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Thread: black holes - whats the problem?

  1. #1 black holes - whats the problem? 
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    I have a few initial questions and as this goes there will probably be many more...

    1. Why would the emmense ammount of gravity cause people to think it would change the laws of physics beyond the event horizon?

    2.Why is there the information paradox? I don't see how information is being lost... is it not just being moved to the inside of the event horizon?

    well thats the start but i can almos guarntee more will come up :wink:


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    Case researchers may have solved

    Contact: Susan Griffith
    susan.griffith@case.edu
    216-368-1004
    Case Western Reserve University

    The masses on the edge of the incipient black hole continue to appear into infinity that they are collapsing but never fall over inside what is known as the event horizon, the region from which there is no return, according to the researchers.
    http://www.eurekalert.org/pub_releas...-crm062007.php


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    please explain. I read the article but I am not quite sure what it is saying.
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    Hi shawngoldw

    The problem (the way i understand it) occurs when you try combine quantum mechanics and GR which is what ahppens close to the singularity. At those energies and distance scales both theories break down, in that effects one theory predicts cannot be included in the other theory.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  6. #5 Re: black holes - whats the problem? 
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    Quote Originally Posted by shawngoldw
    I have a few initial questions and as this goes there will probably be many more...

    1. Why would the emmense ammount of gravity cause people to think it would change the laws of physics beyond the event horizon?

    2.Why is there the information paradox? I don't see how information is being lost... is it not just being moved to the inside of the event horizon?

    well thats the start but i can almos guarntee more will come up :wink:
    the problem is that the gravity is so heavy yet concenttrated ina tiny space, so you have to use quantum mechanix and general relativity and when u get down to it the theories conflict and gets nonsensical and errthang...
    blahblahblahablahblahblahablah blahablah
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  7. #6 Re: black holes - whats the problem? 
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    ok. that makes sense. What about number 2?
    Quote Originally Posted by shawngoldw
    2.Why is there the information paradox? I don't see how information is being lost... is it not just being moved to the inside of the event horizon?
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  8. #7  
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    Once something has crossed the event horizon it is lost - you can't get it back.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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    so? Why does it matter if we can get it back... isn't it still there just out of our reach? it doesn't get destroyed. it just moves somewhere else.
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    In classical physics, information is conserved from a physics point of view. For example, if you burn a book the ashes still contain the information; in the sense that if it contained different information the make-up of the ashes would be different so it's theoretically possible to recover the information. With a black hole however, regardless of what goes into it, the radiation (Hawking radiation) given off is the same and thats where the paradox arises.
    Although I gather Stepehen Hawking has found a way around this by suggesting that information is conserved in the quantum perturbations on the event horizon.

    I'm not certain about this so anyone who knows better, pleae explain it properly!
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    i thought hawking radiation was the solution to the paradox... but i dont see why there was a paradox in the first place.
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  12. #11 Re: black holes - whats the problem? 
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    Quote Originally Posted by shawngoldw
    I have a few initial questions and as this goes there will probably be many more...

    1. Why would the emmense ammount of gravity cause people to think it would change the laws of physics beyond the event horizon?

    2.Why is there the information paradox? I don't see how information is being lost... is it not just being moved to the inside of the event horizon?

    well thats the start but i can almos guarntee more will come up :wink:
    1. That is Immense Amount. The reason as to why it distorts our presently held physical laws, is due to the singularity scientists claim exists beyond an "event horizon". Space "Bends" to the point where it creates a "rip" in space-time, and thus you have distorted laws of physics. See: Gravitational Singularity

    2. I hold that it is not "lost", for it still exists within the Black Hole. Assuming a Singularity, as well as the ensuing time distortion, the information will reach a "critical point" where it is permanently frozen in time (relative to viewers of course) until the Black Hole collapses. Hypothetically this information could be retrieved if one could get close enough to the event horizon to see it. Which is presumably before the speed of light, so you just need obscene amounts of fuel to do it.

    Quote Originally Posted by river_rat
    Once something has crossed the event horizon it is lost - you can't get it back.
    I don't think anything is capable of fully crossing an event horizon. That would mean going faster than the speed of light. As Zelos, or other physicist-wannabes on this forum have stated, that just "doesn't happen".

    So going by what they say, it merely advances to a point where it becomes completely frozen in time until the Black Hole collapses, where it is essentially destroyed. Do correct me if I'm wrong.
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  13. #12 Re: black holes - whats the problem? 
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    Quote Originally Posted by Jeremyhfht
    I don't think anything is capable of fully crossing an event horizon. That would mean going faster than the speed of light. As Zelos, or other physicist-wannabes on this forum have stated, that just "doesn't happen".

