Thanks, I suspected that idea needed more processing.

Non-conditional probabilities are not the sole determinants of conditional probabilities. You're conflating P(photon exists) with P(photon exists|simulated universe).

Your conclusion does not logically follow from your premise. You need to separate out your conditional probabilities.

I'm going to be honest and admit that I do not actually know how to write in a P(photon exists|simulated universe) style manner, and when I tried to find out how, I failed that as well because didn't know the name and it didn't appear under any of the names I guessed. Otherwise, I would try to rewrite my idea in that format and doublecheck the notation.

I'm also not sure the belief is particularly odd: why should you be at the center of the simulation? What makes your horizon more special than someone else's, or the union of all observer's horizons?

To unpack what I meant when I said the belief was odd/very unusual, It might have been more clear to say "This isn't necessarily wrong, but it doesn't seem to be an answer I would expect, and this thing I thought of just now appears to be my only justification for it, even though I haven't yet seen anything wrong.

And as for why I picked that particular horizon, I think I was thinking of it primarily as a "Eliezer said this was true. If that is the case, what would make it false? Well, if I was living in a simulated world and things were getting deleted when I could never interact with them again, then it would be false." but as you pointed out, I need to fix the thought anyway.