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How do black holes destroy information and why is that a problem? (backreaction.blogspot.com)
197 points by sohkamyung 50 days ago | hide | past | web | favorite | 89 comments

man, watch the PBS YouTube channel SpaceTime. They're short, informative, and very well done. they dedicate a handful of episodes to getting you ready for Hawking radiation.


I love their dedication to building up over multiple episodes instead of dumbing things down every time.

Seconding that recommendation. The clear explanations allowed me to grasp several concepts that I've been trying to understand for decades, for example the "one-electron universe"

"Why Quantum Information is Never Destroyed" re: determinism and T-Symmetry ("time-reversal symmetry") by PBS SpaceTime https://youtu.be/HF-9Dy6iB_4

Classical information is 'collapsed' quantum information, so that would mean that classical information is never lost either.

There appear to be multiple solutions for Navier-Stokes; i.e. somewhat chaotic.

If white holes are on the other side of black holes, Hawking radiation would not account for the entirety of the collected energy/information. Is our visible universe within a white hole? Is everything that's ever been embedded in the sidewall of a black hole shredder?

Maybe even recordings of dinosaurs walking; or is that lemurs walking in reverse?

Do 1/n, 1/∞, and n/∞ approach a symbolic limit where scalars should not be discarded; with piecewise operators?

> The important thing is that all evolution equations that we know of are time-reversible.

I've heard this before, but it's so surprising to me, when one of the simplest mathematical operations - addition - is not reversible. e.g. if a+b=4, you can't infer the values of a and b (beyond their linear relationship). This non-injectivity is a kind of summarising, with less information, where more than one state maps to one.

So "evolution equations" (reality) are not like addition; state changes never summarise.

It is not reversible because you’re ereasing information. If you want to have a reversible addition you are not allowed to destroy the information.

The same happens if you apply the standard AND operator to two bits because the output is only one bit, therefore it is impossible to figure out the two input bits. To have a reversible AND operator you can define it like this: f(x1, x2, b) = (x1, x2, b XOR (x1 AND x2)). E.g: f(1,1,0) = (1,1,1). From this output you can get back to the input. This way you can implement a NOT gate as well, and all others gates. At the end you can implement addition using bits and your summation becomes reversible :) You can see that with this definition we are not ereasing any information, hence it becomes reversible.

Quantum computing is reversible in this way. Rabbit hole starts here:


Famous last words...

After reading: “oh my god it’s full of stars!”

You’d have to do that for all results, not just one. This is basically what an event sourced system does: you store all the events and fold your state, so you can “play back” to any point in time. You could theoretically reverse from the end, but I haven’t seen it done.

Urbit ;-)

A transactional database would tick that box, events are stored and can rollback to a point in time.

Not quite. Dropping a column or updating a row is typically irreversible.

That does depend upon the database, but can be done in some without resorting to a backup.

In PostgreSQL, schema changes are transactional.

> In PostgreSQL, schema changes are transactional.

With a few exceptions (that refuse to run in an explicit transaction): E.g. {CREATE, DROP} DATABASE, {CREATE, DROP} TABLESPACE, {CREATE INDEX, DROP INDEX, REINDEX} CONCURRENTLY, REINDEX {SCHEMA, SYSTEM, DATABASE}.

Also, try adding a value to an enum via ALTER TYPE ... ADD VALUE

Not anymore ;). Well, at least in the upcoming PG 12.


  commit 212fab9926b2f0f04b0187568e7124b70e8deee5
  Author: Thomas Munro <tmunro@postgresql.org>
  Date:   2018-10-09 12:51:01 +1300
      Relax transactional restrictions on ALTER TYPE ... ADD VALUE (redux).
There's still some restrictions:

> This patch removes that restriction, and instead insists that an uncommitted enum value can't be referenced unless it belongs to an enum type created in the same transaction as the value.

Actually addition is reversible, as long as you do it inline. The inverse of `a += b` is `a -= b`.

