Lots of interesting questions pop up when you start to think about what is quantum mechanics telling us about the world, This has been discussed in many places and is written up and described in many textbooks. Particularly Modern Physics and Quantum Me chains texts. One of the first questions that comes to mind is at what scale to you have to make the transition from a classical description to a quantum description of what you are studying? Where do you switch from Newton's second law to Schrodinger"s equation? Where does the classical world make the transition to the quantum world? The answer given sometime is that when h--> 0, h being Planck's constant. This doesn't really answer the question since its not an equal sign. I guess one answer could be when does applying classical equations fail to describe experimental data? Or also where does looking at the problem classically not work?
This question and many more are still being asked today with no definitive answers.. What does quantum mechanics really mean? What is quantum mechanics trying to tell us about how the universe works or is described? The fact that quantum mechanics has worked in every instance it has been tested and its results are accurate to whichever decimal place it has been measured has led to the philosophy of "shut up and calculate".. Basically, don't worry about what it means just use it. But some physicists and philosophers of physics want to know what it really means. Peter Woit in his blog Not Even Wrong has as its newest post an inquiry about this topic. In this post are some links to papers discussing the measurement problem which is related to what happens when the experimental device which is a macroscopic object is used to make a measurement of a system described by quantum mechanics. It is a fascinating question and has led to a variety of interpretations of quantum mechanics. The post is interesting to read in itself but as in all good physics blogs the comment section is also wonderful and enlightening. The post also has a link to a conference going on at the present time at one of the IBM research labs outside New York City on the topic "Quantum Foundations of the Classical Universe". An interesting and debatable title itself. Sean Carroll is attending this meeting and blogs about it here. He is also Tweeting from this meeting and these can also be read on his blog or his Tweet. One of the Tweets is fascinating in that they can't agree on a universal definition of what is a quantum fluctuation. I've never understood the details of a quantum fluctuation or even its definition.. Wiki's definition is lacking in details. Lots going on in trying to understand what does quantum mechanics really mean and what is it trying to tell us about the Universe we all live in.
Another interesting question along the quantum menu is the following. If one thinks about quantum mechanics for a living does one develop an intuition for the quantum world? An interesting interview with a new Caltech faculty member who works on quantum information and condensed matter talks about this question. Great stuff, or as Confucius said "may you live in interesting times".