Thursday, January 30, 2014

If it quacks like a black hole

Unless you’ve been sitting in a white hole, you probably read somewhere that Stephen Hawking now claims black holes don’t exist. I was about to close my eyes and let this wave of media nonsense pass over me, but even my mother asks what that’s supposed to mean. So here is the brief explanation.

It is often said that a black hole is defined by the presence of an event horizon. The event horizon is the boundary of a region from which no information can escape, ever. The relevant word to pay attention to here is “ever”. The event horizon is a mathematically well-defined property of space-time, but it’s a mathematical construct entirely. You would have to wait literally till the end of time to find out whether an event horizon really is an event horizon in the sense of this definition.

Instead of the event horizon physicists thus often talk about the apparent horizon. The apparent horizon is, roughly, something that looks like an event horizon for a finite amount of time. Since all we can ever measure of anything can be done only in finite times it’s the apparent horizon that we ask for, look for, and observe.

For all practical purposes – and with that I mean actual observations of astrophysical black holes – the distinction between apparent horizons and event horizons is entirely irrelevant. Which is why you and probably many science journalists have never heard of this.

That actual event horizons might not be formed when matter collapses, but only apparent event horizons that eventually vanish, is not a new idea. It’s been discussed in the literature since 20 years or so. In my paper with Lee, we discussed the option of there being no event horizon but only an apparent horizon on very general grounds. See Fig 3, read caption, for further literature check references.

So what then did Hawking mean? The actual quote is:
    “The absence of event horizons mean that there are no black holes – in the sense of regimes from which light can’t escape to infinity.”

If you define a black hole as a space-time with an event horizon then that is a correct statement. But then you will still have objects, let me call them “apparent black holes”, that look almost exactly like black holes for times that exceed the lifetime of the universe by several orders of magnitude. You will not, by any observation that is presently possible, be able to tell whether eg the center of the Milky Way harbors a black hole with event horizon or an apparent black hole that looks like a black hole with event horizon.

What Hawking is saying is essentially that he believes that a matter collapse only leads to a temporary apparent horizon but not to an eternal event horizon. That is an opinion which is shared by many of his colleagues (including me) and there is nothing new about this idea whatsoever.

It is very unfortunate that this statement by Hawking has been misinterpreted in this way because there are in fact people who claim that black holes don’t exist. They argue that what we observe are actually just very dark massive objects that never collapse beyond their Schwarzschild radius, but they do have a material surface. This is a fringe opinion to say the least, because it requires substantial changes to Einstein’s theory of gravity, not to mention that it’s in conflict with observation. I am very sure this is not what Hawking was referring to.

Having said that, Hawking’s “paper” is really just a writeup of a talk he gave last year. It’s mostly a summary of his thoughts on the black hole firewall, none of which I found very exciting or remarkable. Had this paper been posted by anybody else, nobody would have paid attention to it.

In summary, nothing has changed in our understanding of black holes due to Hawking’s paper. Move on, there’s nothing to see here.

80 comments:

Arun said...

Just Hawking hawking his old wares...

kashyap vasavada said...

What is the range of time scale in which the apparent singularity may disappear? Also is ellimination of singularities by tranformations which are themselves singular, a believable procedure?

Uncle Al said...

Low mass primordial black holes are not observed decaying. Stellar event black holes are colder than the cosmic microwave background. They can only accrete. If we wait a few multiples of the visible universe's lifetime... Entangled particles are now connected by a wormhole, explaining their instantaneous communication. Entangled photons separating at lightspeed suggest the wormhole's spring constant and (force)(distance).

A 1963-proposed molecule had 10!/3 interconverting degenerate structures. Skeptics christened it "bullvalene." Synthesized in two steps with no chemicals added to starting material, bullvalene works to spec. Physics should be richer in the "valene" part.

Sabine Hossenfelder said...

kashyap,

Depends on the mass of the black hole. The larger the mass, the longer it will take. If the black hole is in vacuum that is. Actual astrophysical black holes aren't in vacuum. Not only do they pull in matter from other stars and interstellar gas, they also eat up the cosmic microwave background and will not start to lose mass until the CMB has cooled to a temperature lower than the black hole. That happens, well, several thousand billion years into the future, I might have forgotten some dozen orders of magnitude here. Best,

B.

Jumplive/Getty Images said...

http://www.psychologytoday.com/blog/two-takes-depression/201106/if-it-bleeds-it-leads-understanding-fear-based-media

"News is a money making industry. One that doesn't always make the goal to report the facts accurately. Gone are the days of tuning in to be informed straightforwardly about local and national issues. In truth, watching the news can be a psychologically risky pursuit, which could undermine your mental and physical health.