An example of an action that's not reversible is masking: `a &= b`. But if you dig deep enough into the physics, you find that these kinds of irreversible actions are actually always implemented in a way analogous to the following:

    // a &= b
    acquire zero'd register z from environment
    z ^= a & b
    z ^= a
    a ^= z
    z ^= a
    discard z into environment
Which can be reversed if you're able to get the discarded `z` register back.

See also the Linear logic, a logic in which discarding information is disallowed:


The function (a,b) -> a+b is not reversible. The function a -> a+b is reversible, and so is (a,b) -> (a+b, b).

That quote is not exactly correct, there are plenty of evolution equations which are not time-reversible beginning with the linear heat equation. If you look at the solution given by convolution (usually taught in first PDE course) you see that this equation has infinite speed of propagation. Any parabolic/dissipative equation is not time-reversible (which is analogous to addition not being reversible... dissipation involves an averaging process).

Elsewhere the author says "all fundamental evolution equations in physics are time-reversible." By fundamental I'm assuming she means: Maxwell's equations, Einstein's field equations and the Schrodinger equation.

I don't think they mean Maxwell's ones, since they can be derived from the Schrodinger equation with a well chosen Hamiltonian.

But then, the observation principle is as fundamental as Schrodinger's equation and irreversible. It's just not an equation.

Your state changes from two numbers to one number, such a transition is of course not going to be bijective unless carefully designed. In physics most states stay the same "shape", making invertibility easier to achieve.

The difference between them is that physical evolution takes one state to another state, whereas addition takes two numbers to another number.

  |a| = 2
  a^2 = 4

Most functions are not invertible.

In modulo arithmetic (numbers wrap around like days of the week, months, hours in a day, or the units column, e.g. mod 10 has numbers 0 to 9, and 9+1=0) we can count them.

There are n^n possible functions (each of the n inputs could map to any n values), but only n! invertible functions (the first input can be to any of n, the second can be to any but the first's, etc (n)(n-1)(n-2)...(1)).

n!/n^n < 1/2 for all n>2

Does this converge to a fraction as n->infinity (i.e. for the naturals)? As a recurrence relation, we have:

n!/n^n = (n-1)!/(n-1)^(n-1) x n(n-1)^(n-1)/n^n

We could change variables to rewrite the factor as (n+1)n^n/(n+1)^(n+1) = n^n/(n+1)^n

Since n+1 converges to n, I think this converges to 1. Meaning that the whole thing converges to something - but working out what it converges to is beyond my abiility.

EDIT Wolfram says the limit is actually 0 https://www.wolframalpha.com/input/?i=n%21%2Fn%5En

  lim_(n->∞) n^(-n) n! = 0
Reversibility is very rare indeed! At least, with the prior pr density implied from this comception of functions.

Stirling's approximation says that n! ~ sqrt(2 pi n) (n/e)^n.

So n!/n^n ~ sqrt(2 pi n)e^-n.

Cool! So the 1/e^n factor will bring it to 0, as n goes to infinity, I think?

Yeah, e^n grows much faster than sqrt(2 pi n), so sqrt(2 pi n)/e^n will tend to 0.

Ha! I had not looked at it that way before.

Insofar as addition is an abstract representation of merging two collections, we are abstracting away the information that links each element of the resulting collection to the one it came from.

Isn’t this exactly the same for subtraction, multiplication and division?

Considering integer operators specifically: in subtraction, you partition a collection and then discard one part. Multiplication is more abstract, as one of the operands denotes the number of applications of an operator (addition), and in division, the result is a count of the number of applications of a subtraction. I'm not sure if that can be called the same as addition in this regard, but they all lead back to that case.

Addition is reversible, in the physics sense.

So for example one typical quantum gate is called for physicists CNOT, or you would call it in computing a generalization of the XOR gate. We physicists would not think “Oh XOR is irreversible because A ⊕ B = B ⊕ A even when A ≠ B, so the same output can come from two different outputs.” That is just not what reversibility means to us.

Contrast this with boolean AND, which we would say is irreversible. What’s the difference? It's that we think of all of our operations as being automorphisms, they map a system back to itself. So when we are looking at CNOT/XOR, we are thinking about a system which looks like this:

    (t increasing)--> 
      A ---.-----
      B ------⊕--
and if you have the output "1, 0" from this system you can infer that the input was "1, 1". In that automorphic sense XOR is reversible, even though given the output on wire B alone you cannot decide what A or B was.

Contrast with boolean AND, where if I give you the output "0, 0" you cannot genuinely determine whether that came from "0, 1" or "0, 0". It could have come from either place.

So the automorphism (x, y) ⇒ (x, x + y) in fact is reversible in this sense; there is an automorphism which undoes it. The weirdness that you are identifying comes from the fact that you were actually considering the automorphism (x, y) ⇒ (0, x + y), which is a composition of the addition gate above with an ERASE gate, (x) ⇒ (0). Ignore the erasure and you get a reversible process again.

You might know that AND, OR, and NOT are universal: you can write any circuit from N bits to 1 bit by enumerating all of the inputs which could set the bit to 1, using AND and NOT to build “masks” for those inputs, and then using a final big OR-gate to see if any of the masks was triggered. By de Morgan's laws, you can build an OR gate out of NOT and AND; and then it is not too hard to see that you can build both NOT and AND from NAND: so we say that “NAND is a universal boolean gate.”

To get a universal reversible system you just need to go to three bits. Two working options are the Toffoli gate “doubly controlled NOT” and the Fredkin gate “controlled swap,”

    Toffoli = ([x, y, z]) => [x, y, (x && y)? z : !z]
    Fredkin = ([x, y, z]) => [x, x? z : y, x? y : z]
The universality of Toffoli is very easy to see from the universality of NAND: because Toffoli(x, y, 0) is actually just (x, y, x NAND y). However the fact that you start with an “isolated” bit and then it becomes “involved” in the computation, this is where you eventually start to need to erase bits if you do not have unlimited amounts of memory. [Fredkin is a little more difficult to reason about but for example Fredkin(x, 0, y) = (x, x AND y, (NOT x) AND y) and so you can then build both an AND gate directly from this construction and a NOT gate with y=1.]

A closer mathematical operation would be unitary matrix multiplication

Do they destroy information? Last I checked they don't: https://physics.stackexchange.com/questions/29175/why-is-inf...

Maybe there is some recent development I am not aware of an Susskind is wrong though.


- https://physics.stackexchange.com/questions/450326/why-is-th...

That’s why it’s a problem — the two best tested laws of physics contradict each other.

Which law of physics say information must be lost in a black hole?

AFAIK if information is lost in a black hole it will also violate the second law of thermodynamics - so really you have many many laws saying it cannot be lost - and Hawking temporarily claimed it will be lost in black holes before recanting and saying it won't.

So ... I don't quite follow. I mean this title is as concerning to me as something that claims the earth is flat.

I believe the 'No-hair theorem' is closest to a 'law' that says Black holes destroy information [1]. If it is true, then when you throw anything into a black hole, information about what you threw in (whether it is a chair, a star, a planet, etc.) is 'lost' as to the outside world they all yield the same observable parameters of the black hole.

[1] https://en.wikipedia.org/wiki/No-hair_theorem

IANAP but here is a physicist talking about no hair theorem and information loss paradox: https://www.youtube.com/watch?v=I55e6chHUs0

TLDW: They probably do have hair.

IANAPhysicist, but couldn't information be radiated away? When you have a particle and antiparticle annihilating, the information about what collided and when is carried away by the radiation from that annihilation event; nothing remains at ground zero to be inspected.

As matter traverses the accretion disk and falls towards the event horizon, couldn't information about it be radiated away? As an observer, you could definitely tell whether somebody threw a planet or a planet-sized bunch of paperclips into a black hole by observing the accretion disk as it happened.

When it comes to black holes, no one is a physicist.

The problems appear when you try to apply GR and the rest of classical physics - which all assume spacetime is continuous and analytically smooth - to a situation it can't handle.

It's a good tool for normal spacetime, it's fine for making predictions all the way up to an event horizon, but it's absolutely unable to say anything useful about what happens at an event horizon - never mind beyond one.

Because the question isn't "What happens to an astronaut or a chair at the event horizon?" It's "What happens to wave equations and quantum fields at the event horizon?"

If all information is lost at the the event horizon, quantum theory stops working in a catastrophic way. There are no fields, no particles, no interactions, possibly not even raw spacetime.

If it isn't lost, then something else happens, but no one is sure what it is yet.

Hawking's theory works on the basis that some relationships persists across the horizon - actually they stretch back to the formation of the black hole - but he seems to have assumed that it's possible to ignore the limits set by the Planck length/time. There are good reasons for thinking this is unlikely to be true.

Without a theory of quantum gravity - or rather of quantum spacetime - this is all guesswork. It isn't even possible to prove the No Hair Conjecture.

So although it's currently assumed that mass, angular momentum, and charge are conserved (and therefore not all information is lost), there's no proof for this, and no explanation why these features would be conserved while others aren't.

I know nothing, but from reading Wikipedia, I ran across something that really appealed to me - the idea that "black holes" are really fuzzy balls of strings (or whatever lies within the particles we know) where you would otherwise expect an event horizon. Anything falling into them comes apart into that stuff when it gets there.

To me, that feels right, even though I can't say anything about the math.

> the information about what collided and when is carried away by the radiation

This is where the thermal nature of the radiation emitted by the black hole comes in. Physicist use the term "thermal radiation" to mean it is in a mixed state that cannot encode information (crude analogy: as if someone has pressed all the keys of a keyboard at once, you see that some keys are being pressed but this "signal" cannot be decoded).

As it stands, as far as we know, Hawking radiation is completely thermal and random, so as the article states, you can't tell the initial state from the final state even if you collect all the radiation.

> observing the accretion disk

Well that is not part of the black hole now, is it.

> As it stands, as far as we know, Hawking radiation is completely thermal and random

Is it? Can you cite?

IANAP but the best I could find on the matter is:


> There are various ideas about how the paradox is solved. Since the 1997 proposal of the AdS/CFT correspondence, the predominant belief among physicists is that information is preserved and that Hawking radiation is not precisely thermal but receives quantum corrections.

Maybe that is wrong, but not sure what the basis for the claim to the contrary is.

Another citation which speaks to the views of Hawking on the matter:


> Now if information is really lost down a black hole as Hawking originally proposed [64], and if the Hawking radiation really has negligible correlations between what is emitted early and late, then it might be true that A/4 −tr(ρ ln ρ), suitably regularized, would never decrease. But since this information-loss proposal has been controversial since near the beginning [65, 66], and since now even Hawking has given it up [67];

Direct quote from Hawking:


> “If you jump into a black hole, your mass energy will be returned to our Universe, but in a mangled form, which contains information about what you were like, but in an unrecognisable state.”

The reason the black hole information paradox is a paradox is because it presents us with an unresolved contradiction ("There are various ideas about how the paradox is solved"). So there are several theories with try to resolve the contradiction, but they are all competing theories (i.e. physicists do not agree). Also, some of those theories assume Anti-de Sitter space which contradicts the positively mesaures cosmological constant.

So in the sense that before the paradox is resolved, we don't know if the radiation is thermal or not, but the idea of the radiation being thermal was based on the existing bog-standard theory of QM and GR. What is under debate is how that needs to be modified, which we haven't agreed yet.

Kindly riddle me this. If a black hole was a closed system, then the premisses, that information inside will become lost, would be trivially true by the (2nd?) law of thermodynamics.

There's energy going in, so it isn't hermetically sealed. Thus, the accretion disk is part of the system. But if there's no correlated information coming out, it's closed one-way. You say there is radiation coming out, theoreticly, and I know that radiation is information. It's information in one strict sense, but not in the other--what are the different scopes; Is the radiation not observable?

Are the laws of thermodynamics seemingly violated, that is, is the theory not complete (rhethoric question); Thus your remark was in effect non-constructive, as you cannot prove one unknown with another, can you?

