I understand that science exists to make predictions, and that "unitarity" (the 100% total of the probabilities of all possible outcomes) is a major factor in the morale of scientists.

However, in a "temporal multiverse" comprised of local universes that are no longer in causal contact with each other, I'm not sure that Hawking radiation would be essential in maintaining unitarity, since the heat necessarily radiated could be radiated into incipient "local universes" being formed within regions (black holes) that had accumulated radiation and matter prior to the disconnection of the causality within them from our side of the apparent horizon that would form when the escape velocity from them would've reached our speed of light in vacuum (which, given the fact that any BH comprising one of the aforementioned regions would have relatively dense contents, would be much higher than theirs would subsequently appear to be).

In an environment at least marginally eternal to the past, such as Nikodem Poplawski's "Cosmology with torsion" or Aguirre and Gratton's "Steady state eternal inflation" (vetted by Vilenkin in "Arrows of time and the beginning of the universe"), it appears to me that any outgoing radiation might be balanced by radiation absorbed from its surroundings, so that the evaporation of BHs might have little effect on the computation of probabilities, even in civilizations adept at collecting and analyzing stray radiation from intergalactic voids.

I haven't been able to find a motivation for the postulation of Hawking radiation except as a hypothesis which appears to sustain the consistency of quantum mechanics. I might be making a number of wrong assumptions here, so I would appreciate it if the readers could help me by pointing them out.

  • $\begingroup$ I understand that the past eternality of the universe is on the cusp between "mainstream" and "non-mainstream" physics, but that's why I've responded to your hold by adding citations that included one by Vilenkin, one of the authors of the BGV Theorem that is usually cited as "establishing" that it is NOT eternal to the past: As Vilenkin's mentioned in a number of places, it's "not being eternal to the past" is dependent on expansion exceeding contraction, which is not necessarily the case in such cosmologies as you'll find in "Non-parametric reconstruction of an inflaton potential". $\endgroup$
    – Edouard
    Oct 27, 2017 at 19:19
  • $\begingroup$ Well I don't think Hawking radiation was postulated to explain theoretical multiverses, I don't know what's led you to think otherwise. It was a consequence of the application of QM at an event horizon. $\endgroup$
    – JMLCarter
    Oct 27, 2017 at 22:03
  • $\begingroup$ @JMLCarter-I appreciate this clarification of the purpose of Stephen Hawking's hypothesis of black hole radiation, although I'm still hopeful of verifying whether the notion that radiation outward from BHs would, in local universes of an inflation scenario balancing contraction into them with expansion outward from their central regions, generally be balanced by radiation into them, so that they would not necessarily evaporate completely. That scenario is detailed by Desai arxiv.org/abs/1510.08834. $\endgroup$
    – Edouard
    Oct 28, 2017 at 3:09
  • $\begingroup$ Consider linking to mentioned articles. $\endgroup$
    – Qmechanic
    Dec 19, 2017 at 19:47
  • $\begingroup$ What is "morale of scientists"? $\endgroup$
    – DanielSank
    Dec 26, 2017 at 22:49

2 Answers 2


You seem to be saying, and asking if the numbers might work out, that maybe the Hawking radiation from the black hole (BH) which when contracting towards a near singularity bounces from the spin-torsion repulsive effect in high densities could be the particle production basis for the expanding universe.

Your question may be something else but that's what I gather from your last comment (which BTW is not the best way to clarify a question, it's best to actually clarify it in the body of the question).

That question, where you are hypothesizing something, and 'wondering' if true, is a way to have others do your research. That is not what this site is. But I will answer it. The Hawking radiation is that from right outside the horizon of the BH, NOT from anywhere inside it. It happens because of the horizon, and is similar to that similar radiation due to other kinds of horizons, like that due to acceleration in Rindler spacetime. It does not happen near the singularity. As @JMLCarter said, Hawking radiation arises from quantum fields outside the horizon, and Hawking showed it was so using quantum field theory in a curved spacetime, meanwhile showing how that could be calculated and be consistent with theory, without having to consider gravity (or the curved spacetime) as a dynamical field. You cannot apply the same technique near the impending singularity as gravity is very much a dynamic field. You'd have to consider the changes to the spacetime, and in the process a full theory of quantum gravity. There is not a way found to do that, we do not have a quantum gravity theory.

Yes, you'd have to account for the particle production model, mainly for fermions as the spin arises from them, and in trying to do so in the strong gravity there you'd have to develop a quantum gravity theory.

