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Regular structures of matter may decay over extremely long periods of time (especially if proton decay occurs, which is not proven but it remains a possibility)

Even if that happens, are there any states or configurations of matter (https://en.wikipedia.org/wiki/State_of_matter) that would avoid decay and persist? Perhaps some kind of exotic condensate? Or maybe something more normal?

Or maybe could there be bound states made from other standard model particles that we know for sure that can exist (i.e. they are not speculative) that could form structures?

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  • $\begingroup$ On extremely long time scales, even black holes decay through Hawking radiation. I have never heard it mentioned, but wouldn't it also make other objects decay too? $\endgroup$
    – mmesser314
    Commented Jun 23 at 15:38
  • $\begingroup$ one angle to investigate is: as nuclear structure can stabilize neutrons against beta decay (or destabilize protons against it)....is there a nucleus bound enough that the GUT proton decay is blocked? (Ofc, then you'd have to worry but neutrons GUT decaying, too)....idk. $\endgroup$
    – JEB
    Commented Jun 23 at 18:38
  • $\begingroup$ Related (I assume): this answer and vengaq's comment on it. $\endgroup$
    – benrg
    Commented Jun 24 at 0:55
  • $\begingroup$ @JEB do you know about any such case? $\endgroup$
    – vengaq
    Commented Jun 25 at 9:55
  • $\begingroup$ @vengaq no, not following GUTs since $SU(5)$ flopped, but looking at $p\rightarrow \pi^0 e^+\nu_e$, that has enough energy to overcome any nuclear binding, so cancel the thought. $\endgroup$
    – JEB
    Commented Jun 25 at 15:04

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Baryon decay can be avoided if you build something out of stable non-baryonic matter. Given our currently known particles that leaves electrons/positrons, and neutrinos.

Stable electron clouds are tricky to do, since they need a gravitational potential that balances their electromagnetic repulsion. Since electromagnetism is much stronger than gravity, this is not doable with electrons. Coulomb repulsion dominates gravitational attraction for any pair of electrons.

However, neutrino stars have been suggested in atrophysics as possible compact objects (back when neutrinos were thought to be heavy) or explaining part of dark matter potentials (now when neutrinos are seen as light). Basically, being fermions cold neutrinos could form spherical condensates kept together by gravity that could be stable. They are not very likely to form according to current theory and observation but are certainly allowed by known physics.

The limit to neutrino star survival is likely set by quantum gravity decay: ocasionally small pieces tunnel into a black hole state that decays into photons that escape. Over very long timescales (I got a number around $10^{555}$ years, but my math is shaky) they would evaporate. Assuming this scenario actually happens.

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  • $\begingroup$ thank you! A couple of questions on this: 1. As far as I know there could also be "bags" or "clouds" of neutrinos around gravitational potentials (that perhaps are more likely than compact neutrino stars). As neutrinos would be weakly bounded, could these have high amounts of angular momentum? Or they would be static and unmoving so that neutrino particles don't get expelled? 2. Would neutrinos bounded in such rather diffuse structures also suffer tunneling? I mean, could single neutrinos turn into black holes in these "bag" or "cloud" like structures? @AndersSandberg $\endgroup$
    – vengaq
    Commented Jun 27 at 10:02
  • $\begingroup$ Neutrino halos likely have little angular momentum, just like other dark matter halo models. They could be static if they have the right profile, although if they have interactions they may gradually suffer dissolution or collapse. The tunneling effect likely applies to anything. $\endgroup$
    – Anders Sandberg
    Commented Jun 27 at 16:25
  • $\begingroup$ That is a mind boggling number. $\endgroup$
    – Joa
    Commented Jul 2 at 7:18
  • $\begingroup$ and although is likely that they have low angular momentum, is it at least physically possible that a rare neutrino halo may have a high angular momentum? Also, even if they have low angular momentum, if we have a large enough neutrino halo, could the total angular momentum be large (as we would have a lot of mass in form of neutrino particles)? Finally, if a single neutrino particle is converted into a black hole, it would evaporate almost immediately with a very high Hawking temperature, thus emitting massive particles. Would neutrinos be emitted again by the black hole? @AndersSandberg $\endgroup$
    – vengaq
    Commented Jul 5 at 10:27

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