Hawking Radiation - how could it shrink a Black Hole?

Discussion in 'Physics & Math' started by MyBrainHurts, Sep 29, 2008.

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  1. Gravage Registered Senior Member

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    No, you're wrong. I don't believe in Hawking's radiaton, because the particle with positive energy that escapes the event horizon, is already outside of the event horizon. It isn't exactly on the boundary of event horizon, otherwise it would fall into it, it is all still happening in quantum vacuum (where all particle/anti-particle transformations are made) which is exactly around (OUTSIDE) event horizon.
    Basically what irradiates is not the black hole or event horizon, but the space just outside the black hole's event horizon-black hole itself does not irradiate.
    This is the most illogical Hawking's creation so far.
    Sorry, I have to say this hypothesis, not theory, is totally meaningless.

    Cheers.
     
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  3. prometheus viva voce! Registered Senior Member

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    I don't care what you believe. This is about science, not belief.

    This is true classically, as you can show with the Painleve version of the Scwarzschild metric. Classically there is a maximum possible energy of a particle (that is finite) and a required energy to escape the black hole (also finite) that are the same. Quantum mechanically this is like the potential barrier penetration that has experimental evidence via alpha particles and STM's

    What? Inside the horizon is a vacuum as well you know.

    Firstly, you mean "radiates," and "radiate." Secondly, I have posted a reference in the post you quoted that shows if you consider a shell of matter at the position \(r = 2M - \epsilon\), ie inside the black hole it can tunnel out an escape. You can also show it has a temperature of exactly the temperature that Hawking originally predicted.

    "I don't understand the logic, therefore it's illogical." Nice logic there batman.

    You haven't read or understood the original calculation and you haven't read or understood the modern approaches like tunnelling. Therefore, it's your opinion that's worthless.
     
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  5. Gravage Registered Senior Member

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    Than explain it to me. I must say, I'm not the guy who can't be convinced when it comes to Hawking radiation, all I need is a greater, more complex dose of explanation because I read in Hawking's book at least 10 times this, and I was never convinced. Actually, I'm science-lover, my hobby is science, I usually write to proffesional scientists from different fields to explain me some things that I do not understand, but when it comes to Hawking's radiation, NONE HAS EVER really offered more detailed and more reasonable explanation. I even asked several quantum physicists, but nothing.
    Honestly speaking, the explanation of Hawking's radiation in simple terms is impossible, I'd rather go step by step on how did they come to this conclusion, even if it means to go through complex mathematics.

    You will most likely get angry on me, because of the following questions because there are many.
    The main problem with Hawking's radiation is that it does not explain how exactly radiation comes from the black hole-at least it has never been explained in details in the books I've read by Hawking and the likes.

    Virtual particles/anti-particles. You know what "virtual" means?
    It means it does not exist in the real world, the question that bothers me why did Hawking put a pair of virtual particles?
    What do virtual particles mean in astrophysics/quantum physics?
    What do they represent?

    Rotating black holes should create and emit particles-does the inertion decreases black hole's event horizon?

    I know that Hawking's radiation talks about quantum vacuum which is full of particle/anti-particles pairs?
    But has this been actually proven?
    Has there ever been proven that cosmic vacuum is full of these matter-antimatter particles?

    You said: One virtual particle has negative energy, not mass. It has been shown by Frank Wilczek and Maulik Parikh that the brief history of time description that you have just given is incomplete - the negative energy particle must tunnel into the black hole. They did the calculation in a completely different way to Hawking and got the same result.

    But does it mean that particle with negative energy (anti-particle) actually nullifies one particle with positive energy inside the black hole-which is fully made of smashed particles with positive energy, or simply speaking gravitational field of event horizon which is also made of positive energy shrinks, when anti-particle (particle with negative energy) enters the black hole, because of the positive and negative energy/particle/anti-particle collision?
    Shouldn't that explain why event horizon is shrinking without anything getting out of the black hole's event horizon?

    I found something on wikipedia (I don't know how good guide wikipedia is when it comes to science, especially quantum theory):
    Basically, it describes proofs of existence of virtual particles:
    http://en.wikipedia.org/wiki/Vacuum_fluctuations
    http://en.wikipedia.org/wiki/Hawking_Radiation
    What do you think?

