We also don't need someone to interject (for instance) that Ohm's Law is not a fundamental law of physics into these discussions. Conductivity can be a function of many things. Take stress (as a tensor) for one and you could possibly find some microscopic directionality in some strangely doped...
Fundamental only in the sense that a noiseless input signal is thermodynamically impossible. The Brownian motion of the air surrounding the microphone diaphragm can not be eliminated (except possibly at 0 Kelvin or in a vacuum). Ample literature on signal detection and noise exists where the...
Olson and Johnson, The Ritz Bros, Colonel Stoopnagle and Bud, Fibber McGee and Molly, Don Ameche and Frances Longford (The Bickersons)).
Re: Olson and Johnson, we tried everywhere around 1970 to get a copy of this to screen but failed (small sample here).