Exactly because "they can't run simulations instead of their experiments" you can't simulate an atom and thus a brain.

You can simulate atoms and you can simulate the brain. The outcome of CERN's experiments has nothing to do with brain emulation (other than the fact it's pushing hardware innovation forward).

The reason CERN has built a 27km, 14TeV, super-cooled, superconducting magnetic particle collider is because we know so much about fundamental Physics that it takes something really crazy, like the LHC, running billions of collisions, in order to find something which we might find surprising. So far, it's not surprised us; although it has confirmed the ideas Peter Higgs developed 50 years ago.

Of course, there is still debate and surprise to be had in other, non-fundamental areas; yet these are studying the consequences of the fundamental laws (they're debating the output of a simulation, not its code).

Is there anything physical we can simulate that does involve atoms?

Is that a trick question? The answer is: it depends on what you consider a satisfying result.

You can stop higher than atoms anytime you think the result satisfies your experimental measurements.

No, I am simply trying to understand your argument.

It seemed to me that your argument was "There are details of how an atom works that we currently don't know how to simulate. A brain's behaviour is a result of the behaviour of the atoms it consists of. Therefore, it's impossible to simulate a brain to any degree of accuracy at all."

Using the same logic, and given that most everything we interact with is made of atoms, one could deduce that it's impossible to simulate anything at all, except for electron beams, maybe. That seems to me to be obviously in contradiction to how well we can navigate and manipulate the world in our day-to-day lives (let alone in engineering), which depends on us simulating the world all the time, at least to some degree.

Now, I'd be interested in understanding how you reconcile that.

Yes, this is my argument. But understanding day to day things doesn't need atomic level details. For most things your measurement precision matches a model at a much higher level. You can stop at Newton's or Einstein's equations whenever that fit's your view of reality.

People use that to extrapolate in the other direction, and assume that because Newton's laws can be simulated, you can simulate an atom, thus everything. We don't have a view of reality at subatomic levels that says: "this is it and there's nothing beyond it". You don't know if your simulation of a brain will show an emergent intelligence if simulated with 'float', 'double' or 'infinite'.

OK, and could you now explain how you start from not knowing what it takes to emulate a brain and then deduce from that that it's impossible to emulate a brain? Your original argument was a supposed reason why emulation is in fact impossible, not why it might later turn out to be impossible, which is why I (and others) disagree - which you still haven't established, though, as far as I can see.