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Thread: Is there anyplace in the universe where there's no gravity?

  1. #31
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    Quote Originally Posted by mkline55 View Post
    Forget about the "light cannot. . . " diversion. What about a "clock" that was generating gravitational waves? Would it appear to be faster, slower, or non-existent compared to a similar "clock" outside the BH?

    <edited to change the word choice>
    We cannot get any form of information from inside a BH. None. Your question just can't be answered.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  2. #32
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    The question from DaCaptain was, "Wow, so what would happen if we could place that same clock at the center of a black hole? Would we would be seeing into the future or into the past?"

    All I see are attempts NOT to answer that question. Let's take a different approach. Lots of you like to play games with semantics instead of directly answering questions. "Place" doesn't mean "toss". To place a clock in the center of a black bole, you would have to be within that black hole. You would have to physically put it there and leave it there. There is no assumption of the size of that black hole. So for this question, I choose a black hole exactly 20 billion light years in radius. The matter is not very dense, and therefore not crushing you as you place the clock at the center. The forces of gravity are pretty nearly balanced out in all directions. Mathematically (not practically) would I, no longer at the precise center of this black hole be able to calculate the rate of time on the clock to be any different than that on on my watch?
    Depending on whom you ask, everything is relative.

  3. #33
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    Quote Originally Posted by mkline55 View Post
    The question from DaCaptain was, "Wow, so what would happen if we could place that same clock at the center of a black hole? Would we would be seeing into the future or into the past?"

    All I see are attempts NOT to answer that question. Let's take a different approach. Lots of you like to play games with semantics instead of directly answering questions. "Place" doesn't mean "toss". To place a clock in the center of a black bole, you would have to be within that black hole. You would have to physically put it there and leave it there. There is no assumption of the size of that black hole. So for this question, I choose a black hole exactly 20 billion light years in radius. The matter is not very dense, and therefore not crushing you as you place the clock at the center. The forces of gravity are pretty nearly balanced out in all directions. Mathematically (not practically) would I, no longer at the precise center of this black hole be able to calculate the rate of time on the clock to be any different than that on on my watch?
    As I think I understand mainstream explanations of black holes, the clock at the center would be crushed beyond recognition in a finite amount of time as reckoned locally, and you would be done in likewise in a finite amount of time as reckoned by your watch. During the descent from the event horizon to "crush depth", if the clock is between you and the center you would observe it to be time dilated. An observer outside the event horizon would see nothing.

    In a thought exercise we could have a low-density spherical body which has just contracted into its event horizon, and is still low density throughout. This would only be temporary, as the material would fall headlong into the center. An observer outside the event horizon would see or feel nothing during this final infall. An observer falling in with the aforementioned material would feel nothing initially but would start becoming spaghettified within a finite time as reckoned from his watch. We could not have a steady state here, if I understand the explanations of the theory correctly.

  4. #34
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    Quote Originally Posted by mkline55 View Post
    The question from DaCaptain was, "Wow, so what would happen if we could place that same clock at the center of a black hole? Would we would be seeing into the future or into the past?"

    All I see are attempts NOT to answer that question. Let's take a different approach. Lots of you like to play games with semantics instead of directly answering questions. "Place" doesn't mean "toss". To place a clock in the center of a black bole, you would have to be within that black hole. You would have to physically put it there and leave it there. There is no assumption of the size of that black hole. So for this question, I choose a black hole exactly 20 billion light years in radius. The matter is not very dense, and therefore not crushing you as you place the clock at the center. The forces of gravity are pretty nearly balanced out in all directions. Mathematically (not practically) would I, no longer at the precise center of this black hole be able to calculate the rate of time on the clock to be any different than that on on my watch?
    Thank you mkline55. All I asked for was an answer using a little imagination. Where would we be without it?
    I know that I know nothing, so I question everything. - Socrates/Descartes

  5. #35
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    Quote Originally Posted by DaCaptain View Post
    Thank you mkline55. All I asked for was an answer using a little imagination. Where would we be without it?
    But any imagined answer would be a fantasy based on an unreal scenario. Basically you'd have to change the BH until it wasn't a BH, for the question to reflect any possible scenario where it was answerable.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  6. 2018-Sep-27, 11:25 PM

  7. #36
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    Quote Originally Posted by DaCaptain View Post
    Thank you mkline55. All I asked for was an answer using a little imagination. Where would we be without it?
    Nobody's being unimaginative. And nobody's attempting to not answer the question.

    The only meaningful answer is that - as the clock nears the EH - it will be increasingly time dilated.


    If what you're asking is: what would the laws of physics do if we changed the laws of physics?
    Then the answer is whatever you want them to do! Unicorns appear.
    (I'm not being facetious. That question often comes up on science forums, and this is a standard answer.)

  8. #37
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    Quote Originally Posted by DaveC426913 View Post
    Nobody's being unimaginative. And nobody's attempting to not answer the question.

    The only meaningful answer is that - as the clock nears the EH - it will be increasingly time dilated.


    If what you're asking is: what would the laws of physics do if we changed the laws of physics?
    Then the answer is whatever you want them to do! Unicorns appear.
    (I'm not being facetious. That question often comes up on science forums, and this is a standard answer.)
    Very true. My apologies. It was one of those questions that I asked on the spur of the moment. My imagination got the best of me.
    Last edited by DaCaptain; 2018-Sep-28 at 12:01 AM.
    I know that I know nothing, so I question everything. - Socrates/Descartes

  9. #38
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    Quote Originally Posted by DaCaptain View Post
    Very true. My apologies. It was one of those questions that I asked on the spur of the moment. My imagination got the best of me.
    I should add a qualifier:

    There's absolutely nothing wrong with creating Thought Experiments that explore an idea that we can't actually test. One can take liberties with certain impracticalities that would get in the way of a good exploration. But it's a skill to determine what details can be bent for the sake of the thought experiment and what details cannot be violated.

    eg: What if the Sun instantly disappeared? Would the Earth feel it right away?
    We can bend the physics of how the sun could be instantly "snuffed out", but we can't ignore the fact that the mass cannot simply teleport away. Getting snuffed out doesn't explicitly violate a law of physics that's relevant to the experiment, but pretending the mass can vanish without physically dispersing (and the consequent ripples in space time) would definitely be a break from the laws of physics that would render any subsequent conclusions invalid.

    Keep up the creative thinking.

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