    And is it possible that everything in the black hole is literally destroyed?
    What happens with quarks in such extreme graviational field?
    Does it really end up into one single point, or perhaps even that point is smashed/destroyed, but into what?
    Maybe everything what is left quark-gluon plasma?
    I just don't believe black hole destroys everything if it actually exists, it must be made of something, gravitational field must be made of well gravitons?

    The existence of gravitons has not yet been proven, right?
    What about indirect proof of gravitons' existence?

    I hope I didn't cause you too much headache.
    I hope you will have time and patience for answering this. I hope I didn't cross the line.

    And thanks in advance for explanations.

    Cheers.
     
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  7. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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  8. Gravage Registered Senior Member

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  9. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    I've got nothing else to do anyway.

    Please Register or Log in to view the hidden image!

     
  10. Gravage Registered Senior Member

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    First observational proof for Hawking radiation existence (although not for black hole, but numarical simulation)?
    http://arxivblog.com/?p=300
    http://arxiv.org/abs/0803.0507
    http://www.redorbit.com/news/space/1293008/simulated_black_hole_yields_hawking_radiation/

    This is the same, although, incredibly detailed:
    http://www.iop.org/EJ/article/1367-2630/10/10/103001/njp8_10_103001.html

    Sonic Disruptions Create Artificial Sonic Black Hole:
    http://www.popsci.com/scitech/article/2009-06/sonic-distruptions-create-artificial-black-hole

    New experiments seem to disprove Hawking Radiation from sonic black hole:
    http://blogs.myspace.com/index.cfm?fuseaction=blog.view&friendId=433427688&blogId=494923644

    Black hole effect created in lab
    Scientists seek greater understanding of Hawking radiation:
    http://www.msnbc.msn.com/id/23509238/
    http://cerncourier.com/cws/article/cern/33795

    That's all what I found out for now.
     
  11. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Um, my first reaction to that would be "well duh!".
    A sonic black hole doesn't even begin to approach the energy levels of a real one.
    Without seeing the maths and reasoning on why they'd expect Hawking Radiation from one I wouldn't have expected there to be any anyway.

    From the referenced arXiv document:
    Note the word analogue: i.e a facsimile with some of the features, not all.
     
  12. Gravage Registered Senior Member

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    Maybe yes, maybe no, the fact is physics is trying to explain something that we don't know anything about it and that's the problem, it's a pure speculation, this is why I don't put too much credit into Hawking's radiation or anything that belongs "to the edge of known science".
    The only that we can be 100% sure is that black holes exist, and that's all. What exactly are they none knows, since none has ever visited the black hole, and never will, since he/she would be torn apart before he knows what will be left of him.
    That's all.

    Cheers.
     
  13. BenTheMan Dr. of Physics, Prof. of Love Valued Senior Member

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    This displays a relative ignorance about the calculation.

    Hawking's calculation doesn't make any drastic assumptions---it's a perfectly legitimate field theory calculation done in a classical, time-dependent background. There is no basis to refute either Hawking's assumptions, and there is no basis to refute his conclusions. In fact, Hawking's argument about information loss and black hole radiation can be promoted to a theorem: absent any large quantum gravitational effects (which we can't calculate anyway, and may never be able to), and given the existence of black holes, there WILL be both information loss and radiation from the horizon.

    To challenge the validity of this theorem, you have to show why quantum field theory in a curved background is an unacceptable formalism for treating the problem. This can be done by
    1.) showing that there are large fluctuations from the underlying theory of quantum gravity; or
    2.) invoking witches.
    There may be another way out, but I can ask some people if you'd like.

    Let me give you another example, of a similar calculation, which every student of quantum mechanics is familiar.

    Take a box of length L with infinitely tall walls and put a particle in it. The particle will have well-known energy eigenstates, which are inversely proportional to the length of the box, a fact which you can see by dimensional analysis. Now change the length of the box instantly. The particle, which had a particular set of energy eigenvalues, now has a new set of energy eigenvalues, and has to transition to a different energy level. By conservation of energy, particles must be created to compensate for the change.

    The point is that the ladder operators before the transition and after the transition are different. The eigenstates of the hamiltonian are also different.

    Another example is a harmonic oscillator with a time dependent frequency.

    Anyway, rejecting something out of hand because you don't understand it is an all around pretty ignorant way to go about things.
     
  14. Gravage Registered Senior Member

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    What, just because I disagree with your interpretations, you need to insult me, math geek?
    Ignorant or not, I need experimental and observational proofs, not calculations.
    It's not my fault that I'm down-to-earth person.
    Hawking's radiation is still a hypothesis. I'd give, anyone would give to Hawking Nobel prize if they prove the existence of Hawking's radiation.
     
  15. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I don't do any QFT, but have a different way of understanding the virtual pair.

    They are a system with two positive masses (that is net energy) which can briefly add ~1Mev to that part of space (assuming the pair is electron and positron).

    I don't like the idea that one of them has "negative mass" as I have no problem with brief lack of conservation of energy as long as the uncertainty principle (delta T x delta E) limit is not violated.

    This POV (no negative mass) is also consistent with Dirac's discription of a positron as an electron traveling backwards in time. (i.e. has sign of charge and time's "flow" reversed) I do not especially put much faith in the reality of that POV, but have always liked the aspect of it that explains why all electrons are identical. (Many scaterings of the same one in both the past and in the future so in the "now" we have "zillions'' of views of that one electron. Coupled with the idea that our instrument travel forward in time and can much more easily detect electrons, which also travel forward in time, than the positrons, which are electrons traveling backwards in time.)

    Probably modern physic has some better explaination why all electrons are identical now, but this old POV has a certain charm to it, IMHO.
     
    Last edited by a moderator: Dec 4, 2009
  16. Gravage Registered Senior Member

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    Ok, I apologize but what does POV stand for?
    And what does STM stand for?
    I'll ask you all for a favor for writing full term, please.
     
  17. Gravage Registered Senior Member

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    Never mind, I found it on the net.
     
  18. Gravage Registered Senior Member

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    One thing that bothers me is that temporary violation of conservation of energy even in these most extreme sub-atomic conditions. Everything is energy, all processes, all matter, all anti-matter, all fields, either negative or positive.
    How can energy be ability to work, if entropy destroys/unables usable work, basically no work can be done in entropy, because the entropy is part of energy where there is no usable work?

    Cheers.
     
  19. BenTheMan Dr. of Physics, Prof. of Love Valued Senior Member

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    Apologies, of course. I had assumed that, since you were making statements as someone who has spent a good deal of time actually trying to understand the underlying physical hypothesis, that you would have understood a bit of the vernacular...or, perhaps that you had tried to educate yourself before running across a few words you didn't understand and crying foul.

    Surely, though, none of those descriptions fits you, and you have spent a good deal more time than any of us thinking about the subject. In spite of your lack of training in the subject, or even your lack of comprehension of basic quantum mechanics, you have somehow grasped the essence of the problem, and have something intelligent to say nonetheless. We should all take your opinions on the matter in earnest, because questioning your most sound logic is naive on our part.

    Please, accept my most sincere apologies on the matter.
     
  20. temur man of no words Registered Senior Member

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    It is a nice idea, but it seems to be refuted. I think the idea is due to John Wheeler, not Dirac.
     
  21. NMSquirrel OCD ADHD THC IMO UR12 Valued Senior Member

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    do i dare post here?

    i have read the previous posts..i can understand a little of it..
    if i had to rate myself by the previous posts i would have to put myself below gravage,
    if my life went differantly, i would pry be in one of the science fields,i subscribe to Scientific american and discover, found my interest lie towards space based science..
    i say this so if i ask a stupid question, i will not be berated cause of it..

    first of what is QFT? (quantum field something?)

    second i have been trying to get an answer to my question that i have posted at least twice on this board..to date no-one has responded to my question..

    i am still curious as to whether it is possible or not..

    my question is
    can a black hole be formed in an area with sufficient matter around it, to 'pack' such matter around it, in essence creating a shell around the black hole?..
    now i think this would not be possible with massive black holes,but i have read that black holes can be ANY size (no i do not think the LHC will create a black hole to destroy the earth)
    i do not know the math nor do i wish to learn it so late in my life..
     
  22. AlphaNumeric Fully ionized Registered Senior Member

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    Where to start.....

