The March 2013 issue of the American Journal of Physics has a very
interesting and perhaps important article by Art Hobson on the modern (last
few decades) perspective on quantum mechanics, namely quantum field theory.
Maybe this is familiar to Phys-L readers, but it wasn't to me. The basic
idea he reviews is that everything is fields; "there are no particles" (to
put it provocatively). Here is what seems to me a key paragraph in the
conclusion:
Thus Schrodinger's Psi(x,t) is a spatially extended field representing the
probability amplitude for an electron (i.e., the electron-positron field)
to interact at x rather than an amplitude for finding, upon measurement, a
particle. In fact, the field Psi(x,t) is the so-called "particle." Fields
are all there is.
A key notion is that "wave-particle duality" is not a useful framework, and
that it has been superceded by quantum field theory in which everything is
fields.
There is a popular science book on the subject by Rodney Brooks, who was a
student of Schwinger and who argues that Schwinger, and the quantum field
theory developed initially by him, has not gotten the attention it deserves
from the physics community at large. At amazon.com search for "Fields of
Color: The theory that escaped Einstein". I'll mention that the Kindle
edition is very badly "printed" but usable (and only $5). It's not very
well written, but it is thought-provoking.
One comment he makes that is specifically relevant to this Phys-L
discussion is that while he sees quantum field theory as dealing
effectively with a very broad range of issues, many of which have been
problematic in the old quantum mechanics, one of the "gaps" or shortcomings
is that it too does not explain is the unpredictable "collapse of the
field".
To give an example of where this leads, consider two-slit interference of
electrons sent one at a time toward the apparatus. In the old quantum
mechanics, even Feynman (or especially Feynman) talked of the unresolvable
conflict or paradox or mystery of the wave and particle descriptions. As I
understand it from Hobson and Brooks, the electron particle never does go
through the slits. Rather there is only an electron matter field extending
throughout all space, with an amplitude at all locations, and a calculable
probability of the collapse of the field at a particular position on the
screen with an interaction we have been calling "an electron". The entire
field throughout all space collapses in an instant because it cannot yield
a fraction of an electron due to the quantization of the field.
Doubtless in my ignorance I'm not saying this quite right -- it's quite new
to me. But I did check with a powerful theorist colleague who verified that
the views expressed by Hobson are indeed standard in the theoretical
community, and that "wave-particle duality" is now considered to be a
mistake. He did say however that he wouldn't use the phrase "there are no
particles", and he commented that all quantum field theory textbooks spend
a lot of careful time on the meaning of the word "particle".