Claim

If theism and functionalism are true, then there’s at least a 50% chance you are literally an idea in the mind of God.

Argument

If theism is true, then there is an omniscient god. If there is an omniscient god, then he knows everything that is going on in your brain, down to the finest detail. This is akin to running a complete simulation of your brain. But if functionalism is true, then a complete simulation of a brain has exactly the same experiences as the brain being simulated. So if theism and functionalism are true, there are two beings undergoing your exact experiences: one in the real world, and one in God’s mind. By the self-sampling assumption, it’s 50-50 which one you are.

Corollaries

Actually, the chance of you being an idea in the mind of God is probably much greater than 50% if theism and functionalism are true. That’s because of two corollaries to the argument in the previous section:

• Since God also has complete knowledge of every non-realized possibility, all the people in these non-realized possibilities exist in his mind (though not in the real world)
• Since God also has complete knowledge what has happened in the past and what will happen in the future, all people involved in these events exist in his mind even after they have died or before they will be born

Given these two points, there are significantly more instances of you in God’s mind than in the actual world, so it’s extremely likely that you are an idea in God’s mind. (Cf. the simulation argument.)

Assessment

Is the argument sound? As stated, probably not. The problem is with the move from God knowing everything that is going on in your brain to him simulating your brain. One way of representing knowledge of something is with a simulation, but that’s not the only way. Imagine a book that describes, for each time, the complete physical state of my brain at that time. If someone memorizes that book, then they know everything that is going on at my brain at every time, but there’s no simulation involved.

In response, a proponent of the argument could claim that although memorizing these things might count as knowing everything that happens to my brain, it wouldn’t count as understanding everything that happens to it. Understanding something arguably requires being able to explain and predict what happens to it. And to be able to explain and predict what happens to something, you arguably need to be able to represent it in a way that amounts to a simulation. If we add to this the claim that omniscience requires full understanding in addition to full knowledge, the argument from section 2 might be saved.

There are still questions here. For example, to count as understanding something in this sense, do you need to be constantly simulating it, or do you just need to be in a position to simulate it if you want to, say, answer a question about it? In general, it seems like you just need to in a position to simulate the thing. But if you are omniscient, and fully understand everything at all times in the deepest possible sense, it’s more plausible that you would need to be running these sorts of simulations constantly.