the lunar colony of the same name does not run on dollars, euros, yuan or any other earthly currency. It runs on something called the slug.

A slug, short for Soft-Landed Gram, is exactly what it sounds like. One slug is the right to have one gram of mass soft-landed on the Moon. You can spend slugs on food, you can pay rent on your “slab” (the coffin-sized capsule most colonists sleep in), you can tip a bartender, you can buy a bribe. The protagonist, Jazz Bashara, smuggles contraband and gets paid in slugs. Tourists arrive with slugs. The entire economy of a city of two thousand people, on a rock a quarter of a million miles from Earth, settles on the slug.

When I first read the book it struck me how plausible this felt. Not as a clever world-building flourish, but as a serious answer to “what is money, actually.” Then it struck me why it felt plausible. The slug is the same kind of thing as Bitcoin. Both are energy made transferable. Both emerged from the bottom up because the people using them needed a unit of account that nobody could fake. Once you see it from this angle, Artemis stops reading like science fiction and starts reading like a thought experiment about the deep structure of money.

This is a short essay about that thought experiment and what it teaches us.

Meet the slug

In the world of Artemis, the slug did not begin as money. It began as a service contract. The Kenya Space Corporation, which by the time of the novel has effectively monopolised Earth-to-Moon logistics out of its equatorial launch advantage, sells pre-paid shipping credits to anyone who wants mass delivered to the lunar surface. One slug equals one gram, soft-landed. If you hold a thousand slugs, KSC owes you one kilogram of Moon-delivery whenever you want to redeem it.

That property alone would make the slug useful as an industrial coupon, the way you buy printing credits at a copy shop. What makes it money is what happens next. Because everything on the Moon is imported, and because imports are expensive, every economic actor in the colony already cares about the cost of soft-landed mass. The grocer cares because every banana on the shelf was a paid-up slug, plus profit. The bar owner cares because every bottle of whisky started as a slug-denominated invoice. The slug stops being just a shipping credit and becomes the natural unit of account, then the natural medium of exchange, then a store of value.

By the time the novel opens, slugs are tracked digitally in everyone’s account, transferred between people the way you send money on a phone, and nobody questions that they are the currency. The colony’s government, the Kenyan parent state, has not declared the slug legal tender; it has barely had to acknowledge it. The slug became money because everybody on Artemis needed a number that meant something, and the cost of getting things to the Moon was the only number that everybody already paid.

The supply is mildly inflationary. Every time KSC flies another lander, new slugs come into circulation, because the new shipping capacity has to be sold to someone. There is no hard cap. But the inflation is anchored to a physical process. KSC cannot conjure a million extra slugs by pressing a button, the way a central bank can conjure money. To create more slugs, KSC has to actually launch more rockets. The slug supply schedule is the rocket schedule.

The slug is energy

This is the part that makes the slug feel real. To soft-land one gram of mass on the Moon you have to fight physics. You have to climb out of Earth’s gravity well, coast to the Moon, slow down, and touch down gently. Each of those steps demands energy, and the energy is large.

Earth’s gravitational binding energy, the theoretical minimum to escape to infinity, is about sixty-three megajoules per kilogram. Getting to the Moon and braking into a soft landing adds more. Real rockets are wildly inefficient because of the rocket equation: most of the propellant you load is burned just to lift the rest of the propellant. So the actual energy paid per gram of payload that arrives intact on the lunar surface is several times the theoretical minimum, on the order of a hundred megajoules, plus the cost of the vehicle and the launch infrastructure. There is no shortcut. Newton does not negotiate.

That is the slug’s secret. It is not backed by a promise. It is backed by an act. Every slug in circulation represents physical energy that was actually expended to lift mass against gravity. Counterfeit a slug and KSC will refuse to honour the gram. Print extra slugs without flying the lander, and your books no longer balance against the laws of motion. The slug is energy made transferable, and the rocket equation is its proof of work.

Bitcoin is energy too

Now look at Bitcoin through the same lens.

