The Black Hole information loss problem is unsolvable
backreaction.blogspot.com
backreaction.blogspot.com
Ancient philosophers debated the existence of atoms for centuries; then Boltzmann took the theory up to second gear by discovering the implications on temperature and entropy, and then Einstein proved their existence beyond a shadow of a doubt through his work on Brownian motion.
It might take centuries of mathematical work to discover an artifact of quantum gravity that's observable within our macroscopic world, but the work must be done.
I suppose her reason to assume we can't observe this is that evaporation takes extremely long time. For example, a solar mass black hole will take about 10^64 years to evaporate [1] (this is approximately 7 * 10^54 times the age of the universe). Note that astronomical black holes are heavier than the Sun, so take even longer to evaporate.
I suppose the micro black holes [2] might offer a glimmer of hope, but these objects are entirely hypothetical.
[1] https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e... [2] https://en.wikipedia.org/wiki/Micro_black_hole
No. She said there isn't any data. I know the word falsify has become prominent in the last 15 years or so, but a "theory" that doesn't agree with some real world data is just a hypothesis. In other words a theory needs confirmation in addition to not being falsified. This is where the divide should exist between physics and mathematics. You can have a bunch of cool math, but that's not physics. It's not scientific theory by itself. You can hypothesize that it describes the real world, but until there is confirming evidence that assertion is just mental self-gratification.
I'd say this is a bit overly negative. There's value in developing theories and frameworks which aren't yet provable but should be as soon as technology or other theoretical frameworks catch up.
I said "You can have a bunch of cool math, but that's not physics. It's not scientific theory by itself. You can hypothesize that it describes the real world, but until there is confirming evidence that assertion is just mental self-gratification."
The math can be cool - and often is. It's the unsubstantiated claim that it underpins reality that is whackin' ones brain.
I think this is correct to some extent, ultimately unavoidable, and some assumptions can be "inferred" as more reasonable than others, even in the absence of falsification.
By Sabine's stance, the problem of induction [0] hasn't been "solved" because we actually have no reason to assume that past events are at all related to future events. So when we say that induction is possible, we say so because we "like best" that theory of causality, rather than my alternate theory that when you finish reading this sentence, all physics will cease to function and the universe will end.
It didn't happen, but we had no reason to know so ahead of time deductively. However, it is still reasonable (in my view) to believe in induction.
So sure, it's perhaps 'unsolvable', but if a plausible explanation comes around that is consistent with modern physics that seems good to me.
On the other hand, as a friend of mine pointed out, for the anti-inductivists that manage to exist, although they keep suffering from making wrong predictions, they will not see this as a reason to change their philosophy, so they are stuck in an epistemic trap. Since evidence has no meaning for them, no evidence can change their minds.
You have no deductive or a priori reason to know this, rhetoric about "epistemically traps" aside.
All of our data about gravity is equally consistent with the theory “If I drop an apple it will fall only if it is before December 2020” as it is with our theory that the law of gravity will continue to exist in the future as it does today.
Now, if one were to try to construct a theoretical argument, I suspect it would go as follows: "If we assume the world could change in every aspect from moment to moment (e.g. pieces of matter could teleport anywhere in the universe, physical constants might change by the second, laws of physics might change over time or space, the very concepts of space and time might become invalid, ...), then the space of possible worlds is enormous and incomprehensible. If we don't have any rational way of assigning probabilities to any of the possible worlds, then this method of thinking doesn't have any implications for correct actions, because every action could be the best in some possible world; in that case, as long as you assign nonzero probability to the "laws of physics remain constant" universe most of us believe in, you may as well act as though it's the truth." If someone does claim to have a rational way of assigning probabilities to the possible worlds, then that would have to be addressed on its own terms, and any conclusion may be possible; but most such ways that people have proposed will tend to imply that "simple" possibilities are most likely, and "the laws of physics remain constant" will tend to rank highly among them.
I like the tenor of your second argument, it reminds me of Pascal's wager. That said, you're not really addressing the problem of induction. We have no reason why you'd assign a higher probability to the "law of physics remain constant" to the "laws of physics are flipped in the next second", outside of gut reasoning.