...

The success of fear-based news relies on presenting dramatic anecdotes in place of scientific evidence, promoting isolated events as trends, depicting categories of people as dangerous and replacing optimism with fatalistic thinking. News conglomerates who want to achieve this use media logic, by tweaking the rhythm, grammar, and presentation format of news stories to elicit the greatest impact."

L. Edgar Otto said...

This has been a very fast month for me and I must say I am feeling a little confused on all this lately. Bee and Lee with a paper on AdS/CFT is reassuring but in some sort of computer time is a million years ago or by thinking about this my QM like observing the great singularity of the past from the spacious Now shows up to myself a time not that long ago when outside this polar vortex, malestrom of predestined or accidental dialog I do see that time of a great silence stretched out in some dawn of my ignorance. An ape with a baton with ape normal dreams and no depth more than that full circle before a monolith so as to evolve now future looking in half truths forward into the future Odessy 2001. A way out of the spacious eye by swimming against some angle in the spin of space and time. To reach a quantized place now an old man looking back at successive versions of himself, an astronaught able to yell back before the message is garbled or lost that the one or many finite bounded monoliths is full of stars. Only to be born again as starbaby not sure what to do but sure he will think of something. In the hope or deliusion the last mini black hole does not evaporate or expansion crushes, isolates my galaxy of dreams and so on past my last atom.

Yes, Uncle Al, it is about valences too. But all is forgotten of such awakening of things inside. That I was hopelessly romantic drawn like the ape or chasing it like Hawking, either way the late sensate perfection bored again that we build, fetus long in REM sleep too busy to know of what we dream to the soundtrack of Wagner having survived chaos and imperfections. I am Pentose, the father, trying to find the key to DNA by assembling wooden puzzle pieces from the outside.

So if space can be exchanged for time what did Hawking mean saying time is imaginary and eternal while space begins and ends as finite?

johnduffieldblog said...

Bee: I noticed this:

"They argue that what we observe are actually just very dark massive objects that never collapse beyond their Schwarzschild radius, but they do have a material surface. This is a fringe opinion to say the least, because it requires substantial changes to Einstein’s theory of gravity, not to mention that it’s in conflict with observation".

This sounds like the frozen-star black hole interpretation which is totally in line with GR and observation. And your heading sounds as if you're subtlely suggesting that Hawking is a quack. Ooooh, Sabine!

Shantanu said...

Bee,
Isthe model you considered in your paper with Lee
without event horizon same as " naked singularity"?
There is a lot of recent literature by astrophysicists
on how one can distinguish between black holes and
naked singularities (which I think also don't have event horizon)

shantanu

Theophanes Raptis said...

In the famous "Third Policeman" novel by Flann O'Brien there's somewhere a mention that the effect of "night" should be understood as a dense cocentration of dark air masses. On the other hand, all this Blak-Hole-ology makes me think of an ancient ancestor..
http://www.brainyquote.com/quotes/authors/s/socrates.html

L. Edgar Otto said...

Theophantes, in the COBE map if this is the one universe of patterns like our classical one of named constellations we can name them. The cold regions as seas I call Aristotle, Socrates (a little human form) and Plato. Also the straits of Heraclitus and Parmendes.
But as Zephir points out in his Euclid's flat aether we do not need an expanding universe to explain the paradox that the sky is not a solid blaze of stars.
Sabine has not undermined Einstein or Planck and certainly did not imply Hawking a quack, those who superficially say so should read more carefully her work.

Sabine Hossenfelder said...

Shantanu,

I know these papers, but so far I'm not very convinced. It's interesting though. No, the point of my paper with Lee was to say if there is no singularity, there's no information loss problem. And nobody really believes there's a singularity, so there's really no problem. Best,

B.

Sabine Hossenfelder said...

John,

"Frozen stars" is how black holes were called before they were called black holes and it's not what I was referring to. I was, as I wrote, referring to objects with a material surface hovering just outside the Schwarzschild horizon. According to GR, these objects should be unstable and collapse. It requires a significant deviation from GR on scales that we know there's no deviation to make this option work and, as I wrote above, it's in conflict with observation. Before you go on to misread me, maybe follow the links I have provided. Best,

B.

Albert Zotkin said...

Hawking is right. Nature prevents the formation of black holes because of the existence of quantum tunnelling through strong gravitational barriers. The stronger and narrower is a gravitational barrier the easier is to surpass it by massive particle.

Regards

Zephir said...

