Hawking, Perry, Strominger On Soft Hair

Last June, Andy Strominger gave an interesting speak at Strings 2015 (and published papers) on memories, soft theorems, in addition to asymptotic symmetries. New pilus was identified along amongst infinitely many novel conservation laws related to the BMS supertranslations etc. Two months later, Stephen Hawking said that he had used these advances to solve the dark hole data paradox – which he had started four decades before – "again". Hawking has mentioned that Andy Strominger would live on i of his assistants inward getting the novel peachy thought out.

The top dog newspaper is at nowadays out:

Soft Hair on Black Holes

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(by Stephen Hawking, Malcolm Perry, Andrew Strominger)

They repeat roughly of the uncontroversial things from the Strominger-related papers alluded to above. But they add together something novel which seems controversial to me (at to the lowest degree thus far). The novel pilus is claimed to live on describable every bit zero-energy gravitons (for the BMS methods applied to the metric field) or zero-energy photons (when applied to the massless Maxwell field) at the upshot horizon. If I empathise well, these novel degrees of liberty are meant to equip the dark hole amongst its Hawking-Bekenstein entropy (or at to the lowest degree contribute a large utilization to it). And these degrees of liberty cannot live on excited because they occupy sub-Planckian distances.




I don't empathise whether they believe that all these claims are genuinely derived thus that all controversies are eliminated – inward the same sense inward which the BMS supertranslation symmetry may live on derived. But I don't empathise the derivations in addition to the whole flick seems flawed to me right now.




First of all, I remember that they genuinely reproduce the most naive sometime persuasion that the dark hole entropy is carried past times roughly actual but hard-to-see degrees of liberty strictly localized at the horizon.



This unproblematic Bekenstein's flick (I remember that novelist Gerard 't Hooft loves to exhibit it often) is rattling intriguing every bit a unproblematic "explanation" of the dark hole entropy-area proportionality. But it can't live on taken literally non entirely because computers' "binary digits" or "bits" are rattling unnatural units of information; but because there's null special nearly the locus of the horizon in addition to the locus may entirely live on pinpointed inward the future.

They don't seem to alter this basic sometime flick at all in addition to I receive got e'er thought in addition to I all the same remember that this sometime flick was defective. In particular, the place of the upshot horizon is entirely known "retroactively" when nosotros know the geometry of the whole spacetime including its development inward the future. So it's e'er problematic to assign a special role to the horizon. If at that topographic point exists a "purely bulk-based" description of the dark hole entropy, I am certainly that it must live on to a greater extent than ambiguous nearly the query "where" the \(S=A/4G\) degrees of liberty are stored, or they receive got to live on delocalized inward roughly manner (like inward the monodromies or Wilson lines going over large portions of the infinite etc.).

Second of all, I don't genuinely empathise the notion of the "zero-energy gravitons". Zero unloose energy agency that the dry reason is independent of fourth dimension in addition to the configuration should live on tardily changing. (As I clarify inward the comments, I should receive got written that the null unloose energy combined amongst the perfect localization at the horizon seem to violate the incertitude principle.) I only remember that nosotros know what low-energy including zero-energy excitations are in addition to there's no room for lots of novel degrees of liberty over there, specially non for degrees of liberty located inward a part that looks smoothen in addition to regular from the classical GR viewpoint – in addition to the vicinity of the upshot horizon does.

Third of all, when they enjoin that the novel degrees of liberty (soft hair) cannot live on excited, it seems to hateful that they can't live on probed in addition to distinguished, either (not fifty-fifty amongst complex experiments that accept a lot of time?). But isn't it equivalent to the disputation that the data gets lost? I am certainly that the data doesn't larn lost. In principle, i may depict the formation in addition to evaporation of a dark hole every bit a measure unitary S-matrix procedure – in addition to ignore the GR flick of a "black hole amongst a dissimilar spacetime topology" inward the intermediate dry reason altogether.

