Physicists Theorize Out How To Retrieve Information From a Black Hole (sciencemag.org)

sciencehabit writes: Black holes earn their name because their gravity is so strong not even light can escape from them. Oddly, though, physicists have come up with a bit of theoretical sleight of hand to retrieve a speck of information that's been dropped into a black hole. The calculation touches on one of the biggest mysteries in physics: how all of the information trapped in a black hole leaks out as the black hole 'evaporates.' Many theorists think that must happen, but they don't know how.

Comments

Easy

[penguinoid]

Ask a politician or CEO or salesman. They routinely pull information out of a "black hole".

Re:Easy

[davester666]

It's more of a brown hole. Many people refer to it, as well as the politician/ceo/salesman, as an "ass" or "asshole".

Reservations re Hawking radiation

[Black Parrot]

Ignorant amateur here. ISTM that if a virtual pair appears straddling the event horizion, the one that gets away never was inside the black hole to begin with, and thus would not carry away any matter or energy. Isn't the black hole just working as an engine to extract matter/energy from the vacuum near the event horizon? Half of which goes in, making the BH bigger, and half of which escapes to the external universe.

In the unlikely event that that conception is correct, it would be interesting to think about what happens to the vacuum near the event horizion. Does it get depleted of its vacuum energy, or is it an infinite source? If depleted, does vacuum energy flow in from other nearby vacuum to replenish it?

Is the vacuum inside a black hole anything like the external vacuum?

Re:Reservations re Hawking radiation

[maugle]

Not quite. The virtual pair has a net energy of 0, and therefore isn't really "extracting" anything from the vacuum. If the pair weren't straddling a black hole, they'd recombine and disappear and nothing would happen. However, when one member of the pair is sucked into a black hole while the other particle escapes, the escaping particle must have a greater-than-zero amount of energy. Because of that, and the requirement that the two particles balance each other out, the black hole has necessarily absorbed a negative-energy (not negatively-charged, mind you, actually negative energy) particle, causing the black hole to shrink ever so slightly. Basically, while the particles originally came from vacuum, the energy was taken from the black hole.

Also, to an external observer this process looks exactly the same as if the black hole itself was slowly emitting particles and shrinking away. And if the black hole is emitting particles, we can use that to determine something about its internal state.

Re:Reservations re Hawking radiation

[burtosis]

Not quite. The virtual pair has a net energy of 0, and therefore isn't really "extracting" anything from the vacuum. If the pair weren't straddling a black hole, they'd recombine and disappear and nothing would happen. However, when one member of the pair is sucked into a black hole while the other particle escapes, the escaping particle must have a greater-than-zero amount of energy. Because of that, and the requirement that the two particles balance each other out, the black hole has necessarily absorbed a negative-energy (not negatively-charged, mind you, actually negative energy) particle, causing the black hole to shrink ever so slightly. Basically, while the particles originally came from vacuum, the energy was taken from the black hole. Also, to an external observer this process looks exactly the same as if the black hole itself was slowly emitting particles and shrinking away. And if the black hole is emitting particles, we can use that to determine something about its internal state.

This is correct. The article is specifically addressing a mechanism by which quantum teleportation could release this information across the horizon. Granted to tell exactly what this is you would need to know the instaneous spin to a ludicrous precision, understand how quantum gravity works, understand the exact structure within the black hole, and several other far off concepts. However it is an interesting approach to solving this problem and could further research efforts.

Re:Reservations re Hawking radiation

[burtosis]

It's not negative energy.

The farther away the particle is from the event horizon, the more energy it has---the closer it is to the event horizon, the less energy it has. As the particle falls into the blackhole, the combined system (particle + black hole) actually lose energy, resulting in a drop in mass---which is conveniently carried away by the particle leaving the event horizon area.

That sure sounds equivelant to a negative energy or mass to me.

Re:Reservations re Hawking radiation

[maugle]

Here's another way to think about it: Don't think of the black hole event horizon and singularity as different things. That is probably what's confusing matters. Instead, think of the black hole as a single object, with its event horizon as its "surface". Anything that touches the "surface" disappears and adds its mass/energy to the black hole. However, because of the requirement that the virtual particle pair has a sum energy of 0, and the fact that the escaping particle has a net positive energy, the particle that falls into the black hole must have negative energy, and adding that negative value to the black hole is what causes the black hole to lose energy.

Alternatively, the particle that falls in could be thought of as leeching energy from the black hole and transferring it to the escaping particle, in a way that would look to an outside observer as though a particle inside the black hole suddenly appeared outside it. That's what the article probably means by particles "teleporting" out.

Susskinds "Black Hole Wars" gives background

[peter303]

Of the information loss paradox and various fixes. The "holographic universe" is another fix. That is copy of information inside the BH exists imprinted on the event horizon.

Re: junk physics

[HiThere]

It doesn't seem to match the definition of information that programmers use routinely in their work. I'm fairly certain that they is a mathematical identity between the two uses of the word, as they both tie back to Shannon, but the use seems to have developed extremely differently.

To a programmer every feature that is used to describe an object represents a certain number of bits of information. Clearly it is being asserted that physicists use a very different meaning. It sounds is if it's something like "the log of the number of bits required to fully describe what is knowable about the state". This may actually be closer to Shannon's original meaning, as he was concerned about the amount of information that could be transmitted through a channel of a given bandwidth in a given amount of time, but that's a bit removed from the standard meaning used in computer science, programming, etc.

Re: junk physics

[Anonymous Coward]

The connection between statistical mechanics and information theory was made by von Neumann right when talking with Shannon about his now famous work. If you want to complain the defition is bad, you can start by complaining about their work. Or you can be like Viol8 and equivocate in response to every article about physical theory (it has happened at least several times before) and pretend that refusing to learn about a topic is some form of insight.

Re: junk physics

[HiThere]

I'm not saying the definition is bas, as it clearly isn't. In either field. I'm saying the two fields apparently use the term quite differently. This doesn't make either wrong. And I think that both would agree on the basics, e.g. that a bit is a unit of information.

P.S.: I tend to think of this as an oversimplification, but it's one we've built all our digital hardware around. The problem is it seems to make any relatively prime chunk of information require an infinite number of bits to express accurately. Try, e.g., to accurately express 1/3 except as a binary number. But practically the higher primes rarely occur, and usually an approximate value is good enough that we don't worry about the finer details. And when we do, there are ways to refer to it...e.g. ratios between two integers. Of course, that doesn't work for the irrational numbers... So I don't think we have an exact theory of information, but only a good approximation. But it's quite a good approximation.

P.P.S.: Perhaps a good theory of information would easily solve the three body problem. Currently we rely on infinite approximations, that we necessarily cut off at some point. Now chaos theory implies that even knowing the exact solution wouldn't help us, because we couldn't specify the initial conditions exactly enough, so that might not be a real benefit, but it would be a good theoretical benefit. There are a few other cases where the two body case is easy (well, relatively easy) and the three body (or five body, or...) can only be approximated. I have a suspicion that in many of these cases it's because somewhere in the fundamental assumptions there is something where a rule is used that works well for pairs of items, but not for relatively prime groupings. (Of course, here *I'm* assuming that a case with 4 elements can be handled as a pair of pairs, and this isn't always true.)