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I Do laws of physics apply below the event horizon?

  1. Jan 12, 2017 #1
    Do laws of physics apply below
    the event horizon? It appears as if
    black holes had such gravity as to have an
    escapr velocity higher than c, which means that
    things are pulled inwards at higher speeds than
    the speed of light. Or am I overlooking something?
     
  2. jcsd
  3. Jan 12, 2017 #2

    Simon Bridge

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    The event horizon of a non-rotating black hole is the place where the escape velocity is exactly the speed of light... not faster then.

    From the POV of a distant observer, if nothing else happened, it would take an infalling mass an infinite amount of time to reach the event horizon... but that is not all that happens.

    Oversimplifying a bit,
    The Schwarzschild radius (the radius of the event horizon) depends on the mass.
    If the total mass is inside this radius, then the object is a black hole with this radius.
    If not all the mass is inside this radius, then the object is a star or planet or something.
    There is no way anyone outside that radius can know what is going on inside it, once a black hole has formed.

    You can have a black hole mass M, with mass m falling towards it.
    The radius for M+m is bigger than for M alone.
    When m gets close enough that it is inside the M+m radius: the black hole gobbles it.
    This happens before it reaches the event horizon... so never gets to the speed of light.
     
  4. Jan 12, 2017 #3

    anorlunda

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    Since no information escapes from behind the event horizon, the only thing we can say with certainty is "We don't know."

    Theory does make some predictions, but since they can't be confirmed, they must be called speculation.
     
  5. Jan 12, 2017 #4

    BvU

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    What makes you think that things are pulled inward with the escape velocity ? This guy answers "no" to such a conclusion. Tough reading, but even if you skip the formulas there's enough left over.

    Any of our PF heavies who can rank this article? I see only 2 quotations for S. Krasnikov:
    Gravitation and Cosmology, 2008, Volume 14, Number 4, Page 362
     
  6. Jan 12, 2017 #5

    ZapperZ

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    I'm more interested in finding out where exactly is "below" the event horizon. There is an inside, and outside, but where is above and below?

    Zz.
     
  7. Jan 12, 2017 #6

    phinds

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    Well, WHATEVER goes on inside the EH, those ARE the laws of physics. Our trick is to find out what those laws ARE.
     
  8. Jan 12, 2017 #7

    Nugatory

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    It's pretty good at what it sets out to do, addressing misconceptions. I expect that it gets so few citations because it's not providing new insights from which new developments can be based. Instead it's explaining to non-specialists that which the specialists already know (or suggesting to specialists how they should be explaining what they already know and have failed to communicate).
     
  9. Jan 12, 2017 #8

    Nugatory

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    We don't know for sure, and have no practical way of finding out. But it's really hard to imagine a way in which the laws of physics could be different inside the event horizon of a supermassive (so tidal effects are negligible) black hole but not across a Rindler horizon.
     
  10. Jan 13, 2017 #9

    anorlunda

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    I agree, but we should point out the possibility is that a yet to be discovered law will be that some things are forever unknowable. What happened inside a BH or inside the other universes of multiverses seem like good candidates.
     
  11. Jan 13, 2017 #10

    phinds

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    Things that are forever unknowable are irrelevant, says the practical engineer.
     
  12. Jan 13, 2017 #11
    I agree. Science works with the assumption that there are laws of physics that apply everywhere in space and time.

    But the question of knowability is interesting. If hypotheses are not testable, then they are outside of the realm of science. I would recast the question as:

    Are hypotheses regarding the laws of physics below the event horizon testable?
     
  13. Jan 13, 2017 #12

    phinds

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    I absolutely agree that it is philosophically very interesting to consider that, and the implications are significant for our understanding of the universe.
     
  14. Jan 13, 2017 #13

    anorlunda

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    We could have fun by staging a PF debate on this. The debate proposition could be "We should invest in quixotic science." I realize that the word quixotic adds a bias from the start, but I think it captures the essence. What happens inside a BH? FTL travel? What happened before the Big Bang? What is the weather like in other multiverses? All those have the properties of being supposedly impossible, yet of enormous value if we could make them possible or knowable. Quixotic is the best word.
     
  15. Jan 13, 2017 #14

    phinds

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    You have an odd sense of what's fun, says the practical engineer :smile:
     
  16. Jan 13, 2017 #15

    BvU

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    Says the humour award winner 2016 ! Congratulations, sharp one !
     
  17. Jan 13, 2017 #16
    I disagree. For me, one needs at least a decent case that actual measurements may one day be possible before allowing something into a conversation as scientific at all.

    NOT TESTABLE = NOT SCIENTIFIC.

    Experimental falsifiability is proper demarcation between real natural science and other forms of philosophical pursuits such as debating how many angels can dance on the head of a pin.
     
  18. Jan 13, 2017 #17

    anorlunda

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    There is a grey zone in the middle. For example, lots of physicists study string theory or mulitiverses, even though so far they have not produced testable hypothesis. They are considered mainstream science because they hope to produce testable hypothesis. But eventually they must produce something or support fades away. Provisional science might be a more accurate phrase. Quixotic is a more colorful word.

    if we took a strict black and white view, even mention of those things on PF would violate the rules.
     
  19. Jan 14, 2017 #18

    BvU

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    But now we have to make do with having fun over whether we can ( / should / should not) have a debate. That's nice too, but it does come in second.

    But we did! That was fun too!

    On odd sense of fun is a sense of fun too !
     
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