Posts published by “centaur”

Hang out with philosophers or theologians long enough, you're likely to run into "Pascal's Wager": the Blaise Pascal's idea that you should believe in God, because if He exists, betting on Him wins you everything and betting against Him loses you everything, whereas if He doesn't, you lose nothing.

Right off the bat, we can see this original version of the wager is an intellectually dishonest argument: you don't "lose nothing" if you choose to believe that God exists and He doesn't. At best, you're being credulous; at worst, if you're being cynical about your belief, you're sacrificing your intellectual integrity.

Pascal backs off from all or nothing a bit as he's trying to dig himself out of the hole, claiming that he's comparing infinite gains of eternity in heaven against finite losses you can experience here on Earth. Some may have sincere trouble in believing, but he argues they should try to convince themselves.

Now, let's be fair to Pascal here: if you read his original text, he wasn't actually trying to convince atheists to believe per se, but instead, trying to show that the world is too uncertain for logical proofs of the existence of God, but we're probably better off acting like God exists, in case it moves us to faith.

Unfortunately, Pascal died before he could fully explain himself: the wager appears to be the introduction of a book on the value of faith that he never finished. But, like a philosophical zombie, the argument has continued its life, hollowed out from its original intent, eating brains in every new generation.

Let's slay this zombie, shall we?

Pascal's wager first appears to be an exercise in game theory: a mathematical formalism for analyzing the best choices in games. In this case, you are playing a game against the Cosmos. Your move is to believe, or not, and the Cosmos's "move" is whether God exists, or not.

[Now, the theologically savvy among you might feel like pointing out that God created Creation, and is not a part of it - which is why I used Carl Sagan's more inclusive formulation of the Cosmos as "all that is, was, and ever shall be," and I'm going to run you off with a broom if you argue about what "is" means].

This leads to a simple table: your choice of belief times the existence of God. If He is, and you choose to believe: payout plus infinity; choose not to believe: payout minus infinity. If He is not, whether you choose to believe or not, the payout is zero, or at least finite. Pick the cell with the highest value.

The emotional force of this argument is strong - for the believer - for, in decision theory, we should weigh the probability of one cell against the other, and intuitively, unless we judge the possibility of God to be literally zero, the infinite payout of the God-exists column dominates finite payouts of God-doesn't.

Mathematically, that's, um, specious at best - it looks true, but it's not a valid decision-theoretic argument. First off, Pascal put infinity in the God column specifically to outweigh any possible finite payout, but technically, we can't multiply infinite quantities by finite quantities this way.

Now, when it comes down to the question of whether infinities are actually real, or just a bad metaphor that leads people astray, I'm firmly ready to go to infinity - and beyond! But, technically mathematically, most of the time "infinity" is just a stand in for "this process can go on indefinitely without a limit."

As soon as you admit that the payout of Heaven might be finite for the purposes of modeling, then the probability assigned to the "God exists" column can be set so low that the "God doesn't" column becomes attractive. But that gets us no further than Pascal and his strict (zero-probability) unbelievers.

To me, the key flaw in Pascal's wager is what physicist E. T. Jaynes called the "mind projection fallacy": assuming that the constructs you're using in your mental models exist in reality. That's how Pascal can even put the wager to someone in the first place: he sets up the board and says "you must wager".

But the gameboard Pascal sets up doesn't exist in reality, and there's no reason for someone else to model the problem the same way. A student of religion might add columns for different views of God: Jesus who saves, Zeus who's a jerk, the Great Electron, which doesn't judge, but just is, whoa whoa.

Equally well, a student of epistemology might add many columns for belief: strict disbelief, partial belief, certain belief; an evangelical might add columns for "the hope so's" and "the know so's". Even the probabilities of columns are up for grabs. We've got a matrix of confusing possibilities.

This flaw in the wager, like the flaws in much science and folk psychology about belief, is that we do not reason about facts provided by others according to the models in the other's head: we reason about the claims that others make about facts, which we internalize based on own beliefs - and trust of the other.

Even in the simplest form, moment you start counting the columns of the wager as beliefs, the infinities disappear: there's only a claim of infinite goods in heaven, and a claim of infinite punishment in hell - and a claim that the alternative yields you only finite rewards.

