What is the Black Hole Information Paradox?

Article written: 28 Oct , 2015
Updated: 23 Feb , 2017

Have you heard that black holes destroy any information that goes into them? Why is this such a big problem for physics?

In my day, things were simple. Robot dogs had wheels and laser noses. School was uphill both ways. Unwanted children removed themselves from lawns, and we didn’t need those horrible electrified tentacle arms. The cut of my jib was completely beyond reproach. Nathan Fillion was the captain of the Serenity all day, every day. … And black holes were holes that were black. By that I mean black holes would compress matter and energy into an infinitely dense singularity, and didn’t create a seemingly insurmountable information paradox. Yep, those were the good ole’ days.

But those days are over. Now it’s all 50 shades of grey, with the laws of physics bending under other laws of physics. “Hashtag not my Christian”. What I’m talking about is the black hole information paradox.

First, let’s talk information. When physicists talk information, they’re on about the specific state of every single particle in the Universe: mass, position, spin, temperature, you name it. The fingerprint that uniquely identifies each one, and the probabilities for what they’re going to do in the Universe. You can change atoms, crush them together, but the quantum wave function that describes them must always be preserved.

Quantum physics allows you to run the whole Universe forwards and backwards, as long as you reverse everything in your math: charge, parity and time. Here’s the important part. The big brains tell us information must live on, no matter what. Think about it like energy. You can’t destroy energy, all you can do is transform it.

Now, the black hole recap. Naturally formed when the largest stars, those with more than 20 times the mass of the Sun, collapse violently and explode. Here the density of matter is so high, the escape velocity exceeds the speed of light. The fancy ones have a super-heated accretion disk of matter swirling around the black hole event horizon, where even light can be pulled into orbit.

Here, we get one of the strangest side effects from Relativity: time dilation. Imagine a clock falling towards a black hole, moving deeper into the gravity well. It would appear to slow as it got closer to the black hole, and eventually freeze at the edge of the event horizon. Photons from the clock would stretch out, and the color of the clock would redshift. Eventually, it fades away as the photons stretched out beyond what our eyes can detect.

If you could stare at the black hole for billions of years, you would see everything it ever collected, stuck to the outside like flypaper. You could point out the clock, the Titanic, the Ranger, and USS Cygnus, and theoretically, you could identify the quantum state of every single particle and photon that went into the black hole. Since they’re going to take an infinite length of time to disappear completely, everything’s fine.

Black hole with disc and jets visualization courtesy of ESA

Black hole with disc and jets visualization courtesy of ESA

Their information is preserved forever on the surface of the black hole. They’re all totally dead, but their information, their precious precious quantum information, is totally safe.

If you could unravel a black hole, you could get at all the quantum information describing everything the black hole ever consumed. And least, that’s how it was in the good old days.

But in 1975, Hawking dropped a bombshell. He realized black holes have a temperature, over vast periods of time, they would evaporate away until there was nothing left. releasing their mass and energy back into the Universe. Unsurprisingly known as Hawking Radiation.

But this… idea created a paradox. The information about what went into the black hole is preserved by time dilation, but with the mass itself of the black hole evaporating. Eventually, it will completely disappear, and then, where does our information go? That information which can’t be destroyed…?

This is strictly not cricket, and puzzled astronomers. They’ve been working for decades to resolve it. There’s a fun stack of options here:
Black holes don’t evaporate at all, and Hawking was wrong.
Information within the black hole somehow leaks back out while Hawking radiation is escaping.
The black hole holds it all in until the very end, and as the final two particles evaporate, all the information is suddenly released back into the Universe.
It all goes into the teeniest possible bits and nothing is lost OR The information is compressed into a microscopic space, which remains after the black hole itself has evaporated.

