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I'd like to request consideration to re-open this: What if black holes doen't evaporate by Hawking Radiation?

It was closed as being not about mainstream physics. Although I understand there is well-established rationale for Hawking radiation, to date there is no experimental evidence for it - direct or indirect. Physics, like other branches of science, ultimately require some form of experimental verification in order to move forward. This is a key principle of all science. Therefore it is in fact "mainstream" physics to question the existence of Hawking radiation, and what the implications / experimental observations would be in the absence of Hawking radiation. Please consider re-opening this question.

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    $\begingroup$ One of the types of questions one should avoid asking is you are asking an open-ended, hypothetical question: “What if ______ happened?”. Seems to me that linked question falls afoul of that policy. $\endgroup$
    – Kyle Kanos
    Commented Dec 26, 2023 at 16:52
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    $\begingroup$ The question is open-ended, speculative and no definite answer can be provided: bad format for the site. $\endgroup$ Commented Dec 26, 2023 at 17:59
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    $\begingroup$ It is very well established in physics to simulate the universe - with various versions of the laws of physics - and see how they compare to our observations and each other. This fits exactly into that well established pattern. $\endgroup$
    – dllahr
    Commented Dec 26, 2023 at 21:36
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    $\begingroup$ @dllahr This site doesn't abide by what one might consider standard research practices; it's a Q&A site with a set of rules defining topicality so that questions posed can get (ideally) a singular correct answer. In this case, asking open-ended "what if" is essentially asking for anything as an answer. $\endgroup$
    – Kyle Kanos
    Commented Dec 27, 2023 at 0:36
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    $\begingroup$ A quick search of the site for "fate of the universe" reveals 8 top hits that are essentially what-if questions. Not literally using the phrase, but the same meaning. For example: physics.stackexchange.com/questions/268385/… physics.stackexchange.com/questions/532050/… physics.stackexchange.com/questions/23308/… $\endgroup$
    – dllahr
    Commented Dec 27, 2023 at 1:35
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    $\begingroup$ Can someone explain why this question was downvoted? $\endgroup$
    – dllahr
    Commented Dec 27, 2023 at 1:35
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    $\begingroup$ Downvotes on Meta indicate disagreement with the post. It is not tied to main-site reputation, so you shouldn't worry about it. $\endgroup$
    – Kyle Kanos
    Commented Dec 27, 2023 at 2:55
  • $\begingroup$ A quick search of the site for "fate of the universe"... that's not the problem with the current question. The current question is framed as, "Suppose KNOWN THEORY is wrong, what happens?" which is not much different from asking what happens if Superman was real. The ones you linked ask very different questions from that (e.g., the second link asks how a particular $\Lambda$CDM model yields knowledge about the end of the universe). $\endgroup$
    – Kyle Kanos
    Commented Dec 27, 2023 at 12:49
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    $\begingroup$ Thanks, I'm not worried about reputation but I'm interested in understanding what the disagreement is with asking this question $\endgroup$
    – dllahr
    Commented Dec 28, 2023 at 0:08
  • $\begingroup$ What do you mean by "KNOWN THEORY"? It's not a theory with any supporting experimental evidence, so can you explain what that means? $\endgroup$
    – dllahr
    Commented Dec 28, 2023 at 0:09
  • $\begingroup$ @dllahr I meant "KNOWN THEORY" as a placeholder for anything you want. For instance, replace it with Newtonian Gravity or Quantum Mechanics or whatever. Asking "what happens" after removing some such theory is just nonsense. As to what's to disagree about your post, I should think it would be obvious: users don't think the question should be re-opened. $\endgroup$
    – Kyle Kanos
    Commented Dec 28, 2023 at 12:01
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    $\begingroup$ Thank you for the explanation. It is absolutely not correct that Hawking radiation is on remotely the same footing as any of those theories (Newtonian gravity, quantum mechanics etc.). Those theories have massive amounts of experimental evidence supporting them; there is currently no experimental evidence for Hawking radiation. As mentioned before, experimental evidence is critical in science. $\endgroup$
    – dllahr
    Commented Dec 28, 2023 at 15:52
  • $\begingroup$ @dllahr I don't think you & I agree what one means by "theory" (you seem to imply there must be physical evidence for it to be a "theory" whereas probably the rest of the world (probably) accepts mathematical evidence), but you're completely ignoring the point (seemingly intentionally, at this point). A question that asks "What happens if..." are considered off-topic, regardless of what you think about the rest of the question. $\endgroup$
    – Kyle Kanos
    Commented Dec 28, 2023 at 15:58
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    $\begingroup$ I'm carefully avoiding the semantics of theory vs hypothesis; independent of that we should be able to agree that the level of experimental evidence is vastly different between these theories. And we should all agree that experimental evidence is critically important. $\endgroup$
    – dllahr
    Commented Dec 28, 2023 at 16:23
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    $\begingroup$ As I said in a comment on the question, without a quantum gravity theory we do not have a solid theoretical foundation for Hawking radiation. Hawking's paper uses a plausible semi-classical derivation. So IMHO it's not non-mainstream to be sceptical of Hawking radiation. However, in its current state the question is too open-ended, and liable to attract opinion-based answers, so I don't believe that it's a good fit for this site. $\endgroup$
    – PM 2Ring
    Commented Dec 31, 2023 at 18:39

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My suggestion to the OP of the original question would be to re-frame the question along the lines of the following:

On what general theoretical grounds is Hawking radiation believed to exist? Alternatively, what principles would seem to conflict with the possibility that Hawking radiation doesn't exist?

That provides a fairly direct question about the reasons that mainstream physics typically assumes the existence of Hawking radiation even in the absence of direct measurement.

As a side note to the OP of this meta post, the weakness of gravity makes direct evidence for gravitational phenomena somewhat sparse, especially when it comes to black holes. Recall that the EHT's first image of a black hole was published only a few years ago, and Hawking radiation is a vastly weaker and more subtle signal to try to detect. As a result, if Hawking radiation exists, it should be wholly unsurprising that there is no direct evidence of it given our current capabilities. Just something to bear in mind.

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  • $\begingroup$ That suggested question would be, in my opinion, sufficiently distinct from the original question that it should be left to OP to make the change, rather than any user. $\endgroup$
    – Kyle Kanos
    Commented Dec 27, 2023 at 0:34
  • $\begingroup$ @KyleKanos Agreed - I mistakenly believed that the OP of this meta post was the asker of the original question. Edited to clarify. $\endgroup$
    – J. Murray
    Commented Dec 27, 2023 at 1:04
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    $\begingroup$ To be clear I understand the challenges in obtaining evidence for Hawking radiation. That said, one of the goals for of the Fermi Gamma-ray Space Telescope was to detect evaporating primordial black holes (PBH); it did not detect any. This constrained either the population of PBH or the existence of Hawking radiation. But it was a practical technique to detect Hawking radiation and it did not detect any. $\endgroup$
    – dllahr
    Commented Dec 27, 2023 at 1:44
  • $\begingroup$ "if Hawking radiation exists, it should be wholly unsurprising that there is no direct evidence of it given our current capabilities." I made the same defense of string theory (people say we cant currently test at that energy, therefore it should be ignored), and was question-banned just for saying it politely. I've become very disappointed in Stack Exchange. $\endgroup$ Commented Mar 13 at 19:26

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