Recent content by ncarron

Eugene, That sounds like an excellent suggestion. I have downloaded Wigner's and Dirac's papers, but I imagine the Lorentz and Poincare groups are discussed in many review articles and textbooks as well. - Neal

Eugene, My natural bent is rather more physical than mathematical. Hence the tone of my previous question(s). Your last reply in terms of the Poincare group does answer the question, but is more formal than I am familiar with. I will have to study both the Lorentz and Poincare groups. Thank...

I assume ##P = \gamma M V## , and ##H = \gamma M c^2##, where ##M## is the total rest-mass of the entire system, ##u## is the given velocity of relative motion of the reference frames, and ##\gamma = 1/\sqrt{1-(u/c)^2}##. The "rest-mass of the entire system" is the mass-energy of the entire...

The number of basic "physical quantities" is arbitrary, and depends on your overall choice of units. It is explained, in the context of Units Systems in Electromagnetism, at http://arxiv.org/abs/1506.01951 This entire article may contain more than you're looking for, but your question will...

Eugene, thanks for the reply. The momentum and energy conservation laws mean the total momentum ##P## and the total energy ##H## are constant in time. Therefore ##V==Pc^2/H## is a constant. So it seems the first two conservation laws already imply that the center of mass moves at a constant...

In physics, a symmetry of the physical system is always associated with some conserved quantity. That physical laws are invariant under the observer’s displacement in position leads to conservation of momentum. Invariance under rotation leads to conservation of angular momentum, and under...

pervect, thanks for your reply. The Baez site and your further explanation have been most helpful.

In the early days after the Big Bang, the universe was very dense and of relatively small radius. Those are the conditions for a mass to be a black hole. So the early universe should have been a black hole. When did it stop being a black hole, or is it still one?

The parity eigenstate arguments in this discussion all make sense if the nucleus is a composite object made of "elementary" nucleons. Then there's a spatial (and spin) wave function, and all the comments make sense. That is no doubt a very good approximation. Then as a general rule it looks...

OK, thanks. I believe the nuclear shell model does not apply to all nuclei. When it doesn't, I'm still a bit amazed that the nuclear state is an eigenstate of parity. I don't see any reason why it should be.

Since the question referred only to the nucleus I doubt atomic structure plays any role. If there is any atomic electron effect, only the inner K shell electrons should play a role, since their's is the only wave function that overlaps the nucleus. And since their wave function is isotropic...

QM says that states which are simultaneous eigenstates of two commuting observables are allowed. If you don't have such states to start with you can construct them with the Gramm-Schmidt orthogonalization procedure. Consider the excited states of a nucleus. (They can be considered eigenstates...