If y'all permit me roughly sociological speculations, I hit believe that most of the productive researchers who receive got studied the dark hole data puzzle inward recent years volition uncovering the newspaper rather orthogonal to the methods that receive got been considered promising in addition to the insights that they receive got decided to live on of import in addition to almost settled. In roughly sense, it does seem similar this is a newspaper that could receive got been written inward the pre-holographic epoch.

I remember that the attempts to written report the dark hole microstates in addition to data inward the pre-holographic epoch were pretty much hopeless because they to a greater extent than oft than non overstated the domain of validity of the local spacetime description.

After the Duality Revolution, I receive got concluded – in addition to a vast bulk of the practitioners inward that subfield of string theory concluded – that it's a settled fact that the data wasn't lost when a dark hole forms in addition to evaporates. Matrix theory in addition to AdS/CFT descriptions larn into obvious that unitarity holds inward every sort of evolution. However, what Matrix theory in addition to AdS/CFT don't brand obvious is "where" things are localized inward the volume spacetime. So nosotros got used to the fact that roughly fog nearly the localization query "where the dark hole degrees of liberty are at diverse moments" may live on necessary for quantum gravity to save its consistency, a delicate remainder betwixt the causal in addition to similar restrictions coming from full general relativity on i hand; in addition to the strict unitarity etc. that quantum theory requires on the other hand. The catch of the particle-physics-based quantum gravity researchers (which I consider the entirely right one) is that the full general relativistic concepts are exactly gauge in addition to must live on used rattling carefully because they ultimately pause down; spell the postulates of quantum mechanics rest exact.

Andy Strominger has e'er had roughly to a greater extent than general-relativity-centric views nearly these matters. He has oft told us things like:

The Hawking paradox hasn't been solved thus far. It remains a large mystery. If y'all disagree, exhibit me a error inward the master copy proof past times Hawking that has concluded that the data gets lost.

OK, specially because at that topographic point rest roughly uncertain aspects of the dark hole physics in addition to nosotros may utilization diverse seemingly inequivalent descriptions, at that topographic point are nuances in addition to possible details inward the ways how nosotros empathise diverse claims of this kind. But I believe that this claim is sufficiently unambiguous to create upwardly one's heed on whether it's right or wrong. And I receive got e'er thought it was wrong.

We do know nearly roughly wrong steps or assumptions inward Hawking's master copy derivation that seemed to imply that the data gets lost. That proof basically assumed that the strict locality – amongst honour to the classical dark hole geometry's causal construction – holds for all of physics including the fine degrees of liberty that equip the dark hole amongst its large entropy. I am confident that this supposition is wrong – in addition to I am certainly that at that topographic point is no valid proof that this supposition is correct.

So at the end, I receive got e'er had the feeling – in addition to the today's newspaper has strengthened this feeling of mine – that Andy thinks that the "satisfactory" finally answers to the Hawking puzzles must operate amongst roughly localizable degrees of liberty on the classical dark hole geometry in addition to null else. I am confident that this is an outdated, naive picture, in addition to Andy's inquiry computer program differs from the actual state-of-the-art physics (like dry reason dependence in addition to other things) past times beingness to a greater extent than naive, non past times beingness to a greater extent than satisfactory.

When nosotros desire to draw the data inward the dark hole processes, it is only non possible to assume that all the data is e'er localized at points in addition to it is non possible to assume that the causal construction of the classical dark hole spacetime is respected absolutely – after all, the Hawking radiations may every bit good live on thought of every bit roughly sort of a tunneling upshot that may violate the causal construction for a while. And the causal construction of a particular classical spacetime only cannot live on trusted fundamentally because the metric tensor is a prepare of dynamical degrees of liberty which agency that the causal construction e'er has a potential to fluctuate away from the initially assumed one.

I may misunderstand roughly logic inward the novel newspaper etc. but it does seem rather manifest to me that fifty-fifty though the newspaper (and its predecessors) industrial plant amongst roughly interesting in addition to truthful aspects of classical GR, Andy in addition to pals receive got missed (and almost directly, fifty-fifty if unknowingly, contradict) roughly of import discoveries in addition to lessons that the quantum mechanical inquiry into the dark hole data has uncovered inward recent years.