The

Hence Hawking said

It didn’t seem to be particularly contentious in 1976. When you look at

__information paradox__was first mooted by Stephen Hawking in 1976. See Brian Koberlein’s__black holes tell no tales or do they?__for a tidy introduction to the subject. Then see Hawking’s paper on the__breakdown of predictability in gravitational collapse__. You can find a copy__online__courtesy of Sci-Hub. Hawking said information is lost down a black hole and the quantum emission is completely random and uncorrelated, and that*“this means there is no S matrix for the process of black-hole formation and evaporation”.*The S-matrix is the__scattering matrix__which is to do with__unitarity__and reversibility and conservation laws. For example you can perform pair production to create a proton and an antiproton, and you can annihilate a proton and an antiproton. Either way you start or finish with zero net charge. However you could start with two identical black holes and throw a succession of protons into one, and a succession of antiprotons into the other. In both cases the Hawking radiation is said to be the same, and charge is not conserved.*Image courtesy of*__phys org__Hence Hawking said

*“there must be nonconservation of information in black-hole formation and evaporation just as there must be a nonconservation of baryon number”*. As to why this should be particularly contentious I’m not sure. In hot metal__typesetting__the used slugs were melted down for re-use. In proton-antiproton annihilation to gamma photons you lose all information about quarks and gluons. We surely wouldn’t expect much in the way of information in the very early universe, and we have baryon asymmetry which looks like proof of nonconservation of baryon number.

A slow startA slow start

It didn’t seem to be particularly contentious in 1976. When you look at

__Hawking’s publications__the earliest mention of information is 1996. In Matt Strassler’s information paradox__article__you can read about what Hawking showed in 1974-1975, and the next date mentioned is 1992. When you use Google scholar to look at__citations__for Hawking’s paper, there were none in__1976__. There’s__1,728__as I write, but there were only sixteen in__1977__, and it looks like the only paper that continues the theme was by__Hawking himself__. There were eight citations in__1978__, then six in__1979__, and none of them concern information loss. There were fourteen citations in__1980__when only one paper concerned information loss. That was__is black-hole evaporation predictable?__by Don Page. His__paper__is somewhat critical, saying black holes may be no more unpredictable than other phenomena. There were seven citations in__1981__including Hawking’s__interacting quantum fields around a black hole__, and eight in__1982__, including Hawking’s paper on__the unpredictability of quantum gravity__. The latter feels like clickbait for quantum physicists, particularly since Hawking talked of*“virtual black holes which appear and disappear again”*. The only paper that responds is again by Don Page:__is quantum gravity deterministic and/or time symmetric?__Again__it’s__somewhat critical. It ends up saying this:*“the most conservative possibility still remains open [2], that H0 and H2 are trivial and that full quantum gravity gives an S matrix which is both deterministic and time symmetric”.*I note that Hawking’s 1983 paper__thermodynamics of black holes in anti-de Sitter space__was co-authored with Don Page.

The black hole war beginsThe black hole war begins

__1983__looks fairly quiet, with only four citations plus four mentions in proceedings. However the__search for violations of quantum mechanics__by John Ellis, John Hagelin, Dimitiri Nanopoulos, and Mark Srednicki refers to Hawking’s 1982__paper__on t__he unpredictability of quantum gravity__with__649__citations, not to Hawking’s 1976 paper on the__breakdown of predictability in gravitational collapse__. 1983 was also when Leonard Susskind and Gerard ‘t Hooft got involved. Susskind is the author of the__black hole war__, a 480-page book published in 2008.__Woit__speaks well of it. See the__Washington Post__for an excerpt: “*Stephen claimed that ‘information is lost in black hole evaporation’ and, worse, he seemed to prove it. If that was true, Gerard and I realized, the foundations of our subject were destroyed”.*Susskind talks about Wile E Coyote running off a cliff, calls Hawking half a cosmologist, and goes on to say this: “*Stephen's lecture was the last that day. For about an hour afterward, Gerard stood glaring at the diagram on Werner's blackboard. Everyone else had left. I can still see the intense frown on Gerard's face and the amused smile on Stephen's. Almost nothing was said. It was an electric moment. On the blackboard was a Penrose diagram, a type of diagram representing a black hole. The horizon (the edge of the black hole) was drawn as a dashed line, and the singularity at the center of the black hole was an ominous-looking jagged line. Lines pointing inward through the horizon represented bits of information falling past the horizon into the singularity. There were no lines coming back out. According to Stephen, those bits were irretrievably lost. To make matters worse, Stephen had proved that black holes eventually evaporate and disappear, leaving no trace of what has fallen in”.*To make matters even worse, Susskind said Hawking*“postulated that the vacuum - empty space - was full of ‘virtual’ black holes that flashed into and out of existence so rapidly that we didn't notice them. The effect of these virtual black holes, he claimed, was to erase information, even if there was no ‘real’ black hole in the vicinity”.*Did you know that black holes were popping in and out of existence inside your head erasing information? Me neither...
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