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How can space know how to curve

  1. Jan 23, 2013 #1
    How can space know how to curve from a black hole.
    My understanding is that the no information can escape a black hole
    so how can space know how much to curve?

    Duordi
     
  2. jcsd
  3. Jan 23, 2013 #2

    PeterDonis

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  4. Jan 23, 2013 #3
    Thanks for the reference.
    There was some interesting discussion.

    So technically nothing actually goes inside a black hole it is all frozen in time outside the black hole.

    Duordi
     
  5. Jan 23, 2013 #4
    Margarine can fool mother nature.
     
  6. Jan 23, 2013 #5
    Technically, something does go into a black hole, and whatever that is does not come out. Sometimes a chair is just a chair.
     
  7. Jan 23, 2013 #6
    Space doesn't "know" anything, it just does what it does, and what it does is curve or bend asccording to Einsteins GR equations. That is a first principal concept, not up for analysis unless you want to challenge the foundations.
     
  8. Jan 23, 2013 #7
    Isn't that putting the cart before the horse? :wink:
     
  9. Jan 23, 2013 #8

    PeterDonis

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    No. Things can fall into the black hole; it's just that nothing that happens inside the black hole's horizon can affect anything outside. So the gravity you feel outside the hole can't come from inside the hole; it comes from somewhere else. (As I noted in my posts in that thread, it actually comes from the past history of the object that collapsed to form the hole.)
     
  10. Jan 24, 2013 #9
    What do you mean by that? First of all, Einsteins GR equations are non-linear, and therefore are only solvable via numerical integration, with perhaps the exception of the shperical Schwarchild thinga-ma-bobber.
     
  11. Jan 24, 2013 #10
    I meant Einstein's equations describe how space curves, rather than space curving to keep in line with Einstein's equations. Just joking! :smile:

    BTW, question to anyone who may know the answer - is space 'bending' a scientific term (as opposed to 'curving')?
     
  12. Jan 24, 2013 #11
    What's the diff? Sounds like the same thing to me.
     
  13. Jan 24, 2013 #12

    PeterDonis

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    "Curving" is the term I usually see in papers (or popular books and articles) written by scientists; "bending" seems to be a more colloquial term used by laypeople.
     
  14. Jan 24, 2013 #13

    PeterDonis

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    This is not correct. There are many exact, analytical solutions known to the Einstein Field Equation:

    http://en.wikipedia.org/wiki/Exact_solutions_in_general_relativity#Types_of_exact_solution

    Nonlinear differential equations are harder to solve than linear ones, but "harder" is certainly not the same as "impossible".
     
  15. Jan 24, 2013 #14
    Ok, so maybe there are more exact solutions than the Schwartzchild one, but, in fact, Einstein's field equations are notorious for being intractable analytically, for exactly the reason I mentioned, the non-linearlity of the differential equations. In neuroscience, we have the same problem with Freeman's KV model which couples thousands of non-linear ODE's to model the solutions. Impossible to solve even the simplest scenarios analytically.
     
  16. Jan 24, 2013 #15

    PeterDonis

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    This is true, but it's not as extreme as it appears to be in neuroscience by your report:

    The exact solutions listed on the page I linked to include "simple scenarios" that are pivotal in our understanding of the universe:

    (1) The black hole solutions (generalized Kerr-Newman, which includes Schwarzschild as a special case but also includes rotating and charged holes);

    (2) The FRW solutions, which are central in cosmology.

    It is true that for more complicated cases, which lack the symmetry of the above classes of solutions, we use numerical simulations; but the exact solutions above have given a lot of insight into the key factors involved. So analytical solutions, idealized as they are, are extremely important in GR.
     
  17. Jan 24, 2013 #16
    Point taken. You still haven't addressed my assertion that margarine can fool mother nature, though...
     
  18. Jan 24, 2013 #17

    PeterDonis

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    You're right, I haven't. :wink: I think I'm a counterexample; at least, I am if "margarine" is broadly interpreted to mean "butter substitute". Those haven't helped me lose any weight.
     
  19. Jan 24, 2013 #18
    I still can't believe it's not butter..
     
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