What does "that" refer to here?

What does "that" refer to here?

The second thing was that experimentally it’s not plausible to say that determinism breaks down only when you make a big black hole and let it collapse because according to quantum mechanics and the uncertainty principle, you would have little black holes popping in and out of the vacuum. And so you would have to violate determinism everywhere. And the experimental bounds on that are truly extraordinary. So experimentally there are very serious consequences if there are even teeny, tiny violations of determinism.

But three things happened that have changed that. The first is that you can’t just throw up your hands and say we can’t describe the universe. You need some kind of alternative—some sort of probabilistic laws or something. And Hawking and other people put out some formalism that enables you to have probabilistic laws, and so on, but it was rather quickly shown to be internally self-inconsistent.

Yes.

So [the black-hole information paradox] is experimentally a problem and it's theoretically a problem. Those are the first two things. The third thing was string theory. I would say up until the 1990s, the community was kind of split 50-50. But then Cumrun Vafa and I showed that certain string-theoretic black holes were capable of storing the requisite information, and they apparently also have some method of letting the information go in and out. And the fact that that worked—I mean, people had been trying for 25 years to reproduce this Bekenstein-Hawking area entropy law, or in other words, to derive the information content of a black hole from first principles. And nobody had been able to do it. And then we did it with complete accuracy. All the numbers, everything worked perfectly. And it had to be some kind of clue to something. It couldn’t just be an accident.

InfraBlue wrote:

Yes.

That is, Hawking has been in progress, continually correcting his own theories?

AS: Infrared structure means the behavior of things that vary at the longest wavelengths. I discovered in the last two years what I think are some hugely surprising facts about the long wavelength structure not just of quantum gravity but also of quantum electrodynamics. It was clear that [these facts] had profound implications for the black hole information puzzle. They implied that some of the things that had been assumed in the argument that black holes destroy information were demonstrably wrong. And that’s how this all got started.

SF: Stephen Hawking is an author on this paper, so I take it he agrees that his original argument was flawed in this way.
AS: Right. I think that’s why he got excited. People have made all kinds of crazy criticisms of his argument, and to the best of my impressions, he’s correctly objected to all of them. But this one, he heard it and he seemed to immediately agree that this was the key. In fact, as you’ve learned from what happened at Stockholm, he’s more certain than I am that this is the missing link in understanding black hole information.