Bitcoin’s arrow of time

Measuring time in new ways makes us think about time in new ways, too.

When Galileo first noticed that pendulums swung in exact increments, no matter their length, time was still measured by the position of the sun, roosters crowing and the daily tasks that needed completing.

After Christiaan Huygens used Galileo’s insight to build the first pendulum clock in 1656, however, time became more precisely measured — a series of uniform ticks instead of our irregular lived experience.

Measuring time mechanically enabled sailors to precisely determine their location (establishing longitude by comparing clocks set in two different locations), trains to coordinate their schedules (by agreeing on time zones), and factories to automate their production (by synchronizing workers and machines).

Eventually, this enabled the Industrial Revolution, forever changing how people both live and work.

It changed how we think, too: “Time is now currency,” the historian E. P. Thompson lamented. “It is not passed but spent.”

Our time became spendable in ever smaller increments when pendulums were replaced first by quartz crystals and then by atoms.

In the 1880s, scientists discovered that applying an electrical current to quartz crystals caused them to vibrate (the "converse piezoelectric effect") — and in the 1920s, it was discovered that this vibration kept near-perfect time.

Vibrating crystals proved to be a far more stable and compact way to measure time than swinging weights; without them, your microwave might have to be built into a grandfather clock.

More consequentially, quartz can measure time in far smaller increments: While a pendulum marks each passing second (the practical limit of a swinging weight), a quartz clock divides that same second into 32,768 precise vibrations.

That’s proved useful for more than just heating up leftovers: “Without the microsecond accuracy of a quartz clock,” Steven Johnson explains, “modern computers would be useless.”

Perhaps sadly, this marked the end of measuring time as a function of how long it takes Earth to orbit the Sun: “Quartz let us ‘see’ that the seemingly equal times of a solar day weren’t nearly as equal as we had assumed,” Johnson adds.

Now measure it with atoms. 

In 1967, the International Conference of Weights and Measures defined an “atomic second” as “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.”

In other words, atomic clocks measure time in increments roughly 280,000 smaller than quartz clocks.

That has enabled things like the GPS receiver on your phone, which triangulates your precise location by comparing the atomic time stamps sent from orbiting satellites (whose sole job is to continually broadcast the time in atomic increments).

“This is in fact one of the recurring stories of the history of the clock,” Johnson writes; “each new advance in timekeeping enables a corresponding advance in our mastery of geography — from ships, to railroads, to air traffic, to GPS. It’s an idea that Einstein would have appreciated: measuring time turns out to be key to measuring space.”

Atomic clocks are probably the final way to measure time — it’s hard to imagine why we’d need to know what happens in less than a tenth of a billionth of a second. 

But they’re not the final way to think about time. 

Satoshi’s timestamp server

When Satoshi Nakamoto published the Bitcoin white paper in 2008, he didn’t describe a new form of money so much as a new form of keeping time.

“In this paper,” he wrote, “we propose a solution to the double-spending problem using a peer-to-peer distributed timestamp server.” 

Bitcoin itself is the timestamp server.

Satoshi’s invention has no access to pendulums, crystals or atoms, so he invented proof-of-work instead — a way to make real-world computers agree on the sequence of events without ever knowing what time it is in the real world.

In academic terms, this makes Bitcoin “a self-referential temporal architecture that transforms distributed randomness into discrete and irreversible events.” 

Or, as Jack Mallers frames it: “Proof of work gives Bitcoin its arrow of time.”

(Unusually, it’s typically portrayed as an arrow that flows from right to left.)

Bitcoin creates its own time through computational work, with each solved block proving that real-world energy and effort have been spent, which creates a universally agreed-upon, irreversible sequence of events.

This tamper-proof, time-ordered ledger, built block by block through accumulated work, is the core innovation of Bitcoin.

We typically think that Satoshi invented a new kind of money, but it might be more accurate to say that Bitcoin is only money because we choose to assign value to his real invention: a decentralized form of time.

If so, the genius of digital gold is that Satoshi buried it in time.

Unlike gold, the supply of which rises with the effort we make to dig it up, Bitcoin’s supply cannot be accelerated: Its built-in difficulty adjustment means that no matter how much computing power we throw at it, new bitcoin is produced only every 10 minutes or so (in real-world time).

“Gold is stuck in the ground,” Mallers explains. “Bitcoin is stuck in the future.”

Could measuring time in this novel way change how we think about it?

Proof-of-work would be no more useful in a GPS satellite than a pendulum clock in a microwave.

In a purely digital realm, however, where nothing happens unless a processor says so, proof-of-work might serve as both compass and clock — a way to create direction and sequence where none naturally exists.

Why might that be useful?

In the virtual worlds of SciFi novels like Fall by Neal Stephenson and Permutation City by Greg Egan, time isn’t a physical property to be measured by atoms or crystals.

Instead, it’s measured by computation: For digital consciousnesses uploaded as code to computers — or AI consciousnesses created there — time is a function of how fast that code is executed.

Bitcoin's proof-of-work, where progress is measured block by computational block, might be seen as an early example of such computational time.

The pendulum gave us mechanical time, quartz gave us electronic time and atomic clocks gave us quantum time.

Bitcoin might be the first form of AI time.

— Byron Gilliam

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