> and with the proper key to decode it one could theoretically peer inside the black hole

I've never seen anything asserting this, and this is not what standard theories say. The idea is that with the right "key" you can recover the information that was encoded in the stuff that fell into the black hole. As far as I know there is no suggestion this gives you any information about what is going on inside it.

Ah, then you might enjoy one of the more fun reads I had this past year:

https://www.quantamagazine.org/new-calculations-show-how-to-...

I wouldn't put money on it being the case, but it's definitely "outside the event horizon" thinking and worth a read.

That is indeed a fun read, but nothing in it contradicts what I said.

You made a malformed statement, implying that time and events continue on, like nothing is wrong and the only difference is we can't see it. But space and time switch places inside a black hole. All directions lead toward the singularity, where as in our world, all directions lead toward the future. The units are incompatible between the two worlds.

Could you perhaps quote exactly what statement I made which is malformed?

In any case the picture of time and space switching places inside a black hole is at best a rather deceptive simplification. The most important thing about the event horizon is that locally (i.e. to one falling in to it) nothing at all interesting happens at the event horizon.

Edit: The "swapping" you are referring to is an artifact of coordinate systems, not of space-time. Thinking something wild happens to space-time as you pass through the event horizon is the same as thinking that something wild happens to the Earth's geometry as you reach the north pole. Sure at the north pole there is no longer any meaningful direction other than "south" but thats an artefact of the coordinate system you're using, the pole is a normal point just like any other.

To any single observer that crosses, I agree with your statement, but it changes the moment you have two observers. I also agree that at the North Pole, "all directions are south", but the difference is you are free to move back and forth.

If you picture us in an X-Y plane (which somehow represents all 3 spatial coords), and "up" is the time dimension, then a black hole would be the X-Y plane deformed into a 90-deg "pipe" facing straight down. Once you are in the pipe, your "X-Y" is our "up-down", this is probably the "artifact" you are referring to.

> If you picture us in an X-Y plane (which somehow represents all 3 spatial coords), and "up" is the time dimension, then a black hole would be the X-Y plane deformed into a 90-deg "pipe" facing straight down.

This is not correct, there is no 90 degree bend. Space-time is locally Minkowskian ("flat") at the event horizon. It looks like a sharp 90 degrees turn in some coordinate system, just as when you walk in a "straight line" (a great circle if you prefer) over the north pole you go discontinuously from "walking north" to "walking south" even though your real motion is continuous.

Strange you think that. Care to explain why you came to that conclusion?

The preprint linked to lays it out more technically if that's your jam:

https://arxiv.org/pdf/2207.06536.pdf

See section 6 on exterior vs interior measurements, and you can see the discussion in the FAQ about how measurements on the radiation after the Page time creates particles in the interior (which cites section 6 for more details). Then 8.2-3 goes more into what information about the interior can be known from observables in the fundamental description before and after the Page time. The "Previous attempts at an encoded interior" section in the discussion could help further clarify things.

It's not saying that it's trivial to see inside a black hole from the Hawking radiation, but it would be incorrect to characterize their model as saying that nothing about the interior can be known in measuring the Hawking radiation.

My understanding (which is highly limited, I am a researcher in quantum information but quantum gravity is very far out of my reach) is that this essentially gives you information about degrees of freedom of "stuff" (I guess quantum fields) that has been thrown into the black hole. I.e. you throw a diary with information in, and you can (theoretically) learn that information from the Hawking radiation if you absorb enough of it.

This is quite different from being able to probe the space-time structure inside (i.e. ask questions like is there a real singularity in there).

If you think about what you'd need there, you need the opposite of what they have in the FAQ, you would need operations in the interior to be able to create a particle on the exterior in order to build a "telescope" to look inside and I'm pretty sure this is ruled out even in this proposal.

Actually that's what their section 6.3 is all about, how if you sent an observer inside the event horizon measurements could influence the outside.

It just admits that the feasibility of this is ridiculous with my favorite line of the paper:

> Physically this seems absurd, as it allows a measurement inside a black hole to produce a record which stays outside, but we are not claiming that any effective-description observer could actually implement this unitary.

But I agree that there's a big difference between the plausibility of measuring the 'stuff' vs it's spacetime configuration - that was a great point.

That “sounds” a whole lot like “water has memory” quackery.

I don’t want to dismiss it off hand because there’s all sorts of funky things out there, but “information encoded radiation” is something that I’d be pretty immediately and heavily skeptical of.

when you burn a piece of paper, the atoms react into new molecules, some energy is given/taken, but fundamentally you could ~~run~~ simulate the reaction in reverse and see writing in the smoke of burnt paper.