If we can use gut reasoning about induction, no reason we can when we assume that quarks are a real thing, or think about this solution to the BHIP.
For those people, it is important to realize that anti-inductivism can't be defeated on its own terms. By usual standards (for some definition of "usual"), the space of possible observations one could make is enormous, and the fact that they keep very, very consistently being in accord with the laws of physics as we've discovered them—often to many decimal places—is immense evidence in favor of "physics as we've discovered it" as compared to "anything might happen". Any viable competing theory would have to be reasonably simple (i.e. not include "billions of specific items that explain all prior observations" as axioms) and would have to make almost exactly the same predictions.
("Newtonian mechanics" is reasonably simple and makes similar predictions at the level most people can see, but with specialized equipment and experiments it has been disproven. "God did it" sounds simple, but either the word "God" smuggles in the extremely non-simple "God is a being whose psychological makeup led him to make the following billions of specific decisions that explain all prior observations", or it amounts to "God is a being who chooses to run the universe according to something approximating Einsteinian mechanics"; in that case, it is possible that God might decide to intervene and do something physics would say is impossible, but if you want to say that God will do any specific intervention, you would have to make a less-simple theory that explains why God would do that particular thing and not anything else, and the longer time passes without any verified physically-impossible miracles, the more unlikely most such theories get. "Intelligent beings vaguely like us arose, and decided to simulate our universe, following rules that approximate Einsteinian mechanics" is also possible—not much different from the God-based class of theories.)
You can't argue that causality is real because it's always worked; that is begging the question.
It's somewhat more fundamental than that: it's attacking the idea that experience can be used in any way. Not believing in inductive reasoning would mean being constantly surprised at everything you see, as it's theoretically just as likely that an object that you saw 1 second ago will disappear as it is that it will not. You would be surprised every day that the sun has risen again.
The "problem" of induction is a different kind of problem from the black hole information loss problem.
Induction can't be tested against experimental data. Induction isn't a testable hypothesis; it's a strategy we have no choice but to adopt if we want to plan for the future at all. So there is no "problem" of induction at all: it's just something we're stuck with.
Proposed solutions to the black hole information loss problem can be tested against experimental data; we just don't have the technical capability to acquire such data yet. That doesn't change the fact that until proposed solutions are tested against experimental data, and some proposed solution passes the test, the black hole information loss problem is not solved.
I could make a theory that says that gravity works exactly as we think it does, except in about 1000 years will cease to function entirely - and that theory would be equally consistent with observation. I would be equally correct in saying that we do not yet posses the technology (time travel) to falsify this theory.
We have to rely on some sort of proxy for the simplicity or elegance of the theory in order to preclude hypotheses like the above. If we find an elegant solution to the BHIP that uses existing QM + GR (which are empirically verified), then that seems like a pretty good resolution even if it can't be observationally verified directly at a black hole yet.
No, we don't. The rule that precludes your hypothesis is much simpler: the laws of physics don't change with time. That doesn't require the laws of physics to be "simple" or "elegant", and doesn't require anyone's subjective judgment about which laws of physics they think are more beautiful.
Why should we believe this rule?
In this context, Sabine is the skeptic of theory writ large.
So many replies taking my argument to be the exact opposite of what it is.
Similarly, science need not, and will not, be hobbled by the "infinite number of unfalsifiable theories" that you raise.
In effect, science tables all these fanciful objections unless and until circumstances and evidence make them relevant. Scence is not metaphysics - it is not attempting to deduce how the world must be; it is trying to find out how it is, and so the sort of arguments that philosophers get entangled in (such as "possible worlds" arguments which ultimately reduce to what a given philosopher can imagine) don't carry much weight. This is not just "something akin" to Occam's razor; it is precisely that, and it is not a vague preference for "beauty" or "elegance".
Elsewhere, Hossenfelder made an insightful comment about falsifiability, along the lines that falsifiability is just table stakes for a hypothesis to make the grade as a theory, and not a guarantor of merit.
I suppose you could - but this vacuous armchair theorizing, which, I hope, took you less than a minute to dream up, has no bearing on scientific theories of gravity, which are based on what has been observed. This does not depend on any concept of 'simplicity' or 'elegance', but, at most, on Occam's razor (which is not, as Wikipedia claims, a matter of "the simplest explanation is usually the right one": it is a matter of eliminating premises that are not explaining anything beyond what can already be explained.)
