multir said:
from a quamtum perspective, is it correct to say that there is no up nor down, left or right, here or there, s'thing can be full&empty, can be dead&alive?
Been reading about Shroedinger's cat?
QM is a system for calculations; in classical mechanics you can describe a system in terms of forces (Newton's original approach), or energy (as in Lagrangian and Hamiltonian formulations). The latter are usually studied in upper level physics courses because an understanding of basic mechanics in terms of forces is required.
For example, you may want to solve for the motion of a system under particular conditions, while noting the stresses that occur instantaneously at all interconnections. This is useful in the design of mechanical systems, and today is much cheaper than building models and carrying out all of the corresponding test steps ... just run simulations until the design looks good; then build it and test it.
Switching gears ...
In QM you start by writing the Hamiltonian of the system of particles/atoms/experimental setup, just like you would in classical mechanics. Then the expressions for your variables are transformed from ordinary variables (e.g., position and momentum) into their corresponding quantum operators.
This results in a differential equation for which the solution are the "eigenvectors and eigenvalues" of the "quantum wave" in its state space. With these solutions you can work out the expected results of the proposed experiment or device which is being designed. If it looks good ... then you build the device/apparatus and conduct experiments to make certain that everything works the way your model does; if not, we expect that the model was incorrect ... or your experiment was carried out incorrectly/with bad equipment/or wrong equipment/or a million other things that can go wrong!
By refining the model, and improving the experimental technique, the model and experiment are brought into agreement.
Note that if I build a model in classical mechanics, but ask questions about atoms ... the model and the experiment will seldom agree. If I tinker with the classical model a bit, and add some ideas from quantum physics ... then we have the state of quantum physics prior to Heisenberg/Shroedinger/Dirac ... and sometimes it works, sometimes not so good, and sometimes completely wrong.
This process of problem/model/experiment results in continual improvement in our understanding of atoms, molecules, light, etc. With these results technology can be improved, and eventually new things can be manufactured and used by everyone - from computers (transistors, solid state manufacturing) to lasers (medical applications, laser pointers, metal fabrication ...), etc.
Nowhere in this process are any of your questions relevant. They are essentially philosophical, and are motivated by a desire to "understand" QM in terms of our classical intuitions. This is why there are "interpretations" of QM, starting with Bohr's "correspondence principle", which appears in the calculations when the usual variables (position, momentum) are converted to operators. So it is an aid to doing the work, perhaps, but it doesn't get you very far in terms of:
A. Building models that work
B. Calculating the results of those models
C. Experimental verification that the models actually work as expected
This is the "shut up and compute" school of QM. It has very little to do with what is written in the pop sci books; it is the difference between doing and talking. :-)