A bitcoin miner runs a specialised computer that does one thing: it guesses, very fast, at numbers that satisfy a cryptographic puzzle. The puzzle is deliberately hard. Solving it takes, on average, an enormous number of guesses, which takes electricity, which costs money. Whoever solves it first wins the right to write the next block of transactions to the ledger, and is paid in newly issued bitcoin plus the transaction fees from that block. The harder the global puzzle, the more electricity the network as a whole has to burn to keep producing blocks at a steady rate. The protocol automatically retunes the difficulty every two weeks to hold that rate constant.

A finished block is, viewed from one angle, a database record. Viewed from another, it is a receipt for energy spent. You cannot produce one without spending real electricity, and you cannot fake the spending, because everyone on the network can check the work by re-hashing it for free. Bitcoin’s most ardent thinker on this point, Jason Lowery, calls Bitcoin a “soft war” power-projection system: a way of compressing real-world energy into a digital ledger that nobody can falsify and nobody can confiscate. Whether you agree with Lowery’s geopolitical conclusions or not, the underlying physical claim is the same as the one we just made for the slug. Every bitcoin in existence represents work, measured in joules, that was actually done. A bitcoin is energy made transferable.

Bitcoin has a fixed supply cap, twenty-one million coins, baked into the protocol. Slugs do not, but the slug supply is anchored to launches and so is also constrained by physical reality. Both currencies refuse to let the issuer cheat. Both are mined, in the literal sense.

And, like the slug, Bitcoin emerged bottom-up. Satoshi Nakamoto published a paper in 2008 describing the protocol. Nobody ordered anyone to use it. The first users were a handful of cryptographers swapping coins for fun, then for pizza, then for ideology, then for savings, then, eventually, in nation-state quantities. No government decreed Bitcoin to be money. People needed a unit of account that resisted tampering, found one, and adopted it. The same arc as the slug, in different decor.

The comparison, line by line

	Slug (SLG)	Bitcoin (BTC)
Kind of work	Lifting mass out of a gravity well	Computing cryptographic hashes
Energy source	Rocket fuel and infrastructure	Electricity, anywhere on Earth
Supply dynamics	Mildly inflationary, no hard cap, anchored to launches	Disinflationary, hard cap of 21 million coins
Issuance	Centralised around KSC	Decentralised mining network
Backing	A redeemable shipping service plus the physics of getting there	Computational scarcity plus the physics of thermodynamics
Emergence	Pre-paid credit → de facto money via voluntary adoption	Cypherpunk experiment → de facto money via voluntary adoption
Strengths	Anchored to a tangible service everyone in the colony needs	Borderless, censorship-resistant, fixed supply
Weaknesses	Single point of failure if KSC stumbles; mild inflation	Price volatility; the energy footprint that critics call wasteful

The interesting line in that table is not any single row. It is the family resemblance running down the page. Two currencies, separated by a fictional century and very different physical substrates, doing the same job by the same logic.

Money has always been crystallized energy

This is not a coincidence. It is what money has always been.

Gold became money because it took real labour to dig out of the ground, real fuel to smelt, real risk to ship. Cattle became money in pastoralist economies because each animal represented years of grass, water, and herding. Wampum took hours of skilled work to grind from shell. Nick Szabo’s old essay Shelling Out called this property “unforgeable costliness” and named it the spine of every successful pre-modern money. The deep structure was always the same: a thing becomes money when producing it is expensive in physical terms and verifying it is cheap.

Fiat currencies are an interesting historical anomaly precisely because they break this rule. Producing a new dollar costs the issuer almost nothing. Their value rests on institutions (central banks, legal systems, military power) rather than on physics. That has worked, mostly, for about a century. Whether it keeps working is a topic for a different essay.

What the slug and the bitcoin make explicit is that the older logic never went away. Strip out the institutional scaffolding and humans, given a fresh canvas, reach for energy-backed money. The colonists of Artemis reach for the slug because their lives are organised around the cost of getting things to the Moon. The early adopters of Bitcoin reached for it because they were tired of trusting institutions to behave. In both cases the move was the same: anchor the unit of account to a physical process that cannot be cheated. Hayek would have recognised both as spontaneous orders. Szabo would have recognised both as unforgeable costliness. Lowery would have recognised both as compressed energy.