Isn't this hampered by the old 'needing a universe-sized supercomputer to run a fully accurate 1:1 simulation of the universe'? It seems like the complexity of this kind of reverse simulation would be enormous and grow bigger and more complex when you're dealing with something on the scale of black holes.

At least unless you can somehow reduce the data complexity dramatically without tainting the simulation, but that seems difficult to do when you're trying to work backwards to an unknown state. At least the pre-burnt piece of paper is known to exist alongside various rules of physics that we know - unlike in the black hole, where those rules all come with a "warrantry maybe void" asterisk.

The question isn't whether this is possible in practice or not. It's that the laws of physics are defined as differential equations of a state (think e.g. Newton's laws) so they should be "the same" forwards and backwards in time.

I thought that was only true for classical mechanics and not true for QM. Like not only are there time-dependent equations, Heisenberg says we can’t know both position and velocity of a particle which would make it hard to capture state. Also everything is expressed in terms of probabilistic events which adds to the likelihood that it’s again impossible to capture state.

The wave equation of QM is just a differential equation too. The interpretation of what its values actually are is quite contentious AFAIU, and what the Born rule used to derive the probabilities "means" depends on the interpretation.

But yes, if you have "collapsed the wave function", you don't have the information to "backtrack" anymore. But I don't think the information paradox is about this (although unsure why). AFAIU one problem is that black holes throw out even the statistical information available in the wavefunction.

I would say it's generally understood that the quantum information being radiated from a black hole is still effectively unrecoverable by any practical machine, but there's plenty of such information in our real world already. You don't even need to "go quantum" to get that result, it's not hard to have perfectly classical cases where information is completely impractically recoverable, even in thought experiments in which one can rearrange the entire physical universe to the sole task of recovering some bit of classical information, let alone any physically-realizable machine. (You can even quantify the rate of information loss in such systems with the right theories.)

What really bothers the quantum physicists is not a macro-scale unrecoverability, but the event of the loss itself. The equations of quantum physics do not have anywhere to "lose" information. If a black hole loses information, then that means there is some box you can draw in spacetime where the information goes in and doesn't come back out, and that necessarily implies that something in that box broke the fundamental equations of quantum mechanics.

I think you could analogize this issue into classical physics fairly well as finding a violation of the conservation of energy in a putatively classical system. (I have to qualify this because at it stands at the moment, conservation of energy is not absolute; at cosmological scales it seems to be violated by the expansion of the universe. So ignore that for the moment.) If someone produced a true perpetual motion machine, let alone one that actually provided over-unity energy, that would be a problem for classical physics because there is nowhere in the mathematics that energy can be produced in excess. It is written into the most fundamental formulations of the theories and backed by Noether's Theorem. Such a machine would mean that somewhere the laws of physics are being violated, and that would mean we have a hole in them. The quantum theorists are "worried" about quantum information loss in the same way a classical physicist is "worried" about over-unity machines. A real, physical quantum physicist or classical physicist might in fact be over the moon to discover such a thing; it would be a career maker and who knows what else might be implied by such a discovery. But the anthropomorphized theory that was just "violated" would be very "upset".

The other major relevant different being that the classical physics has those classic physics "in hand", in the sense that many real experiments on classic physics can be and are realized in the real world, and at this point, physicists as a whole do not take the idea that an over-unity machine is going to be produced very seriously. However, it is quite difficult to have black hole in hand to experiment on; such mathematical analogs as we have are intrinsically limited and probably quite likely to fail to exhibit the phenomena we're interested in. So there's a lot more "room" for problems to come from. Plus, classical physics already has very firmly built into it the understanding that it is only an approximation. Quantum physics is still struggling with that question; sure, we basically know it is incomplete, but we don't know exactly how to resolve that, so unlike classical physics where we know that technically, yes, it's predictions can be violated in certain ways at certain scales and we accept that, we're a lot more nervous about QM. Maybe the real theory of the universe would allow information destruction. In English, that sounds pretty harmless ultimately, like, I mean, OK, maybe that's a bit of an issue but who cares? But pushed through the aforementioned Noether's theorem it gets much more interesting considered from the mathematical point of view, and much more challenging.

re: computational complexity, I am not informed enough to answer that, but I've wondered it too. But we've said things like that before about, say, factoring huge numbers, only to find out that quantum computers can solve it with a fraction of the energy ("orders of magnitude" doesn't even cut it here).

