I'm writing a short story where humanity lives in a section of the universe that's causing the nuclei to be unstable.
To explain what I mean, we here have hydrogen, deuterium and tritium where hydrogen and deuterium is stable and tritium is unstable and has a half-life of 12 years.
I would like the rest of the universe to have eg. tritium be stable and only hydrogen-4 be unstable with a 2000y half-life instead. Similarly have all the elements have more (in most cases many more) isotopes and be remarkably stable even in the very bottom of the periodic table (and possibly have one more row there too). While increasing stability of the known elements might just shift the "unstable section" of the periodic table further down, I'm unsure if the new, heavier fissible elements would even happen.
So are there any other effects this would have on the universe? I'm thinking big stuff like stars not happening, planets not able to have a molten cores or stuff like that.
I know I need to handwave the source of that effect but I'd like to handwave as little as possible