Most of this is specific to videogames and probably will not be applicable anywhere else:
An emergent property in the context of videogames is one the designers of the game did not intend, [more strictly: yet is not a programming error].
Excluding the possibly, since this example is ambiguous using it:
In the game Super Smash Bros, jumping is not emergent, since the designers programmed it into the game specifically.
Wavedashing [dodging into the ground so that you will be able to move while attacking] (and in fact, every single bit of strategy for every character) is emergent; it’s not programmed into the game, it’s just that if you put together all the intended rules of the game, wavedashing appears also.
What does “this is emergent” tell you, in this context?
It tells you first of all it’s unintentional, which then tells you it has a vastly greater chance of being unbalanced or broken.
Using the stricter definition, it also tells you whatever it is profits the player in some way, because if it did not profit the player in some way it would not have emerged; someone would have found it, not used it or told anyone, and it would just fade away. (But this is only valid for emergent things when they’re structured in a certain way. This part can be generalized to, say, the economy, but not, say, to traffic jams, because traffic jams are more tragedy of the commons types of things.)
It also tells you, most importantly, that it is probably not possible to know all the specific causes of this thing and instead to try wide and general causes. (i.e: “World War I happened because of a general attitude among nations that military force was a good way to solve problems.” It’s possible to say it happened “because Alice thought… and Bob thought… but Carol thought… and Dave thought....”, but this is going to be either much less accurate or not worth the effort to make it accurate.)
What does “this is non-emergent” tell you?
There are one or more obvious specific causes that it would not be worth breaking down. (In the case of videogames, the developers, but it also works for cases like “there is a big dent in the front of my car because I crashed it into a tree” [but wait, you say, isn’t that also phrasable as “because the force from the tree caused this molecule and this molecule and this molecule to move backwards”? Yes, but it doesn’t matter; the only cause is still the force from the tree.])
(Finally, random other example I thought of after reading the Go example:
In chess, the position of the pieces at the beginning of the game is not emergent: there is one cause for that: because it’s part of the rules of the game.
The fact that the best first move for white in most cases is pawn to e4 is emergent. Nobody wrote that into the rules of chess; it’s just a consequence of the positions of the pieces.)
What’s the difference between a “programming error” and an “emergent consequence of the program as written”, other than whether the programmers decide they like the result? Is it just a question of whether the rules involved can be described intuitively at the level of user-interface objects rather than lines of code?
Answer to your question: Honestly, I should not have included that line about errors in there at all; it doesn’t need to be special cased out because most errors are emergent. (Not always; a missing negative somewhere is not emergent. But when you get to the complexity of a video game, most errors that will make it through QA are emergent.)
But also: I actually have thought about this a bit since I wrote this, and I think I can come up with a decent general definition for emergence: (don’t worry, I’ll get to your question in a moment)
Something is emergent when it is caused by a rule that works similarly to the second law of thermodynamics. (More specifically, the property of the second law that it isn’t actually a hard law at all; it’s just that when you crunch all the probabilities for all the particles involved, it is vastly more likely that the result will obey the second law then will not.)
Similarly, the ways economies develop aren’t hard laws; it would be entirely possible for an economy to develop in such a way that it lets you get a free lunch. It’s just that that, considering all the actors involved are out to find and take those free lunches, that you are about (using about very broadly here) as likely to find an actual free lunch as you are to find your foot has suddenly turned into gold.
(Also: I think it’s a mistake to point at some finished product of laws of emergence and say it’s emergent. “The economy is emergent” is just a short and slightly misleading way to say “The laws that govern an economy are laws of emergence”.)
But going back to what this predicts: It predicts mainly that there is something equivalent to atoms in thermodynamics or actors in economics; some small unit of behavior that you can test for. It also predicts (in very complex systems it might not be possible to do any actual math on this, but in theory it predicts) how often the law will fail. (As noted, sometimes all you can say with confidence is “it might fail sometime”; of course if it fails OFTEN it doesn’t have enough predictive value to justify keeping around.)