    So going by what they say, it merely advances to a point where it becomes completely frozen in time until the Black Hole collapses, where it is essentially destroyed. Do correct me if I'm wrong.
    You cross the event horizon and hit the singularity in finite proper time though Jeremy, remember time only makes sense on a local level as a rule of thumb in GR.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  14. #13 Re: black holes - whats the problem? 
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    Quote Originally Posted by shawngoldw
    1. Why would the emmense ammount of gravity cause people to think it would change the laws of physics beyond the event horizon?
    When you move into the realm that exists inside a black hole, you can't follow standard Newtonian physics anymore. The rules have changed. This is kinda like how GR explains very massive systems, but fails when you look at very samll systems (where quantum mechanics becomes useable).

    Quote Originally Posted by shawngoldw
    2.Why is there the information paradox? I don't see how information is being lost... is it not just being moved to the inside of the event horizon?
    Well, there's a couple of theories surrounding this argument. The first is that as matter gets "sucked in," the black hole will eventually spit it back out in another form, so the original information (in the form of what the matter originally was) is lost. For example, if you cram a star into a black hole, all that matter will eventually come back out...but not as a star. The star is gone forever.

    Another viewpoint is that black holes never spit out what they have. For example, they just grow and grow, or fill up and stop. So what goes in, never comes back out. Therefore it is lost to the universe, because it cannot do anything else. Matter that used to be one thing, such as a star, can be ejected back into space during a super-nova and become something else...reused. Matter that gets sucked into a terminating black hole, can't do that...so it's "lost." Think of it like an un-reclaimable sector of computer memory.

    Yet another theory suggests that when matter goes into a black hole, it can be annihilated, so even though some matter may come back out, the original whole is lost.
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  15. #14 Re: black holes - whats the problem? 
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    Quote Originally Posted by river_rat
    You cross the event horizon and hit the singularity in finite proper time though Jeremy, remember time only makes sense on a local level as a rule of thumb in GR.
    Yes, but who says the black hole will not collapse before you hit? "finite" time doesn't mean "will arrive before the black hole ends".
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  16. #15  
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    I'm not in the mood to work out the equations - so here is the answer from the Black Hole FAQ

    http://cosmology.berkeley.edu/Education/BHfaq.html

    Won't the black hole have evaporated out from under me before I reach it?
    ---------------------------------------------------------------------
    We've observed that, from the point of view of your friend Penelope who remains safely outside of the black hole, it takes you an infinite amount of time to cross the horizon. We've also observed that black holes evaporate via Hawking radiation in a finite amount of time. So by the time you reach the horizon, the black hole will be gone, right?

    Wrong. When we said that Penelope would see it take forever for you to cross the horizon, we were imagining a non-evaporating black hole. If the black hole is evaporating, that changes things. Your friend will see you cross the horizon at the exact same moment she sees the black hole evaporate. Let me try to describe why this is true.

    Remember what we said before: Penelope is the victim of an optical illusion. The light that you emit when you're very near the horizon (but still on the outside) takes a very long time to climb out and reach her. If the black hole lasts forever, then the light may take arbitrarily long to get out, and that's why she doesn't see you cross the horizon for a very long (even an infinite) time. But once the black hole has evaporated, there's nothing to stop the light that carries the news that you're about to cross the horizon from reaching her. In fact, it reaches her at the same moment as that last burst of Hawking radiation. Of course, none of that will matter to you: you've long since crossed the horizon and been crushed at the singularity. Sorry about that, but you should have thought about it before you jumped in.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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    I've already read that, and I disagree. Your point of view, and someone outside, is "the same". As you are speeding to the black hole, hundreds/thousands of years of time is passing on the "outside". This also means the black-hole is aging hundreds of thousands of years. Assuming time would slow down enough before you were atomized, the black hole would suddenly "vanish", releasing you.

    This, by the way, would account for an explosion of matter from a black hole. assuming hawking radiation, as a black hole vanished, the matter caught up in the black hole (read: Anything it ever "caught") would be released.

    Meanwhile, an outside observer would actually see you as you slowly made your decent (year after year, you'd barely move).

