In article <81omtn$f9e at web.nmti.com>, peter at abbnm.com (Peter da Silva) wrote:
>In article <383FAD5A.5DA023B4 at earthlink.net>,
>kenneth Collins <kpaulc at earthlink.net> wrote:
>> they are engineered with the a priori presumption of 'particles', so
they 'see
>> particles', when everything is continuous.
>>You know, Einstein's Nobel Prize was for explaining an experiment that saw
>particles when everyone assumed everything was continuous. If you can come
>up with a better explanation of the photoelectric effect, or with some kind
>of experiment that would differentiate your energy soup universe from the
>one everyone else works with, you might be able to get somewhere.
I'm happily ignoring most of the crap in this thread, but I'd like to
clarify this because this misunderstanding is one of the reasons people
get so bent out of shape about QM.
(1) There are no particles, only fields. There is an EM field, an electron
field etc.
(2) In a model of NON-INTERACTING fields, the "amount" of field (VERY
roughly, it's amplitude, more carefully its energy) can only change by
discrete amounts. This is in contrast to a classical field where the
amount of energy can change by any amount no matter how small.
(3) Because the relevant equations of the NON-INTERACTING fields model are
linear, one can model this change in the field as a simple count of
identical "fragments" of field---this field consists of 16 fragments of
type A and 4 fragments of type B. These fragments are what what
mathematical physicists call photons or electrons. Note that they a
mathematical construct based on a simplified theory.
(4) What really makes a field theory a quantum field theory (and gives you
the behavior above) is that the entity one cares about, the state, the
element of one's Hilbert space, is now a superposition of all the possible
classical field configurations weighted with some complex number.
(Appreciating this also makes it clear the link between QFT and
statistical mechanics where one likewise deals with configurations of all
possible classical fields weighted in some fashion, only this time by
Exp[-kT].)
(5) When one adds in interaction, life becomes a whole lot messier. One
can try to approximate what happens by constructing states that
approximate the real world by summing states from our idealized
non-interacting world. How satisfactory this is depends on what you're
after. For calculating QED effects it works pretty well. For QCD it seems
like a kinda lame starting point.
However in all of this, particles never appear. The interactions that are
claimed as particle interactions (eg photoelectric effect, compton effect)
are still field-field interactions (electron field interacting with EM
field) with all that entails with respect to being spread over space and
time.
Apart from the mathematical photons and electrons discussed above, there
are "experimental" photons and electrons that are supposedly the particles
one sees when one looks at a bubble chamber photograph, or a scintillation
screen. What you have to appreciate here is that one is not literally
seeing an electron in a cloud chamber photograph. What one is seeing is a
metastable state that is constructed so as to amplify the effects of any
quantum interactions. The interaction that occurs with an electron is
spread out over space-time in our usual field scheme, but something
happens to squelch the various superposed classical field states to
project out just one of them which happens to correspond to localized
fields. What is causing the localization is NOT that the entities involved
are particles, but that whatever it is that causes collapse of the wave
function (which as I have said before looks to be gravity) favors a
particular basis for Hilbert space which is based on localized fields.
Yes this stuff is hard and abstract. To understand it well, one needs to
start by learning a lot of somewhat recondite mathematics, and one then
has to wade through some pretty badly written QFT texts. None of that
changes the fact that in dumbing it down and presenting poorly understood
accounts of it, one loses pretty much all that is essential in the theory,
all that gives it coherence, and one lands up with merely a bunch of
mumbo-jumbo mystic incantations, "wave-particle duality, virtual
particles, uncertainty principle", much like say the atomic theory of
Democritus.
Maynard