We know that entropy is the measure of disorder , which is related to a system having constituent particles , and this entropy gives us the concept of 'the arrow of time' , i.e. time has only one direction . But for those constituent particles they are not made up of other things so does that mean that they don't have entropy and if that is true then does it mean that time's unidirectional nature doesn't apply to them ??
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Entropy is a bulk concept. So if your question is "does the concept of entropy apply to a closed system consisting of a single electron" then the answer is no. In a closed system containing a single electron and nothing else there is no arrow of time. The laws which determine the motion of the electron are time-reversible (even if we include quantum mechanics, there is nothing in the system to cause the electron's wave function to collapse) and there are no macro states.
Of course, once we consider a system that contains a large number of electrons then we can define entropy for the system as a whole (although not for each individual electron) and the arrow of time emerges.
answered Nov 28, 2019 at 10:33