Pax is a good sounding word to me, Amos, and I was even considering not to post this link as a comment to your remark whether I recall Twain's assertion.

But then I read this sentence from you: Applying physical measuring systems to humans is a disservice of magnitude.
That's exactly what I am doing since two and a half decades both as a job and from loving to do it. You have a right to have and to voice this opinion, of course, but maybe you can imagine how it feels when what you do as profession is called a disservice of magnitude by someone else. That's the reason you'll get a longer response instead of echoing 'pax'. The most charitable assumption I can have is that your understanding of 'psychology' is extremely restricted and that there are many areas of psychology you don't know about.

When I came from physics into psychology I started doing research in psychophysics, a subfield of visual perception. Psychophysics is studied since the 1860s when Weber and Fechner looked e.g. for the amount of additional light necessary for that an observer confidently says that one part of the visual field is brighter than the other. They found a beautifully simple law, namely that the amount of additional light was over a wide range of brightnesses directly proportional to the absolute level of light. Yes, and the humans are lumped together in this law for empiry shows that independent of your emotions, upbringing, culture or length of last night sleep this law holds with only the parameter changing from person to person and not the basic function.

Then I moved on to attention, measuring reaction times as dependent variable. On that field too, there are many human universals (independent of... see above) like for instance that (and how) the choice reaction time increases with the number of choice alternatives.

Then I did research on memory. Way back in the 1890s, Ebbinghaus has shown that under well specified conditions human forgetting follows the same law as radioactive decay. For all humans the basic form of that function (exponential) is identical, the differences are only in the parameter. Lumped together again, for empiry has shown that to be correct.

Mind you, I'm not claiming that by these experiments everything about humans is known or knowable, far from that. Many things about love, moral etc. which mean a lot to humans are not known. But I claim that the knowledge on humans gathered this way is sound knowledge and useful knowledge.

BTW, a paradox of observer influence plays nearly no role in these areas of psychology and if one thinks it does, there are easy experimental precautions against.

Knowledge about visual perception is used e.g. for the choice of gray levels in computers, knowledge from reaction time experiments is used e.g. for the (computer) mouse control, knowledge about memory is used e.g. for advices how to learn best. When you sit at your computer and post, you profit from human engineering, a field which takes part of its input from cognitive psychology. A disservice of magnitude to humans?

Wolfgang