Most of this is specific to videogames and probably will not be applicable anywhere else:
An emergent property in the context of videogames is one the designers of the game did not intend, [more strictly: yet is not a programming error].
Excluding the possibly, since this example is ambiguous using it:
In the game Super Smash Bros, jumping is not emergent, since the designers programmed it into the game specifically.
Wavedashing [dodging into the ground so that you will be able to move while attacking] (and in fact, every single bit of strategy for every character) is emergent; it’s not programmed into the game, it’s just that if you put together all the intended rules of the game, wavedashing appears also.
What does “this is emergent” tell you, in this context?
It tells you first of all it’s unintentional, which then tells you it has a vastly greater chance of being unbalanced or broken.
Using the stricter definition, it also tells you whatever it is profits the player in some way, because if it did not profit the player in some way it would not have emerged; someone would have found it, not used it or told anyone, and it would just fade away. (But this is only valid for emergent things when they’re structured in a certain way. This part can be generalized to, say, the economy, but not, say, to traffic jams, because traffic jams are more tragedy of the commons types of things.)
It also tells you, most importantly, that it is probably not possible to know all the specific causes of this thing and instead to try wide and general causes. (i.e: “World War I happened because of a general attitude among nations that military force was a good way to solve problems.” It’s possible to say it happened “because Alice thought… and Bob thought… but Carol thought… and Dave thought....”, but this is going to be either much less accurate or not worth the effort to make it accurate.)
What does “this is non-emergent” tell you?
There are one or more obvious specific causes that it would not be worth breaking down. (In the case of videogames, the developers, but it also works for cases like “there is a big dent in the front of my car because I crashed it into a tree” [but wait, you say, isn’t that also phrasable as “because the force from the tree caused this molecule and this molecule and this molecule to move backwards”? Yes, but it doesn’t matter; the only cause is still the force from the tree.])
(Finally, random other example I thought of after reading the Go example:
In chess, the position of the pieces at the beginning of the game is not emergent: there is one cause for that: because it’s part of the rules of the game.
The fact that the best first move for white in most cases is pawn to e4 is emergent. Nobody wrote that into the rules of chess; it’s just a consequence of the positions of the pieces.)
What’s the difference between a “programming error” and an “emergent consequence of the program as written”, other than whether the programmers decide they like the result? Is it just a question of whether the rules involved can be described intuitively at the level of user-interface objects rather than lines of code?
Answer to your question: Honestly, I should not have included that line about errors in there at all; it doesn’t need to be special cased out because most errors are emergent. (Not always; a missing negative somewhere is not emergent. But when you get to the complexity of a video game, most errors that will make it through QA are emergent.)
But also: I actually have thought about this a bit since I wrote this, and I think I can come up with a decent general definition for emergence: (don’t worry, I’ll get to your question in a moment)
Something is emergent when it is caused by a rule that works similarly to the second law of thermodynamics. (More specifically, the property of the second law that it isn’t actually a hard law at all; it’s just that when you crunch all the probabilities for all the particles involved, it is vastly more likely that the result will obey the second law then will not.)
Similarly, the ways economies develop aren’t hard laws; it would be entirely possible for an economy to develop in such a way that it lets you get a free lunch. It’s just that that, considering all the actors involved are out to find and take those free lunches, that you are about (using about very broadly here) as likely to find an actual free lunch as you are to find your foot has suddenly turned into gold.
(Also: I think it’s a mistake to point at some finished product of laws of emergence and say it’s emergent. “The economy is emergent” is just a short and slightly misleading way to say “The laws that govern an economy are laws of emergence”.)
But going back to what this predicts: It predicts mainly that there is something equivalent to atoms in thermodynamics or actors in economics; some small unit of behavior that you can test for. It also predicts (in very complex systems it might not be possible to do any actual math on this, but in theory it predicts) how often the law will fail. (As noted, sometimes all you can say with confidence is “it might fail sometime”; of course if it fails OFTEN it doesn’t have enough predictive value to justify keeping around.)