/* what we observe are actually just very dark massive objects that never collapse beyond their Schwarzschild radius, but they do have a material surface. This is a fringe opinion to say the least, because it requires substantial changes to Einstein’s theory of gravity, not to mention that it’s in conflict with observation */

This is what I'm saying all the time and it's just the consequence of vacuum catastrophe, i.e. the immense disproportions between predictions of vacuum density for quantum mechanics and relativity theory. The black hole surface just averages it, so you shouldn't expect some "minor corrections" for relativity for to achieve it.

BTW Which observation actually conflicts with this stance? We are observing the occasional eruptions of black holes, which are otherwise free of any neighboring objects (even inside of our Milky Way). How is it possible, that the black holes inside of old galaxies are smaller than these inside of fresh ones?

Zephir said...

The Sabine's stance is just typical stance of theorist, who does understand the physics just from perspective of two mutually incompatible sets of equations (QM and GR).

These two sets usually don't collide with observations, when the density of matter remains significantly different from density of vacuum,so that the theorists did learn to ignore the real life phenomena at the surface of Earth. But the immense space-time curvature of black hole surface just blurs the boundary between the space and matter. But it cannot never blur it completely, because the existence of gravity field just depends on this boundary (in dense aether model the gravity results just from shielding of longitudinal waves of vacuum with particles of matter). The Einstein's equations (which just consider the collapse the matter into pint-point singularity and which don't care about actual origin of gravity) have really nothing to say about it.

Zephir said...

/* nothing has changed in our understanding of black holes due to Hawking’s paper ... it requires substantial changes to Einstein’s theory of gravity */

I'm not sure, if you're prepared to ignore Hawking paper with respect to it's alleged insignificance or just because it would require the substantial changes in your perception of reality. I could say, you're trying to apply the dual perspective of black hole complementarity here...;-)

Zephir said...

If you're feeling uneasy with this situation, I could refer you to another article of yours, where you're describing the situation, where "time stops existing and turns into space. Physicists say space-time becomes Euclidean". This is essentially the same situation, like at the surface of black hole - just observed from intrinsic perspective instead of extrinsic one..


scheme

The Euclidean space-time represents actually the classical surface of black hole, governed with laws of classical physics, where we are living in. It's not secret for me, that the galaxies around black holes do share many characteristics with fuzzballs or firewalls proposed with recent ideas.

Phillip Helbig said...

This is a fringe opinion to say the least

This is what I'm saying all the time


Right, no contradiction there.

L. Edgar Otto said...

Zephir, in the horizons of your fiery vision and taking Sabine as an example of what is wrong with theorists are you saying if Sabine does not exist then Einstein does not exist?
By her statement "no one believes in a singularity anymore " informally I think she means by singularity something at the deepest start of the big bang or not. Not some lesser frozen alternate idea if that in a quasar or black hole.
Sure linear thinking is a part of it as your Yin Yang duality avatar. But the content as waste or solid reduction if seen digested in a 4D Flatland such as yours is after all some sort of density blobs in pinching wave motion. My four way indefinite Yin Yang. So where is the information lost other than you are offended something exists as science beyond the fringe if your vision?
I think you need a little Feenament in your Firmament or some other brand like Exlac all chocolately and sugar coated. :-P~

johnduffieldblog said...

Sabine: I did follow your links. I saw Evidence for the Black Hole Event Horizon by Ramesh Narayan. I was expecting instead to see some contentious paper/s by people who claim that black holes don’t exist. Did I miss something?

Sabine Hossenfelder said...

John,

Well, just clicking on the link isn't enough... Even if you only read the title it should have told you as much as that there exists evidence for the existence of a black hole horizon, meaning object that are only almost black holes and have a hard surface are extremely disfavored by the data. If that was not your question, I don't know what you want. Btw, here is a newer paper. Try to read at least the introduction, it contains further references about the type of black hole substitute I am referring to. Best,

B.

Sabine Hossenfelder said...

Philip, You beat me to it... :p

Sabine Hossenfelder said...

Zephir,

The only thing I'm feeling "uneasy" with is that your nonsensical and uninformative comments clog my comment section and discourage people with more understanding of the physics from joining this discussion. So please stop it or I'll weed out your blather. Thanks,

B.

Jay Cross said...

One thing about Hawking Radiation that has always left me wondering is this: Suppose a virtual pair is created straddling the apparent event horizon: one falls in, and the other is not free. It is well inside the radius of smallest stable orbit. It would need to have been created with enormous energy, and a velocity almost perpendicular to the AEH. It's only hope of escape in any way would e to interact with an anti-particle of itself in the attosecond or so before it too falls back in, and then one of the photons from the annihilation would escape, but very highly red-shifted from say 511 keV down to radio wavelength.
So there is some assumption about the creation of the pairs I am not getting. Is there some quantum reason that the pairs should be created with such high energy? Perhaps enough energy for one member to shoot out past the radius of smallest stable orbit? This is a piece I never read about.

