Well, there's a lot I don't understand about them. And the more videos I watch and the more I learn about them, the less I understand...

I thought the original problem was that Hawking proved black holes evaporate and therefore everything trapped inside one disappears. However, Leonard Susskind and others argued that this violates a fundamental law of physics in that information cannot ever be totally lost. I believe this is now settled and Hawking admitted he was wrong. So...

- What does happen to information that was inside a black hole?

- Exactly how does a black hole evaporate? Water on earth evaporates, but we know what happens to it. The molecules become part of the atmosphere, so information is not lost.

- I thought black holes are born from large stars collapsing and the resulting small mass is so dense and the gravity so strong that nothing can escape it including light. But my understanding of gravity is that it is a warping of space time. If so, does the space that the black hole occupied get untwisted and return to the way it was?

I guess all my questions for now come down to how a black hole evaporates. Just about everything I know about black holes comes from watching Youtube videos. But I can't find one that explains this. The closest I've come is one that hypothesized two different realities. One as if you're inside the event horizon and a completely different reality if you're on the outside looking in. Although, I think this also had something to do with the universe as a hologram (another fascinating topic to me).

I'm not sure if this is an appropriate question to ask here. If someone can provide a link where I might learn more I'd really appreciate it. Thanks.

Read the usual links like

http://en.wikipedia.org/wiki/Hawking_radiation

and eventually most work done by Don Page and others after Hawking (to see exactly the physics of the semi classical understanding of the emission process).

Essentially assuming all of the physics of the Hawking effect and the core theory of black holes (as compact objects/solutions of GR) is correct (not so safe but lets wait a few years) what the hole does is radiate very very slowly photons of super tiny energy (huge wavelength, essentially the black body radiation spectrum an object of such super tiny temperature would have) for like (for say astrophysical type black holes) 10^66 years type of time if you can imagine how big that is and then near the end as the majority of the mass of the hole has been radiated (Temperature rises as this happens inversely to the mass, just study the equations in that link) in that fashion of low energy photons, it starts emitting eventually also higher energy particles, ie neutrinos, then electrons, positrons etc and near the end big ones like hadrons and almost everything seen in particle physics.

So what you end up having eventually is a bunch of low energy (thermal) photons and then some small fraction (in terms of initial mass) of other particles.

Obviously the process has now violated baryon number conservation etc as the main product is photons but the hole was built mostly by fermions etc. But the idea is that the way it has been emitted it retained the information that went into forming it in a theoretically recoverable manner (through the correlations and the back reaction of the metric etc as the hole emits and gets smaller etc (very semi classical idea however and string theory is total bs exaggeration as presented in reality in any hope to realistically describe all this mess properly, only in some highly symbolic academic nirvana until proven better sense in my opinion). Also the hole radiates away its charge and angular momentum eventually as part of all that emission (charge towards the later stages, just study the work by Page and others).


In reality in our universe due to microwave background radiation 2.7k >>> than the bh temperature for solar mass and higher size bhs currently, no big astrophysical black hole is actually emitting anything right now in a net sense, they are in fact only absorbing even those "little" poor energy 2.7k cosmic photons, growing and they will continue to do that until they (CMBR) drop down to so small levels of temperature (as the universe expands) that the hole takes over (good luck with that lol) and starts finally radiating, reducing its mass for the next 10^(whatever over 66) years lol.

I actually never heard of Page. Again, I watch a lot of Youtube so I'm only familiar with Susskind, Krauss, Weinberg, etc. But I'll try to look up Page.

The topic is way over my head, but what I can understand from what you wrote is very interesting. Thanks!

This video from 0:00 to 4:21 explains the evaporation pretty good. After that they are starting to talk about other things on black holes, please ignore it.






And then about that information is not lost on the most basic level even if things get crushed when falling into a black hole: www.dummies.com/how-to/content/string-theory-and-the-black-hole-information-parad.html

Thanks. That was an interesting video. What perplexes me, is that I can't understand how they can possibly know half of these things. How do they know that particles pop in and out of existence in empty space? How do they know that the negative pair goes into the black hole, while the positive one does not? And I thought that NOTHING can escape once it's past the event horizon.

I'm sure that much of what they know comes from math and since I can never hope to understand the math, I'm doomed to always being frustrated. But I really appreciate your effort and links to explain it me. Thanks!

It has been changed to almost nothing: hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q10.html

do black holes actually have a size? (I dont mean the event horizon, I mean the actual collapsed matter). I mean is all the mass inside actually compacted into a point of infinite density, or is there actually a chunk of matter in there that varies based on the mass of the blackhole? So there is actually something say the size of a basketball in there somewhere

I've heard it's infinitely small, even if that sounds weird, with the physics broken down. The mass and spin are left though.

It comes down to how seriously one takes GR and the singularity. Classically, all the mass of a backhole is at the singularity, which has 0 volume. But the string theory picture removes the singularity and describes black holes as basically a ball of strings with non zero size and non infinite density.

http://en.wikipedia.org/wiki/Fuzzball_(string_theory)

It's been my understanding that a virtual particles form all of the time in empty space which is a boiling brew of them. Regularly enough a virtual particle will form EXACTLY at the event horizon so that only half of the virtual particle is inside the EH and the other is not. I'm supposing that somehow the negative mass half is in the proper position to fall in but the positive mass shoots off since it's not w/i the EH. Eventually, and I'm guessing only for Black Holes that are not feeding, the tiny negative mass will dissipate the BH.

