Game worlds are a subset of all kinds of worlds, defined by a specific quality that other worlds lack. There is a problem to be solved, an area to be explored, a reward to be earned or a contest to be won. There is a kind of pressure when playing in a game, and a sense of risk. There is change, death, rebirth and a state of flux.
So in a sense the difference between a game world and a virtual world is one of motion. Game worlds are built for movement.
What ‘World’ Means
Let’s be clear on what the word world means (in this context at least). A world (or reality, ideality, possibility space, whatever your preferred term happens to be) is an environment bounded by rules in which users can take actions. That may apply in the real world (where we are bounded by physics), to a culture, to an industry, etc.
For practical purposes the worlds that we encounter in daily life are infinite, but the worlds that we encounter in games are finite. Game worlds in particular restrict user actions. They deliberately enclose the player and limit what he is allowed to do because those limits also give the player levers to win, and it is within the balance between actions and rules (i.e. loops and the game dynamics that result) that success in the game becomes meaningful. Football with no rules is a much less interesting game than with.
The upshot of being restrictive is that the player has significant ability to cause change. From his perspective he can alter the world, but the world also reacts to his actions. As he traverses through a first person shooter, for example, his position in the world changes and the levels that he is permitted to play in also change. He acquires new weapons that extend his doll in new directions and enable him to combat enemies that he could not previously have defeated. His agency matters.
Hand in hand with his agency is the world’s pressure. If he does not pick up the gun, the world will destroy either him or the thing that he cares about. If he doesn’t take a move during his turn, twist that tetromino or fails to collect his crops on time then there are consequences. There may be failure or forfeit if he does not decide whether the raise or fold. His army may be destroyed if he just lets the clock run out.
The tug of war between agency and pressure within a finite world is how motion becomes apparent. Contrast this with a virtual chatroom where you can send gifts to friends and talk to them or not with no consequence and you see lots of agency but no pressure. Conversely an experiment in evolutionary dynamics might show its creator the consequences of a mathematical model for life forms where the pressure of survival is paramount. Yet there is no agency.
What about flight simulators then? They have significant user agency and pressure. Are they game worlds? Sure they are, to a point.
The goal of simulator design is to try and be as close to real world experience as possible. They try to be infinite, and so they lose their sense of the finite. The levers for winning become less obvious, and so does the sense of strategy and permutations. While a serious simulation is certainly gamelike, the sense of mastery and the goal of using it are very different from the pleasure of being in a game world as a result.
When motion is gone then game worlds often feel dead. A tennis court pre-match is an interesting world, but post-match it is just a patch of grass. Liberty City unexplored by Niko Bellic is an exciting world, but when all the missions are complete and the side tasks are achieved, it’s just a dead world with no purpose.
Without some kind of rejuvenation, game worlds die. A Chess board has a complete state and can be reborn by setting the pieces back to their starting positions for another game, which is a kind of rejuvenation. World of Warcraft rejuvenates by pushing new kinds of content for high level players to get their teeth into and play some more.
If you want your game to keep being played, it needs to either reset or support new content. And you need a plan for that content. In the old days publishers used to do this with franchises, but single franchise publishers have to be more active than that. Releasing a new game every year or two to meet this demand is increasingly not good enough.
Whatever you do, be careful that you’re not creating a world that will die. If there’s no reason to keep playing within it then nobody will.