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Thread: How does a black hole trap entities?

  1. #1 How does a black hole trap entities? 
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    Of course, I'm an uneducated swinewho watches YouTube videos on space topics and then thinks I'm smarter than the average fry, but of course, there are many things I fail to understand.

    I'd imagine space is bent by objects as seem in this quasi-re
    alistic 2 dimensional image here, especially the sun:

    https://cdn-images-1.medium.com/max/960/1*Z6LougKsljhP6lFJnCwRvg.jpeg

    And I've been told that light can't escape black holes, because your velocity would have to be greater than the speed of light to escape one... yet, I think somehow I got it in my head that I visualized a black hole as if the gravity well is as curved as the sun, but unlike the sun, the black hole's volume isn't proportional with it's mass.
    In essence, I imagine it as if the black hole is small and strong enough to curve space so hard in such a small area it has just enough power to wrap around itself in a circle. Look at the picture of the sun's gravity well in the URL above, except image a black hole there, and the dent in space time is much smaller. It would affect less area of space yet with the same strength so it would space would bend into a circle around itself.
    Okay, you might be asking, how is this relevant to black hole? I always thought of it like this; I'm a beam of light, and the sun is present. I'm traveling alongside it, but the sun's curvature affects my linear path by a just enough so I curve only barely. But a black hole is so dense that by passing by it, I enter the event horizon, but traveling straight in my initial hypothetical path isn't possible, because just like the sun, my path bends a bit. But with a black hole, I always imagined trying to go straight while captured inside the event horizon, you'd just end up going in a circle, because there's physically no path to go; the exit is nonexistent due to heavy curvature. I could be wrong, this could just be a figment of my imagination.

    But then, I think, nothing's speed "nothing's speed ≥ C (light-speed)" so if some object would need to travel the speed of light or greater to escape a black hole, then that means the gravitational pull has got to cause an object to travel faster that light towards the singularity, correct? This just doesn't make any sense to me, because nothing can travel C? This has been bothering me for years and I just can't stand it anymore.

    Please send help!


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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Can't see the link. I'm visualizing the 2D rubber sheet representing space time grid. Are you saying the mass of a black hole does not sit at the bottom of the gravity well it formed in the fabric, but that it somehow busts through the well bottom or hangs by a point attached to the bottom , in the shape of a ball? There's no exit from it unless you can break light speed barrier? The implication being that space time can be tunnelled through by a black hole, something like that?


    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by QuinnMcChief View Post
    I'd imagine space is bent by objects as seem in this quasi-realistic 2 dimensional image here, especially the sun:

    https://cdn-images-1.medium.com/max/...lFJnCwRvg.jpeg
    That sort of image is quite a common way of showing the curvature of spacetime, but I don't think it is very helpful. Especially when it comes to black holes.

    And I've been told that light can't escape black holes, because your velocity would have to be greater than the speed of light to escape one...
    It is true that the escape velocity of a black hole is equal to the speed of light but that is not the reason that things can't escape. After all, you can throw a ball up in the air at less than the Earth's escape velocity and it will go up before coming down again. And, if you have a rocket, it can leave the Earth at less than escape velocity because the engines are firing continuously.

    Neither of these are true of black holes: things can't leave temporarily or permanently by providing continuous thrust.

    The real reason is related to the curvature of space time. The geometry gets more and more curved so that, inside the event horizon, all paths lead inwards. There are no directions that are "out" of the black hole. In fact, weirdest of all, the radial direction becomes the time dimension inside the event horizon. So the centre of the back hole is in your future and so, as we know all too well, unavoidable.

    In essence, I imagine it as if the black hole is small and strong enough to curve space so hard in such a small area it has just enough power to wrap around itself in a circle.
    That is pretty close.

    Look at the picture of the sun's gravity well in the URL above, except image a black hole there, and the dent in space time is much smaller. It would affect less area of space yet with the same strength so it would space would bend into a circle around itself.
    Okay, you might be asking, how is this relevant to black hole? I always thought of it like this; I'm a beam of light, and the sun is present. I'm traveling alongside it, but the sun's curvature affects my linear path by a just enough so I curve only barely. But a black hole is so dense that by passing by it, I enter the event horizon, but traveling straight in my initial hypothetical path isn't possible, because just like the sun, my path bends a bit. But with a black hole, I always imagined trying to go straight while captured inside the event horizon, you'd just end up going in a circle, because there's physically no path to go; the exit is nonexistent due to heavy curvature. I could be wrong, this could just be a figment of my imagination.
    I think you've got it.

    But then, I think, nothing's speed "nothing's speed ≥ C (light-speed)" so if some object would need to travel the speed of light or greater to escape a black hole, then that means the gravitational pull has got to cause an object to travel faster that light towards the singularity, correct? This just doesn't make any sense to me, because nothing can travel C? This has been bothering me for years and I just can't stand it anymore.
    This is where it starts getting a bit more complicated. The "nothing faster than c" is from special relativity which only applies locally in the absence of gravity. So it doesn't really apply here. From the point of view of someone outside the black hole, something falling in will reach c at the event horizon (the escape velocity is the same as the velocity a body would reach in free fall) and, although it can't be observed, would be going at more than c inside the event horizon. But to any observers near the falling object, its speed would always be less than c.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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