it takes place in a universe where consensus reality is true, and thus the scientific method fails as a way to understand the universe, since the laws of physics are determined by how many people believe in them.

I know nothing about the story/game you're talking about, but I think this is an important and common misconception, and fanfiction that addressed it directly might be worthwhile.

If it were an utterly chaotic universe, like what Brunner portrays in the Traveller in Black stories, then I might agree, but what you describe sounds instead like a universe with a regular and predictable relationship between people's beliefs and events in the world.

I'd love to see stories about a rigorous thinker in such a universe working out ways to exploit its ground rules.

That's a good point. In this version, the Avatar doesn't have to be a spiritual Chosen One - he/she could just be genetically lucky the way extremely high-IQ people are in our world.

Edit: However, I think that would defeat the point of fantasy rationalism, and might make the world too mundane. It would, however, be really interesting to see Aang go to the Spirit World and try to convince whatever spirits originally created the Avatar to make another one, possibly one with more raw intelligence to be more effective. (And then maybe deal with the fallout if this new Avatar is not as moral or noble as he is - FAI analogy, anyone?) The point of most of these rationalist fanfics is that one good rationalist can cause some Big Changes to their world, right? Multiple Avatars would be a Big Change.

A simulation consists of an inner part that is being simulated and an outer part that is doing the simulating. However perfect the inner part is, it is not the same as the historic event because the historic event did not have the outer part. There is also the issue that in some cases a thing's history is taken to be part of it identity. A perfect replica of the Mona Lisa created in a laboratory would not be the Mona Lisa, since part of the identity of The Mona Lisa is its having been painted by Leonardo.

Well, one can still think of it causally - you can still draw a graph with arrows, at least. But it's atypical causality.

Typical causality is like kicking a ball. The ball sits still until you kick it, and you can kick it however you like and it will roll away. But once you have loops, it's like if the ball had to go through a portal to the past and kick itself. As soon as you try to kick the ball, the ball you would have kicked has already gone back to the past and hit itself in a way consistent with the motion of your foot, so it will feel quite unlike kicking the first ball. And in fact it is physically impossible to move your foot in a way inconsistent with the ball being the cause of its own motion, even though trying to kick the ball restricts the possibilities - or rather, being able to try to kick the ball tells you that the possibilities were already restricted...

In typical causality, the ball has a reason for moving the way it does - you can trace the motion backwards to some acceptable starting point, like "I kicked it as hard as I could toward the fence." When you add cycles, tracing the chain of arrows back does not need to end at anything you find remotely satisfactory or even unique - "the ball moved because it hit itself because it moved because it hit itself..."

The great virtue of valid logic in argument, rather, is that logical argument exposes premises, so that anyone who disagrees with your conclusion has to (a) point out a premise they disagree with or (b) point out an invalid step in reasoning which is strongly liable to generate false statements from true statements.

Further to that, there is an advantage to the maker of an argument, in that they have to make explicit assumptions they may not have realised they were making. Speaking of imoplicit assumptions...

For example: Nick Bostrom put forth the Simulation Argument, which is that you must disagree with either statement (1) or (2) or else agree with statement (3):

(1) Earth-originating intelligent life will, in the future, acquire vastly greater computing resources.

(2) Some of these computing resources will be used to run many simulations of ancient Earth, aka "ancestor simulations".

(3) We are almost certainly living in a computer simulation.

(3) is not entailed by the conjunction of (1) and (2). You also need to assume something like "the kind of consciousness we have is computationally simulable". If that is false, no amount of computing power will make the argument work.

If there is a better way to see a merely real zebra than to have the photons strike a surface, their patterns be stored, and transmitted to my brain, which cross-relates it to every fact about zebras, their behavior, habitat, physiology, and personality on my internal map of a zebra, then I don't know it and can't experience it, since that's what happens when I am in fact actually there, as well as what happens when I look at a picture that someone who was actually there shares with me.

...from Venus, and only animals left on Earth, so one more planet than we had before.