OK, I think I have it now. Weinberg can be a little mystical but I like the argument.

I’d like to look at this as I like Weinberg’s book. Can you suggest a reference to define discuss and define the terms in your link?

Thanks for the suggestion. I was aware of the two currents. However, your boldface “not” made me question an assumption I was making and I am now OK with the derivation. Basically, I was thinking of everything in terms of the action but Noether’s theorem is derived on variations of the lagrangian density with necessary surface terms derived from the variations. Thanks!

Thanks for this info - very useful. I will try that.

I didn't downvote. Actually, I just upvoted to cancel it.

Regarding QM: Practically modification to the theory would produce macroscopic consequences so I, too, would rule these out. Similar with the standard model - it is difficult to imagine changes in, say ,QCD that would change only an obscure fission cross section. So the question is something of a "magic" what if. What if the laws of physics, in all their glory, did not allow fission of U235 (and its chain reaction properties). Would our lives (prior to 1938) have been changed in any way(aside from natural reactors)?

The question was indeed a science fiction question but one I hope would have a scientific answer. The plot above (thanks - informative) indicates many elements with various degrees of stability but, in the whole plot, only one isotope exists that is both amenable to fission chain reactions and is observed in nature in any appreciable abundance. I would guess that the latter property would be required for there to be any significant implications for the macroscopic world.

Sorry for the confusion - the question was about removing fission chain reactions only, either by reducing the neutrons or by eliminating fission itself. And I was wondering if there are processes other than bombs and reactors whose absence or modification would be important to the macroscopic world.