Jay Cross said...
This comment has been removed by the author.
Sabine Hossenfelder said...

Jay,

There is a reason I never use the analogy with the pairs created in the vicinity of the horizon. That's because it is extremely misleading. It is one of my favorite examples for how "simple" popular science explanation can cause more confusion than resolve it.

Roughly speaking the origin of the confusion is that the particles have a size (wavelength) about comparable to the diameter of the black hole and cannot be localized better than that. They are not created 'near' the horizon in any meaningful way. (Technically, it's the definition of a particle itself that becomes difficult in this region.)

Best,

B.

johnduffieldblog said...

Sabine: I didn't just click it. I read the abstract, skimmed the paper, then read the conclusion. But thanks for the gravastar link. I wondered if that what you were angling at. Maybe you linked to the wrong paper?

Re what you said to Jay, the Wikipedia/popscience explanation for Hawking radiation is such junk, isn't it? Question: is there an explanation that isn't?

Jay Cross said...

Thanks!

Echoing Johnduffieldblog's request: I assume that this business of the wavelength of the particles has something to do with the quantum mechanics in an environment of extreme gravity. Aside from that the only particles I'm aware of that might have wavelengths that long are hypothetical - axions and gravitons... both of which (IIRC) are bosons.

If you can please point me to some source that could explain this business of particle wavelength near the apparent event horizon, I'd be grateful.

jaybeegee said...

tl:dr

Einstein's theory is a mathematical theory depending on perfect (non-natural) assumptions of equivalence principle and relativity.

Black-holes obviously don't exist because they are ridiculous objects, along with time travelling worm-holes, Godel's relativistic model and other stupid things that come out of believing Einsteins theory is actually an exact description of Nature.

Classical GR is obviously a very good large scale approximation to how things behave but it is beyond idiotic to think it is a perfect description of Nature.

Very close to black-hole objects exist, and we have observational evidence for this - but the textbook Black-Hole with a singularity and event horizon is part of pure mathematics - not Nature

Marcus Anderson said...

If a spinning black hole was a shell - hollow inside - due to angular momentum, then the entire mass of it could be at the event horizon. This would tend to make the surface unstable with the possibility of the black hole itself forming the shape of a Taurus - or perhaps ultimately a very flat ring.

Shoxx Ib said...

Please do excuse my ignorance in this regard, but I am a bit confused, does matter falls into a black hole? If it does then would they become Hawking radiation or else? Thanks

Zephir said...

The energy density of Hawking radiation depends on the diameter/curvature of particle. When some tiny particle appears in strong gravity field near event horizon of black hole, it will completely evaporate first before it could reach it. The larger massive bodies could survive it partially and they will be swallowed with black hole. Usually more than one half of matter will be evaporated into accretion radiation.

L. Edgar Otto said...

From a linguistic view I have trouble with the parts if Hawking's
words reported and wonder what they mean separately or if anything taken together. What does the term infinity add to the unity of what so many now feel is almost there in our models? Someone should ask him. Even my own third model from a more structural sense falls short of deeper understanding of mass or gravity as an almost theory.

I understand why string theorists would think to explore structures as kinks and knots, or comprehensive theories of those based on combinations as if three blind men in Zen art crossing a bridge carefully yet in possible descent almost falling into some real or imagined valley, bottomless or not.

Leibniz and his monads, subjective or not, physical or apparent have yet have no windows. If in the best of possible worlds or landscapes wisdom or intelligence proves universal then in our suspicion this just reflects our unique selves, of what are we imagining about radically different intelligences potentially in a finite or infinite universe?

Matter and gravity seems in that gap or paradox between force or fall, between the everlasting or eternal as to the nature of a universe or a proton.

Science seems to have surpassed in current speculations, the reaching out beyond metatheory, beyond first philosophy. It still borders on our questions of the ultimate, as if the substance of theology.

If the vowels are the soul of a word we have now grown up to a diacritical universe. Somewhere between Greek philosophy and Judson - Christian Mysticism as creative tension in the West while even Plato has his counterpart in the East.

Light as signal carries the message that speed, but into infinity as if some confused light entangled, bright or empty at the end of a tunnel or in a confused unity of skipping stones therein, Where does the information or the meaning go?

Can a loop or circle superimposed so to count nodes but not crossovers meet or like Lacan's three rings no two but all three hold together although they never touch.

Sabine Hossenfelder said...