    I fail to see why, exactly, that FAQ claims that only light would experience time distortion. That would mean time-travel is impossible, which defies the effects listed for a black hole. oops.
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  18. #17  
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    It sounds like you are calling on some universal time that the outside observers are privy to. Reference frames are local things. It also seems like you are getting hung up on a co-ordinate singularity. You can't use the Schwarzschild metric at the event horizon!

    You need to move to Gullstrand-Painlevé co-ordinates to make sense of what is happening on the event horizon - and in those co-ordinates the event horizon does not feature like it does in the Schwarzschild co-ordinates.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  19. #18  
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    I believe this discussion futile. You are incapable of comprehending my "simplified" statements (as I don't have a physics degree), and I am unwilling to spend excess time trying to understand your jargon (I have a GED to study for!).

    So, perhaps I'll continue it in PM's at a later date.
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  20. #19  
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    I think you guys have slaughtered this post. :wink:
    Wolf
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  21. #20  
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    lol, ok my simplified post:

    You are confusing time scales - the time it takes for a black hole large enough for you to cross its event horizon without being shredded apart is of the order of 10<sup>99</sup> years. The universe's age is only of the order of 10<sup>10</sup> years. See the problem?
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  22. #21  
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    Quote Originally Posted by river_rat
    lol, ok my simplified post:

    You are confusing time scales - the time it takes for a black hole large enough for you to cross its event horizon without being shredded apart is of the order of 10<sup>99</sup> years. The universe's age is only of the order of 10<sup>10</sup> years. See the problem?
    That's assuming we actually do understand what's going on inside the black hole.

    Personally I beleive you trip over the event horizon and fall out of the universe.
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  23. #22  
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    Quote Originally Posted by river_rat
    lol, ok my simplified post:

    You are confusing time scales - the time it takes for a black hole large enough for you to cross its event horizon without being shredded apart is of the order of 10<sup>99</sup> years. The universe's age is only of the order of 10<sup>10</sup> years. See the problem?
    How is that a problem? You skipped explaining that vital detail. And how you worded it wasn't too good either.

    Rephrase, if you please?
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  24. #23  
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    I'm gonna throw this out there now, before I forget and maybe when those 2 finish their cat-fight :wink: someone will answer it. If at a singularity space-time "rips" and everything falls to infinity or out of existence or to another universe or wherever, would the black hole itself not fall too and the black hole would be gone?
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  25. #24  
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    Quote Originally Posted by Jeremyhfht
    Quote Originally Posted by river_rat
    lol, ok my simplified post:

    You are confusing time scales - the time it takes for a black hole large enough for you to cross its event horizon without being shredded apart is of the order of 10<sup>99</sup> years. The universe's age is only of the order of 10<sup>10</sup> years. See the problem?
    How is that a problem? You skipped explaining that vital detail. And how you worded it wasn't too good either.

    Rephrase, if you please?
    Ok, i played with the equations and got the following results:

    Lets assume we have a black hole of around 10<sup>12</sup> solar masses (so its quite large). We want it to be large so we can cross the event horizon without being torn to shreds by the tidal forces i.e. spagettification = the difference between the gravitational force acting on your head vs your feet which tears you in two. This black hole would have an event horizon of around 0.2 light years in radius, so our candidate black hole would really be a super massive black hole. However, we would barely notice crossing the event horizon as we would only be experiencing 1g's worth of gravity when we did.

    Now the time it would take for this black hole to radiate all of its mass away by hawking radiation would be around 10<sup>102</sup> years.

    The time it would take for us to free fall from 0.8 light years to the singularity (assuming our starting velocity is 0.6 c) would be around 2.5 years.

    I'm just double checking the rest of my calculations as they do not look right - watch this space
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  26. #25  
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    Lets say an object was initially already flying toward the center of the black hole, and the black hole's gravity further accelerates it up to the relativistic limit of C (or lower, if it has a lower relativistic limit) and it's still not at the center yet.

    What form does the energy it should be experiencing as additional acceleration take? Does it start to gain in mass at that point? (Or maybe it has already been gaining in mass for a while by then).

    Does the fact it's spending a longer time than it should in the gravitational field change the amount of force per second that is exerted upon it?

    These are just things I'm curious about. Thought I might as well ask, in case anyone knows. I like how black holes bring out the intricacies of relativity, but I'm never sure what exactly relativity will have to say about some things.
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  27. #26  
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    Someone correct me if I'm wrong but... As the object accelerates towards the center of the black hole the change in energy and/or mass is potential energy being converted to kinetic energy. There is no need for gaining mass.
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