And those claims are mixed in with everything else we know. As a mathematical exercise, the self-contained four-cell version of the wager has a maximum payout in the "believe in a God who exists" cell; as something that corresponds to reality, the cells of the wager start to leak.

Mathematics is an abstraction of reality - an act of creative human imagination to create repeatable forms of reasoning. I'm on the side that there is an actual reality behind this repeatability of mathematics, or it would not work; but applying mathematics to any particular problem must leave out certain details.

This is leads to the law of leaky abstractions: the notion that, no matter how good the abstraction, sooner or later it is going to fail to model the world. Forget game theory, decision matrices, and probabilities: even something as simple as the mathematical concept of number can break down.

One of the reasons I haven't published my tabbouleh recipe is that it's hard to quantify the ingredients - two bunches of parsley, four bunches of scallions, six tomatoes, two cups of fine bulgur, the juice of a lemon, etc - but since tomatoes are of different sizes, that "six" is a messy number.

But at least tomatoes come in integral quantities. Parsley comes in bunches, which are not just of different sizes; they're composed of individual stems, picked from different plants, which have different degrees of growth, freshness and wilt. Parsley needs to be cleaned and picked to use in tabbouleh.

Sometimes, you need to buy three bunches of parsley in order to end up with two. That's the law of leaky abstractions for you: you have to purchase parsley in integral units of bunches, but the bunches themselves don't correspond to the quantities that you can actually use in your recipe.

Picking beliefs for use in our minds is far more complicated than assembling a heritage Lebanese salad. There are thousands of potential facts affecting any given problem, more intertwined than the branching leaves of those leafy greens; but like them, some are fresh and edible, others black and wilted.

This was the actual point of Pascal's argument, the one he hoped to expound on his unfinished book. But the wager, because it's a mathematical abstraction - because it's repeatable reasoning - has lived on, a zombie argument which purports to give a rational reason why you should believe in God.

Ultimately, we need to carefully winnow through information that we get from others before incorporating it into our beliefs; there is no royal road to convincing anyone of anything, much less God. As for belief in God, many Christians think that must ultimately come not from reason, but from grace.

Fortunately, God gives that gift of belief for free, if we want it.

-the Centaur

Pictured: Blaise Pascal.

Many Christians believe that we can only do good by the grace of God. In its most extreme form, this theory of "total depravity" suggests that we are literally incapable of choosing the good, choosing to follow God, or to even believe in Him without His direct supernatural aid, offered as a free gift.

Total depravity is false, but it contains an important truth about why we need God's help not to screw up.

In artificial intelligence, we model smart things like people as "intelligent agents". An agent, broadly stated, is something that exists in a larger environment, observing situations, taking actions, and receiving rewards - a bit like the entities navigating through Markov decision processes last time.

But agents are a broader concept, not strictly tied to the Markov property: anything that makes decisions about actions in a larger environment can be an agent. The line between agent and environment can be clear, as with humans contained within our skins; or it might be fuzzy, like a control system for a factory.

While the idea of "intelligence" is fuzzy, one of the things that makes an agent smart is rational behavior - making the right choices. Another thing that makes an agent smart is learning - improving your behavior in the future based on the experiences that you've had in the past.

The field I work in, deep reinforcement learning, focuses on building learning agents that improve their rationality based on their experiences, generally within a partially-observable Markov decision process in which it's reasonably clear what counts as rational, even if the agent can't clearly see the whole world.

This "partial observability" is one real-world limitation that virtually all agents in Creation share. Robot sensors have a limited range, the factory controller doesn't have a sensor on all its circuits, and we can't see behind our own heads (hey, there's a creepy man standing behind you right now - don't look!)

Partial observability means we need to make the best decisions we can based on the information that is available to us. We look both ways at a crosswalk to try to reduce our uncertainty, waiting if a car is coming, and we call out "corner" in a restaurant kitchen to try to reduce the uncertainty of others.

Obviously, if you don't know which door holds the lady or the tiger, it's hard to pick. But even if an agent had perfect knowledge of the current state of the world around it - not that current state is well-defined in general relativity / quantum mechanics, but nevermind - making perfectly correct decisions is impossible.

Well, not necessarily impossible: a perfectly omniscient agent could make perfectly optimal decisions, because it would know the true value of each action, not just its immediate reward. But without that kind of revelation of information from the future, we can only learn from our past experiences.