Jay Cross,

I recommend you read the standard textbook: Birrell & Davies, "Quantum Fields in Curved Space", in particular p. 264 and 269. Best,

B.

Sabine Hossenfelder said...

John,

The link is the correct link. It refers to evidence for the black hole horizon. I'm not sure I understand your question. Is there a 'non pop sci' explanation for Hawking radiation? How about Hawking's papers? I'm sure they're quoted in the Wikipedia article. Best,

B.

Sabine Hossenfelder said...

Jay, John: Btw, please don't let yourself get confused by Zephir's "explanations" of the Hawking effect. They're plain nonsense, but he isn't interested learning anything from me. Best,

B.

Sabine Hossenfelder said...

Shoxx,

Yes, matter falls into black holes. I'm not sure what you mean with "becoming Hawking radiation". In some philosophical sense one could probably say that. Best,

B.

Sabine Hossenfelder said...

Marcus,

It is well known how to describe spinning black holes and that's not what happens. The shell solutions are all unstable. You need higher than infinite pressure to realize them. Best,

B.

Jay Cross said...

Thanks! I've made an interlibrary loan request, and should have it soon.

Zephir said...
This comment has been removed by a blog administrator.
Jim Graber said...

Do I infer correctly that both you and Hawking believe "black holes" are really "bags of gold"?

Zephir said...

Bee, my posts just follow
this insight. There's no need to censor them... If you want to increase your popularity with public blog, you should be prepared to public consequences - all other ways are coward ones.

Sabine Hossenfelder said...

Zephir,

I do not want to increase my popularity. I want my readers to learn something about physics. It seems you have a really hard time understanding what I have been very patiently telling you for several years now: I do not like the way you are clogging my comment section with irrelevant nonsense, because it makes it very hard for other people to have a sensible exchange here.

I have repeated this often enough and you have finally reached the end of my patience. I now have a comment rule especially for you: You'll be allowed one comment per each post. Everything you post after that first comment I will delete. I hope that'll make you think before you write. Best,

B.

Sabine Hossenfelder said...

Jim,

I don't know what Hawking believes and I actually don't care very much. But yes, I favor the bag-of-gold scenario. Best,

B.

Zephir said...

/* .. because it makes it very hard for other people to have a sensible exchange here.. */

IMO this is just an evasion, as my posts can be minimized and ignored so easily... In the same way the USA government censors all interviews with Sheldon for not the have its citizens confused with his findings...;-) It just illustrates, that when the people feel threatened, their carefully built image of protective parent disappears immediately. It doesn't matter, if it's German physicist or NSA agent, after then...

Anyway, I'd be interested about opinion of another people here in this matter. Should I leave the Sabine blog and find my playground somewhere else?


If yes, I'll do it.

kashyap vasavada said...

Hi Bee: I understand you said similar things long before Hawking. As you said in your reply to me BH would take billions and billions of years to evaporate (by quantum tunneling). This is consistent with observations that we see matter falling in but not going out. If the emission was a slow process, we would have surely seen it by now. In your and Hawking’s theory is (apparent) event horizon a function of time i.e. does it disappears after a long time. How do you arrange that?

Jim Graber said...

Thanks Bee,
As I understand what Hawking is now saying (in the last ten years or so) is that he has shifted from regarding the Hawking radiation as being purely thermal, with very low information content, to regarding it as subtly coordinated, with a higher information content, thus saving unitarity and avoiding the information loss problem he earlier worried about. To me, this also implies that astrophysical “black holes” are really “bags of gold”. (A position I agree with.)

kashyap vasavada said...

Sorry in above comment, I meant "if emission was a fast process" !!!

johnduffieldblog said...

Sabine: I can find no explanation of Hawking radiation that makes any sense. Re your response to Jay:

"I recommend you read the standard textbook: Birrell & Davies, 'Quantum Fields in Curved Space', in particular p. 264 and 269. Best

A gravitational field is curved spacetime. Not curved space. See the last paragraph of this:

http://math.ucr.edu/home/baez/einstein/node2.html

Curved spacetime relates to inhomogeneous space, not curved space. I said a bit more about it here:

http://blog.physicsworld.com/2014/01/31/super-bowl-super-chilled-leeches-a-black-hole-cake-and-more/

...but my comment is awaiting moderation at the moment. PS: this is a lively blog. IMHO cut-and-thrust comments bring a blog to life.

Marcus Anderson said...

"I want my readers to learn something about physics."..

Thanks B! I really appreciate your feedback. Zephire can go elsewhere. I'll be happy to listen, learn, and be enlightened by you. :-)

L. Edgar Otto said...

Hehe, I think Zephir has a word typo correction error here, unless he really meant Sheldon (of the big bang sitcom) and not Snowden.

