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Thread: Newtonian physics

  1. #1 Newtonian physics 
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    I read that Newtonian phisics breaks down on the event horizon of a black hole. Could someone explain why if this is so?

    Thankyou.


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    Forum Radioactive Isotope mitchellmckain's Avatar
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    Newtonian physics breaks down when you are traveling a significant portion of the speed of light or when square root of two times the gravitational acceleration times the distance to the center of gravity becomes a significant portion of the speed of light.

    At 75% of the speed of light (or 1.76 times Schwartzschild radius distance from a black hole), Newtonian physics will be off by nearly 50%. Velocities won't add the same way and Newton's law of gravity does not predict the correct motion. Thus under such circumstances you need Einstein's physics. But even Einstein's physics breaks down at the center of a black hole.

    The Schwartzschild radius is the distance from the center of a black hole past which which nothing can ever escape it. At this distance the square root of two times the gravitational acceleration times the distance to the center becomes equal to the speed of light and the deviation from Newtonian physics becomes infinite.


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    How then can we trust either? Is it an illusion that they work at all? Shouldn't we strive for somthing that works accross the board?
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    Forum Radioactive Isotope mitchellmckain's Avatar
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    Why? We use cars don't we? We don't stop using cars just because we can't use them to get from England to Hawaii. We don't stop using planes just because we cannot use them to get to the moon do we?
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    Forum Sophomore biohazard87's Avatar
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    Quote Originally Posted by mitchellmckain
    At 75% of the speed of light (or 1.76 times Schwartzschild radius distance from a black hole), Newtonian physics will be off by nearly 50%. Velocities won't add the same way and Newton's law of gravity does not predict the correct motion. Thus under such circumstances you need Einstein's physics. But even Einstein's physics breaks down at the center of a black hole.



    But this is all just theory, isn't it? I mean no one has been able to prove that this is true, since no one can survive a black hole. Right? I am just courious.
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    Forum Radioactive Isotope mitchellmckain's Avatar
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    Quote Originally Posted by biohazard87

    But this is all just theory, isn't it? I mean no one has been able to prove that this is true, since no one can survive a black hole. Right? I am just courious.
    What I said relies only on the Special and General theories of relativity both of which have a good deal of evidence to support them. Like Newtons theory they may be incomplete and not apply in all circumstances but no physicists doubt their validity where they apply. There is good evidence of but not absolute proof of black holes but although what I said mentions black holes it does not require them to exist. I can simply modify what I said as follows.

    At 75% of the speed of light (or 1.76 times Schwartzschild radius distance from a black hole, if they exist), Newtonian physics will be off by nearly 50%. Velocities won't add the same way and Newton's law of gravity does not predict the correct motion. Thus under such circumstances you need Einstein's physics. But even Einstein's physics breaks down at the center of a black hole, if they exist.
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