And that's where the no free lunch theorem comes in: there is no guaranteed way to learn correctly.

Imagine a simple decision problem: to turn left or right on a forking path in a garden. (Perhaps only one of those directions leads to the "straight and narrow" - sorry, this is a Lenten series, gotta bring that in somewheres). At each fork in the road, there are two more potential paths than there were before.

A path that forks at each stage is like that problem where you double the number of pennies you give someone each day for a whole month. It starts with small change - first day a penny; the second, two, the third, four, and so on - but last day of the month, you're shelling out ten million bucks - a billion pennies.

In this garden of forking paths, there are a billion possible destinations. But in the mind of an agent trying to learn what to do, the problem is even harder: there are also a billion intermediate steps, and at each point, the agent must make a decision, with two possible choices.

If you perfect knowledge and tried to write down a guidebook, it would have a billion entries, with a recommended decision at each point. But if you don't have perfect knowledge, if you're a learning agent, then your best option is to go into the garden and fill out that guidebook yourself.

This is almost inconceivably hard. If you imagine a library with every possible guidebook, one in which each book differed from every other by at least one decision out of those billions, then there are two to the power of a billion possible books - that's a number with roughly three hundred million digits.

The only way to fill out the guidebook correctly is to visit all billion possible paths. If you can't do that, then at some point, you're going to need to guess the entries for the parts of the garden that you haven't visited. And then it gets tricky, because there are two to the power of a billion possible gardens.

If you're in a garden where the straight and narrow can be approximated by alternating left and right to stay near the middle, you might guess that outer entries of the table should turn inward, the far left turning right, and the far right turning left. But for all you know, more reward can be found further out.

The no free lunch theorem says that there is no principled way to fill in parts of the book you haven't seen. At best, you can assume that parts of the garden you've seen are similar to the ones you haven't, but if you could be in literally any possible garden, then those assumptions will inevitably fail.

What does this all mean for free will versus total depravity?

Well, first off, if you are an intelligent agent, then you can sample actions from your action space. The actions you can take aren't good or evil, they're decisions in your brain and actions of your body. Some of those actions can, by chance, be good ones; God has not so ordered the world to exclude the good.

And if you do good works and see that they are good, why, then, you could learn to do them again. There's nothing preventing this; again, God has not so ordered the world to exclude the good. But there's no guarantee that you're going to learn the right lessons, and there lies the problem.

In deep reinforcement learning, we see this problem writ large. I teach robots the size of people how to navigate buildings meant for people, and while you think that would be simple, we often observe robot control policies that have completed thousands of successful runs suddenly run straight into a wall.

Deep learning systems do not generalize the way human beings would. While a human that learns to drive without hitting things in their hometown will often be able to transfer this skill when they go off for college, a robot moving to a new environment may expose strange "pathologies" in its behavior.

This is the meaning of "my thoughts are not your thoughts, neither are your ways my ways" in Scripture: even if a human being honestly chooses to believe in God, sincerely tries to do good, and accidentally gets it right, there is no guarantee that what they've learned from that experience will transfer.

In fact, it's more likely to not transfer. Sins of pride, self-righteousness, scrupulousness, and intolerance lead us astray as much as temptations to indulge in things that are "lawful but not expedient". We can turn to Scripture, to church Tradition, or to our own Reason to try to improve, but we'll likely screw up.

This is why God's grace is so important. God is actively and spiritually trying to help us come to believe, know and love him, and hopes that this love will prompt us to do the right thing, bringing the Kingdom of Heaven into being here on this Earth.

But across a broad spectrum of possible universes, it's mathematically impossible for us to always get it right even if we're trying really hard - literally the only way that we could actually be consistently good is to have perfectly omniscient knowledge of the entire future of the Universe - to actually be God.

We can't be God. The position is taken. We don't know what He knows, and we are going to screw it up. Fortunately He's ordered the universe so it's possible to get it right, He's sent his Son as an example of how to get it right, and His Spirit acts in the world to give us the grace we need to actually get it right.

-the Centaur

Pictured: David Wolpert, who discovered one of the depressingly many No Free Lunch theorems.

Original Sin is the idea that all humans are irretrievably flawed by one bad decision made by Adam in the Garden of Eden. One bite of that apple (well, it wasn't an apple, but nevermind), broke Creation in the Fall, corrupted everyone's souls from birth, leading to the requirement of baptism to liberate us.

