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Thread: black holes and light

  1. #1 black holes and light 
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    I have heard about the effects on light when passing a black hole.I know that a black hole has a gravity so high that it sucks light.And that there is a point light orbits a black hole. So I was wondering if there is a point where light gets turned around and flies back into the direction it came from. And we could see the earth as it was thousands of years ago. If of course we had a telescope Capable of looking a distance that big. (please don't mind my English, I'm Dutch)


    Last edited by jras; February 3rd, 2013 at 05:23 PM.
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    Quote Originally Posted by jras View Post
    I have heard about the effects on light when passing a black hole.I know that a black hole has a gravity so high that it sucks light.And that there is a point light orbits a black hole. So I was wondering if there is a point where light gets turned around and flies back into the direction it came from. And we could see the earth as it was thousands of years ago. If of course we had a telescope Capable of looking a distance that big. (please don't mind my English, I'm Dutch)
    Understanding that English is not your first language, it's still important to use words that accurately describe what it is you're referring to.

    Think of a road that is properly banked-or tilted in a curve. As you drive into the curve that is properly banked (that is to say the outside edge of the road is higher than the inside edge) you will not need to turn the steering wheel. You will move in a straight line- through the curve.
    Light does this as well and one example is gravitational lensing.

    In the case of a Black Hole (BH), the spacetime around the BH is so heavily warped that light is constantly banked back inside of the BH. It moves at "c" the entire time. Since light has no mass, it is not gravitationally bound to the BH. However, spacetime is and light must travel through space.
    With the space so heavily warped, all paths lead back inside of the BH.


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    if i understood steven hawking correctly than light can never escape a black hole. but if light orbits a black hole than we could fligh to a black hole and watch us. but then we have to invent technology wich is more powerful than light. or am i wrong?
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  5. #4  
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    Since light has no mass, it is not gravitationally bound to the BH.
    it is otherwise you wouldn't get lensing. having or not having mass doesn't come into it. light will follow the geodesics in space like any other object. plus you have the photon sphere...

    Photon sphere - Wikipedia, the free encyclopedia
    Sometimes it is better not knowing than having an answer that may be wrong.
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