# Hawking radiation and Information conservation

HAWKING RADIATION |
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## Hawking radiation and Information conservation |

The idea that black holes radiated was initially quite disturbing to the GR community, and an early popular interpretation was that if the information radiated came form the hole itself, then the physics of black holes would appear to be saying that GR was wrong, or at least, that physics somehow conspired to make it look exactly * as if* GR1960 was wrong, which was just as bad. It would be awkward to be in the position of insisting that a theory was correct even though the predicted physical phenomena appeared to agree with the idea of theory

*not*being correct.

Since HR information could not be coming form the hole, a popular suggestion was that we knew that the radiation had to be totally random in order to protect GR. This provoked some soul-searching in the QM community, since although QM emissions certainly looked random to the untrained eye, there was a deeper principle at work under QM that in fact, there was still an underlying causality. Even if the information was so scrambled that we had little or no chance of "reading" it, it was not truly random.

If we lost **microcausality**, then since quantum outcomes could dictate outcomes at arbitrarily-large sales (a point that Heisenberg originally used his "cat" thought-experiment to demonstrate), the large-scale history of our universe would no longer be considered fully causal. aspects such as the shape of our galaxy, seeded by chance parameters in the early noisy universe, would not just be "random" in the loose, everyday sense of the word, but actually *physically* random, with no physical origin. Physical data would be appearing in our universe "from nowhere" and disappearing "to nowhere". Losign microcausality was like pulling on a loose thread of a knitted jumper and watching the arms fall off. If we lost the pricniple of causality at small scales, we lost it *everywhere*.

After experimenting with a revised quantum mechanics that discarded the idea of causality, the QM community eventually decided that enough was enough, and that this had been one of the worst ideas in the entire history of physics.

If a black hole interior was losing information, and the region outside the horizon was receiving emitted information, and the quantities of information were required to be identical, and the timings of the two sets of events were also linked, then then there was already a linkage between the two – there was already a limit on the degree of randomness that was allowed. Emitted signals and the disappearing internal information were already intimately correlated regarding timing and quantity, meaning that the two set of events could not be *independently* random, and if we had information disappearing from region"A" and other information appearing in region "B", both with correlated timings and magnitudes, the simplest interpretation was simply that this was the same information, moving from A to B.

{{Notes|One of the differences between conventional causal statistical randomness and this new form of suggested fundamental randomness was that ultimate randomness there were really no rules, and no statistical models. It marked a dead end for science and mathematics – we could no longer predict even the patterns of randomness, because there would be no underlying physical or statistical model that the data would be obliged to conform to. Physics in such a universe would be, quite literally insane and irrational, and if we lived in such a universe, there was no obvious reason to be a mathematical physicist.

## Notes

To fully lose causality in Hawking radiation would mean that every black hole in the universe might suddenly, simultaneously start emitting pink elephants or bottlenose dolphins, and we wouldn't be able to object, because, hey, it's random, right?