It’s a common science fiction conceit that the universe is a giant simulation, some computer algorithm in which the code is written ahead of time (the laws of physics) and then that program is executed to see what will result. Presumably, the code can be tweaked and then run again, or perhaps each individual universe in the multiverse is a different variation with different parameters, each leading to a slightly different result. Another variation of this theme is that new branches of the timeline are being continuously created, every decision leading eventually to alternate universes, like a complex tree, ever expanding and growing. It is a reconciliation of the old high-school debate topic, destiny versus free will: that which is not forbidden is mandatory, and everything allowed by the rules must be happening somewhere. In a fractal universe, even severe limits set by physical law still leave room for infinite variations.

Physicists speculate about this sort of thing, and artists play with the idea. “And the Princess and the Prince discuss, what is real and what is not.” The ideas of hierarchically nested realities is a common artistic trope these days. The Matrix films have exploited it shamelessly, The movies “Existenz” and “The Thirteenth Floor” explore the idea even better. Phillip K Dick constantly wrote about it. But it isn’t necessary to posit hidden simulated worlds and computer universes and other speculations. We know the real world is put together that way.

There is a very real world which physicists study, one of fields and waves, particles and forces, weird statistical rules and relativistic and quantum phenomena. This is a universe we didn’t even know existed a century ago, but which our entire science and technolgy is now based on. Prior to that we lived in the classical reality of Newton and Maxwell which now seems hopelessly mechanistic and contrived, but which is still useful for routine engineering purposes. We ignore these worlds at our peril, but they play very little role in our day-to day existence. You don’t need to understand quantum gravity to throw a good curve ball, and celestial mechanicians do not necessarily make good baseball pitchers.

We live in a physical world, a historical world, a cultural world, an economic world, a social world, a psychological world. The universe is made up of endless sub-universes, each based on the other like the layers of an onion. All they have in common is that we are at the center of each. We live in all of them simultaneously, but we rarely deal with more than one at a time. When we’re running a business or managing a political campaign or overhauling an engine we are engaged with very distinct realities that are all equally valid and real, but are only obliquely related to and dependent on one another.

The human brain is very adept at popping in and out of these worlds effortlessly, and selecting only what it needs to know from one to deal with another. This is really not all that different from waking up from a dream, except it is conscious. And we sometimes dream we are dreaming. Dreams are not “real” realities, but if we don’t know that, what difference does it make? We have no choice but to respond to the reality we perceive, whether it is real or not. The physicist deals with one subatomic reality, as we have seen, but when he is involved with departmental politics at work, or worried about his juvenile delinquent son, or having an extramarital affair, or trying to regain control of his skidding car on an icy road, he is dealing with equally real and legitimate and important aspects of his total reality. He is perceiving the world differently, and he is perceiving different worlds. What happens in one may have some influence on another, but it isn’t always too useful to know that.

We do not exist in the real world, whatever that is is. There is no external reality, or more correctly, it is incomprehensible to us. We have created a model of it, an abstraction, a simulation, if you like, and that is where we operate. It is our own personal dream world we have been forced to devise to make sense of an incomprehensible universe. In fact, we have created a multitude of alternate universes, models, simulations, where we exist temporarily. The evidence of our senses is gathered in those worlds and compared and interpreted by referring to assumptions we have made about those worlds. And those worlds are constantly changing, depending on whether we are cheating on our spouse or sliding out of control on an icy road. We have to be careful how the decisions, and perceptions, we make in one are going to affect events in another. This is why we have evolved the ability to simultaneously hold contradictory concepts in our minds. Its not a bug, its a feature.