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How do black holes destroy information and why is that a problem?
61–70 of 93 posts
Re: How do black holes destroy information and why is that a problem?
#62Earlier quoted context omitted.
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…
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:
https://en.wikipedia.org/wiki/Black_hole_information_paradox
> 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:
https://iopscience.iop.org/article/10.1088/1367-2630/7/1/203...
> 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:
https://www.newscientist.com/article/dn6193-hawking-concedes...
> “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.”
Re: How do black holes destroy information and why is that a problem?
#63> 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…
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 disc…
You’re just hiding the loss:
The loss in your operation occurs when you zero out z, and there’s no way to implement it without that loss.
If it’s reversible, how do you zero out z, from the environment?
The energy cost of a computer fundamentally comes from having to use energy and discard information (heat) in clearing z.
Re: How do black holes destroy information and why is that a problem?
#64> 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…
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…
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.
Re: How do black holes destroy information and why is that a problem?
#65Earlier quoted context omitted.
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: https://en.wikipedia.org/wiki/Black_hole_information_paradox > 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 Hawkin…
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.
Re: How do black holes destroy information and why is that a problem?
#66A black hole is not a singularity. If that were true, they would ALL emit the same Hawking radiation pattern.
Re: How do black holes destroy information and why is that a problem?
#67Earlier quoted context omitted.
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 infi…
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.
Re: How do black holes destroy information and why is that a problem?
#68(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!
Re: How do black holes destroy information and why is that a problem?
#69The 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
Re: How do black holes destroy information and why is that a problem?
#70(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 do…
(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.