Sabine Hossenfelder said...

John,

The book is about curved space-time, the title is just a shorthand for the technically correct term. Which you would know if you had done as much as open the book... Best,

B.

Arun said...

Zephir asks: "Anyway, I'd be interested about opinion of another people here in this matter. Should I leave the Sabine blog and find my playground somewhere else?"

--- This is Bee's playground, not yours. Please abide by her rules.

johnduffieldblog said...

Noted, Sabine. But I have to say I am forever seeing physicists confusing curved spacetime with curved space. Ethan Siegel gives you a nice mention by the way.

t h ray said...

Another nice article, Bee.

I have to disagree a little bit on the significance of Hawking's second about-face (the first being several years ago when he reversed himself on the conservation of information).

I think it's quite important that singularities disappear in finite time. As you say, "You would have to wait literally till the end of time to find out whether an event horizon really is an event horizon in the sense of this definition."

Mathematically, Perelman's proof of Thurston's geometrization conjecture using Richard Hamilton's Ricci flow, plus surgery, shows the striking generality of thermal flow on an "invisible" manifold -- such that the flow on a topological 3-manifold, the surface of a 3-sphere, continues for infinite time on the half-open interval [0, oo). So with surgery -- which one may liken physically to choosing another orientation -- allows extinguishing of all singularities in finite time by reversing the flow (Hawking radiation?).

Joy Christian's quantum measurement framework is on the paralellized 3-sphere, which suggests to me that real physical spacetime is like this -- a topological structure of classically complete, information preserving, measure functions.

Tom

Phillip Helbig said...

"Joy Christian's quantum measurement framework is on the paralellized 3-sphere, which suggests to me that real physical spacetime is like this"

Two related questions: Does anyone other than Joy Christian claim this? Has any mainstream physicist said he agrees with Christian's conclusions?

t h ray said...

@ L. Edgar Otto:

"what did Hawking mean saying time is imaginary and eternal while space begins and ends as finite?"

Imaginary time has to do with the mathematics of the complex plane, which is 2-dimensional. When compactified on a sphere, with a simple pole (like the North pole of the Earth) the plane's points all meet in a finite point, so as Hawking put it, one cannot go "north of the North pole." The local observer's time interval at that extreme cannot be distiniguished from a space interval.

Tom

t h ray said...

Philip,if science were done by mainstream consensus, we would never get anywhere. Joy's research is still relatively new.

Phillip Helbig said...

This is the third blog comment I've written today involving a false dichotomy. Yes, science is not always done by mainstream consensus and radical proposals have often proved to be correct. However, more often than not they have proved to be incorrect. In any case, Joy Christian's ideas are right or wrong, regardless of what the consensus is. So, I asked whether anyone else (apart from Joy's followers, of course) shares his ideas about the 3-sphere and whether any mainstream scientist has claimed that his ideas are correct. Note that one, or even just a few, (otherwise) mainstream scientists do not automatically make his claims mainstream.

In other words, answer my question without saying anything about consensus etc.

Steve Bryson said...

Hi Sabine - What a fantastic article and discussion. I'm particularly happy to see your characterization of the "pair production near the event horizon" account of Hawking radiation as misleading.

Regarding an "explanation of Hawking radiation that makes any sense", here is my wanna-be-expert-but-not-expert understanding: the very (measured) existence of a particle depends on how you break spacetime up into space and time. If you have time pointing in one direction in spacetime while I have time pointing in a different direction, and the relationship between our time directions are not constant in space or time (the last is important for particle production) then you may not see particles (you see a vacuum) but I will. Near the event horizon the curvature of spacetime means that a vacuum there will appear to have particles to an observer far away. This is not just a coordinate effect: the particles have real existence, propagate, and carry energy away from the curvature near the event horizon, which ultimately comes from the black hole.

Even if this is correct, I don't know if it counts as "makes any sense" to people in general, but the basic insight is that quantum fields that define particles are wrapped up in spacetime, and a particle field in one region of spacetime curvature will describe different particles from the same quantum field (loosely speaking) in a different spacetime curvature. This is summarized as "spacetime curvature can creates particle". There are other examples (cosmological particle creation, particle creation for accelerated observers).

This is how I summarize the third or so of Birrell and Davies that I read long ago. Close?

Steve Bryson said...

Oops - can't edit comments, so take "spacetime curvature can creates particle" as lolcat grammar and the meaning should be clear.