You're literally stumbling into my conclusion and then arguing that it is different from what I was saying. You can even look at my other replies to you referencing Occam's Razor as exactly the sort of thing I'm talking about.
> not something that needs to be explained
I agree, and I'm saying that Sabine is discounting the same tool that you used to reject my hypothesis. That is my point. If there is an explanation for BHIP that does not introduce any new assumptions or very small assumptions to existing theory, that lends it credence even in the absence of direct observations of black holes, just as we lack direct observation of gravity 1000 years from now.
To put that aside and address your larger point, then if we had just one candidate that provides "an explanation for BHIP that does not introduce any new assumptions or very small assumptions to existing theory", then it would indeed be a plausible candidate explanation. That is not, however, the situation we are faced with: Hossenfelder's argument is that there are many equally plausible (and equally speculative) ways in which the paradox could be resolved (though none that "[do] not introduce any new assumptions or very small assumptions to existing theory"), with no prospect of us getting the data to choose between them (note that Hossenfelder is highly skeptical of choosing between theories on the basis of 'beauty', 'elegance' or other subjective distinctions[1]. As I explained above, Occam's razor is not in this category.)
As far as I know, this argument might fail if some data from a seemingly unrelated field supports just one of the candidate resolutions of the paradox. This might be the point you are trying to make, but if so, your "gravity might fail" analogy isn't helping, as we are not currently faced with multiple, equally-plausible theories of gravity, one of which will be preferred if gravity stops working in 1000 years (speculating that it might do so is neither an observation nor a theory of gravity, it's just speculation.)
[1] https://www.amazon.com/Lost-Math-Beauty-Physics-Astray/dp/04...
> Hossenfelder's argument is that there are many equally plausible (and equally speculative) ways
This is just not true. Most of the resolutions of the past required new conjectures like EP=EPR, whereas recent solutions rely on newer sort of uses of a path integral, but are still built up from basic QFT+GR.
Claiming agnosticism between those two theories is discarding Occam's Razor entirely, as the latter relies on constructing way less strong of assumptions and provides a believable mechanism for information preservation.
>> Hossenfelder's argument is that there are many equally plausible (and equally speculative) ways
> This is just not true. Most of the resolutions of the past required new conjectures like EP=EPR, whereas recent solutions rely on newer sort of uses of a path integral, but are still built up from basic QFT+GR.
As far as I can tell, what I wrote here seems to reflect what Hossenfelder is saying in the article. Here, for the first time, you seem to be making a reasonable argument that the specific hypotheses are not, in fact, all alike, and that they may differ in a way that at least opens up the possibility of applying Occam's razor correctly - i.e. by rejecting any that make unnecessarily broad or strong assumptions.
This brings us to Hossenfelder's follow-on point: we're going to need more data in order to figure out which, if any, is correct [1]. Without more data, neither Occam's razor nor any other principle (and certainly not subjective simplicity) is sufficient to do this - the most you can do is have a preference, based possibly on which you think is least likely to run into problems with Occam's razor. That's not enough to turn a hypothesis into a theory.
This is the point that you started this thread by objecting to, and I do not think you have yet made a strong enough case to overthrow it, though you are now making better arguments than before.
[1] I'm not sure about Hossenfelder's apparent claim that this data can only come from observing black-hole decay, but that's a separate matter.
The problem is that information conservation is a fundamental part of quantum mechanics. QM is a hugely successful theory which has proven itself to be accurate to absolutely incredible precision.
The black hole information paradox implies that there is no way for information to escape the black hole, breaking conservation of information.
The implications of this is huge: Either information can escape a black hole, which suggests general relativity is wrong. Or information cannot escape a black hole, in which case QM is wrong.
So the key to coming up with a solution to this problem is to explain what happens without breaking physics. One suggestion have been that the information actually never enters the black hole in the first place, it's just spread out over the surface of the event horizon.
Not quite. When Hawking radiation is included, it becomes possible in principle for information to escape the hole. That's not the main issue.
The main issue is that any information carried by an object that falls into the hole and hits the singularity inside the black hole gets destroyed. So either that information is lost, which violates QM unitarity, or the information has to get copied into the Hawking radiation that gets emitted, which violates the QM no cloning theorem.
> One suggestion have been that the information actually never enters the black hole in the first place, it's just spread out over the surface of the event horizon.
This doesn't really help, because the information can't just stop at the horizon; if an object falls in, it carries its information with it. So "spread out over the surface of the event horizon" really has to mean the information gets copied there, which, as above, violates the QM no cloning theorem. Some physicists, such as Susskind, claim that this actually isn't an issue because no single observer will ever observe both copies of the information, but this argument strikes me as contrived (and I don't think it's been proven that it must be the case).
Two possible resolutions that seem to me to at least avoid the problems I stated above are:
(1) Quantum gravity effects change the singularity inside the black hole to something else: one commonly suggested possibility is that a "baby universe" is born there, and that baby universe carries the information that fell into the hole. In other words, the information stays inside the hole and doesn't come out in the Hawking radiation, but it doesn't get destroyed either.
(2) Quantum gravity effects prevent a true event horizon and a true black hole from ever forming in the first place. That means there is never any singularity or any place where information ever gets destroyed; quantum gravity effects end up converting all of the objects that fell into the "hole" (which is now not a true black hole, but will still look like one to us on the outside, at least for a very long time) into the Hawking radiation that the hole emits as it evaporates. So no information ever gets destroyed and no information ever gets cloned.
She seems to have a beef with extrapolating (even well-accepted) math, rather than doing experiments. But this kind of work clarifies where the theories clash and break down, how they can work together, maybe even testable predictions.
I wonder if she would have been critical of the Casimir effect, back when it was thought to be untestable.
You know, regular waves (and particles, as waves) go in to the black hole, Fourier-transformed waves (as Hawking Radiation, or whatever else goes out) come out of the black hole...
Now you see it... now you don't!
Hmm, not to go all crackpot or anything (but to go all crackpot! <g>), now that I think about it, it makes me wonder if disappearing sub-particles do that by Fourier-transforming themselves into smaller sub-particles(!) (as waves!), which then radiate outward in space (undetectably, because they're now multiple smaller/higher-energy particle/waves!) from the point at which they "disappeared" from!
If this crackpot theory is true (and let's not kid ourselves, it is a completely crackpot theory! <g>) then NO INFORMATION would ever be lost to the Universe, ever, basically, the Universe would just be doing a whole lot of Fourier Transforms (and Reverse Fourier Transforms!) in the background, all the time, at all particle sizes, but at different time scales relative to that particle size!
In fact, if a particle goes out of scope ("disappears") relative to a Fourier Transform, then perhaps Fourier Transforms are what also, equal-and-oppositely CREATE particles!
And all of this "creation" and "destruction" of particles -- would be at different beat FREQUENCIES relative to scale!
It also leads to a very weird question, which is:
What is the relationship of Gravity to the Fourier Transform?
And, Is Gravity itself just a Fourier Transform -- just at a specific scale?
Also, if Black Holes are Fourier Transforms -- maybe Suns and Stars are too -- just reverse or "Inverse" Fourier Transforms...
?
The multiple solutions to the black hole information loss problem all depend on a set of assumptions that do not have that same degree of experimental evidence and so the concern is that physicists will converge on the solution that they find most comforting, likely based on ideology or whatever is fashionable, rather than converge on the solution that has the most evidence. The article says that getting actual empirical data to determine which competing solution is correct is virtually impossible.
So sure, Hawking radiation can be wrong and we have very little empirical data to support it, but it's not a theory that's competing with any other theories strictly on the basis of math equations derived from a set of assumptions. It's a theory that is almost uniquely derived from a pre-existing set of assumptions that do have a large body of empirical support whereas the solutions to the black hole information loss problem are not.
What additional assumptions (on top of the ones Hawking made) does the new calculation use that don't have a large body of empirical support?
https://en.wikipedia.org/wiki/Black_hole_information_paradox...
> This is why the headline that the black hole information loss problem is “coming to an end” is ridiculous. Though, let me mention that I know the author of the piece, George Musser, and he’s a decent guy and, the way this often goes, he didn’t choose the title.
