Brain computer confusion

There is a never ending discussion, which very concisely can be summarized in this tweet below:

And frankly any time I see similar exchanges (and I see a lot of them) I get mildly irritated. Let me get to the essence. 

Computer analogy

Computers have been undoubtably the shaping invention of the recent century and hence they have became a strong theme in our culture. Since the theory on which computers have been built is a branch of mathematics, by definition an abstract discipline, computers have also had a major impact on philosophy. We learned for example that everything we can write an equation for can be in principle calculated on a computer. This leads to somewhat profound philosophical consequences summarized as follows:

  1. Stuff we can write equations for is in principle computable
  2. We can write equations for physical interactions of molecules
  3. Everything is made of molecules
  4. Hence everything is computable
  5. Hence in principle we could simulate an entire brain in a computer
  6. And since we can in principle simulate a Turing machine in a brain, hence brains and computers have to be equivalent
  7. Furthermore, in principle we could simulate entire Universe
  8. Hence universe must be a computer too 

When …