EnumaElish said:
Hi, this is from a non-physicist who hopes to follow the glitz, so to speak. My uneducated impression is that "preservation of information" is being treated similar to the postulate of "conservation of matter and energy." I am arriving at this from an understanding that seems to be part of the background to Hawking's speech: if information is not being preserved in this universe, then it must be leaking to another universe, hence the possibility of time travel etc. My question is, how is this commensurate with the 2nd law of thermodynamics (increasing disorder)? Doesn't one rather expect the information content of the universe to be decreasing over time, because of the 2nd law? Isn't a black hole gobbling up information and spewing out thermal energy the perfect mechanism for the "enforcement" of the 2nd law? Why was there a need for the information to go to "someplace else," in the first place?
If this sounds elementary, or even worse, confused, and just possibly, inconsistent, it is because this is the equivalent of me drumming fingers in an attempt to produce a Deep Purple concert, and yet hoping to be in sync with the musical giants at some level.
This looks like a good question to me, but of course I am at best self-educated on these topics, or perhaps semi-educated, or really, to be honest, only just barely house-broken with occassional infantile lapses. However, for what it is worth...
Seems to me that disorder is not the opposite of information, but a kind of information in itself. How do we know the entropy of a universal system? Certainly it must require information to be able to say a system is disordered...
I recall reading about the heat-death theory of the end of the universe...sometimes called the big freeze, which depends on the idea that the total mass of the universe may not be enough to overcome the forces of expansion, so that in the end, each bit of dust in the universe becomes widely separate from every other bit of dust. Eventually no information about location or temperature or anything else can be exchanged between bits. This condition is thought to lead to another big bang...total disorder becoming a new kind of order. The extreme vacuum pressure of such an empty system pulls a new universe out of the hat, so to speak.
I guess if I were to pursue this question I should have to go back to review the field known as Information Theory.
However, Hawking in this paper seems to be talking about something else. In scattering experiments, we shoot xrays or other small probes at a target and get information about the target based on where the xrays come back out. Some of the xrays are absorbed, some are bent or reflected, and some are unaffected. Think of a medical xray photograph, I am sure you must have seen one. Bones and things show up as shadows because the atoms in the bones scatter or absorb the rays.
Only Hawking is taking the case to the extreme. He considers an otherwise empty universe, with a very small radiative input from infinity. You see even the smallest amount of radiation, coming into a center point from infinity in every direction, has to produce a black hole at the center. No matter how small the radiation input at infinity, it all has to add up to an infinitely intense radiation at the center. Infinity times almost nothing is still infinite. Of course you do not need to obtain infinitely intense radiation to produce a black hole, but I hope you get the idea.
But the uncertainty principle throws a ringer. We cannot know, from infinity, exactly where the center is, so, we cannot say that all the radiation from infinity meets up in the exact center to produce a black hole. We have to use a sum over path integral method, which means that each ray has to be thought of not as having a single path, but as being a sum of every possible path. In short, a black hole does not have to form, since the energy from infinity cannot be said to meet up at a commonly determined center. Since the radiation from infinity cannot be said to meet up at the center, it doesn't all just simply add together, so a black hole does not have to be produced.
You see we can only know the three things about the black hole, that is, charge, mass, and entropy. Location is not included. In this simplified case, the information we want is one of location...is there a place where a black hole forms, or is there no such place, hence no such black hole? So you see information (in the form of a very small contribution of energy from infinity in every direction) goes in, but nothing comes back out except a question mark.
So Hawking concludes that information going into a black hole may come back out again, but if it does, it is in a form we cannot use. Hence the analogy of the burning book. Presumably the information in the text is still there in the cloud of smoke, but no one will ever have enough time or energy to get it back out again.
Now I should like to add a personal thought or two, if I have not exhausted your patience already. We have this idea of a universal set, one which contains, well, everything. Then we ask, is there anything which is not part of the universal set? That is, if there is a universe, can it have a baby, connected to itself, but not part of itself? If you say yes it can have a baby, then you are saying it is not really universal.
What is outside of the universe? Nothing. Is nothing something? You will have to decide for yourself, or, as I have done, conclude that the question is meaningless.
Now about black holes. We have ample astronomical evidence that they exist. Are they part of our universe, or do they lead to another universe? Well, what do you mean, another universe?
Here is a potential solution, but you probably won't like it.
Consider two people, let's say, George W. Bush, and Marcus the Honorable Librarian. George gets on Airforce One and proceeds to fly toward Marcus, who is sitting next to his fish pond cursing the racoons. George is in his universe, which includes everything he could ever possibly know about anything. His universe, defined this way, is limited by the speed of light. Even if George is immortal and will live forever, there are definable places from which George will never receive information. This is not due to the fact that he has a pointy little intellect, but more simply because he is moving. His motion toward Marcus (don't be afraid, Marcus, I swear I am just making this up as I go along) results in the irretrievable loss of information about the universe behind him.
Marcus, on the other hand, is sitting quite still, waiting for the little masked bandits to make their approach. He is not moving away from the end of the universe which George is fleeing, so, may he live forever, Marcus could get information about places which George can never know anything about. This is not due to the great scope and depth of Marcus' perception, but due to the fact that he is sitting quite still. As compared to George, anyway.
Marcus and George live in different universes, by this definition. There are things in the Marcus universe that will never be found in the universe George gets to inhabit, and to be fair, George has things in his universe that Marcus cannot ever know. To be sure, there is an overlap. In fact the overlap is nearly identical, but there is still this small difference.
So, The Universe does include everything, but, everything to Marcus is not identical to everything for George.
In fact, we have to give each location and each motion a universe of its own, distinct and separate, to some degree, from every other universe. There is no Universe which contains all universes. To some of the posters on PF, this will no doubt be tantamount to saying that there is no God, but I will leave that argument for another universe.
Thanks for being here,
Richard