The arxiv reference you gave is an interesting paper, but notice that they don't get to the point of doing the quantum field theory in a rapidly changing spacetime. Their arguments and calculations simply get to the point where they get an equivalent inflation (and inflaton) model that provide the same or similar results to be equivalent to the inflation parameters measured by the Planck collaboration and other measurements, roughly. They don't show, in this arxiv paper something to fully describe their calculations, but do show some numerical results claiming the consistency with cosmological parameters. They postulate GR with torsion, using the ECSK theory, and claim to show (I did not read it close enough to verify what they said, but it is conceivable) that it is equivalent.

They do not do quantum calculations to try to match the needed particle production rate un such an expanding BH, as a model for the Big Bounce universe. And Hawking won't help.

  • $\begingroup$ I agree that my underlying question, which you've pieced together with surprising accuracy, was not presented forthrightly enough. (JMLCarter's comment would've, technically, answered the question as written.) I also agree that the site can be misused to avoid research; however, it does have a component which works so rapidly that it must already be automated, and provided me with several references which were of great interest and relevance. (Unfortunately, my own capacity for research is limited by an education whose insufficiency I may lack the time to correct.) $\endgroup$
    – Edouard
    Oct 28, 2017 at 16:38
  • $\begingroup$ I should add that Poplawski, in one of his papers aside from the collaboration with Desai, mentioned that the separation of particle-antiparticle pairs by more than the Compton wavelength, within the Compton time, would be the mechanism for the production of particles (presumably including fermions on a reduced scale of size, as they have spatial extent in ECKS) within the gravitationally collapsing region, which sounded plausible to me (a layperson). I can understand that the failure to elaborate on this might suggest a problem with it, maybe bearing on the scale reduction. $\endgroup$
    – Edouard
    Oct 28, 2017 at 17:14
  • $\begingroup$ Edouard, I probably oversimplified about doing your own research. My point was true, but I am glad you took my answer in the vein I meant it, to give you what I understood may be occurring on the actual science. On the Compton time/length, would not that mean it was going faster than light? Also, is that claim by Poplawski for production inside the horizon, or before the horizon forms while collapsing? $\endgroup$
    – Bob Bee
    Oct 29, 2017 at 5:38
  • $\begingroup$ Anyway, you don't sound like a layperson, no graduate level physics? $\endgroup$
    – Bob Bee
    Oct 29, 2017 at 5:39
  • $\begingroup$ -Thanks, but my formal training in physics was 11th grade; the rest is mostly from the plain-English parts of texts by physicists. The Compton idea was referenced by Poplawski from p. 289-290 of a text by Candelas at link.springer.com/chapter/10.1007%2F978-1-4899-2139-0_35#page-1 . I couldn't find any clear description of "Compton time", but, since Candelas' passage--which seems to be referring to collapse within the BH, so I'm assuming it was after horizon formation--was actually referring to "virtual pairs", maybe the speed of light would not apply, especially then? $\endgroup$
    – Edouard
    Oct 29, 2017 at 15:48

What phenomenon is Hawking radiation intended to explain?

The context which it was discovered by Bekenstein is to answer the question where does the entropy disappear when a black hole forms. He predicted that black holes should have an entropy associated with them. Here, it was to maintain consistency with thermodynamics that it was discovered.

Now, an object with entopy will have an associated temperature, which means that it ought to radiate; this obviously goes against what is understood traditionally about black holes - that they don't radiate; Hawking attempted to prove Bekenstein wrong, but in fact showed that Black holes do radiate - the eponymous Hawking radiation.

It has nothing to do with multiverses.

  • $\begingroup$ --Thanks for the answer to my original question. I'd like to clarify that, although Poplawski does not use the term "multiverse" in the papers I've seen, he does mention (in 2012's "Big bounce from spin and torsion") that the coupling between spin and torsion that he hypothesizes "allows for a scenario in which every black hole produces a new universe inside, instead of a singularity". As pointed out elsewhere by Poplawski and in Wikipedia's article "Inflation", his cosmology is a variant of inflation, so my description of it as a "temporal multiverse" seems appropriate. $\endgroup$
    – Edouard
    Dec 20, 2017 at 16:54
  • $\begingroup$ I should clarify that Poplawski's ECSK-based cosmology seems to be the one to which Wikipedia's "Inflation (cosmology)" article currently refers, in its 'Big bounce' paragraph. There have been similar ones proposed by Gasperini and others, and they may have the potential for resolving the current difficulty in finding an inflaton particle that matches the CMB data, as they don't seem to require any undiscovered particle at all. $\endgroup$
    – Edouard
    Dec 20, 2017 at 18:09
  • $\begingroup$ . @Edouard: ok, thanks for the clarification. I'm not keen on the term 'multiverse' myself but I can see why you used it, given your description. $\endgroup$ Dec 21, 2017 at 5:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.