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I've heard Kip Thorne repeatedly state that matter is destroyed when a black hole is created, that all you are left with is distorted spacetime.

"The idea that black holes are made from very compacted matter is wrong; it's simply wrong. It may have been created from very compacted matter, but the matter is gone. It has been completely destroyed. It no longer exists." https://www.youtube.com/watch?v=HSr95NgdAPg&t=8m34s

"When a black hole is born, the energy gets transformed from the energy of the matter to the energy of warped spacetime, so it's a transformation fo the form of the energy from the one to the other, but the energy is still conserved." https://www.youtube.com/watch?v=HSr95NgdAPg&t=9m43s

I understand this theory, as far as it goes: it's similar to how you need a starter coil on a tesla motor, but once the field is set up, it is self-perpetuating. I also understand how it could conserve rotational momentum, but there my understanding stops, and the confusion starts.

What about other conserved quantities, like electric charge and (maybe) baryon and fermion numbers? Wouldn't this understanding require some kind of theory unification, such that all matter is just a warp in spacetime, in which case it renders the observation tautological and uninteresting?

This confusion makes me think that I'm missing something about what he's saying. Alternatively, it could just be that, since what happens beyond the event horizon is unknowable in a scientific (as opposed to philosophical) sense, this is all scientifically unmoored and is in the realm of interpretation rather than reality.

Thanks!

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    $\begingroup$ Don't take things you hear in videos too literally, even if they are "science documentaries". Jerry Schirmer's answer here explains why (spherically symmetric) black holes can have charge. $\endgroup$ – ACuriousMind Aug 20 '15 at 14:30
  • $\begingroup$ Normally, I would agree with you, but Kip Thorne says this over and over, in both popular and scientific contexts, and I think in his "Interstellar" book. He feels strongly about it, he is precise in his language, and it is in his area of expertise. I don't see how the difficulty could be from his dumbing it down, given all of that. $\endgroup$ – Todd Lewis Aug 20 '15 at 19:58
  • $\begingroup$ Here, Thorne describes the pure spacetime character of black holes as their characteristic that he finds most compelling. It's not an incidental aspect of his understanding; it's a core attribute. youtube.com/watch?v=oj1AfkPQa6M&t=1m38s $\endgroup$ – Todd Lewis Aug 20 '15 at 20:10
  • $\begingroup$ Here again, he is very clear that he thinks that "all of the matter is destroyed, and all that is left is warped space, and warped time." youtube.com/watch?v=oj1AfkPQa6M&t=3m29s I know that other physicists have different understandings from Thorne's, but my question is, if you asked him where the electric charge went, what would he say? In other words, my question is internally exploratory of his theory, not externally critical of his theory. $\endgroup$ – Todd Lewis Aug 20 '15 at 20:14
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The mathematics of general relativity is clear and unambiguous. The trouble comes when you try and describe what is going on it non-mathematical terms, because there is no precise way to do it. Kip Thorne is attempting to talk about black holes in non-mathematical terms, and he is adopting a different perspective from (probably) most of us. That doesn't mean he's wrong, or that the rest of us are wrong, simply that unless you stick to the maths any statement you make is going to be imprecise.

Let's take the first statement:

Anything falling into a black hole reaches the singularity in a finite (and usually very short) time as measured by the falling object. The trouble is that what happens at the singularity is not described by general relativity. Indeed, the singularity is not part of the manifold that makes up the universe. So when the matter reaches the singularity you could argue it is not longer part of the universe. I suspect this is what Kip Thorne is getting at.

Note however that few of us actually believe a singularity forms. Most of us believe some form of quantum gravity will intervene and prevent a singularity forming. So Kip Thorne's statement is unlikely to apply to the real world.

Now the second statement:

Mass seems obvious to us. If something has a mass of 1kg then, well, it has a mass of 1kg. But in general relativity mass is surprisingly hard to define. It surprises most students to learn that the Schwarzschild solution that describes a black hole is actually a vacuum solution i.e. it is a solution that describes a spacetime with no matter. However we can assign a mass called the ADM mass to that spacetime geometry, and when we do this we get a mass parameter that matches what we think of as the mass of the black hole. This is what I suspect Kip Thorne means. The ADM mass is a property of the spacetime geometry and isn't the mass of an object as we usually think about it.

However, once again most of us would feel that Kip Thorne is been excessively purist. Most us us would consider the mass to be the parameter we use in the Schwarzschild metric i.e. the mass of the matter that originally formed the black hole.

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    $\begingroup$ So he is suggesting that an actual singularity is formed, and the matter is destroyed. Charge (etc) is something we would then have to figure out by more work. That I can understand; thanks! $\endgroup$ – Todd Lewis Aug 20 '15 at 21:23

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