Why each money fits its world

The slug works on Artemis because the dominant economic activity in an early space colony is moving physical stuff. As long as life on the Moon depends on imports, the cost of soft-landed mass is the single most important price in the colony, and a unit of account anchored directly to it is almost too good a fit. The slug is also conveniently local. You do not need to coordinate with Earth’s financial system; you just need KSC’s manifest.

Bitcoin works in the digital age because the dominant economic activity is moving information. There is no “natural” import good to anchor a global, online economy to. What there is, everywhere, is electricity, and a global network of miners spending it. Bitcoin uses electricity the way the slug uses rocket fuel: as the universally available, universally costly substrate from which to build a tamper-proof unit of account.

The weaknesses fall out the same way. The slug’s weakness is its dependency on a single launcher. If KSC has a bad year, the colony’s money has a bad year. Bitcoin’s most-criticised property is its energy footprint, which is genuinely large. But under the framing of this essay, that criticism is upside-down. The energy footprint is not a bug to be optimised away. It is the mechanism by which the system resists falsification. A hypothetical Bitcoin that did the same job using one millionth of the electricity would, by the same factor, be one millionth as expensive to attack.

Forward look

It is hard to read Artemis without thinking about what money looks like once humans actually live on other rocks. The book’s answer is the right answer, in the sense that it is the answer that has worked every time humans have had to invent money from scratch: pick something physically costly to produce, easy to verify, and useful, and let it spread.

The next round of human settlement, whether on the Moon, in cislunar orbit, on Mars, or somewhere in the asteroid plans slowly graduating from PowerPoint into hardware, will not start with a sovereign issuing legal tender. There will be no Federal Reserve of the Moon. There will be private launch operators, ice miners, life-support contractors, and a few thousand humans who need to pay each other for things. They will reach, as the Artemis colonists reach, for the locally cheapest, locally most-trusted unit of stored energy. A slug-like unit anchored to the cost of moving mass is one obvious candidate. A Bitcoin-like network anchored to computation is another. The two are not mutually exclusive: a real colony might denominate cargo in slugs and savings in bitcoin, the way an earth-based economy denominates groceries in local fiat and long-term wealth in something harder.

Andy Weir was a hard sci-fi novelist trying to imagine a plausible Moon economy. Satoshi Nakamoto was a pseudonymous cryptographer trying to solve double-spending. They could hardly have known about each other’s work. They arrived at the same answer because that is where the physics points.

Money has always been crystallized energy. Sometimes the crystal is a gold coin. Sometimes it is a soft-landed gram. Sometimes it is a 256-bit hash. The packaging changes. The deep idea does not.

References

1. Andy Weir (2017). Artemis. Crown Publishing Group / Del Rey.
2. Satoshi Nakamoto (2008). Bitcoin: A Peer-to-Peer Electronic Cash System. https://bitcoin.org/bitcoin.pdf
3. Jason Lowery (2023). Softwar: A Novel Theory on Power Projection and the National Strategic Significance of Bitcoin. MIT System Design and Management thesis. https://dspace.mit.edu/handle/1721.1/151221
4. Nick Szabo (2002). Shelling Out: The Origins of Money. Nakamoto Institute archive. https://nakamotoinstitute.org/shelling-out/
5. Nick Szabo (2005). Bit Gold. Unenumerated blog. https://unenumerated.blogspot.com/2005/12/bit-gold.html
6. Konstantin Tsiolkovsky (1903). The Exploration of Cosmic Space by Means of Reaction Devices. The rocket equation. Accessible modern explainer: NASA, Tsiolkovsky Rocket Equation. https://www.nasa.gov/learning-resources/for-educators/the-tyranny-of-the-rocket-equation/
7. F.A. Hayek (1976). Denationalisation of Money: The Argument Refined. Institute of Economic Affairs.
8. Saifedean Ammous (2018). The Bitcoin Standard: The Decentralized Alternative to Central Banking. Wiley.