An artist's representation showing outflow from a supermassive black hole inside the middle of a galaxy.  Credit: NASA/CXC/M.Weiss

An artist’s representation showing outflow from a supermassive black hole inside the middle of a galaxy. Credit: NASA/CXC/M.Weiss

And maybe, physicists will never figure it out. Hawking recently proposed a new idea to resolve the black hole information paradox. He has suggested that there’s a way that new Hawking radiation could be imprinted by the information of new matter falling into the black hole.

So, the information of everything falling in is preserved by the outgoing radiation, returning it to the Universe and resolving the paradox. This is a hunch, since Hawking radiation itself has never been detected. We are decades away from knowing if this is in the right direction, or even if there’s a way to resolve the paradox.

In situations like this that we’re reminded how little about the Universe we really understand. Some aspect of our understanding of this whole process is unclear, and it’ll take much more detective work and experimentation to get closer to the truth.

What information would like to be destroyed from the Universe forever? Tell us all your secrets in the comments below.

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8 Responses

  1. Bo Zo says

    Sutely it’s because I am dense, but I still don’t understand why information supposedly must be conserved, and why it would make any difference to physics if there were exotic ways of destroying it.

    Seems like: The laws of physics LOOK like they work equally well whether time runs forwards or backwards, but if time never DOES run backwards, then there’s no physical dilemma, just a (minor) mathematical one.

  2. btraymd says

    Of course this is a big mystery. Trying to define answers to questions about objects that are purely mathematical conjecture will always create “paradoxes” and “mysteries”. To people with common sense they will appear to be nonsense but mathematicians will advise them they are just too stupid to understand.
    Let’s set the record straight. “Black Holes” are mathematical constructs that have never been observed or experimentally confirmed. The mathematics that was used to create the concept has been shown to be fatally flawed ( see Steven Crothers elegant and understandable proofs). And for the record they are neither black nor holes.
    The structures referred to as “black holes” should be termed “galactic centers”.
    Recent radio telescope data has revealed important information which thoroughly invalidates the current standard model of these structures. First of all they emit massive amounts of electromagnetic radiation, primarily as x-rays. So much for gravity preventing the release of electromagnetic radiation. I have yet to hear Mr. Hawkings describe the escape velocity for em radiation in the xray spectrum and how it would differ from the escape velocity for em radiation in the visible spectrum. Secondly, massive magnetic fields have been detected surrounding these galactic centers. This strongly suggests massive electric currents within these structures. Finally. multiple jets of plasma have been confirmed emanating from these bodies. I guess infinite gravity from infinite mass was on a lunch break.
    The newly observed data leads to one inescapable conclusion. The centers of our galaxies consist of super dense, rapidly rotating plasmoids. They are big time electromagnetic events and result in galaxy and star formation. A thorough knowledge of plasma physics and electrical engineering is required to recognize the true nature of our universe. Ignorantly clinging to failed gravitational models is inexcusable.

    • mewo says

      >“Black Holes” are mathematical constructs that have never been observed or experimentally confirmed.

      Yes, they have.

      >see Steven Crothers elegant and understandable proofs

      Stephen Crothers is a ranting crackpot who spends all day spamming scientists with dubious viXra links.

      >Mr. Hawkings

      Prof. Stephen Hawking.

      >First of all they emit massive amounts of electromagnetic radiation, primarily as x-rays. So much for gravity preventing the release of electromagnetic radiation.

      The radiation is released from the accretion disc surrounding the black hole, not the black hole itself. Do your homework.

      >Finally. multiple jets of plasma have been confirmed emanating from these bodies.

      Again, from the accretion disc. Do your homework.

      >I guess infinite gravity from infinite mass was on a lunch break.

      Who ever claimed black holes have infinite mass or infinite gravity? Seriously, obtain at least a grade school understanding of physics and astronomy before you presume to make pronouncements on these matters.

      The electric universe idea is crackpot nonsense.

