Earlier quoted context omitted.
> it's effectively impossible to prove a negative. Really? "There is no cat in this box". Opens box. No cat inside. Proved.
You're totally correct. I should also consider the fact that you can prove that negative voltages exist. The opportunities for pedantically ignoring the context of the discussion at hand are endless.
Well, proving a negative is certainly feasible:
>In some circumstances it can be safely assumed that if a certain event had occurred, evidence of it could be discovered by qualified investigators. In such circumstances it is perfectly reasonable to take the absence of proof of its occurrence as positive proof of its non-occurrence.
http://en.wikipedia.org/wiki/Evidence_of_absence
You might want to check the whole Wikipedia lemma on "Proving a negative" before retelling old wives tales: