Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Bojowald and Ashtekar: Black hole evaporation paradigm

  1. Apr 7, 2005 #1

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    http://arxiv.org/abs/gr-qc/0504029

    Black hole evaporation: A paradigm
    Abhay Ashtekar, Martin Bojowald
    18 pages, 4 figures
    IGPG04/8-4, AEI-2004-072

    "A paradigm describing black hole evaporation in non-perturbative quantum gravity is developed by combining two sets of detailed results: i) resolution of the Schwarzschild singularity in loop quantum gravity; and ii) time-evolution of black holes in the dynamical horizon framework. Quantum geometry effects introduce a major modification in the traditional space-time diagram of black hole evaporation, providing a possible mechanism for recovery of information that is classically lost in the process of black hole formation. The paradigm is developed directly in the Lorentzian regime and necessary conditions for its viability are discussed. If these conditions are met, much of the tension between expectations based on space-time geometry and structure of quantum theory would be resolve."

    this paper studies black hole evaporation under the arbitrary assumption that the future does not fork at a black hole-----no new universe with a new future is formed. Ashtekar and Bojowald make it clear that this is an assumption, not a conclusion.

    "...the article, we will focus on this scenario. A space-time diagram that could result in scenario b) is depicted in figure 2. Here, the extended, ‘quantum space-time’ has a single asymptotic region in the future, i.e., there are no ‘baby universes’. This is an assumption. It is motivated by two considerations: i) the situation in the CGHS model where detailed calculations are possible and show that the quantum space-time has this property; and ii) experience with the action of the Hamiltonian constraint in the spherically symmetric midi-superspace in 4 dimensions. However, only detailed calculations can decide whether this assumption is correct.

    the CGHS model here refers to some 1992 work by Strominger and others.
     
    Last edited: Apr 7, 2005
  2. jcsd
  3. Apr 7, 2005 #2

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    I am looking forward to the investigation of the case where there are two assymptotic regions in the future.


    Shoot, looks like we are just going to have to wait some more. At least until Ashtekar and Bojowald's other paper comes out. They refer to it here and say it is "in preparation"

    Non-singular quantum geometry of the Schwarzschild black hole interior,

    I have put some more about that paper (which hasnt been posted yet) in the loop gravity links thread.
     
    Last edited: Apr 7, 2005
  4. Apr 8, 2005 #3
    Hi Marcus

    If one had a small to medium size black hole and wanted to keep it around for a while, what might one feed it, in order to counter the evaporation?

    Thanks

    Richard
     
  5. Apr 8, 2005 #4

    Mk

    User Avatar

    Hey nightcleaner,
    I still think of you as a janitor. :)

    Literally, anything. But not too much, because you wouldn't want it to get to big, and not to little, because you wouldn't want it to evaporate.
     
  6. Apr 8, 2005 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    for the size black hole I have in mind, I think feeding once a day would suffice, and I think I should give it one grain of pollen at dinnertime.


    the math puzzle here is to figure out what size black hole would have that big an appetite. perhaps I might be able to calculate it. nice question, Richard
     
  7. Apr 8, 2005 #6

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    it occurred to me to wonder what size black hole would have about the same size appetite as a black goat, or a black lab retriever, such as one might wish to have as a companion on walks.

    the easiest way to calculate it would be with natural units so I will put it in that thread

    I did the calculation in that thread
    https://www.physicsforums.com/showthread.php?p=522389#post522389
    and found that if the mass of a black hole is 6 quadrillion pounds
    then a healthy diet would be about 1000 Calories per diem.

    that is about how much a large dog requires, if one thinks in food Calories however in terms of mass this is still a very small amount. It comes to 3.65 natural mass units per year. 3.65 fleas, 3.65 grains of pollen.
    Black holes have a very efficient metabolism compared to dogs, they get the full E = mc^2 energy out of every bite they take. Most of the energy that you feed a dog goes THROUGH the dog, which is not the case with black holes as far as we know, so perhaps it is not such a good comparison.
     
    Last edited: Apr 8, 2005
  8. Apr 8, 2005 #7
    Hi Marcus

    6 quadrillion pounds is large for a dog. Snow is almost all melted here, just slush in the shady places, and I have been participating in the annual Spring dog poop ritual. It is very like picking up Easter eggs, only you use a special scoop and the object of the hunt is less desirable than a colored egg.

    I have to wonder what the poop of a 6 quadrillion pound black hole would look like. Of course one would have to wait around for it to come out the other end, and that might be a while. Still, maybe there might be some 6 quadrillion pound black hole poop left over around here since before the last Universal Turnover, do you think? What do you suppose fossilized six quadrillion pound black hole poop would look like?

    I was just reading about a collector of dinosaur dung, a mineral called coprolite. When people come across it in rock shops, often the first thing they do is smell it. I don't really have much hope for the future of monkeys. Still, one wonders immediately what coprolite smells like. Hopeless, I tell you.

    nc
     
  9. Apr 8, 2005 #8

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    this is why you should really consider a black hole as a pet. NO POOP!
     