    Let's start with the 'math geek' comment. It seems to be a common view in people who don't understand much physics that mathematics isn't required to do physics and that its a crutch for those physicists who aren't very good at grasping concepts or thinking about mechanisms, the "Shut up and calculate" crowd. This is false. It's false now, it was fallse 100 years ago, it was false 350 years ago. Newton, possibly the greatest physicist ever, literally invented calculus to help him describe and understand Nature. He lectured mathematics at Cambridge. Stokes, the person whose work leads to the entirety of fluid mechanics, was another mathematics professor, at the very same Cambridge college as Newton (but 200+ years later). James Maxwell, whose 'Maxwell Equations' allow the construction of radios, electromagnets, mobile phones, microwaves, radar, generators and electric motors, was a mathematician. Infact, he too went to the same Cambridge college as Newton and Stokes! Paul Dirac developed quantum mechanics and later its relativistic extension quantum field theory. He went to the Cambridge college next door to the one Maxwell, Stokes and Newton were at (damn you Johns!), as a mathematics student and lecturer.

    Go to any university in the world which teaches physics and you'll be required to sit several mathematics courses because its essential to be able to describe things accurately. Most universities have their relativity research groups in their mathematics departments. Oxford and Cambridge have their entire theoretical physics departments in their mathematics department.

    Saying "Math geek!" to a theoretical physicist is like trying to insult an English major for knowing grammar and being able to spell.

    Now your 'I disagree with your interpretations' comment. Given you were unfamiliar with basic terminology Ben used it suggests that you have not done very much reading around. Your naivity as to the position and use of mathematics within physics further justifies this conclusion. It would seem to be a logical and rational approach to make oneself as informed as possible on a topic before telling other informed people how to go about their job (Ben's job is physics research). I don't tell a doctor he's prescribing the wrong drug just because I've seen an episode of House, I say to myself "I have very little knowledge in this area and so its likely that I'm unable to grasp or know all of the relevant material pertaining to the conclusion I've been given. As such I'll not proclaim the doctor's conclusion as wrong, at most I may suggest he rechecks or gets a second opinion". This seemingly obvious and sensible thought process is clearly not something you're familiar with.

    My explaination about why jumping in saying "You're wrong, wrong, wrong, wrong!" when you don't know the area and have made no effort to find out the information for yourself explains why you don't appear to be 'down to earth'.

    The question of "How does Hawking radiation evaporate a black hole" is not dependent upon the validity of Hawking radiation. How does X do Y doesn't require X to be true, you simply wonder how it arrives at its conclusions.
     
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    The problem with answering you is that the question is not well formed, in the sense one must guess what you mean by:

    "sufficient matter around it, to 'pack' such matter around it"

    If you are asking is it possible for there to be a shell of matter around a black hole, the answer is yes, but it would need to be well outside of the Event Horizon, EH, of the black hole, BH. One could probably have a solid shell of steel, uniformly thick, centered on the black hole only a few times more distant than the radius of the EH, if the BH were small enough. I.e. the compressive force on the steel shell due to BH's gravity did not exceed compressive strength of steel.

    I thnk this configuration would not be stable in that any diviation of the center of the spherical steel shell's center from the BH point, would subject the side of the shell closest to the BH to have a greater force on that side towards the BH; However, it could get to be quite an interesting problem as the Hawking Radiation presure trying to push that side further away should be considered. Perhaps for a very brief time (by human time scales) the net force assocated with a tiny displacement from shell being exactly centered would be one of restoration? (I doubt this is possible, but calculation would be required to know.)

    The question is complicated as one needs to know what is the spectral absorption and reflection of the shell as fct of wavelenght and also same data for transmission of the radiation (gamma rays) that just passes thru the shell, with little momentun transfer to it (Compton recoil electrons escaping from the outside of the shell, etc.) The shell would also get very hot and be radiating too, assuming it is not melted. This radiation from the shell and part of the Hawking radiation that is reflected (or back scattered) has a chance to be reabsorbed by the BH.

    These (and probably other) consideration is why no one has given you a simple answer, in addition to the fact that I at least do not have the slightest idea what you mean by:

    "sufficient matter around it, to 'pack' such matter around it"

    Also you need to specify how long the matter packed around it must stay outside of the EH and how densely it is "packed together." For example one could consider the solar system is matter packed around the large BH at the center of our Galaxy. It is likely to eventually enter within that BH's EH and become part of the BH, but I would guess the universe is many times older than its present age before it does. I.e. just how "stable" do you want your matter around the BH to be?

    Your question is so ill posed that almost any answer (or none) is possible, but I have discussed around it a little to help you pose it better.
     
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