Saturday, 7 May 2016

Pilate's game



After the Welsh Assembly elections - in which UKIP did rather well - I had a Twitter exchange with an angry Welshman. He said:

I challenged this, of course. But in the ensuing heated discussion, I misquoted him:


As far as I am concerned, I misquoted him because I had not remembered his tweet accurately. Memory is fallible. But as far as he is concerned, I misquoted him because I am a liar. We do not disagree on the facts, but on their interpretation. Who is right?  What is the truth?

In Greece, the Debt Truth Committee has drawn together facts about the origins of Greece's debt. And from this, it has deduced what it believes to be the truth. Greece's debt is odious and should be rejected. But others, even if they agree with the facts, disagree with the conclusions drawn from them. For them, Greece owes this money and should pay it in full. Who is right? What is the truth?

Legal systems exist to establish the truth. Facts (evidence) are important, but they are insufficient to establish truth: there must be a plausible psychological case (motivation) too. And establishing truth is only possible when everyone tells the truth as they see it. Many legal systems require participants to swear a solemn oath promising to tell "the truth, the whole truth and nothing but the truth". Most enact severe penalties for lying to the court (perjury). The reason is evident: the court has no means other than the testimony of witnesses of establishing the truth, so if witnesses lie, miscarriage of justice is inevitable.

Miscarriages of justice are not only lethal for those wrongly convicted, they are socially destabilising: a legal system seen as arbitrary and discriminatory does not long survive. It is no accident that "Thou shalt not bear false witness" is one of the Ten Commandments. Life and death decisions depend upon establishing the truth, not simply the facts.

But what exactly do we mean by "truth"?

The question "what do we mean by truth" reverberates down the centuries. The trial of Jesus* includes an extraordinary round of verbal sparring in which - unusually - Jesus does not have the last word. "The reason I was born and came into the world is to testify to the truth", says Jesus. "Everyone on the side of truth listens to my voice".

Pilate's riposte is one of the most famous lines in the Bible: "What is truth?"

Thinking he has proved that Jesus is just a harmless nutter, Pilate goes out to the crowd and says "I find no basis for a charge against him". He wants to let Jesus go. But the crowd - whipped up by powerful individuals - insists that Jesus must die.

Are they right? Is the majority view the truth? An entire religion has been built on trying to explain and justify Pilate's decision to give in to the crowd. And thousands - nay, millions - have died over the centuries because of that decision. With hindsight, the decision of the crowd has been seen by many to be a terrible mistake. But we still do not "objectively" know whether Jesus deserved execution under Roman law. And we never will. We can never objectively know what motivates an individual to do as they do. They may not even know themselves.

Truth is subjective. My "truth" (that I unintentionally misquoted) is different from my antagonist's "truth" (that I lied). And the onlookers are no more objective. All they have is the fact that I misquoted, my antagonist's assertion that I lied, and my claim that I misquoted because my memory was faulty. And they are swayed by their own knowledge of previous behaviour by both sides, and perhaps also by other influential voices. Those who know me are likely to believe that I made an innocent mistake, unless their previous experience of me is that my word is untrustworthy. Those who know my antagonist are more likely to believe that I am a liar. So if "who is right" is determined by the crowd, whether or not I am a liar depends entirely on whether I have more supporters than my antagonist. There is no "objective truth".

 It is therefore disturbing that, in a piece by Ethereum's creator Vitalik Buterin about "subjectivocracy", he implicitly assumes that there must always be an objective truth. This, for example:
Objectivity has often been hailed as one of the primary features of Bitcoin, and indeed it has many benefits. However, at the same time it is also a curse. The fundamental problem is this: as soon as you try to introduce something extra-cryptoeconomic, whether real-world currency prices, temperatures, events, reputation, or even time, from the outside world into the cryptoeconomic world, you are trying to create a link where before there was absolutely none. To see how this is an issue, consider the following two scenarios:
  • The truth is B, and most participants are honestly following the standard protocol through which the contract discovers that the truth is B, but 20% are attackers or accepted a bribe.
  • The truth is A, but 80% of participants are attackers or accepted a bribe to pretend that the truth is B.
From the point of view of the protocol, the two are completely indistinguishable; between truth and lies, the protocol is precisely symmetrical.
There is, of course, a third possibility: the participants do not know the truth but are expressing their own validly-held opinions. They do not have to be liars or attackers to get it wrong. They just need to be ignorant or biased.