She's against where the popular media wants to go with the article, and against the headline, but not so much against the article itself.
> In my opinion, the black hole information loss problem is the most overhyped problem in all of science, and I say that as someone who has published several papers about it.
So I'm not sure that she thinks it isn't worth studying. I think she thinks it isn't valid to declare that something "solves" it, though.
Until someone can prove the universe cares whether the info is in a black hole or not, its not really a problem is it? If anything the universe usually shows it doesn't care what we humans think, its going to do its own thing, regardless: i.e., weak nuclear force and "symmetries"
One way to escape this is:
* You accept that the Hawkin radiation contains the original information.
* But it is scrambled in a reversible way, but so hard that you cannot reverse it with the energie available in the universe.
There are nice talk by Scott Aaronson about this, e.g.: https://simons.berkeley.edu/events/theoretically-speaking-se...
Where would the information be encoded?
i.e., hawking radiation is itself unconfirmed, so its a "solution" for something that remains unproven :|
That mismatch is what sets up the BH information “paradox”.
No, it isn't; it hits the singularity inside of the hole and gets destroyed. At least, that's what Hawking's original model, the one he used to predict that black holes evaporate, says.
One way of seeing why Hawking's model had to say this is to combine the following facts about the evaporating black hole and the Hawking radiation in Hawking's model:
(1) The hole itself cannot contain any information other than its mass, charge, and spin (because of the "black holes have no hair" theorem), which is far too little information to describe everything that fell into the hole.
(2) The Hawking radiation cannot contain any information about what fell into the hole because it is thermal, black-body radiation, i.e., the only information it contains is its temperature, which is related to the mass of the hole.
So the information can't be stored either inside the hole or outside the hole, which means it must be destroyed, and the only place it can be destroyed is by hitting the singularity inside the hole.
The black hole information loss problem is that the above is inconsistent with quantum unitarity. So Hawking's original model can't be right; but nobody knows what model should replace it.
Maybe the information gets encoded in digits of value of mass expressed in some unit. There is enough digits to store any finite number of bits.
The particular idea suggested in the GP actually isn't. See my post upthread.
No, it can't, not all the information. Two objects of the same mass but different internal composition would add the same mass to the hole, but would be described by different information. So the hole can't store in the value of its mass which of the two objects fell in.
More generally, a hole of, say, ten Solar masses could have gotten that mass by an infinite number of possible combinations of things falling in. The mass itself can't distinguish between any of those possibilities; all it can tell you is that ten Solar masses total of stuff fell in.
Because that's what the physics says. See below.
> Different composition means different interactions during the fall and different amount of radiated energy.
All of that can be taken into account before the object falls into the hole; the observer outside can measure it all and deduct it from the mass he expects to be added to the hole.
We are talking about the mass that gets added after all that; and for any given mass added to the hole after all those things are taken into account, there are many different possible combinations of objects falling into the hole that can add that mass.
> Infinite number of bits can be encoded in single real number.
We are not talking about math, we are talking about physics. The number of bits that can be stored in an object of finite size is finite as far as physics is concerned.
Approximately, sure, best scales can do around 5 significant digits and null measurements can get us few more digits. But we can't verify equality of mass to arbitrary precision. For elementary particles of same kind, we can assume their masses are the same. But there is infinity of digits available. Perhaps there are no two differently composed bodies that have the same real number as mass (too many options to be different). Then maybe any mass addition to mass of the black hole can encode all the information there is about the body.
This is irrelevant to the argument; our finite ability to measure masses is not what we are talking about. We are talking about what masses are physically possible, whether or not we can measure all of them with unbounded accuracy.
> there is infinity of digits available
You can't have it both ways. If it is physically true that there are an infinite number of digits available to specify an object's mass, then it is also physically true that there are multiple possible combinations of objects whose masses can sum to that same mass (in fact there will be an infinite number of them).
Conversely, if it is not physically true that there are multiple possible combinations of objects whose masses can sum to a given mass, there cannot be an infinite number of digits available to specify an object's mass: there must be only a finite number of possible masses, and the numbers specifying the possible masses must be such that no two such numbers add up to another such number.
