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Thread: hawking radiation... why?

  1. #1 hawking radiation... why? 
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    What is Hawking radiation?

    My conception is that it has something to do with particles and anti-particles which mutually pop into and out of existence. In this case however, the anti-particles fall into the black whole while the other of the pair remains on the outside of the event horizon... is this what is going on?

    Why are the anti-particles falling in and the normal particles not?


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  3. #2  
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    dang man cant remember exactly what is going on but i see in your question you seem to think that only one type falls in. Its both particle and anti particle can fall in.

    So a particle and anti particle are created next to the event horizon.

    sometimes neither falls in and they annihilate each other.

    sometimes the anti particle falls in and the particle then gets a chance to exist and heads off on an adventure

    sometimes the particle falls in and the anti particle gets to head off.

    and i'm sure there are times they both fall in and thats the end of both.

    hawking radiation is the stream of particles and anti particles that leave. Apparently at that level you also cannot assume that all the particles and anitparticles will eventually annihilate each other.i was wondering that myself and found some physicists explaining it at askascientist(i think) but couldnt find the explanation when i looked just there. can any one else explain it?


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  4. #3  
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    ok here it is. can i put this here?its lifted straight from askascientist

    Question: Dear Sirs,

    Regarding Hawking Radiation, the usual
    description is that one member of a virtual particle pair enters a
    black hole, leaving it's orphaned partner roaming our universe,
    appearing to have been radiated out of the black hole. If two such
    processes take place, the first orphaning the virtual matter
    particle while the second orphans the virtual antimatter particle,
    can these two orphans meet and annihilate each other? If your answer
    is "yes" this suggests Hawking Radiation is only a temporary
    phenomenon, awaiting only sufficient time for all orphan /
    anti-orphan particles to either: meet and vanish, or vanish into a
    black hole which need not be the same black hole into which its
    original pair creation particle vanished.
    ---------------------------------------
    Christopher,

    The one fault in your analysis lies in your interpretation of
    probabilities. Your analysis assumes that every particle, given enough
    time, will eventually meet up with every other particle in the universe.
    If a virtual antiparticle exists, it will eventually meet up with a
    virtual particle of the same kind. It is quite possible for an event to
    have less than 100% chance of occurring over infinite time. If not,
    then one could conclude that EVERYTHING has a 100% chance of occurring,
    given enough time. This then leads to the conclusion that everything
    that CAN happen eventually WILL happen.

    A simple example that such an interpretation is incorrect lies in
    radioactive decay and half-lives. Within a second's time, a radioactive
    particle has a certain probability that it will decay. If this is 50%
    per second, we cannot say that the probability is 100% after 2 seconds.
    Should the particle survive one second, then there is only a 50%
    probability that it will decay during the next second. Should it
    survive the 2nd second, there is only a 50% probability that it will
    decay during the 3rd second. This continues on. A radioactive particle
    does not ever have to decay. If you have 100 million such particles,
    the odds are quite high that half of them (50 million) will decay during
    the first second. It is quite likely that half of what remain (25
    million) will decay during the 2nd second, and so on. This pattern
    continues so long as there are a very large number of particles present.
    There is always a chance that no particles will decay in the first
    second, but it is not likely to occur. When you get down to the level
    of individual particles, probability behaves quite differently. It is
    truly random.

    One can never say that something with less than 100% chance of happening
    will definitely happen. This is one of the properties of quantum
    physics that Albert Einstein could not bring himself to accept. You
    cannot say that the antiparticle will meet a corresponding particle.
    You cannot say that it won't. And even if they do come close together,
    you cannot say that they will interact. That too is based only on
    probability.

    Dr. Ken Mellendorf
    Physics Instructor
    Illinois Central College
    ================================================== ================
    This is not my area of expertise, but your propositions seem reasonable.
    The probability of virtual anti-matter particle and a matter particle
    meeting in space-time, while not zero, would be quite small it would seem.
    The same is true, I would think, for the virtual anti-particle encountering a
    star, another black hole, etc. would also be very small. What is unknown is
    whether matter particles, e.g. electron itself, has a finite lifetime. Yes
    it is long, but it may not be infinite. These very fundamental questions
    await answers.

    Vince Calder
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  5. #4  
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    but if both particles and antiparticles fall in with equal probability, then this will not result in a reduction of mass of the blackhole over time.

    I would like to understand the effects which lead to a anti-particle being more likely to fall into a black hole while the normal particle stay outside. this would reduce the black holes mass over time - cosistent with the statement ' black hole evaporation '
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  6. #5 Re: hawking radiation... why? 
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    Quote Originally Posted by mbstarr
    What is Hawking radiation?

    Imagine a very steep hill 1,000 miles long. At the 750 mile mark from the bottom, you place two cricket balls next to each other. One rolls downhill (into the black hole) and the other rolls uphill and escapes it's gravity.

    Sure it does! Doh!
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  7. #6  
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    Quote Originally Posted by mbstarr
    but if both particles and antiparticles fall in with equal probability, then this will not result in a reduction of mass of the blackhole over time.

    I would like to understand the effects which lead to a anti-particle being more likely to fall into a black hole while the normal particle stay outside. this would reduce the black holes mass over time - cosistent with the statement ' black hole evaporation '
    It is not that the antiparticle is more likely to fall into the black hole; antiparticles no more have negative mass than regular matter does. What happens is that the energy to create the virtual pair doesn't really exist. This is okay as long as the particles rejoin before a time determined by the uncertainty principle. IOW, you start with "nothing" then get "something", and as long as that "something" goes away again before a certain period of time occurs, all is right in the world. The creation of the pair is "borrowing" energy that is not there, but that borrowed energy must be paid back. Its like writing a check on an empty account. For a short time you have more money than you really have, but you have to put that money into the account before the check clears or you are in trouble.

    However, if one of the particles falls into the event horizon, and the other doesn't, then they cannot rejoin. the particle outside the event horizon becomes "real". But since energy must be conserved, the energy for this must come from somewhere, and that somewhere is the mass of the black hole.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  8. #7  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Ah. I was wondering about that. Makes a lot more sense now.
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  9. #8  
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    What I wondered was if you have an "empty area" between the event horizon and the core of a black hole, then virtual particles could appear there, and if not charged, no anti-particle, so a black hole could endlessly gain mass that way by any particle that appears becoming part of the central mass before it can disappear again.
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  10. #9  
    Forum Radioactive Isotope MagiMaster's Avatar
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    If they're both inside the event horizon, they'll cancel out, just as if neither were near a black hole. It's only when a virtual pair appears very close to the event horizon that Hawking radiation occurs.
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