turbo-1 said:
This passage is located in Susskind's paper: "I make a number of comments about Smolin's theory of Cosmic Natural Selection."
[quote from paragraph 8 of Susskind 29 July paper]
From the final (side by side) statements:
[quote about Overbye, Gerald 't Hooft, etc etc. information that goes in hole can't be lost]
I find this statement to be a bit tough to take. Indeed, "nothing can be lost from the outside world"? If a black hole strips the matter from an orbiting star, and that matter ends up on the opposite side of the BH's event horizon, then matter (and the information that it represents) has disappeared from our universe. In contrast, Hawking radiation - promotion of virtual particles to real status just outside the event horizon, results in a net gain of information in our universe, if we regard virtual pairs as quantum probabilities and real particles as information-bearing entities. Susskind is a smart man, and he drags 't Hooft (a Nobel laureate) in as ballast for his ideas on this point, but I sense a disconnect in his definition of "information". Perhaps it arises from some fundamental differences in the way information is handled in String and QFT as opposed to GR.
Turbo, thanks for pointing me to the right spot. I see that the two black holes coallescing business is harmless. It's just a quibble about how you do the statistics, or indicates Susskind hasnt understood the CNS idea.
If you stipulate in the model that for one hole you get one baby universe then the model will predict parameters that maximize the total number of holes formed----the total number of galaxies times the average number of holes per galaxy.
About the information loss point----your second quote---Smolin answered that in his half of the side-by-side statement. I will bold the relevant passage about information preservation or loss.
---quote---
The rest of this note concerns Susskind's comments about black holes. He says, "...we have learned some things about black holes over the last decade that even Stephen Hawking agrees with [13]. Black holes do not lose information." From this he draws the conclusion that "the quantum state of the offspring is completely unique and can have no memory of the initial state. That would preclude the kind of slow mutation rate envisioned by Smolin."
This is the central point, as Susskind is asserting that black holes cannot play the role postulated in CNS, without contradicting the principles of quantum theory and results from string theory. I am sure he is wrong about this. I would like to carefully explain why. This question turns out to rest on key issues in the quantum theory of gravity, which many string theorists, coming from a particle physics background, have insufficiently appreciated.
The discussion about black holes "losing information" concerns processes in which a black hole forms and then evaporates. Hawking had conjectured in 1974 that information about the initial state of the universe is lost when this happens. Susskind and others have long argued that this cannot be true, otherwise the basic laws of quantum physics would break down.
As Hawking initially formulated the problem, the black hole would evaporate completely, leaving a universe identical to the initial one, but with less information. This could indeed be a problem, but this is not the situation now under discussion.
The present discussion is about cases in which a black hole singularity has bounced, leading to the creation of a new region of spacetime to the future of where the black hole singularity would have been. In the future there are two big regions of space, the initial one and the new one. If this occurs then some of the information that went into the black hole could end up in the new region of space. It would be "lost" from the point of view of an observer in the original universe, but not "destroyed", for it resides in the new universe or in correlations between measurements in the two universes.
The first point to make is that if this happens it does not contradict the laws of quantum mechanics. Nothing we know about quantum theory forbids a situation in which individual observers do not have access to complete information about the quantum state. Much of quantum information theory and quantum cryptography is about such situations. Generalizations of quantum theory that apply to such situations have been developed and basic properties such as conservation of energy and probability are maintained. Using methods related to those developed in quantum information theory, Markopoulou and collaborators have shown how to formulate quantum cosmology so that it is sensible even if the causal structure is non-trivial so that no observer can have access to all the information necessary to reconstruct the quantum state [c]. Information is never lost — but it is not always accessible to every observer.
So there is nothing to worry about: nothing important from quantum physics [d] is lost if baby universes are created in black holes and some information about the initial state of the universe ends up there.
A second point is that there is good reason to believe that in quantum gravity information accessible to local observers decoheres in any case, because of the lack of an ideal clock. In particle physics time is treated in an ideal manner and the clock is assumed to be outside of the quantum system studied. But when we apply quantum physics to the universe as a whole we cannot assume this: the clock must be part of the system studied. As pointed out independently by Milburn [e] and by Gambini, Porto and Pullin [f], this has consequences for the issue of loss of information. The reason is that quantum mechanical uncertainties come into the reading of the clock — so we cannot know exactly how much physical time is associated with the motion of the clock's hands. So if we ask what the quantum state is when the clock reads a certain time, there will be additional statistical uncertainties which grow with time. (In spite of this, energy and probability are both conserved.) But, as shown by Gambini, Porto and Pullin, even using the best possible clock, these uncertainties will dominate over any loss of information trapped in a black hole. This means that even if information is lost in black hole evaporation, no one could do an experiment with a real physical clock that could show it.
I believe this answers the worries about quantum theory, but I haven't yet addressed Susskind's assertion that "we have learned some things about black holes over the last decades. Black holes do not lose information."
I've found that to think clearly and objectively about issues in string theory it is necessary to first carefully distinguish conjectures from the actual results. Thus, over the last few years I've taken the time to carefully read the literature and keep track of what has actually been shown about the key conjectures of string theory. The results are described in two papers [g].
In this case, I am afraid it is simply not true that the actual results in string theory — as opposed to so far unproven conjectures — support Susskind's assertions [h]...
---end quote---
According to standard cosmology, the universe was about a million years old before it was cool enough to allow the first atoms to form. Then we had to have a period of condensation (perhaps 100My), and another period (maybe another 100-200My or so) to allow the formation of the first generation of super-massive stars to provide heavy elements from which life could arise. Then, those materials had to be dispersed and cooled, you get the picture... By the time some rudimentary form of life could have arisen (to play the role of observer), the universe would have had to evolve in an orderly fashion for probably at least a billion years without an observer.