And then, as I said, there will be an infinite number of possible combinations of other masses that will add to that mass. The fact that we can't verify that experimentally is irrelevant; your model allows it and that means that, in your model, the unique ID of a given black hole's mass would not uniquely identify the original pieces of matter that formed it, and therefore would not provide the information that you originally claimed it could provide, in the post of yours that started this subthread.
Only if mass conservation is broken, and current theory does not predict this (where does the extra mass go to?). Same applies for the other 'no-hair' theorem properties - spin and charge.
Reference, please?
"Soft hair", so not exactly enough to resolve the information loss problem.
This transition is impossible in Quantum Mechanics and it would suppose a killing blow to Quantum Mechanics if true. So a better way to rephrase our worries is that if Black Holes do not respect unitary evolution then our most precise physical theory is fundamentally wrong.
> The black hole information loss problem is not a math problem. It’s not like trying to prove the Riemann hypothesis. You cannot solve the black hole information loss problem with math alone. You need data, there is no data, and there won’t be any data. Which is why the black hole information loss problem is for all practical purposes unsolvable.
We lack experimental data. We lack a way to get experimental data. All we have is some beautiful mathematics. That's nice, but we don't know if it corresponds to reality. That's true of the paper under discussion, and it's true of all the other papers proposing solutions as well.
https://en.wikipedia.org/wiki/Nordstr%C3%B6m%27s_theory_of_g...
Some theorize that evaporating micro black holes could/should be an observable effect of the Large Hadron Collider. https://en.wikipedia.org/wiki/Micro_black_hole
Sounds like pseudoscience to me.
I wonder what happens if a particle is in early orbit in a black hole and another black hole gets close by and changes the net force. Is that impossible somehow? Can't you grab that particle with a spoon and bail if you are quick?
> Another option is that the black holes do not entirely evaporate and the information is kept in what’s left, usually called a black hole remnant.
One of the topics covered in https://www.startalkradio.net/show/cosmic-queries-black-hole... was about the debate on the black hole information loss problem.
Normally, these particles annihilate each other - however if one crosses the threshold and is not able to escape, it can't annihilate the other particle and that escapes as radiation.
> A pair of virtual waves/particles arises just beyond the event horizon due to ordinary quantum effects. Very close to the event horizon, these always manifest as a pair of photons. It may happen that one of these photons passes beyond the event horizon, while the other escapes into the wider universe ("to infinity"). A close analysis shows that the exponential redshifting effect of extreme gravity very close to the event horizon almost tears the escaping photon apart, and in addition very slightly amplifies it. The amplification gives rise to a "partner wave", which carries negative energy and passes through the event horizon, where it remains trapped, reducing the total energy of the black hole. The escaping photon adds an equal amount of positive energy to the wider universe outside the black hole. In this way, no matter or energy ever actually leaves the black hole itself. A conservation law exists for the partner wave, which in theory shows that the emissions comprise an exact black body spectrum, bearing no information about the interior conditions.
Does it make sense to worry about paradoxes created by black holes evaporating, if we have no evidence that they actually do evaporate in our physical reality?
Is that the same kind of negative energy that comes up in talk of stabilizing wormholes and building Alcubierre drives?
At least that's my super-layman recollection, a lot of space to be wrong in that 1 sentence.
Photon pairs form in the vacuum all the time. When a pair forms at the event horizon of a black hole, it rips the pair apart. Half falls in, and half shoots out into space. The half the falls in, through the effect that rips the pair apart, winds up with negative energy, lowering the energy level of the black hole.
https://www.forbes.com/sites/startswithabang/2018/11/03/ask-...
Most importantly, he argues that Hawking's own popular explanation (often repeated across the media, about the particle-antiparticle pair) is too simple to be correct:
"It's not right, though, in a number of ways. First off, this visualization is not for real particles, but virtual ones. We are trying to describe the quantum vacuum, but these are not actual particles that you can scoop up or collide with. The particle-antiparticle pairs from quantum field theory are calculational tools only, not physically observable entities. Second, the Hawking radiation that leaves a black hole is almost exclusively photons, not matter or antimatter particles. And third, most of the Hawking radiation doesn't come from the edge of the event horizon, but from a very large region surrounding the black hole."
Additionally, the article also writes enough to explain the whole context and gives enough details for those who are interested to learn more.