  10. Apr 8, 2005 #9

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    the black hole gets the entire E = mc^2 value of what you feed it

    if you want to feed a hole 100,000 Calories for dinner, well E5 Calories is one energy unit and that is the equivalent of one mass unit, so you just have to feed the hole one small flea, or flea-sized bit of dust.

    but if you want to feed a dog 100,000 Calories of food, that is roughly 100 cans of organic buffalo burger or whatever at 1000 Calories per can, well first of all it might take a while to do it, even if the dog is trying to cooperate. And the reason it is so much more bulky is that the dog only absorbs a bit here and there and passes most of it through.
     
  11. Apr 8, 2005 #10

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    I mean in this universe, where you feed it. What happens in the other universe is their problem

    I remain impressed with the monkeys and basically hopeful. It doesnt seem like such a bad idea to sniff a coprolite, if one is curious.
     
    Last edited: Apr 8, 2005
  12. Apr 8, 2005 #11
    Hi Mk, nice to hear from you again.

    I still am a janitor, sort of, for a little while longer. But there is the smell of change in the wind, and I really don't know what scenes fate has in store for me next. Something will turn up.

    Do you know the origin of the word, Janitor? Roman god, Janus, the two faced one, who stood in the doorway between the years. A doorkeeper. Two faces, one to greet the guest, one to inform the master of the house.

    There is a curious tale about Albertus Magnus, a prelate of the church from some time about the end of the middle ages. I can't reference it for you, but perhaps Marcus will know.

    It seems Albertus was a cleric who lived in the sticks in Italy someplace, and one day he was walking in the woods when he came upon an overturned tree. It was an ancient oak, some hundreds of years old, and there, clutched in the roots, was a glint of something which looked like gold.

    The job of cleric was not highly paid at the end of the middle ages in the sticks of Italy, and maybe we can forgive Albert, who was after all a very lowly cleric and not at all highly trained in the arts of the church, for his sudden interest. He dug and he cut and he dug some more until he had the thing in his hands.

    We are not told what it looked like, but you can assume it was some heathen paganish idol if you want, or, as I do, you can imagine it was a simple and elegant figure of the torso of a naked woman. Such things were often buried under trees in the middle ages, but the ones that remain to us were stone, not gold.

    This wasn't gold either. It was too hard for gold, and perhaps not heavy enough, altho it was heavy. Albert couldn't scratch it, so he knew it wasn't gold. Maybe it was bronze, but how it had not turned green after all those years in the acid soil, we will probably never know.

    Albert was basically a good boy and wanted to do right, so after the customary agonizing he decided to turn the thing over to the proper authorities, and in those days that meant the local bishop. But hayseed clerics don't walk up to the houses of bishops carrying a sack with something lumpy in it. So he took it to the abbey and asked to see the Abbot.

    They made him wait outside at the bottom of the garden. He sat on a stone and held the sack close to his feet. It was a long wait and the afternoon slowly settled toward evening. If you had seen him then, you might have noticed that he sat with his hands folded as if in prayer, but no one of importance noticed hick clerics in those days. If you had come closer, you would have seen his eyes were strange, fixed on the small angular object which he held almost concealed by his palms and fingers. And there was a surrsurrated whirr of words on his lips, like a prayer, but more, like a conversation.

    I could tell you what the object was, or at least what it might have looked like, but I have taken up too much space and time in this subject on PF already, and this is hardly science, unless there is a field of study called Janitorology. Needless to say the fathers of the church took the thing in the sack away from him.

    All I can tell you from history is that the icon or whatever it was played a significant role, perhaps the significant role, in all that later happened to Albertus Magnus who eventually became a famous prelate in the church. And one other thing from history.

    It is recorded that at the gate of the estates of Albertus Magnus which overlooked the harbor and the sea, and whose smooth white stone walls were cool to the touch on the hottest afternoons, there was a niche, a little stone grotto, where a visitor might stand before an ancient, heavy bronze door, carved with figures from church history. And in the door was set a polished face, but we have too many descriptions of the face to believe that any one of them was true. Or this face was animated, and could even greet or address passers by. Such was the power of Albertus Magnus, who had been a simple rustic cleric, but who rose to become a warrior pope, and sole heir to the throne of empire. Rumor has said, if I remember correctly, that there was another face, on the inside of the door, which addressed the Master only.

    I would tell you much more of this story but I have to work tonight and will also need to go do some yard chores before dark. And perhaps Marcus or Warren or someone will wish I would take this chatter elsewhere. I hope not, though, for I am enjoying this corner by the fire, and the little bowl I clutch is often filled.

    Be well,

    Richard,

    ps (Soon to be the The Poster Formerly Known as NightCleaner, now actively seeking a new title and ownership. My current owner has given me two week notice. I come fully equipped for adventurous experiences, and am certified to be only three percent shopworn. Prospective owners may contact me via pm or email. nc)
     
    Last edited by a moderator: Apr 8, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Bojowald and Ashtekar: Black hole evaporation paradigm
Loading...