The simulation argument by Nick Bostrom seems to take for granted that there are (or will be) many other human-level civilizations in our universe.
For example the first of the three options in the conclusion is “The fraction of human-level civilizations that reach a posthuman stage is very close to zero”.
But what if we are the only human-level civilization that exists or ever will exist in our universe? In that case we wouldn’t be able to work with fractions, we would either reach a posthuman stage or not, so there would be no “fraction” to work with.
I am not looking for unrelated reasons why the simulation argument is wrong, I am looking to understand if the simulation argument must assume there are (or will be) other human-level civilizations in our own universe to get off the ground.