But the Fall didn't happen. The universe is not broken, but is unimaginably old and vast. The evolution of humans on the earth is one story out of myriads. The cosmology of the early Hebrews recorded in Genesis is myth - myth in the Catholic sense, a story, not necessarily true, designed to teach a lesson.

What lessons does Genesis teach, then?

Well, first off, that God created the universe; that it is well designed for life; that humanity is an important part of that creation; and that humans are vulnerable to temptation. Forget the Fall: the story of the serpent shows that humans out of the box can make shortsighted decisions that go horribly wrong.

But what's the cause of this tendency to sin, if it isn't a result of one bad choice in the Fall? The answer is surprisingly deep: it's a fundamental flaw in the decision making process, a mathematical consequence of how we make decisions in a world where things change as a result of our choices.

Artificial intelligence researchers often model how we make choices using Markov decision processes - the idea that we can model the world as a sequence of states - I'm at my desk, or in the kitchen, without a soda - in which we can take actions - like getting a Coke Zero from the fridge - and get rewards.

Ah, refreshing.

Markov decision processes are a simplification of the real world. They assume time steps discretely, that states and actions are drawn from known sets, and the reward is a number. Most important is the Markov property: the idea that history doesn't matter: only the current state dictates the result of an action.

Despite these simplifications, Markov decision processes expose many of the challenges of learning to act in the world. Attempts to make MDP more realistic - assuming time is continuous, or states are only partially observable, or multidimensional rewards - only make the problem more challenging, not less.

Hm, I've finished that soda. It was refreshing. Time for another?

Good performance at MDPs is hard because we can only observe our current state: you can't be at two places or two times at once. The graph of states of an MDP is not a map of locations you can survey, but a set of possible moments in time which we may or may not reach as a result of our choices.

In an earlier essay, I described navigating this graph like trying to traverse a minefield, but it's worse, since there's no way to survey the landscape. The best you can do is to enumerate the possible actions in your current state and model what might happen, like waving a metal detector over the ground.

Should I get a Cherry Coke Zero, or a regular?

This kind of local decision making is sometimes called reactive, because we're just reacting to what's right in front of us, and it's also called greedy, because we're choosing the best actions out of the information available in the current state, despite what might come two or three steps later.

If you took the wrong path in a minefield, even if you don't get blown up, you might go down a bad path, forcing you to backtrack ... or wandering into the crosshairs of the badguys hiding in a nearby bunker. A sequence of locally good actions can lead us to a globally suboptimal outcome.

Excuse me for a moment. After drinking all those sodas, I need a bio break.

That's the problem of local decision making: if you exist in a just very slightly complicated world - say, one where the locally optimal action of having a cool fizzy soda can lead to a bad outcome three steps later like bathroom breaks and a sleepless night - then those local choices can lead you astray.

The most extreme example is a Christian one. Imagine you have two choices: a narrow barren road versus a lovely garden path. Medieval Christian writers loved to show that the primrose path led straight to the everlasting bonfire, whereas the straight and narrow led to Paradise.

Or, back to the Garden of Eden, where eating the apple gave immediate knowledge and long-term punishment, and not eating it would have kept them in good grace with God. This is a simple two-stage, two-choice Markov decision process, in which the locally optimal action leads to a worse reward.

The solution to this problem is to not use a locally greedy policy operating over the reward given by each action, but to instead model the long-term reward of sequences of actions over the entire space, and to develop a global decision policy which takes in account the true ultimate value of each action.

Global decision policies sometimes mean delaying gratification. To succeed at life, we often need to do the things which are difficult right now, like skipping dessert, in favor of getting more reward later, like seeing the numbers on your scale going back down to their pre-Covid numbers.

Global decision policies also resemble moral rules. Whether based on revelation from God, as discussed in an earlier essay, or based on the thinking of moral philosophers, or just the accumulated knowledge of a culture, our moral rules provide us a global decision policy that helps us avoid bad consequences.

The flaw in humanity which inspired Original Sin and is documented in the Book of Genesis is simply this: we're finite beings that exist in a single point in time and can't see the long-term outcome of our choices. To make good decisions, we must develop global policies which go beyond what we see.

Or, for a Christian, we must trust God to give us moral standards to guide us towards the good.

-the Centaur

Pictured: Andrey Markov.