🚀 go-pugleaf

I think everyone has been pretty much missing Kens point here (or maybe I am).

Consider the following. Prepare an excited particle in a state with finite  
uncertainty in momentum. Around the particle, put a sherical detector that 
measures exactly (it's a thought experiment, ok :-) the momenta of massive
particles and the position of photons. Allow the excited particle to return
to ground state. Now, my detector tells me the momentum of the recoiling
particle. It also tells me the position of the photon. If conservation of
momentum holds, from the momentum of the recoiling particle and the the
momentum of the excited particle, I know the momentum of the photon to within
some finite uncertainty dp. But since dx = 0 for the photon, I have 
dp dx = 0. So, it seems that I have to either abandon conservation of energy
or Heisenberg's uncertainty principles.

What this seems to indicate is that conservation of momentum is true only
when you measure it to be true, ie, if you have not measured the momentum of 
all components of a system before and after an event, you cannot say anything 
about conservation of energy. This is in accord with my general understanding
of observation and measurement in QM. Or is there more to it?
--
########################## _`|'_ ##############################################
##  Warren G. Anderson     |o o| "... for its truth does not matter, and is  ##
##  Dept. of Physics       ( ^ )  unimaginable." -J. Ashbery, The New Spirit ##
##  University of Alberta  /\-/\      (anderson@fermi.phys.ualberta.ca)      ##