As to how the scientists know all this stuff? They have maths and brains that are not like most of ours.

This is basically correct, but just to add.....classically there is a theorem for black holes that says that a black hole can be described just by its charge, mass and angular momentum alone (no hair theorem) . So if you had 2 black holes identical in those regards, no observer outside the event horizon could in principle tell them apart. So all the detailed information about what kind of star the black hole used to be or whether a spaceship fell in later can never be known by an outside observer. This by itself wasn't a big deal in the 60s(?) or whenever this was understood. People just thought that information wasnt destroyed but that somebody outside the black hole could never recover it. Hawking then showed that black holes radiate and the radiation must be dependent on only the charge, mass and angular momentum. The process continues until the black hole no longer exists. So now it really looks like the information is lost, because we can no longer say the info is really in the black hole, we just can't get to it, and the hawking radiation doesn't tell an outside observer anything more than charge, mass and angular momentum.

Has it changed since 2011?

physicsworld.com/cws/article/news/2011/aug/15/information-paradox-simplified#
Looks there are several alternatives:

en.wikipedia.org/wiki/Black_hole_information_paradox

Yeah, it wasnt clear but I was just providing more details on why it was considered a paradox in the first place. The consensus view now is that information is not destroyed, the exact method by which the info gets out of the black hole is still being debated. AMPS firewalls are a very recent possible solution, or that hawking radiation contains higher order detailed info about the black hole that Hawkings semi classical calculation misses.

Interesting, frontline research

Firewall (physics)

These are pretty much all the solutions I'm aware of.....I think firewalls and info slowly leaking out are the combined heavy favorites vs the field. Part of this is upbringing..... I've really only worked with string theory and particle/high energy people so its easier for me to give up semi classical gravity than anything from quantum field theory.

Does this have anything to do with something else I saw where say, a spaceship crossing the event horizon appears to be frozen in time by those watching outside the EH, while to the spaceship its journey continues?

I thought I heard Susskind also refer to the holographic principle as well. I didn't understand it, but it seemed he was saying that both events are simultaneously possible? Man I wish I were even a little bit smarter so I could better understand this stuff.

Yeah, he was maybe talking about Black hole complimentary.

http://en.wikipedia.org/wiki/Black_hole_complementarity

The holographic principle is largely believed because of the Maldacena conjecture. If the conjecture is true (and i mean generally not just to 5D anti diseter space) black holes cannot destroy information. The rough explanation is that you have an equation x=y and x involves gravity and black holes and it's not clear at all if information is always preserved. But y has nothing to do with gravity and must preserve information. So we can conclude x doesn't destroy info cuz y doesn't and x=y. Hawking conceded to the bet because of that.


Dont worry too much....Maldacena, hawking , susskind etc all feel the same way.

I forgot to comment on this:

Of course, I don't get to choose what's true, but this is my favorite scenario. To my simple mind, it seems a bit too coincidental that we know of singularities inside black holes and we also know that our universe came from a singularity. (do we know of existing singularities anywhere else?). It seems perfectly reasonable (again, to my simple mind), that the singularities of black holes could create big bangs in some alternate universe or dimension thereby giving credence to the multi-verse hypothesis.

What is the reason for the belief that information must be conserved? How do you reconcile this postulate (or is it a theorem?) with, for example, the ability to destroy a hard drive and the information it contains?

Even if you render a hard drive unusable and unrecognizable, you are not destroying information. IOW, everything that was the hard drive still exists in the universe, albeit in a different form. Even if you were to put it in a blast furnace, theoretically the atoms could be reconfigured to their original state.

If you put it in a blast furnace, some of the information gets radiated away at the speed of light, and you can't ever catch up with it to reconfigure it, not even theoretically. You'd have to have had detectors in place ready to catch them. Even if you did, you don't have knowledge of the exact process that produced all the heat and light, so you don't know how to reconfigure the information. When a physicist says that information can't be destroyed, he's not talking about meaningful information. Meaningful information can be destroyed. Information is just a function of the probabilities of bits being in particular states.

I actually debated whether to use the word reconfigured, because I thought it might get me into trouble and it did. But the main point remains that information is not lost.

So the technical definition from wikipedia: "a sequence of symbols that can be interpreted as a message" is not the definition physicists are using? (Because sequences of symbols can obviously be irreversibly destroyed)

What is the exact definition physicists are using when they say information cannot be destroyed?

It can be viewed as a sequence of symbols that can be interpreted as a message, just not the same message you started with. If it used to be your bank statements, those are gone. Information has a technical mathematical definition that doesn't mean what it means to ordinary people.


Self-information. The expected value of information is information entropy.

I should add, it's only the amount of information that can't be destroyed, not it's content. It's content can be destroyed. For example, if 2 different inputs can produce the same output, then there's no way to know which input produced it, so there's no way to recover the input without a history of the process that produced it which may no longer exist.