Nevermind the kind of scary question whether any system in the grand scheme of things is closed at all.

BTW another comment mentioned conservation of momentum and charge. I wonder, in the focal point of an ideal lense, in theory, can the image be reconstructed? Well, by looking at the flame quite trivially, at least, albeit not in the perspective of the focal point (not easily without ambiguity, surely). Is this what Tao's one-pixel-cam is about?

Outside the event horizon, sure. But imagine the (extremely) far future when the universe is dominated by black holes and even those photons have been absorbed. You would not be able to extract any information about the past universe aside from its mass.

This may be a naive question, but, how do we know that the mass we measure for a black hole is equivalent to the things that went into the black Hole? We can’t have any observational data on what went into them in aggregate - is it not possible that the mass of black holes that we estimate is incorrect in some fundamental way? Or just that e.g. energy that enters them also becomes mass?

Yes the radiation from the infalling body gives the remote observer some information about what is going on with the body. From their viewpoint, the process of fall into the hole takes infinite time, or in other words, it never completes. The longer the time of observation, the longer the wavelengths of the radiation from the body, so the less and less information is obtained, until the radiation is so red shifted that it is not measurable. That is when the acquisition of information stops. The body still falls down after that, it is a never-ending process but for practical purposes the body is gone.

This was actually a really accessible description for a layperson. Thank you.

> Think of mixing dough. You’ll never be able to unmix it in practice. But if only you could arrange precisely enough the position of each single atom, you could very well unmix the dough. The same goes for burning a piece of paper. Irreversible in practice. But in principle, if you only knew precisely enough the details of the smoke and the ashes, you could reverse it.

This was a nice description of entropy.

This is literally what the holographic principle addresses... https://youtu.be/B2ksDczJOAs Leonard Susskind has enough accessible vids and lectures to give a conceptual idea of how it works out.

Also see Black hole Firewalls - with Sean Carroll (speaking at 20:25) and Jennifer Ouellette https://www.youtube.com/watch?v=_8bhtEgB8Mo

which explains the paradox and several different competing theories at a high level.

The other major example of a time-irreversible operation/object is much more mundane: the collapse of a wave function. I've never been able to find a decent layperson's explanation of what the wave function collapse really means, and why physicists seem to have no issue with it being time irreversible but seem quite concerned with black holes

It is a problem. Quantum mechanics, as it's normally taught, basically has two components:

1. Schrödinger's equation, which governs how the wavefunction (or quantum state) evolves in time. This equation is time-reversible: given a state at time t, you can calculate what the state was at time t-T. Technically, that means that the "time evolution operator" is invertible. All the information about the history of how system's state is contained in the present state. No information is ever destroyed.

2. Observation. A quantum state looks like a_1 * psi_1 + a_2 * psi_2 + ... + a_n * psi_n, where psi_i are all the possible states of the system and a_i are complex numbers called "amplitudes." When you observe a state (I'm obviously leaving out some mathematical details here, so anyone with physics knowledge please forgive me), you observe it to be in one of the possible states, psi_i, with i between 1 and n. The probability of observing it to be in state i is proportional to |a_i|^2. This operation destroys information, because the state collapses to psi_i, and all the amplitudes, a_j, j≠i, are lost. You can no longer reconstruct the previous state of the system.

I think most physicists who "seriously" think about quantum mechanics do not believe that step 2 above actually happens. It is a simplification of a much more complicated process called "decoherence." In order to understand decoherence, you have to change your perspective on what observation means. If you treat the observer as a system governed by Schrödinger's equation, which interacts with the system that's being measured, you find that the observer becomes entangled with the system under observation. The observer ends up in a superposition of states, each of which has observed a different outcome. It appears to each state of the observer as if there has been wavefunction collapse, but there actually is a larger quantum system containing both the observer and thing being observed, in which no information has been lost.

The theory of decoherence and the "many-worlds interpretation" began to be developed in the 1950s by one of Wheeler's students, Everett. Somehow, it hasn't really made it into undergraduate physics yet, and most physicists can get by without thinking too deeply about what observation means. You can do most calculations assuming wavefunction collapse happens.

