(Information) Paradox Regained? A Brief Comment on Maudlin on Black Hole Information Loss

Abstract

We discuss some recent work by Tim Maudlin concerning Black Hole Information Loss. We argue, contra Maudlin, that there is a paradox, in the straightforward sense that there are propositions that appear true, but which are incompatible with one another. We discuss the significance of the paradox and Maudlin's response to it.The black hole information loss paradox (Hawking, 1976) is a widely discussed (putative) puzzle that arises when one attempts to make sense of physicists' expectation that global quantum dynamics will be unitary in light of the postulated phenomenon of black hole evaporation (Hawking, 1974(Hawking, , 1975 Unruh, 1976), which is apparently a consequence of Hawking radiation. 1 In a provocative recent manuscript, Tim Maudlin (2017) forcefully argues that "There is no 'information loss' paradox." The "solution" to the "paradox", he claims, requires no new physics and indeed, was already available, though not appreciated, in 1975. The appearance of paradox arises only because of persistent errors, both mathematical and conceptual in character, by prominent members of the physics community.There is much to admire in Maudlin's treatment of the subject. We agree, for instance, with his discussion of the (non-)role of "information" in the putative paradox. What is really at issue is predictability, or even better, retrodictability, and not information (at least in the sense of information theory): as we will describe in more detail below, the puzzle concerns whether any specification of data on a particular surface is sufficient to retrodict the physical process by which that data came about. We also think that Maudlin draws helpful attention to the core issues, which sometimes get obscured in physicists' discussions of solutions to the paradox. For instance, as Maudlin correctly observes, one can only expect unitary evolution between states defined on a special class of surfaces, known as Cauchy surfaces; any conceptually adequate discussion of black hole information loss will need to consider the conditions under which suitable Cauchy surfaces are available in the first place.Still, we do not agree with his central claim. As we will presently argue, we take it that there is a paradox, in the precise sense that there are well-motivated and widely accepted Email addresses: jmanchak@uci.edu (JB Manchak), weatherj@uci.edu (James Owen Weatherall) 1 See Unruh and Wald (2017) for a recent (opinionated) review of the issues and the literature over the last four decades.

A Role for the Fauxrizon in the Semiclassical Limit of a Fuzzball

“…In this section, I elaborate on the three assumptions about global spacetime structure in semiclassical gravity that jointly comprise the evaporation paradox, as presented by Manchak and Weatherall [2018]. But first, a caveat.…”

“…First, it sharpens our attention in quantum gravity research toward the ongoing status of naked singularities in the classical theory, now construed as a subject to be understood in terms of a semiclassical limit. As elaborated by Manchak and Weatherall [2018], building on themes familiar from Earman [1995], it is a mistake to think of the naked singularity as merely some 'missing point', at which the metric cannot be smoothly, locally extended. Indeed, the present discussion might suggest that we are learning about that naked singularity's ultimately stringy structure, so that what we ordinarily have cause to think of as a formal, quasi-local breakdown of the theory in the semiclassical limit is, in fact, a kind of fun-damental physical -namely, stringy -system in itself.…”

“…1 Introduction Manchak and Weatherall [2018] have argued that the familiar black hole 'evaporation' paradox in semiclassical gravity may be presented succinctly as three "well-motivated and widely accepted assertions", which jointly entail contradiction. (Why does this suffice for paradox?…”

“…The reference here is to the same article byMaudlin [2017] as is discussed at length byManchak and Weatherall [2018]. (Maudlin's construction within that article is discussed obliquely in footnote 5 above.)…”

Black Hole Philosophy

“…An early philosophical discussion of black holes was given by Weingard (1979) and some additional issues were discussed by Earman (1995), Romero (2013bRomero ( , 2014aRomero ( , 2014bRomero ( , 2016b, and Romero and Pérez (2014). Papers with various philosophical implications of black holes have been published recently by Curiel (2019), who deals with the many definitions of black holes, Maudlin (2017) and Manchak and Weatherall (2018), who discuss the firewall paradoxes, Lesourd (2019), who investigates the causal structure of evaporating black holes, and by John Dougherty and Craig Callender (2016), who discuss philosophical aspects of black hole thermodynamics. Also, some philosophical issues are to be found in the specialized scientific literature, which remains almost inaccessible to most philosophers.…”