Dhruv Bansal Profile picture
Feb 8, 2018 17 tweets 5 min read Twitter logo Read on Twitter
1\ A thought experiment: The year is 2277. You're the bartender at a spaceport in a faraway Earth colony on a planet orbiting α-Centauri: a distance of ~4 light years. Guy walks into your bar, slams down a credit chit, and asks for a drink.

How do you know his money is any good?
2\ If the credit chit were guaranteed by a bank or a blockchain or something local to α-Centauri it'd be easy, just like it is here on Earth in 2018.

But say this guy is fresh-thawed after his long journey from Earth aboard a lighthugger. What kind of wealth could he even have?
3\ He's unlikely to be carrying base metals. Like natural resources, they'd still be valuable, but too heavy to transport from Earth. Physical fiat (bank notes) wouldn't be accepted either: too easy to 3D-print forgeries.

So what form of wealth survives interstellar voyages?
4\ Information! Wealth transfer between stars must be digital.

So the guy could present a statement from Bank of Orion or sign some blockchain transaction with his private keys to prove to you he is solvent.

"One Corellian Ale, coming right up sir..."
5\ But what if, just before arriving, the guy beamed a transaction back at Earth spending all his funds? It would take 4 years to get to Earth and 4 years for Earth to relay acknowledgement back to α-Centauri.

During those 8 years, he could double-spend freely on α-Centauri!
6\ Relativity can be confusing, so physicists use Minkowski diagrams to hone their intuitions in situations like these. Below is an idealized Minkowski diagram which depicts the scenario outlined above.

See en.wikipedia.org/wiki/Minkowski… for more details on how to read these diagrams.
7\ Another problem: say two ships leave Earth and α-Centauri at the same time, each bound for the other. Later, both Earth and α-Centauri broadcast spends. Due to the relativity of simultaneity, the two ships will receive the spends in *the opposite order*! What should they do?
8\ These examples are not pathologies. They are fundamental problems of interstellar commerce.

I read a lot of sci-fi but I don't know of many authors who write about interstellar distributed consensus. Everyone writes about the engines, but the money is just as vital...
9\ I'm writing about these problems not just because they're fun but because I think they motivate clearer thinking about distributed systems here on Earth, today.

Also, I simply don't know the solutions! How would you solve these problems, if you were a future financier?
10\ I think that "long integration times" must be part of the solution: a 20-year "pending transaction period" for a bank or a 20-year target block time for a blockchain. Combine that with still "waiting for 6 confirmations" and you get century-long transaction timescales. #whoa
11\ Such a system could never be used for day-to-day transactions (space-coffees). Something else would be necessary.

Banks might let you borrow against your holdings in another star system until they can be transferred locally (and your opportunity to double-spend eliminated).
12\ For blockchains, this problem could not be solved with bigger/faster blocks -- the only way to deal with the uncertainty caused by light lag is to wait.

Lesson: Different chains do different things. Layers (#LightningNetwork) and sidechains are necessary for space-coffees.
13\ Hashpower ratios between star systems are also critical. If hashpower on Earth is many times that of α-Centauri, newly mined blocks on α-Centauri will constantly get uncled. Users on α-Centauri will only trust Earth blocks. Mining will become centralized to Earth: colonialism
14\ Today's analogy for light-lag is low-bandwidth: both limit your ability to mine and thus cause centralization. Some ignore this issue, but it's real.

Lesson: Increasing block sizes with constant network connectivity speeds disadvantages miners with low-bandwidth (~light-lag)
15\ In summary, pondering these absurd scenarios may help you understand constraints on consensus inherent to the physical universe.

Analogies for these constraints can help us design better distributed systems today.

Also, don't tell me blockchains have no real use case :)
\16 ADDENDA: @vgr Provided two great links with more on this subject:

First is a wonderful article which addresses the issues I raised above in much more depth from @jasonmorton. I especially like the part about interstellar advertising :)

\17 The second is a 1978 thesis from famous Bitcoin-booster @paulkrugman ;)

Paul raises another fascinating problem: if time passes differently for observers in different reference frames, what's the best way to handle compounding interest?


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More from @dhruvbansal

Jul 22, 2018
1\ Do any other Bitcoiners like the book "The Once & Future King" by T. H. White?

It's one of my favorites and I've been revisiting it recently, thinking about cryptocurrency, political representation, & blockchains.
2\ It opens with Merlyn teaching a young King Arthur (Wart) about different forms of government, the fallacy of "might makes right", all through a series of adventuresome allegories.

Disney's "The Sword in the Stone", is a cute (if imperfect) adaptation of this part of the book.
3\ But "The Once & Future King" is ultimately a tragedy.

With the help of his storied Knights of the Round, Arthur builds Camelot, the fairest kingdom.

But Arthur is manipulated into self-conflict, his personal desires at odds with the principals he must uphold.

Camelot falls.
Read 10 tweets
Jul 10, 2018
\1 I continue to struggle with @ParityTech's software design decisions. My #Parity node keeps dropping peers. The advice I get is "upgrade to the latest unstable version". Parity is even configured to auto-update itself by default. Why do I have to run at the edge just to work?
2\ Parity is either (a) consumer software or (b) bad software.

It's (sometimes) OK when consumer software forces you to upgrade b/c, as a consumer, you're dumb & insecure. Business (or prosumer) software achieves a higher level of security & control by sacrificing ease of use.
3\ Consider: if Parity upgrades itself automatically that means /usr/bin/parity can edit itself. I have to completely trust that the Parity code, DNS, &c. prevents any peer from causing my Parity to change to something unintended. I hate this "feature", so I turned it off.
Read 6 tweets
Jan 28, 2018
1\ Have you heard this reasoning? "#Ethereum is better than #Bitcoin because it can do more." => "The EVM is Turing-complete and Bitcoin Script isn't, so Ethereum is a better cryptocurrency." => "Bitcoin's creators were too early/stupid/blind to make Bitcoin Turing-complete."
2\ This is a blatant misunderstanding! To a non-technical person, Turing-completeness and being able to compute anything is *obviously* better. But programmers know that Turing-completeness is Pandora's box: you don't know what it contains and you can't close it once opened...
3\ ...Turing-completeness is like a nuclear explosion. Once the threshold density/temperature is breached, fission fuel self-ignites and explodes. The hard part isn't blowing past the threshold, but staying as close to it as possible: energy => criticality => balance => control.
Read 10 tweets
Jan 22, 2018
1\ Physicists have a word "crank": a person who doesn't know physics but persists in promulgating their personal theory. Cranks pop in all fields of physics but especially in certain areas: quantum mechanics, field theories, relativity, cosmology, &c.
2\ Why these subjects? B/c they are abstract & esoteric. It's hard to crank in Newtonian mechanics because your bogus theory is easily disproved by direct human experience. It's easier to crank in quantum b/c few outside the tribe of physics really understand quantum mechanics.
3\ Bad cranks are just crazy people. But good cranks are interesting. Their work *looks like* physics (has math, equations, diagrams) and, because its engaging an abstract subject like quantum mechanics, can be mistaken for real physics by laypeople who can't tell the difference.
Read 9 tweets

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