Physicists do have a problem with it.

See : https://backreaction.blogspot.com/2019/08/the-problem-with-q...

Sabine Hossedfelder also discusses it in her book Lost in Math.

Two books on the subject are reviewed in the Booklab podcast, episode 20:


Featured Books:What is Real? by Adam Becker; and Beyond Weird by Philip Ball.

Quantum physics has been with us for more than 100 years – but what is it actually telling us about the world?

That’s because physicists do have a problem with it, and not all believe the wave function collapse is real.

Q. At time t1 = 0, we know the state of our system. Then we send a photon into an atom. Assume the atom absorbs the photon by having an electron move to a different energy level.

Some time later, at time t2, the electron returns to where it was and emits a photon. As I understand, t2 - t1 is random, with exponential distribution, and independent of everything else in the universe. So, at time t2, we cannot recover the state at time t1 or even know just when t1 was. That is, the reversible time evolution equation of state at time t2 can't tell us the random time t2 - t1 or t1 so cannot recover the state at time t1 -- at time t2, we just do not know just when or how we got to the state at time t2.

So, the time evolution equation is time reversible but the event of the emission of the photon is not time reversible.

This thought experiment seems to conflict with the OP. Where am I going wrong?

You are collapsing the wave function at t1 and t2. At t1 explicitly by stating that the state is known, and by t2 implicitly by defining that you have a defined distance t2- t1.

The emission of an photon at an explicit time t2 is not reversible, the emission of an photon according to the wave function of the atom leads to an photon entangled with the atom and the total has a reversible wave function. (For illustrative purposes, when you measure and you find the photon at a distance (t- t2)*c from the atom, then you will also find the atom in a state that has emitted a photon at t2, no Idea if that is especially illustrative.)

It is a bit more difficult to see this because you are describing a continuous time process, however, the answer is that yes you would be able to to figure out the time t1 given you knew had a snapshot of the whole system through the time evolution equation.

Perhaps your confusion stems from the fact that the time t2 is observed, and it seems like you can't go back after that. An easier to grasp manifestation of this problem is that if you find Schrodinger's cat dead you can't tell if was always dead or if was dead only after your experiment. The reason is because that's only with the narrow knowledge of that cat being dead (maybe the would call this the cat state subsystem). It might be unsatisfactory to you, but in the theory of quantum mechanics, if you knew the state of everything (say the room, measurement apparatus, and so on), then you would be able to trace back to whether the cat was alive or dead. The moral is that the measurement looks irreversible if you look only at the system you are observing, but overall, people accept that there is a overarching greater space (the "environment, universe" where everything is just a unitary operation in motion according to the time evolution equation [1]). To be clear, the time evolution equation only admits reversible solutions. So with full knowledge, of say, the room and measurement apparatus, it would be possible to deduce the original state of the cat.


The final state wavefunction, which you need to recover the initial state, contains an exponentially decaying distribution of different t2s. The final state wavefunction is not "here's a definite t2"---that requires measurement.

(I am not a physicist.) One thing I've struggled with around black holes is what it means for anything to fall into a black hole.

From a reference frame outside the black hole, observing an object falling into the black hole, don't we observe time slowing down as the object approaches the event horizon? In this reference frame, does it ever cross the event horizon, or does it just asymptotically approach it? If it doesn't cross the event horizon, how can anything ever fall into the black hole?

(From the reference frame of the object falling into the black hole, my understanding was that the event horizon shrinks away from you as you approach it.)

Please correct/inform me!

The object has physically fallen through the event horizon and long disintegrated but the imprint of its falling toward the event horizon is slowing down to the outside observer. The falling object emits photons along the way which are what the observer sees. These photons of the falling object shining toward the observer have to travel greater and greater distance in the warped spacetime as the object getting near the event horizon so the photons appear to slow down. The spacetime is being "stretched" (warped) more as getting closer to the blackhole. The event horizon is at the point where the spacetime is "stretched more than" the distance the photons can travel to come out.

