> we'd first need to establish that biological systems are reducible to strictly physical systems.

Or even more fundamentally, that physics captures all physical phenomena, which it doesn't. The methods of physics intentionally ignore certain aspects of reality and focus on quantifiable and structural aspects while also drawing on layers of abstractions where it is easy to mistakenly attribute features of these abstractions to reality.

>also drawing on layers of abstractions where it is easy to mistakenly attribute features of these abstractions to reality.

Ok - I get that bit. I have always thought that physics is a description of the universe as observed and of course the description could be misleading in some way.

>the methods of physics intentionally ignore certain aspects of reality and focus on quantifiable and structural aspects

Can you share the aspects of reality that physics ignores? What parts of reality are unquantifiable and not structural?

Not all of physics is relevant to a brain simulation. For example, humans appear equally conscious in free fall or in an accelerating vehicle, so a simulation can probably safely ignore the effects of gravity without affecting the outcome. We also know that at body temperature (so about 310K) there is a lot of noise, so we can rule out subtle quantum effects. There is also noise from head movement, pressure changes due to blood flow, slight changes in the chemicals present (homeostasis is not perfect). We won't be simulating at the level of individual molecules or lower.

To me it seems highly likely that our knowledge of physics is more than sufficient for simulating the brain, what is lacking is knowledge of biology and the computational power.