"Physics Considerations for a Simulated Reality"

Physics considerations for a simulated reality Max Hodak 1 Why build a simulated reality? ined, but that of defining a suitable physics system. We conjecture that there is a relationship between Video games have a powerful natural appeal. Our the depth of a virtual world and the sophistication of physical world imposes harsh constraints: atoms are its underlying physics. difficult to work with compared to bits, and the Any non-trivial universe must contain informa- scarcity of both materials and the capacity to trans- tion, and we can phrase the central problem in world form them leads to a tough environment. By con- design as one of writing down the information that trast, video games can be anything we want them defines a universe; informally, we can state that a to be: players can fly, use magic, or even have their universe without information has zero depth. We can own planet, all the while exercising mental faculties start from a premise that information in any universe in just as satisfying a way as they would in our base is found in two forms: matter and its interactions. reality. As computer processing power continues to improve and the space of games we can build expands, a natural opportunity arises to build simulated real- 2 Naturalness ities that are as engaging and emotionally immersive as our base reality, but with fewer constraints and a Before we think about physics as it is usually under- greater capacity for easier creative expression. stood, let's briefly look at video game \physics" as Video game design is challenging on multiple lev- it exists today. The physics of a game is encoded in els. Scripted worlds may be engaging for a short pe- its source code, and implemented by the game en- riod of time, but ultimately suffer from the limited gine. The logic laid out in the source determines the hand-crafted information embedded by the develop- complete range of things possible in the game envi- ers for the player to experience. It is possible to build ronment. open sandbox worlds that support a great degree of This physics is probably built from a lot of non- creative expression (for example, Minecraft or Sim- linear branching logic like \if" and \switch" state- City), but game mechanic design is a difficult art. ments. Also, the logic is probably structured in a Most variations are neither engaging nor fun, and all way such that the phenomena you tend to get in the of them are characterized by severe limits to their game are generally \discrete". For example, when depth. you walk up to a door suddenly the character \E" It's often been observed that immersion in vir- has a new behavior, or how picking up an object is tual worlds is far more related to psychological and an all-or-nothing event. This logic has a lot of compli- emotional depth than graphical fidelity.[1] It is an cated structure that is irreducible to simpler unifying important point that in considering the physics of a principles. Most of the information about the world simulated reality, we are not principally concerned is encoded specifically and is incompressible. It is with the quality of the graphics, though presumably highly “fine-tuned”. they would follow as \for free." We are principally On the other hand, essentially everything that we concerned with the range and sophistication of the understand day-to-day about our world is understood emotionally satisfying creativity that the world sup- in terms of a small set of very deep things. The color ports. of the sky is nowhere hard-coded into our universe; The physics of our world enables a vast range of it emerges automatically from quantum field theory. creativity to be expressed and its results enjoyed. A There is some intuitive feeling of improved \smooth- central part of our argument is that, in developing a ness" over the game logic example. \complete" virtual world, one that players will find This is a very informal statement. There's no real engaging for indefinite periods of time, the primary specific claim about the structure of our physics being challenge is not game design as it is classically imag- made here. All we have right now is a vague intuitive 1 sense of the difference between \natural" universes mation defines the physics of this world, and while and heavily fine-tuned ones. it admits a non-zero range of game mechanics, the lack of depth becomes quickly apparent. We cannot deform the shape of the ball; we cannot cause its 2.1 Is naturalness important? bouncing to suddenly become damped or cause the We conjecture that universes built from more natu- plane to impart new energy into the ball when they ral physics, if they work at all, will be much richer interact. We cannot change the color of anything in for the users than universes built from highly fine- this universe, and we cannot make any new things. tuned physics. This is because an essential measure We can of course do any of these things by writ- of the depth of the world is the range, sophistication ing additional logic into the game engine. It is easy and coherency of the phenomena it allows, and we to see, though, that the complexity of this problem hypothesize that a universe in which the main effects grows very quickly with the depth of the world. It is we interact with are emergent is likely to have a much straightforward to make the ball deformable so that wider range of interesting things to do versus a uni- when it collides with the plane it is briefly squished verse in which the range of things to do is directly into an oblate spheroid. But this is a superficial prescribed. change unless we also make the ball composed of some At first glance, it seems much easier to build a definite kind of matter, and by extension a definite fine-tuned universe than a natural one. Certainly it density and a set of forces that hold it together. Then, is easier to build a regular video game than write instead of simply detecting a collision with the sur- down a field theory that spontaneously produces a face and inverting the z dimension of the momentum compelling video game. vector, we can calculate the force imparted on the Game developers can construct huge MMOs full plane from the kinetic energy of the ball accounting of quests and social mechanics, but eventually the for the deformation of its material and propagate an players will exhaust them, and lose interest and opposing force back into the material of the ball and leave. Worse, since the players can from early on allow the change in momentum to fall out naturally. feel these limits, however gently, they fail to fully in- Doing this requires us to also build the plane out of vest themelves in the world. With limited attention a definite material and ensure that our logic is sen- and capacity for emotional labor, most people will sical for the interaction of the material ball with the only construct a life and career in the most promis- material surface. ing reality available. Mechanics are known that can Suppose we now wanted to divide the ball in two generate immense variability, but even these even- and use two balls. This requires further special-cased tually become stale and lose relevance to the multi- logic in the game engine to support; nothing we have facteted ambitious human in search of novelty and defined yet automatically allows it. Implementing accomplishment. this in a way that only allows dividing the material There is some essential relationship to be elu- ball but not dividing the material surface is less sat- cidated between the compressibility of a universe's isfactory than an approach that allows dividing any physics and the depth of the universe, assuming an material object in the world. anthropic principle. If the z = 0 plane is an infinite surface, this brings challenges: what does it mean to divide an infinite plane? Are we satisfied with the creation of voids 2.2 Non-smooth physics is difficult to make in its surface? Do we want a way to remove all of highly expressive the (infinite) material from the plane out from some To make this a little clearer, imagine a virtual en- defined point? Further, we have special-case defined vironment with a ball placed at a height of z = 1 the apparent force of gravity on the ball: does that above the x; y = 0 origin of an infinite plane. When force also apply to the plane? If not, we need to de- time is started, the ball experiences an acceleration fine some new mechanism by which gravity acts on in the −z direction and proceeds to fall under this the ball (or subdivided balls) but not the plane. force until it reaches z = 0 (the surface of the plane), The devoted game developer can add a huge num- at which time its momentum vector is transformed ber of rules to their engine to get any specific desired by pz = −1 ∗ pz. behavior, but the problem of getting broadly general In this world, we have directly defined two mate- emergent behavior in circumstances not specifically rial entities (the ball and the plane) and two interac- imagined by the developer quickly becomes an intri- tions (the apparent gravity and the the momentum cate theoretical challenge. change of the ball striking the plane). That infor- The richness of the world as enabled by its physics 2 is of central importance in building a world that is as operator returns zero if the point is empty and one if richly creative, or more so, as our base reality.

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