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Re: [Phys-l] Relativity Question about spring



At 15:51 +0800 5/17/07, <carmelo@pacific.net.sg> wrote:

It seems that the terminology "mass of neutron" must be so absolutely fixed according to some physicists or physics educators, that this could be a stumbling block to the Progress in Physics... Hopefully, Hugh, Jeffery and John D will agree..., one day.

I think this is carrying my comments well beyond their original intent and (I hope) meaning. I was talking about the issue of mass change under different local situations, not some global situations like changing over very long periods of time, or possible variations at levels well below what we are able to detect with present instrumentation. If compelling evidence of such effects shows up, then so be it. I don't think that changes the particular thing I was walking about, which is how to interpret the mass change of a system when it goes to or from bound and unbound states.

I agree that we can talk about how mass changes are distributed between bound and unbound states, but since we have no means at this point to actually measure such changes on an individual particle basis, I don't see too much point in talking about it, unless such talk could lead to insights about how to make such measurements. I don't see that happening either, but I obviously can't rule it out.

When neutrinos were first postulated they were presumed to be massless (although very small mass was not absolutely ruled out). It had a rather nice feel to it, and most of us thought that eventually we would be able to establish a zero rest mass for the neutrino. Later when neutrino oscillation was pretty firmly established and the resulting implication that neutrino rest mass was non-zero, we all accommodated to that result without great psychological stress, especially since it managed to solve the really vexing problem of where the missing solar neutrinos were, and also managed to account for at least some of the missing mass in the universe.

I don't expect us to find evidence in the future of an evolving proton mass, or that the proton mass has a variable component on the order of parts per billion, but that certainly cannot be ruled out as far as we now know (although, I really haven't thought about it and don't know what kind of consequences that information might have for current theories). But if we do, I'm sure we can all adjust to the new status, and I don't think it will change our thinking about how mass change is distributed within bound systems.

At least from the POV on introductory pedagogy, it seems to me wise to emphasize the *system* mass, rather than discussing mass changes of individual objects within a system as their degree of bonding to the system changes.

Hugh
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Hugh Haskell
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<mailto:hhaskell@mindspring.com>

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Hard work often pays off after time. But Laziness always pays off now.

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