What creates motion at microscopic level? I am an undergraduate mathematics student and start learning Quantum Mechanics by my own interest. I am read the following books:

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*The Theoretical Foundations of Quantum Mechanics by Belal E. Baaquie

*A Modern Approach to Quantum Mechanics John S. Townsend
After reading some of the chapters I got some question which I couldn't resolve my own. It will be a great help if someone help me to figure out those (This is the second thread, the first thread is here).

Question: What creates motion at microscopic level (instead of sending any external force/ perturbation like heat or light)?

I would appreciate if someone explained those with some intuition as I haven't a strong physics background.
 A: 
Question: What creates motion at microscopic level (instead of sending any external force/ perturbation like heat or light)?

What creates motion at the macroscopic level? According to the first law of motion by Newton:

Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

Keep in mind that "laws" in Physics are extra axioms imposed on mathematical solutions in order to connect with observations and the units of measurement.
At the microscopic level the same laws are assumed, otherwise there would not be continuity in the mathematical/theoretical models between macro and micro levels.
The difference with the micro level forces is that quantum mechanics has to be involved in the calculations, which means that per event/particle only a probability distribution can be predicted. according to the postulates (extra axioms like laws) of quantum mechanics.
In quantum field theory the force is represented as virtual particle exchanges between particles.
The mainstream theory of physics at present, posits that the lowest level is the probabilistic quantum mechanical level. From this level all the successful classical theories emerge mathematically. For me the easiest way to understand this comes with the density matrix format of quantum mechanics. see also my answer here.

I'm looking at my mechanical wind up clock tick second by second. What is happening at the lowest level (quantum level) to make that clock tick the next second?

Due to the enormous number of atoms and molecule involved, order of $10^{24}$ , the phases between all those wavefunctions are incoherent ( at the level of perception by our eyes ears and instruments), so the classical mechanics model of the clock is accurate within known errors.
A: In the quantum realm there is no "motion" in the same sense as in classical mechanics.
A wavefunction can never be in a position eigenstate, so its position will always have a non-zero dispersion. At best you can give a meaning to "motion" by looking how average position evolves over time (see Ehrenfest theorem).
Interactions in quantum theory are written as potentials which affect the wavefunction (see Schrödinger's equation) because the old vision of forces like simple vectors don't scale down well in this context.
Formalism aside, it isn't much different than the classical case: systems interact, they react in some way (by changing position and velocity in classical mechanics, by changing their wavefunction in quantum mechanics).