The other thing I've wondered is how could you have a detector for those particles without interfering with your measurement (heisenberg's)? Your measurement apparatus will give off heat or very slightly change the shape of spacetime, thus interfering where your particles are detected :(.

I have no idea what I'm talking about, but quantum physics are bizarre enough that I'm not sure you can play it in reverse.

The smallest perturbations in a chaotic system yield completely different results. The slit experinment for instance suggests that measurement changes the system.

I don't understand why you would be skeptical. How do you think cell phones work?

What does “hawking radiation encoding the future through black holes” at all have to do with “humans intervening with and encoding their own signals over radio spectrums”?

Nothing.

Understood. Sorry. I should have given you the benefit of the doubt.

To me, the resolution of the paradox — that the radiated field might contain some encoded information in it — is less weird than the alternative, which is that the information somehow disappears. Information being encoded in a field seems natural to me. There’s a tight interplay between energy, temperature, and information. It’s even right there in the first law of thermodynamics: dE = TdS + dW. (The S is the missing information about the system.)

Information encoded in radiation is how we get pretty much all of the information we have about the universe. Light and radio are radiation.

But I think you're overcomplicating it. Think of it as a snapshot of an object as it crosses the event horizon. That snapshot is etched into the "surface" of the horizon and emits a pattern of radiation that corresponds to it.

It's pretty much the same as dropping a rock onto a planet and observing the crater from orbit. You left a mark on the surface and it emits a corresponding pattern of radiation.

The real crux of the matter is that we're starting to understand that information is a lot like energy. It's generally conserved in the same way, but black holes appear to destroy matter, energy, and information in a way that doesn't really add up.

So Hawking came up with the idea of Hawking radiation. It's a hypothetical way for a black hole to very slowly give back all of the matter and energy it's consumed in the form of particle radiation. If information is a conserved quantity like energy, Hawking radiation must also return all information consumed by the black hole.

Information theory is pretty interesting if you're the type of person who likes to think about black holes and cosmology in their free time.

AFAIK we haven't proven that Hawking radiation actually exists. It seems to work mathematically, but we'd have to go out and observe a black hole up close. It's also extraordinarily slow. As in, it would take the entire lifespan of the universe for a big black hole to evaporate into nothing. Ten to the power of hundreds of years. Just a hair shy of infinity.

In order for space to truly be continuous, particles would have to be represented with effectively infinite position information. Since particles seem to contain finite information, that seems unlikely.

That seems to me to be the wrong way to think about this. I don't think that we have any evidence that a particle stores its position in the same way we might do in a physics simulation, it just sits at some position in space time. What would its position even be, where would the origin of the coordinate system be?

And even you could always just pick a coordinate system with the origin right where the particle is, then its coordinates would trivially be zero. If you have several or moving particles and you want to keep the coordinate system fixed, then this will of course no longer work.

It also makes the assumption that the measurement of position must be continuously detailed, which we know in our universe is impossible because of the Plank length.

So even if spacetime is continuous and particles do move within it in continuous ways, the combination of Heisenberg's uncertainty principle plus the Plank length means we can never observe such continuity anyways.

> which we know in our universe is impossible because of the Plank length

I think the statement that you are implying here is not known to be correct. We have no idea if it is (theoretically) possible to measure the position of a particle to a precision of less than a Plank length. In some formulations of quantum gravity there are fundamental limits like this, but quantum gravity is difficult at best and sketchy at worst and none of those versions of quantum gravity is without their flaws.

The problem is there's no way to measure it in actuality.

If there's not enough energy in the universe to make the measurement, then there's no making the measurement no matter the theory of what would happen if there were more energy.

We could discuss the theory of what happens to a virtual photon going down a split path between Everett or another interpretation, but if we can't ever actually measure the virtual photon, then it's just theorizing around an unanswerable question. Which is part of what leads to "shut up and calculate."

Fun fact - as best we know, it's fundamentally impossible to know if space or time is actually continuous or discrete.

We've known about the limitation in space for a while with the Plank length, and a similar limitation in time was discovered a year or two ago.

So while we have successful models for the universe that rely on the notion of continuous spacetime, our measurable version of it effectively has a minimum pixel size beyond which we fundamentally cannot get any more detail.

Fit the first time the other year I saw a psychics paper that actually presumed discrete spacetime based on simulation theory, which was pretty funny. I don't think the paper is that interesting beyond that aspect, but maybe you'll enjoy it given the presumption of discreteness: https://www.nature.com/articles/s41598-020-76301-0