Re: Momentum problems

<snip>

You posted:
"Am I being thick, or does this mean that momentum and energy
conservation are mutually incompatible constraints in such a
scenario?"

If you can show that the equations that describe your system are
either invariant for translations in space or invariant for
translations in time, but not both, then you can answer "yes" to the
question you asked.

By the way, you can use principles of conservation as constraints when
dealing with a problem, if there is no reason for the principles to be
not fulfilled.

If you had mentioned that you considered potential energy and
explained why the energy balance does not work out, then I would not
have asked you if you ever read about it.

Anyway, I would have formulated the problem a bit differently:
Consider two Hydrogen atoms (quantum mechanics has an analytical
solution for the H atom), spatially separated so that the
wavefunctions do not overlap.
Assume that the electrons of both atoms are in the same excited state
(initial situation).
By coincidence, both atoms emit a photon at the same time, and photon
emitted by one atom moves toward the other atom (assuming that it is
possible to define a direction for the photons).
Now, what happens to the conservation of momentum and the conservation
of energy?

(Personally, I would expect both to be conserved, but then I did not
"do the math"...)

OC