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


  • 3
    $\begingroup$ Keep in mind that the minimum of handwaving is to say "It is so" with no explanation. Things are the way they are because that's how things are. The more you explain the more you'll find yourself needing to handwave. $\endgroup$
    – sphennings
    Apr 25, 2022 at 19:16
  • $\begingroup$ I am aware of that, however since the setting is heavily driven by the difference I would need at least a rough understanding of the problems it would cause. When I read SF I very much dislike "space magic" but will accept "unknown physics" or "point of reference" explanations without issue. $\endgroup$
    – Gensys LTD
    Apr 26, 2022 at 19:38
  • $\begingroup$ Any sufficiently explained magic is indistinguishable from technology, any sufficiently unknown physics is indistinguishable from magic. Whether you call it "space magic" or "unknown physics" doesn't do anything to the explanation. "X is true because magic" is exactly as much of a handwave as "X is true because of unknown physics". Both are distinctly more of a handwave than just saying "X is true" $\endgroup$
    – sphennings
    Apr 26, 2022 at 20:02
  • $\begingroup$ I suppose some form of life we couldn't comprehend would be invoking anthropic (anthro!?) principal to explain the curiously perfect balance of nuclear forces that allowed for their evolution.... instead of us. $\endgroup$
    – Richard
    Apr 27, 2022 at 0:34

2 Answers 2


If tritium is stable in your universe, that means that the weak nuclear force would be WEAKER, because it is the weak force that causes beta decay. As a consequence:

  • Neutrons would need longer to decay resulting in a smaller amount of heavy nuclei, more precisely s-process and r-process produced nuclei which are those that are produced by neutron capture followed by beta decay. You would end up with a universe depleted in elements heavier than nickel.
  • P-process nuclei, that is nuclei produced by proton capture, should be, I guess, enriched compared to s-nuclei and r-nuclei, resulting in a higher number of proton-rich nuclei (which are rare in our universe even if stable) compared to neutron rich nuclei.
  • Generally many radioactive nuclei that are subject to beta decay or beta+ decay would be stable, so you would end up with an increase in stability range for both neutron rich and proton rich isotopes.
  • The proton-proton fusion, which requires that a proton turns into a neutron by weak interaction, would be less efficient. So you would get a universe depleted even in helium and as a consequence in ALL elements heavier than hydrogen, and also depleted in deuterium. Tritium would be stable, but rare. Stars would have to be hotter and denser in order to maintain fusion reactions at all.
  • The weak force is not involved in alpha decay, so nuclei subject to alpha decay should still be subject to alpha decay. Uranium-238 for example should still decay to thorium-234.
  • As far as I understand the weak force is not involved in nuclear fission, so fissibilty may be unaffected, too.
  • The precarious depletion of heavy elements in your universe could be counteracted by a slight increase of the strong nuclear force, which should make fusion processes easier. However that would not affect the lowered efficiency of the proton-proton fusion, so the He/H ratio would remain low, while the metal/He ratio would be high. Additionally, it would make nuclei subject to alpha decay more stable and would reduce fissibility. Maybe curium and californium would be used as nuclear fuel rather than uranium.
  • Instead of strenghthening the strong force, fusion would also be easier if instead you weaken the electromagnetic force, but that would wreak havoc on chemical processes.

That is all, of course, just a qualitative assessment. I do not know by how much the weak interaction would have to be weaker in order for tritium to be stable, so I cannot tell you how exactly your universe would be different, but the general picture should be as described.


Stars would produce different elements, carbon based life would be unlikely to evolve.

By increasing the stability of elements, stars would burn longer in their sequence. This would mean that there wouldn't be a natural fusion stopping point where a star could make a lot of carbon. It would make a lot of other stable things instead (depending on where the new break points are).

Less carbon means carbon based life does not have enough raw material to form and evolve into humans.

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    $\begingroup$ On the other hand, Earth is seriously depleted in carbon compared to other bodies in the solar system, still we have life. $\endgroup$
    – Avun Jahei
    Apr 25, 2022 at 22:09
  • 1
    $\begingroup$ We're not comparing to other bodies of the solar system here, we're talking about the difference between approximately 200 ppm in the aggregate to less than 1 ppm in this scenario, we are talking a drastic reduction, not just a little bit. $\endgroup$
    – Mathaddict
    Apr 26, 2022 at 15:50
  • $\begingroup$ Is all planetary matter then a product of stellar fusion? I was under the impression that it was more of a random process in the initial moments of the universe? $\endgroup$
    – Gensys LTD
    Apr 26, 2022 at 19:59
  • 1
    $\begingroup$ @GensysLTD Yes, you're correct before stars, it was pretty much all hydrogen. There are a few exceptions, but they are barely worth mentioning. $\endgroup$
    – Mathaddict
    Apr 26, 2022 at 22:04

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