Nick Bostrom elevated philosophical concerns to the level of the popular press with his paper, Are You Living in a Computer Simulation? which argues that:
…at least one of the following propositions is
true: (1) the human species is very likely to go extinct before reaching a “posthuman” stage; (2) any posthuman civilization is extremely unlikely to run a significant number of simulations of their evolutionary history (or variations thereof); (3) we are almost certainly living in a computer simulation.
A critical prerequisite of (3) is that human brains can be simulated in some way. And a co-requisite of that requirement is that the environment must be at least partially simulated in order for the brain simulations to believe in the sensorium that they experience:
If the environment is included in the simulation, this will require additional computing power – how much depends on the scope and granularity of the simulation. Simulating the entire universe down to the quantum level is obviously infeasible, unless radically new physics is discovered. But in order to get a realistic simulation of human experience, much less is needed – only whatever is required to ensure that the simulated humans, interacting in normal human ways with their simulated environment, don’t notice any irregularities.
Bostrom’s efforts to minimize the required information content doesn’t ring true, however. In order for a perceived universe to provide even “local” consistency, then large-scale phenomena must be simulated with perfect accuracy. Even if, as Bostrom suggests, noticed inconsistencies can be rewritten in the brains of the simulated individuals, those inconsistencies would have to be eventually resolved into a consistent universe.
Further, creating local consistency without emulating quantum-level phenomena requires first computing the macroscopic phenomena that would be a consequence of those quantum events. Many of these macroscopic physical behaviors are suspected of being essentially irreducible to anything other than the particulate ensemble evolution itself–in other words, there is no analytic macroscopic model that reflects reality without performing the entire simulation. This restates Wolfram’s notion of computational irreducibility.
Taken together, Bostrom’s simulated world seems less likely and his quoted defeater that “Simulating the entire universe down to the quantum level is obviously infeasible,” appears to be a critical requirement for the current observable universe. Therefore, it is unlikely that we live in a simulated universe.