So, let's re-run Jesus's trial using Buterin's subjectivity criteria, as laid out here:
The power behind subjectivity lies in the fact that concepts like manipulation, takeovers and deceit, not detectable or in some cases even definable in pure cryptography, can be understood by the human community surrounding the protocol just fine. To see how subjectivity may work in action, let us jump straight to an example. The example supplied here will define a new, third, hypothetical form of blockchain or DAO governance, which can be used to complement futarchy and democracy: subjectivocracy. Pure subjectivocracy is defined quite simply:
  • If everyone agrees, go with the unanimous decision 
  • If there is a disagreement, say between decision A and decision B, split the blockchain/DAO into two forks, where one fork implements decision A and the other implements decision B.
All forks are allowed to exist; it’s left up to the surrounding community to decide which forks they care about. Subjectivocracy is in some sense the ultimate non-coercive form of governance; no one is ever forced to accept a situation where they don’t get their own way, the only catch being that if you have policy preferences that are unpopular then you will end up on a fork where few others are left to interact with you.
Clearly, there isn't a unanimous decision. Having met Jesus, Pilate disagrees with the crowd. He has information that the crowd doesn't have. But the crowd isn't prepared to back down. So in Buterin's cryptographic world, the blockchain would be split. Decision A would be to let Jesus go: decision B would be to execute him. The community decides Jesus's fate.

Pilate is now "on a fork where few others are left to interact with him". Decision A is not possible, because the community decision is B, and the choice is binary (Jesus either lives or dies). Pilate has lost. It is simply untrue to say that "no-one is ever forced to accept a situation where they don't get their own way". When the choice is binary, anyone on an isolated fork must either accept the majority decision or leave the game. Pilate cannot get his own way, because if he overrides the community decision the crowd will riot and he will lose at least his job and possibly his life.  His solution - publicly washing his hands of the whole thing - amounts to leaving the game.

So the community decides to execute Jesus, and the only dissenter is forced to leave the game. Whether or not "Jesus deserves to die" is objectively true is irrelevant. Using Buterin's logic, the community decision IS the truth. Jesus deserves to die. Sorry, Christians.

To reach the position "Jesus deserves to die", it is not necessary to assume that anyone is lying or malicious. It is only necessary to assume that people have conflicting beliefs. The majority believes that Jesus is dangerous and should be put to death. Pilate's different view is insufficient to change their minds, even though it is based on better information. People are only too ready to discard or ignore information that contradicts strongly-held beliefs, especially when that information comes from a less than trusted source. Confirmation bias doesn't disappear in a cryptographic environment.

Now, Buterin does recognise the possibility that the majority might make an objectively wrong decision out of ignorance. But his solution to this presupposes that there is some way of establishing objective truth using markets. (For goodness' sake, Vitalik, there is a man's life at stake here!)

Here is how Buterin explains it:
So, how does this secondary “public function” of markets apply here? In short, the answer is quite simple. Suppose that there exists a SchellingCoin mechanism, of the last type, and after one particular question two forks appear. One fork says that the temperature in San Francisco is 20’C; the other fork says that the temperature is 4000000000’C. As a VSU, what do you see? Well, let’s see what the market sees. On the one hand, you have a fork where the larger share of the internal currency is controlled by truth-tellers. On the other hand, you have a fork where the larger share is controlled by liars. Well, guess which of the two currencies has a higher price on the market… 
In cryptoeconomic terms, what happened here? Simply put, the market translated the human intelligence of the intelligent users in what is an ultimately subjective protocol into a pseudo-objective signal that allows the VSUs to join onto the correct fork as well. Note that the protocol itself is not objective; even if the attacker manages to successfully manipulate the market for a brief period of time and massively raise the price of token B, the users are still going to have a higher valuation for token A, and when the manipulator gives up token A will go right back to being the dominant one. 
Translation: someone runs a book on the outcome of Jesus's trial, and the bookies' odds are used to reinforce the voting, thus making it more likely that there will be the "right" outcome. **

But in this case, I suspect that the bookies would simply reinforce the crowd. After all, there is no objective measure. No compelling "fact" that can be used to establish whether or not Jesus is a dangerous subversive. There are only beliefs.
Now, what are the robustness properties of this market against attack? As was brought up in the Hanson/Moldbug debate on futarchy, in the ideal case a market will provide the correct price for a token for as long as the economic weight of the set of honestly participating users exceeds the economic weight of any particular colluding set of attackers. If some attackers bid the price up, an incentive arises for other participants to sell their tokens and for outsiders to come in and short it, in both cases earning an expected profit and at the same time helping to push the price right back down to the correct value. In practice, manipulation pressure does have some effect, but a complete takeover is only possible if the manipulator can outbid everyone else combined. And even if the attacker does succeed, they pay dearly for it, buying up tokens that end up being nearly valueless once the attack ends and the fork with the correct answer reasserts itself as the most valuable fork on the market.
Once again, Buterin assumes that there must be dishonesty involved. Of course, the Bible does say that there were two false witnesses, and that the crowd was "whipped up" by powerful individuals. But then it would, wouldn't it? After all, the Christian case is that Jesus's death was the worst miscarriage of justice in history.

