It always surprises me when you make statements like this. What do *you* mean by 'known to be real' and what do *you* mean by theory? General relativity is a theory, is it not known to be real in your opinion? Is the Standard Model known to be real or 'just' a theory. I do not understand how you can make statements like this since I was under the impression that you had a degree in physics.

What do I mean by

*know to be real* and what remains theory...

Things we can observe and/or confirm experimentally are real. The theories we use to describe what we observe and predict what might be, are just that theories.

But this thread is about Hawking radiation and initially as it involves black holes. The theoretical solutions that give us black holes, ultimately also predict mathematical singularities... Which not many credible sources believe exist in reality... And what evidence we have that supports any of the predictions about gravity that leads up to a black hole, does not include evidence that any event horizon exists. So while I believe, we can be fairly safe in asserting that something that at least superficially acts like a black hole - exists, we can't see it, but we can tract the orbits of stars that obit it.., what form it takes in reality remains theoretical. And any speculation about how that unobserved thing, interacts with anything other than the stars we can observe orbiting it remains at best theoretical and tends toward speculation. Most of the time speculation based on a theory that says the black hole is a mathematical singularity..., that I don't believe exists.

The standard model is a theory, that again does a very good job of describing what we can observe of the fundamental nature of matter.

Most of these discussions don't stick with what does GR, or SR of even QM say about the things we can observe directly. They stray into the grey areas of hypotheticals and the what ifs associated with things like, how a black hole event horizon we cannot confirm is real, that surrounds a black hole that our best theory of gravity, tells us is a mathematical singularity, might interact with the virtual particles of a quantum vacuum, that we cannot detect... And it is all done with a certainty that they are real, even where none of these things have been demonstrated to be real. They are mostly all things predicted by otherwise successful theories.

Now are any of those things real? I don't know! Some I believe are likely to prove to be, but until they have been proven.., they remain theoretical.

And no I don't have a degree in physics. I studied physics and mathematics formally in the late 60's, but I was being pushed toward QM and what later became string theory.., and I just wasn't interested... I got bored easily back then, so I quit and took over a family business. In retrospect I wish I had spent more time looking into QM back when it would have been easy.

The Casimir effect certainly seems real enough to me! Casimir predicted the effect from virtual particles in 1948 and experimentation in the 1970's showed the effect was real. So what's the problem?

The Casimir effect does not require the virtual particles of the quantum vacuum to be explained. The EM spectrum of the vacuum is sufficient. Even then it's a theoretical explanation not a proof. I believe the dynamical Casimir effect is closer to proof, but there remains some doubt even there.

Theories and models describe things around us, things we can observe and figuratively reach out and touch.., and they often are use to make predictions about things far beyond what we can test and prove. The theories and models always remain theories and models, the things they describe that we can reach out and touch (again figuratively) are real, and those prediction that reach into the past, the future and the dark distances of space that we cannot yet explore remain theoretical projections, and sometimes out and out speculation.

I don't know if it means anything to anyone, but it is my belief that our imagination is one of.., if not our greatest asset, which makes speculating about what might be, a powerful tool in the quest to understand what lies just outside our reach.

There are a couple of posts from other threads. One by rpenner and the other James R that I think everyone should think about and keep in mind when in discussions like this, mostly because these are lay discussions and how we phrase things gets taken sometimes literally...

Physics isn't about the nature of reality -- Physics is about the behavior of phenomena in reality. Because that's all we can do is poke reality and see how it jumps -- that type of inquiry will never tell you what reality is, only how it behaves. We have very good mathematical models of how it will behave in all sorts of circumstances, but the map is not the territory.

P.S. Regarding "mechanisms":

Physical models are just that: mathematical models of how a system works. They aim to predict, quantitatively, what will happen in a particular experiment or if you make a particular observation. In so doing, physical theories often make use of undetectable entities and unmeasurable properties - that is, properties that are not directly observable but are observable only through their indirect effects.

The only way to determine whether one physical theory's unmeasurables is superior to another's is to compare the predictions of each theory against actual outcomes of measurements or observations. Having done that, we still don't know whether the unmeasurables of the superior theory are real or not. All we know is that one theory is better than the other at making useful, accurate predictions.

Complaining that a physical theory doesn't provide a satisfying "mechanism" is, in one sense, to misunderstand what a physical theory is for. It is also to misunderstand the limits of science. There is no magic crystal we can look into to tell us how nature really is, at the fundamental level. We only have our models of how it might be - and those are constantly being revised to improve their predictive power, as well as their parsimony.