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.