as ever, Greg Egan is the master
Look at some of the narrative from the short story that was expanded into the novel Permutation City by Greg Egan. In fact, read that novel before continuing with these ideas— it will be food for thought.
In the first part (the original story) a character inside a simulation experiments with the effects of changing the granularity of computing the states, and even reversing them! He counts from 1 to 10 to mark off seconds, and the simulation calculated the resulting state of 10 seconds without playing through each one: after he “counts” can he tell that it didn’t really happen? What about computing and realizing the states out of order?
In another part of the novel, they create a universe that includes an access network to the various cells as well as the “inside” connectivity of the stuff in the space. And it has a variable speed and pause function designed in.
In a completely different Egan novel, he has a crystal artifact that is the state of a computer running intelligent beings. It doesn't have a way to change the bits: the compute engine (wherever it is now) created a new instance as it computes the next state. The “beings” in their universe are far in the future now and this frozen image of a past moment means what? Would it bother them if you destroyed it? Looking at a row of these files laid out down a highway, what is their “time” to you, driving up and down the highway at will?
If the universe (or a population who thinks they observe a universe) works in a straightforward way you think of computing the next state from the previous, who's to say how long each step takes (obligatory xkcd reference)? Slowing it or pausing would mean nothing if the eventual result computed was the same.
If there's not a central processor with separate memory, but something more like a cellular automata, maybe every cell is hooked up to a clock and a way to examime its state. Stopping it would mean coordinating the stop to all cells. You might contrive imperfections for the plot so it could be determined.
In our Universe, time and space is one thing and it doesn’t make sence to have an absolute time marching forward. However, on the “outside” a particular slice of spacetime is computed in some order. Once the project is complete the entire 4D state is complete and there is no time outside corresponding to any inside observer’s time. So what does “pause” even mean?
For the concept to mame sence it would have to be a simulation specifically made to host the people inside. The simulation-state time is a time axis very close to that of the planet and people inside. At any given time (on the outside) the computer’s memory holds a state representing all space and a small range of time in that reference frame.
pinning down a definite concept
Now suppose this is done on a cluster of compute units with memory local to a small region of space. Now that doesn’t really work due to entanglement but suppose it’s a simulation we might make in the medium future and meant to appear to be this universe on the inside, so observable nonlocal issues are hacked into the design.
Each processor runs without a real synchronized clock, but accesses data tagged with space-time in adjecent cells, so it doesn’t matter. If they can’t all be addressed with a single command either, but the commands flow across the compute fabric, then stopping becomes a problem.
If a cell doesn't care what time it is per se but computes based on what its neighbors contain, then cells may compute with neighbors that have already stopped and “see” the wrong information. If the command follows the normal connections used for causality, then it will be OK.
It’s restarting that will have problems. The newly restarted cell will have neighbors that are still “cold” for events flowing in the opposite direction. Let’s suppose that the restarted cell is in a state to ease back up, but it’s not perfect: it may linger too long or not enough, and lose information due to neighbors being out of date.
Where it might break worse is where features were hacked in. What if quantum computers (inside) malfunction because the entanglement is messed up when restarting? What about events being observed in the distant universe that is not being simulated to full fidelity but fed-in to the people in the main simulation? Watching a distant supernova in a telescope might glitch.
what this gives us:
As people (on the inside)
- develop more awareness of fine details of far-distant events,
- more detailed reliance on very small quantum effects,
- and technology that uses quantum-scale effects over intercontinental distances,
they might become aware of glitches and imperfections that show up after a pause is restarted.