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Apparently, the universe will reach heat death in the extremely far future, after the last black holes would have evaporated. Even more, it is possible that all objects in the universe will turn into black holed via quantum tunneling 1 2 3, so at the end nothing will remain in the universe except for residual thermal radiation in thermodynamic equilibrium

But, even if objects in extremely long timescales would quantum tunnel into black holes by quantum fluctuations, could there be also some quantum fluctuations that would make new particles to form (using the energy "leftovers" of the universe after heat death)? Or because energy (like electromagnetic radiation) will be redshifted, there will be a point where this would be impossible?

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  • $\begingroup$ Wikipedia $\endgroup$
    – Tobias Fünke
    Commented Aug 4, 2024 at 14:19
  • $\begingroup$ Actually according to one hypothesis, quantum vacuum fluctuations can induce the born of another universe, as per enormous energy fluctuation. It's a very rare event, but it's not totally forbidden by fluctuation laws. $\endgroup$
    – Agnius Vasiliauskas
    Commented Aug 4, 2024 at 18:25
  • $\begingroup$ @AgniusVasiliauskas but if the energy is redshifted how could this happen? From where would the fluctuation get the energy to do that? $\endgroup$
    – vengaq
    Commented Aug 5, 2024 at 10:37
  • $\begingroup$ @vengaq Time frame for heat death. Energy fluctuations are governed by uncertainty principle and/or quantum tunneling, so are the part of quantum mechanics and as such is not subject of classical energy conservation law. I.e. in some cases QM permits violation of classical energy conservation law as per $\Delta E\Delta t\gtrsim \hbar /2.$ Energy is "borrowed" directly from quantum vacuum or in other words "from nothing". $\endgroup$
    – Agnius Vasiliauskas
    Commented Aug 5, 2024 at 10:56
  • $\begingroup$ @AgniusVasiliauskas but as far as I know that "borrowed" energy must be immediately "returned" and in a shorter time as we go to more massive particles. So how could it bypass this? $\endgroup$
    – vengaq
    Commented Aug 5, 2024 at 10:58

1 Answer 1

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To make new particles out of radiation, that radiation has to be sufficiently energetic to account for the masses of the new particles. For example, 0.5 million electronvolt gamma rays can yield electron/antielectron pairs (and vice versa) but UV photons (~3 eV or so) cannot.

This means that once the background bath of leftover radiation (redshifted or not) in the heat death falls below the threshold required to produce the lightest possible particle, then there is no process available to do the trick and no new matter can be formed.

And that's why "heat death" is final.

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  • $\begingroup$ What about the Wien tail? $\endgroup$
    – ProfRob
    Commented Aug 13, 2024 at 8:03
  • $\begingroup$ @ProfRob, let me look that up first. -NN $\endgroup$
    – niels nielsen
    Commented Aug 13, 2024 at 16:01
  • $\begingroup$ @profrob, wien tail is an approximation to the full law which is valid for short wavelengths but fails at long wavelengths. the full law blends it with the rayleigh law to yield the correct blackbody spectrum. for progressively longer wavelengths (lower temperatures) the spectrum asymptotically approaches zero which makes the probability of pair production using photons picked from the spectrum approach zero too. Is my understanding of this correct? $\endgroup$
    – niels nielsen
    Commented Aug 13, 2024 at 16:15
  • $\begingroup$ Approaches zero, but not zero. $\endgroup$
    – ProfRob
    Commented Aug 13, 2024 at 17:12

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