[kazinator]

For sufficiently large N, all computation that isn't O(1) takes infinite time.

Complexity analysis goes out to infinity, but the way we use it as a tool is to inform us about what happens with our practical, finite inputs.

We know that something requires a non-polynomial number of steps, it quickly becomes untractable for small inputs. (So if we code that in a practical program, we need some justification that either the inputs won't occur, or we actively guard against them.)

Whether the entire universe is actually finite is not known, and not really relevant because that subset of it which is available to us as resources is vastly tiny.

The universe is vast, and vastly parallel: things are happening all over it at once, with more objects than have ever been crammed into any of our computing machines.