Classical physicists had conceptual difficulty when something stopped behaving as "body" even macroscopically. For example when they tried to determine coefficient of friction of pure coper, throughly cleaned, in vacuum to prevent any oxidation, the surfaces cold-welded together. The copper did not get the memo that it is supposed to be two physical bodies.

Nice; a classic "Mir Titles" book!

Also checkout Tarasov's other books - https://mirtitles.org/?s=Tarasov Relevant here are his books on Probability and Lasers.

The Physics of the "very small" is essentially probabilities applied to Atomic, Molecular and Optical (AMO) domains where light and matter interact.