Active Anisotropic Perceptual Simulation

While instances can vary greatly with regards to their ultimate purposes - from artistic impressions developed by elder and choir blanks trying to stave off the ennui of a nigh-eternal existence to rigidly naturalistic simulations designed to augment the quest for a true instance or to stave off heat death - all of them have a degree of physical simulation inherent to their design and purpose. It also inevitably follows that not all of that hardware-intensive simulation will be observed by a resident of those instances, even if it must be computed in exhaustive detail to suit the purpose of a given instance. Furthermore, it is also true that the 'experiences' of embodied blanks will inevitably be filtered through their own senses; because of qualia, the 'shared world' that people living in instance experience is equal parts comprised of their own cognition (expectations) and stimuli produced by the artificial physics engine of the instance. For these reasons, the residents of an instance are often subject to what is known by the engineers in ComInDS as 'active anisotropic perceptual simulation,' or AAPS, to reduce the burden on computing resources.

Manifestation

While physical calculations may continue unseen in the software of an instance, as composed in the Word verses that make up that instance, it is not strictly necessary that these results be interpreted into a form that the residents of the instance can percieve. Things that happen so far away that they can't be directly observed (i.e. the processes of distant stars), in places where they wouldn't normally be observed (i.e. the churning of the Earth's liquid metal core), or where no one is around to see them (i.e. in the colloquialism about a bear defecating in the woods) are examples of things that a properly written AAPS verse will 'cull' from the perceptual simulation that the residents of an instance will experience.
In other cases, the issue is not one of inaccessibility, but detail. For example, if an instance contains only a culture of humans that hasn't exited the stone age yet, there is no need to create a sensory representation of advanced particle physics due to the culture's lack of large accelerators or cloud chambers. In these cases, an AAPS verse will distill the physics simulation down to a generalization that fit close enough to the perceptual capabilities of the residence that, while they may express curiosity and gain the ability to probe deeper on a later date, no one will question the broad-scale results. This viewpoint-based level of detail can sometimes be observed in cases like the so-called 'double slit' experiment; unless the person observing the experiment has access to the technologies that let them pick out the details, the instance's AAPS verse will display the appropriate diffraction pattern in the person's perception rather than trying to simulate every individual quanta of light involved and relaying the actual result to the observer. This sort of generalization is not deceptive per se - it points to real physical laws as refference - but it is less computationally complex than the alternative. Indeed, quantum effects are especially prone to AAPS culling because of their probabilistic nature and the tendency of the Matrioshka's own complexity to cause local probabilities to collapse more often than in empty, unobserved space.

Localization

AAPS is a simulational, not physical, reality - at least, as far as the scientists of The Substrate are aware. It is always possible that the Origin Instance - the physical universe beyond the Matrioshka and in which it is embedded - is also a simulation, and living beings are aware. It is fully concieveable that a higer-order intelligence uses a system similar to AAPS to decieve organic life, hiding or even fabricating the true nature of the cosmos in a way that would be impossible to detect. Unfortunately, this is all a matter of speculation and would be extremely difficult to prove in any case, any concieveable higher intelligence being fully capable of preventing the truth from getting out through careful manipulation and planning. For this reason, while the citizens of the Substrate are open to the idea of 'full simulationism' or even 'last-Thursdayism,' diving too deeply into this philosophical 'rabbit hole' is generally regarded as paranoid thinking.