Like organisms evolved in gentle tide pools, who migrate to freezing oceans or steaming jungles by developing metabolisms, mechanisms, and behaviors workable in those harsher and vaster environments, our descendants, able to change their representations at will, may develop means to venture far from the comfortable realms we consider reality into arbitrarily strange worlds. Their techniques will be as meaningless to us as bicycles are to fish, but perhaps we can stretch our common-sense-hobbled imaginations enough to peer a short distance into this odd territory.
Simulation, Consciousness, Existence
Hans Moravec, 1998
Simulation
During the last few centuries, physical science has convincingly answered so many questions about the nature of things, and so hugely increased our abilities, that many see it as the only legitimate claimant to the title of true knowledge. Other belief systems may have social utility for the groups that practice them, but ultimately they are just made-up stories. I myself am partial to such ``physical fundamentalism.''
Physical fundamentalists, however, must agree with René Descartes that the world we perceive through our senses could be an elaborate hoax. In the seventeenth century Descartes considered the possibility of an evil demon who created the illusion of an external reality by controlling all that we see and hear (and feel and smell and taste). In the twenty-first century, physical science itself, through the technology of virtual reality, will provide the means to create such illusions. Enthusiastic video gamers and other cybernauts are already strapping themselves into virtual reality goggles and body suits for brief stints in made-up worlds whose fundamental mechanisms are completely different from the quantum fields that (best evidence suggests) constitute our physical world.
Today's virtual adventurers do not fully escape the physical world: if they bump into real objects, they feel real pain. That link may weaken when direct connections to the nervous system become possible, leading perhaps to the old science-fiction idea of a living brain in a vat. The brain would be physically sustained by life-support machinery, and mentally by connections of all the peripheral nerves to an elaborate simulation of not only a surrounding world but also a body for the brain to inhabit. Brain vats might be medical stopgaps for accident victims with bodies damaged beyond repair, pending the acquisition, growth, or manufacture of a new body.
The virtual life of a brain in a vat can still be subtly perturbed by external physical, chemical, or electrical effects impinging on the vat. Even these weak ties to the physical world would fade if the brain, as well as the body, was absorbed into the simulation. If damaged or endangered parts of the brain, like the body, could be replaced with functionally equivalent simulations, some individuals could survive total physical destruction to find themselves alive as pure computer simulations in virtual worlds.
A simulated world hosting a simulated person can be a closed self-contained entity. It might exist as a program on a computer processing data quietly in some dark corner, giving no external hint of the joys and pains, successes and frustrations of the person inside. Inside the simulation events unfold according to the strict logic of the program, which defines the ``laws of physics'' of the simulation. The inhabitant might, by patient experimentation and inference, deduce some representation of the simulation laws, but not the nature or even existence of the simulating computer. The simulation's internal relationships would be the same if the program were running correctly on any of an endless variety of possible computers, slowly, quickly, intermittently, or even backwards and forwards in time, with the data stored as charges on chips, marks on a tape, or pulses in a delay line, with the simulation's numbers represented in binary, decimal, or Roman numerals, compactly or spread widely across the machine. There is no limit, in principle, on how indirect the relationship between simulation and simulated can be.
Today's simulations, say of aircraft flight or the weather, are run to provide answers and images. They do so through additional programs that translate the simulation's internal representations into forms convenient for external human observers. The need to interpret limits how radical a simulation's hardware and software representations can be. Making them too different from the form of the answers may render the translation impractically slow and expensive. This practical limit may be irrelevant for simulations, such as the medical rescue imagined above, that contain their own observers. Conscious inhabitants of simulations experience their virtual lives whether or not outsiders manage to view them. They can be implemented in any way at all.
What does it mean for a process to implement, or encode, a simulation? Something is palpably an encoding if there is a way of decoding or translating it into a recognizable form. Programs that produce pictures of evolving cloud cover from weather simulations, or cockpit views from flight simulations, are examples of such decodings. As the relationship between the elements inside the simulator and the external representation becomes more complicated, the decoding process may become impractically expensive. Yet there is no obvious cutoff point. A translation that is impractical today may be possible tomorrow given more powerful computers, some yet undiscovered mathematical approach, or perhaps an alien translator. Like people who dismiss speech and signs in unfamiliar foreign languages as meaningless gibberish, we are likely to be rudely surprised if we dismiss possible interpretations simply because we can't achieve them at the moment. Why not accept all mathematically possible decodings, regardless of present or future practicality? This seems a safe, open-minded approach, but it leads into strange territory.
From:
Simulation, Consciousness, Existence -- Hans Moravec, 1998