L. Edgar Otto said...

t y ray,
You are right of course. But topology is much deeper than that. The complex plane and abstract coordinate space, even distance in jumps and values in an absolute sense (a motion within a slice of stillness) is a paradox of false dichotomy beyond ideas of consensus or the said Dickson of the foundations as math or physics.
All this seems to me as I adapt to better understand it is the deeper topic of this thread.
Joy Christian's later insights now seem to me to be right on target. There is no contradiction in presenting an answer that really awakens us to a wider question to which our human rationally intuitively responds to what we all may sense inside.
Unless, beyond the loxidrome implied by map makers that at a North pole pointing North is meaningless to ask as well with this world's spinning clock 'when does the day begin? Or like the Aegyptions think the soul ascends up to the North star of our era.
Where does the loxidrome go and as a singularity is it one or more poles?
"To the corkscrew the knife is crooked "noted Kirkagaard. And logically that pink unicorns do not exist that makes the old grey mare all the more real somehow (I forgot who said that).

Luca said...

Your comment on Stephen Hawking black hole is spotless, as usual. So good that it was translated on the italian blog of "Le Scienze" (more or less the italian version of Scientific American).

What I found quite funny was your presentation box (I try a rough translation from italian): "Sabine Hossenfelder teaches high-energu physics at Nordic Institute for Theoretical Physics (NORDITA), Stockholm. She got her degree at Johann Wolfgang Goethe Universit├Ąt, Franckfurt. She is interested in quantum gravity and string theories".

That's a news for me. Since when you started to work on string theories ? :-)

t h ray said...

Philip,

"I asked whether anyone else (apart from Joy's followers, of course) shares his ideas about the 3-sphere ..."

Does anyone apart from Bell's followers share his ideas about the necessity to introduce probabilism into functions that are essentially classically continuous?

" ... and whether any mainstream scientist has claimed that his ideas are correct."

In the way of analogy, if we take mainstream to mean only the relatively calm middle of a river or stream, the whorls and eddies that punctuate the flow would be excluded from the definition of a river. In fact, though, it is these randomly turbulent waters that determine the direction of the smooth flow of the aggregate of these water molecules.

I don't know firsthand, though I have heard Joy speak publicly of Lucien Hardy's verification of the mathematical model. Is Hardy mainstream? I think most would say so -- yet who endorses Hardy's "Five Reasonable Axioms of Quantum Theory" which finds classical probability differs from quantum by only one word ("continuous") -- 192 citations of what remains only an arXiv preprint? Was Perelman not a mainstream topologist even though his most famous paper was never published in a mainstream journal?

Thing is, "mainstream opinion" is no more a predictor of a successful theory than someone's idea of a "crackpot index" or a "quantum Randi challenge." Social games are nice diversions and sometimes fun, but independent of serious science.

"Note that one, or even just a few, (otherwise) mainstream scientists do not automatically make his claims mainstream."

Right. And neither does mainstream opinion automatically make them wrong.

Best,

Tom

Phillip Helbig said...

You're comment can be summed up as "mostly true, but irrelevant to my questions".

Certainly my impression is that few, if any, people outside of Joy Christian's own circle of followers think that he has found something significant. Certainly there are people who are outside the mainstream themselves who are not convinced, so his lack of reception is not due to the establishment ignoring him. Neither is it due to lack of exposure. Nor is it due to not knowing the "right" people.

No-one can read all new papers. We all rely on some sort of filter to point us to interesting stuff. (Yes, these filters can be wrong---which is one reason for my questions here---but that doesn't mean that everything the reject must be correct.) If Joy Christian has managed to convince one other person who is reasonably well known in the physics community, then more people would probably check out his work. As far as I know, he hasn't. Yes, if everyone waits on someone else no progress will be made, but as I say I know some people who have looked and found his claims wanting. (No, they are not hidebound mainstream physicists, but rather open-minded.) Certainly evading the question doesn't inspire confidence in his results.

t h ray said...

What qualifies as evading the question, Philip? If anyone agrees with Joy, he is "inside Joy's circle" and so not qualified to judge the validity of his work. If anyone outside the circle makes a negative judgment, and is reasonably well known in what you deem the physics community, then you accept that judgment. So your criterion for judgment rests on authority, no matter how you slice it.

I personally can't be said to be "inside Joy's circle." I'm not inside anyone's circle. I am however, well enough acquainted with topology and analysis to spot mistakes -- so if you say " ... I know some people who have looked and found his claims wanting" I have to ask -- who and where? Would you like to evade this question?

Phillip Helbig said...