So it would seem that a charged black hole would evaporate by Hawking radiation until it reached the point where any further mass loss would put it over the charge limit. Physicists don’t think it is then simply going to stop radiating, and so what happens then is I believe still quite open.
There was an article in Quanta a few months ago on this: https://www.quantamagazine.org/black-hole-paradoxes-reveal-a...
https://physics.stackexchange.com/questions/490524/evaporati...
If I understand, the short answer from Stephen Hawking is "no." The only properties they have is mass, angular momentum, and charge.
There are other processes which are not of such kind. Some people don't want to call those quantum processes, but they sure do have a prominent place in QM textbooks. For example spontaneous emission of light from an excited atom or radioactive decay of uranium atomic nucleus. Description of these processes isn't reducible to unitary evolution, instead irreversibility is assumed by employing the golden rule.
The measurement / collapse / decoherence / forking-of-worlds / entanglement-with-the-environment is either time-irreversible by definition, or time-irreversible FAPP.
For example, Penrose proposes that the gravitational field induces one of these time-irreversible processes:
> You need data, there is no data, and there won’t be any data. Which is why the black hole information loss problem is for all practical purposes unsolvable.
She didn't say it was inherently unsolvable, only that it was practically unsolvable. There's still the possibility that it could be solved with some other data that doesn't require observing black hole evaporation.
He seems a little non-committal if not skeptical.
One telling exchange near the end regarding the gravitational path integral they used:
* * *
"1:18:41 SC: And there is this trick that you can introduce, ’cause what you’re supposed to do is say, well, integrate up all of the spacetimes that match on to this particular wave function you’re looking at. But the trick is, instead of integrating all the four-dimensional spacetimes that match on to this condition you’re looking at, you can just say, well, I’m going to integrate over all four dimensional spaces, so I’m going to forget about spacetime. I’m just going to do what we call the Euclidean path integral because Euclid just talked about space, not time. And…
1:19:13 NE: Oh, you went there. [laughter]
1:19:15 SC: I did, I did. This is where I’m going. And so it was sort of like you could justify… It’s a trick. It’s a mathematical trick. And it’s very rigorously justifiable in certain simple cases in quantum mechanics, and it certainly has the smell of being correct in certain more subtle cases in quantum field theory. In quantum gravity, what they were doing with it, it just seemed to be a trick so they could get a finite answer at the end of the day, and it was very unclear why it had anything to do with the real world, but they suggested it did. Maybe they were right. And since then, I think we’ve become a little more comfortable with the idea that we can use this trick of calculating quantum gravity wave functions by integrating over the Euclidean path integral, the set of all the spaces that end up looking like what we want, instead of all the spacetimes that look like what we want.
1:20:05 NE: Yes.
1:20:05 SC: And that’s what you’re doing, isn’t it? That’s the kind of wormholes that you’re invoking.
1:20:09 NE: Yes, right. That’s what I was trying to sweep under the rug.
1:20:11 SC: I know. [laughter] And you were right to do so, but I just like to live dangerously here.
[chuckle]
1:20:18 SC: So Lenny and Juan have wormholes that are literally good old in spacetime wormholes, and you have wormholes that are in these fake Euclidean spaces that you used to calculate the entropy.
1:20:29 NE: That’s exactly right. Yeah, that’s exactly right. And these fake Euclidean spacetimes have more boundaries. There are more edges than our original spacetime, which means that these wormholes are connecting these… More edges than we have in our original spacetime, and therefore, it’s difficult to make sense of them in terms of the original spacetime that we’ve started with."
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Link?
This same argument can be made about a ton of things. For example, we have yet to observe free quarks directly (due to confinement in QCD), but I don't think people are saying that the quarks model is just the one that we happen to find most pleasing. The reason we are confident in the quarks model is because it makes all sort of other predictions that we can confirm.
Who is to say that the various ways of resolving the BH information paradox are indistinguishable simply because we can't observe the evaporation directly? Maybe they make other predictions as well.
Generally, I think that we need to be skeptical of various speculative ideas and in many ways we have strayed off course for a while in theoretical physics, but I don't think the answer is to just explore topics and theories that are completely grounded in observations and experiments.