How exactly would the 1:1 bit correspondence work in practice? What is the binding between simulated and external bit? Wouldn't we need to operate at the edge of Landauer's principle to really rule out this possibility?
If we discard these problems, wouldn't that imply that if such mapping were possible, that the simulation would also have to be strictly Anthropic i.e. the only running "software" are minds being fed data as "sensory" input?
It makes me realize, computers-in-the-simulation aren't really important in my argument. What really matters is that the people in the simulation discover some way of making observations about microscale events. It could just as well happen that, say, they make many observations of sterile petri dishes and eventually notice "soft errors" in the petri dishes (e.g. spontaneous infection occurring due to real cosmic ray hitting simulating computer). So the inhabitants move their petri dishes into a vault, etc., and check whether that was enough to protect the petri dishes.
I think computers are probably the best way to quickly get the idea across, but it could definitely generalize.
Suppose some people live in a Minecraft server, unaware there's anything else. Within the game, they build some computers (search for "working computer in Minecraft", it's been done many times).
They run their computers a long time and observe soft errors. The soft errors are caused by cosmic rays hitting the Minecraft server in the real world, but our heros don't know that. They attempt to protect their computers, moving them underground and setting guards to make sure no creepers get in, etc. But nothing they do stops the soft errors. Of course! What could they possibly do to stop soft errors caused by real cosmic rays hitting the Minecraft server?
Proving the simulation hypothesis true in Minecraft could give ideas on how to prove it in our universe.