That's a caricature of my question. Someone not previously associated with Joy would not be within his circle, even if he agrees. So, I'm wondering whether there is anyone other than people who post comments on blogs saying that Joy is right but otherwise are not well known in the physics community who think that he has found something profound. Note that whether he is right or wrong does not depend on authority, but yes, I admit that if people I otherwise respect (whether or not they are part of the establishment) say "hey, Joy has something interesting here" then I would think it worth my while to examine his claims in more detail. Such filters are used by everyone because no-one has the time to look at all claims in detail. There are even more profound claims, even here in comments on this blog. :-|

t h ray said...

Philip,

I personally have examined each and every one of Joy's claims and the mathematics that support them. I have read the criticisms and the refutations. I have found the criticisms wanting and the refutations sound.

If others have not done the same, they should not, as a matter of moral correctness and intellectual integrity, reject his research on the basis that a famous physicist, or someone they personally know, hasn't openly endorsed it.

And to be clear -- I did not come unskeptically to accept Joy's conclusions. I actually found offensive the word "disproof" which is mathematically unsupportable, and my first reaction to the words, "Bell made a serious error in his choice of topology," was: "So what? He wasn't doing topology!" These are on the public record comments.

When I held my nose and opened my mind, however, I found a beautifully constructed and logically closed quantum measurement framework that obviates the probabilistic framework of quantum theory and guarantees continuous measurement functions consistent with what we observe, without the assumptions of entanglement and nonlocality.

Sabine Hossenfelder said...

Luca,

Thanks for letting me know about the funny bio... I didn't write that and I didn't know about it till now. To begin with, Nordita is not a teaching institution. It is correct of course that I'm "interested" in string theory, but it's a passive interest and I don't normally list it among my research interests. Best,

B.

HoPpeR© said...

I'm a layman but have a better than average layman's understanding of black holes and science in general because I read as much as I can about anything and everything I can. When I read some science news article about "Hawking says black holes do not exist" I immediately went looking to see how this writer could have twisted something Hawking had said into this. I did not take long to find out but still this pisses me off. I am constantly having to filter through these so called science news articles to learn anything accurate and worthwhile anymore. I find myself not even bothering to read about science because the sources I use to skim for news have turned into trash. Where I used to have a fairly clear idea of what the cutting edge of many fields of science were at, things keep getting fuzzier to me. I do sometimes end up going to the source paper to find out, but in many cases cannot because of not having a paid membership or for lack of time. I hope the state of science news improves again. I hate being ignorant.

Nirmalya said...

There's something related that I'm confused about. Solutions to the paradox where GR is modified at low curvatures are criticized and it is said that at that scale one does not expect quantum modifications to play a role. I'm a little confused about the basis of this expectation.

Sabine Hossenfelder said...

HoPpeR©,

Sorry to hear, I feel your pain... Instead of news magazines or papers, you can try to collect news from some institutes or professional societies - every place that doesn't live from making money with their news. They are normally much more accurate, though also a little slower in their reporting. In Physics eg, Physics Today and Physics World one can typically rely on (also the German 'Physik Journal' but I am guessing you don't read German). It is hard for me to tell how readable they will be for you. Best,

B.

Sabine Hossenfelder said...

Nirmalya,

It's a dimensional argument. Quantum gravitational corrections should become important when the curvature comes into the regime R \sim m_p^2, where m_p is the Planck mass. You can see that just by looking at the coupling in the perturbative limit. Nothing should happen before that. Or let me put it this way: If you want something to happen at smaller curvature, you have to come up with a really good reason. Of course BH complementarity does exactly that... Best,

B.

Nirmalya said...

Thanks for the answer!

Jay Cross said...
This comment has been removed by the author.
Jay Cross said...

Birrell & Davies finally arrived. Thanks! You are probably aware that the last word on the top line of your suggested page 269 is "backreaction". Nice.

So now I'm left with another thing to wonder about. If the non-massless particles being emitted have a wavelength about equal to the diameter (radius?) of the black hole, then the particles being released by the most massive black holes must be things from an extension of the standard model, because nothing hypothesized so far has that little mass.

Sabine Hossenfelder said...

Jay,

Well, and then there's massless particles.

Jay Cross said...

Is there some massless particle other than photon that is a candidate here? Gravitons perhaps? Or could we set up a device looking for radio waves with a 4 trillion meter wavelength coming from Sgr A* ?

Sabine Hossenfelder said...

Jay,

Yes, photons and gravitons. I think it's mostly gravitons (more polarizations, larger phase-space). I believe supermassive black holes are presently colder than the CMB so they don't evaporate anyway. Best,

B.

Phillip Helbig said...

Congratulations on being the "interviewed expert" on this topic for Bild der Wissenschaft!