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The practice is paying off with a deeper understanding of reality's rules. In Mr. Tompkins's time, the difference between the mysterious quantum realm and the hard-edged world of everyday life was assumed to be simply a matter of size. Much beyond the magnitude of an atom, as quantum effects faded, objects took on definite positions in space and time. In recent years the situation has revealed itself as somewhat more subtle. Whether an object is dominated by quantum fuzziness has less to do with how big it is than with how well it can be shielded from outside disturbances — tiny vibrations, bombarding air molecules or even particles of light.

No, size isn't the issue!

Get your mind out of the gutter. I'm discussing quantum mechanics here.

A single system, if excited to a sufficiently high quantum number, will exhibit classical behavior. For an example, solve the standard harmonic oscillator for a quantum number of 200. If you've got a sufficiently large number of identical systems, then you'd get classical behaviour as well, if one took the average of some simultaneous measurement on all of them.