(also not a physicist) I think you're correct that objects falling into a black hole never cross the event horizon from our reference frame, but at the same time the light from the object red shifts towards zero energy as it approaches the event horizon as well.


Does the fact that the light red shifts towards zero energy mean that the information has been lost, or just that you can't observe it _at_the_moment_?

If the black hole then shrinks due to Hawking radiation, what happens to the object that _never_quite_fell_into_ the black hole?

If it hasn't yet fallen into the black hole, presumably its light becomes slightly-less-red-shifted once more, meaning that you can observe its information again?

There is a somewhat recent theory that supports this idea. It is unclear whether or not things actually fall-in, but the idea is that the entire surface is a hologram, and the surface alone is sufficient to describe the entire contents. (Thus preventing any information loss).

Much better described here:


Good video - thanks!

I didn't quite follow how information came back out of the black hole as it shrank - is it "encoded" on the Hawking radiation?

I believe Hawking thought so, but that's just one possible explanation. Others think it all escapes at the very end.

Isn't this resolved by the holographic principle? (https://en.wikipedia.org/wiki/Holographic_principle)

Yes, but it introduces other problems. And most importantly, it hasn't been successfully tested yet.

Are there even proposed experiments to test this?

My layman understanding of the Holographic Principle is an object falling into a blackhole has it's 3D information copied onto a 2D surface/perimeter (event horizon) and that 2D information can tell us everything about the energy that continues to exist within the 3D volume of the blackhole.

Fractal Mathematics suggests it is possible right? In other words we can infinity extend the perimeter of a shape while maintaining the same volume, but what are the proposed experiments, if any, to observe this phenomena in nature for quanta?

The Holographic Principle shares with String Theory the problem that it is a generic name for a huge number of theories, some that have been falsified already, some practically impossible to test, and some just out of reach.

Requires string theory

She also has a music video about Schrödinger's cat: https://youtu.be/I_0laAhvHKE

Simple: the laws of most physics say you can look at something now and work it backwards. Once it falls into a black hole the previous state of what falls into it isn't able to be derived from working backwards because it just fell into a black hole. This isn't rocket science! (Maybe eventually though)

I’ve heard this idea a lot and it always strikes me as one of those things that’s technically true but wildly off base. I get that the equations are mathematically reversible. Presumably we’re more interested in the world than we are the math though, and in real life almost nothing can be worked backwards. There’s a lamp on the dresser for example. How did it get there? Go ahead and run the kinematics in reverse and tell me which of the infinite solutions is the truth.

... because it just fell into a black hole

That doesn't really explain anything.

I said simply!

I do not think the issues raised here are so simple that you can answer the question without mentioning entropy, which, at first sight, might appear to show that information loss is routine.

Perhaps this is why we perceive time to be going in one direction. The fact that a black hole exists in our universe means that there is only that direction.

To save you the read, the summation is in the second-to-last paragraph:

>As you have probably noticed, I didn’t say anything about information. That’s because really the reference to information in “black hole information loss” is entirely unnecessary and just causes confusion. The problem of black hole “information loss” really has nothing to do with just exactly what you mean by information. It’s just a term that loosely speaking says you can’t tell from the final state what was the exact initial state.

I think the article is already quite concise. Moreover it is nicely written and explains a current open problem in physics from first principles.

A summary like this is useful if the underlying article is bloated and clickbait-y but in this case potentially detracts a reader from a good article.

As featured on the front page a few days ago [1]: knowledge without understanding is meaningless.

[1] https://www.theguardian.com/commentisfree/2019/aug/24/dougla...

For what it's worth, I think the summary is useful.

It’s the opposite of well written and concise! The writing style is very much like someone talking, full of sentences that are too long or too short.

That's because it's a direct transcript of the Youtube video above.

mv universe.info /dev/null

i see no issues there

A black hole is not a singularity. If that were true, they would ALL emit the same Hawking radiation pattern.

She must be a teacher at Professor Xavier's School for Gifted Youngsters.

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