But as I've already noted, it is not necessary for anyone to be lying. The witnesses may genuinely believe that Jesus is subversive. The "chief priests" may genuinely believe that Jesus is too dangerous to be allowed to live. Indeed, the lethal, socially divisive outcome of Jesus's trial rather suggests that no deliberate dishonesty was involved. When both sides believe they have the "truth", the game is to the death and all bets are off.

So Pilate's question goes to the heart of the matter. What is "truth"? Truth is whatever I believe it to be. In the absence of a "higher power" that can objectively state what "truth" is, I can only establish the truth of my "truth" by asserting power over those whose "truth" is different from mine. The more people I can persuade, bribe or coerce into agreeing with me, the more powerful I am and the more likely I am to win in any "battle of beliefs". In the end, truth is power.

It is thus unsurprising that there is discussion in the cryptographic world of "ultimate oracles" which can be trusted to arbitrate impartially in any dispute:
A solution for oracles will most likely be that an default (centralized) oracle can set an outcome first but there will be an objection period. If someone has an objection (and makes a deposit) another more reliable (and more costly) service should be triggered. If this option is given and the "last resort" oracle is widely believed to be 100% uncheatable than it might get never user. So to have such an oracle would be extremely valuable.
Note that even accessing the oracle requires payment in ever-increasing amounts. This is hardly a legal system that supports the claim of the poor and weak against the rich and powerful, is it? Only the rich have access to justice. The oracle does not eliminate power asymmetries, it reinforces them.

But what form would such an oracle take?
So let's think about the "ultimate oracle" - the most secure one that can be made. For the security it is important to see what people who determine the outcome have at stake. In the case of Augur it will be the REP tokens, in the case of a human Twitter oracle it will be its personal reputation (maybe there is an real world value bigger than what is measurable on the blockchain but if we would purely look at the blockchain it would be the future income from this reputation - or other benefits that comes along with good reputation).
Oracles must be incorruptible and omniscient: furthermore, the penalty for ignoring an oracle must be severe. In the old days, oracles were creatures of the gods, set apart from the world (thus incorruptible) and obtaining their information from supernatural sources (hence omniscient). And as the crowd was far more afraid of the wrath of the gods than of any human, oracles were rarely ignored.

But these modern-day oracles have no divine backing. So the best Koppelman can come up with is the idea that they can be trusted to give the right answer because if they don't. no-one will trust them any more. Forgive me, but this is circular logic. If an oracle must please the crowd with the "right" answer or be thrown down, it cannot be impartial. Indeed this was Pilate's problem. He wasn't a sufficiently trusted "oracle", so could not credibly deliver an impartial judgement.

(This is part of our problem with central banks, by the way: we expect them to be impartial and omniscient, but also to please us with the "right" decisions, on pain of losing their independence....)

However, this is all academic anyway. After all, this logic would only apply in a cryptographic environment. It would never be used in the real world when lives are at stake.

Or.....would it?
Perhaps, in some futuristic society where nearly all resources are digital and everything that is material and useful is too-cheap-to-meter, subjectivocracy may become the preferred form of government.
I think they call this "mob rule".


Related reading:

The Subjectivity/Exploitability Tradeoff - Vitalik Buterin

* In this piece I am taking it as read that Jesus existed and his trial and execution was as documented in the Gospels. I am aware of the lack of reliable historical record and the controversy over whether he existed at all. But as I am using the story simply as an example, I do not think it matters whether or not it is true in fact. Truth is a matter of opinion, after all.

** Schroedinger did this first. Indeed I thought of entitling this piece "Schroedinger's Jesus".

1 comment:

  1. "Truth is subjectivity."—Kierkegaard. By this he did not mean that truth is subjective.

    "What is truth, but a mobile army of metaphors?"—Nietzsche. By this he did not mean that truth is arbitrary.

    ReplyDelete