      • btraymd says

        Using the term “crackpot” is arrogant and dismissive. A basic knowledge of math will allow anyone to see that Crother’s proofs are essentially irrefutable and reveal the intrinsic flaws in the math of “black holes”.
        “Black holes” have NEVER been observed or experimentally verified. Only structures at the galactic center have been identified and they are now being shown to contradict the “standard model”.
        Exactly what is an accretion disc??? Another theoretical concept that attempts to salvage the failed model. The failure of the model was that light cannot escape the “infinite” gravity of the black hole. As it turns out, electromagnetic energy flows from galactic centers routinely. Please define the structure of an accretion disc and how it escapes the gravity of a “black hole”. The concept is utter nonsense.
        And about those magnetic fields recently documented by radio telescope data…….. it is well known that only electric current generates magnetic fields. Given the emanation of electromagnetic radiation and plasma jets from these galactic centers isn’t it common sense that there must be tremendous electromagnetic activity within these centers??
        The force of gravity is so weak when compared to these immensely powerful structures. Infinite mass and infinite density have been suggested just so it can be mentioned in the same sentence. That of course is a farce.
        And let’s get back to a “singularity’, the essence of the “black hole”. What is it exactly and how can it be verified? Sounds like more baloney to me, however important it is to the current cosmological model.
        New radio telescope data is sending the standard model to it’s grave. Wake up, read the literature and smell the roses. Without electromagnetism, any model of cosmology is a fantasy.

      • Bo Zo says

        I don’t know much about black holes, or about physics generally, but I know roughly what an accretion disk is supposed to be and how it generates x-rays at huge energies. Since you asked: The disk lies OUTSIDE the schwarzchild radius, in i rbit, formed of stuff that’s spiraling in toward the black hole. It gets to rotating really (relativistically) fast, and – voila.

        You said several things about black holes and accretion disks that suggest you are confused or misinformed. I don’t know who Stephen Crothers is, and I’m not judging his ideas (which I’ve never heard). But I think you should be careful about taking all or most of your info on any subject from one source, or any one school of thought, especially one which, as in this case, is apparently an outsider. And especially on a subject like black hole physics, some of which is just plain weird. I’d hesitate to “believe” anything about it at all, especially a fringe idea, especially before I was thoroughly versed in the prevailing theories. I’m sure you’ll take that as an insult, but I genuinely hope that you don’t. As I said, it is clear even to me that you are misinformed about black holes.

        At the risk of insulting you again, I will also comment on the electrical universe theory you kept mentioning. Like I said, idk about Crothers. For all I know he could be precisely correct, or he could actually be a character from a Dickens novel – I have no idea whatsoever. But I’ve read one book, many articles, and a great many blog comments, about electric cosmology. They tend to be long and unconvincing, whereas the refutations tend to be short and damning. Such as, “there aren’t enough protons and electrons in the universe by a factor of 10^30.” (I made that number up! But it’s one of those unfathomably large numbers.) Again, I don’t know enough physics to judge for myself, but it really does seem that the electric universe theory might be off by something like 100,000,000,000,000,000,000,000,000,000 %.

        It’s a pity, because I liked the idea when I first heard of it. So much so that I even read a book on the subject. And I remain open-minded; but I won’t consider the theory on equal terms with other theories until you do something with all those zeroes!

        I mention that theory because you seem to be an adherent, but it seems to me you’ve been too quick to join the fringe, before you’ve had a proper chance to understand and then reject the prevailing views.

  3. Member
    Pete says

    Thank you, mewo.

  4. otistheo says

    That’s easy. After a long time of evaporating its mass, a black hole will reach a point when it will no longer be massive enough to be “black” and all will be revealed.

    • Bo Zo says

      How does mass-energy-time-space (all squished together) retain the information when it’s been part of a singularity for trillions of years, then 90% boiled away by billions of eons of literally random quantum fluctuations, then (presumably) escapes in a sort of supernova size explosion? Where in that vanished, exploding mess are the records of the ancient histories of the particles that went into forming the singularity?

      I’m not well informed, but I just don’t see any mechanism for the info to survive the falling in, let alone the disappearing after.

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