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Gravitational Time Dilation and Contradicting Physical Events

  1. Nov 13, 2011 #1
    Thought experiment:

    Say for instance that a Baseball game is being played out on a planet that is orbiting the outer edge of a black hole. You, from deep in space away from any gravitational source, are watching this game from a powerful telescope. The batter comes up to bat; the pitcher throws the ball; the batter hits! The ball sources into center field, up and over the wall. It’s a home run!

    Well, as the observer in space - time, relative to the baseball game near the black hole, is going much faster than it is for the players on the field. The players witness as the ball soars over their heads and into the stand. Nothing seems strange to them - but as the observer in space - you witness everything occurring in slow motion. Being that everything is slowed, the ball being hit soars slower, the swing of the bat is slower. If you were to calculate the mass of the bat, the mass of the ball, the velocity of the bat and the projected path of the ball - it wouldn't line up.

    Similarly - if you were to attempt to reenact the event with the same size bat and ball and the same swing flowing as you observed in slow motion - you would slowly swing, and miss the ball, because it dropped before it reached home plate. But say for instance you did hit the ball with a slow swing it wouldn't go but a few feet - not many yards and over the fence as you had observed in the game.

    The Physics doesn't line up.

    My question is: 1. Am I thinking of this observation correctly (excluding the obvious gravitational pull of the black hole and its physical effect)? and 2. If this is a "correct" way of thinking - why does the physics not line up?

  2. jcsd
  3. Nov 13, 2011 #2


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    The observer would conclude that the game is either taking place on a rapidly receding stadium, or in a deep gravitational field. To conclude the latter, he'd have to see some nonuniformity in the time dilation.
  4. Nov 13, 2011 #3


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    Another way to distinguish is to watch for 'a while'. The receding stadium would visually get smaller, the stadium in deep gravity well would not.
  5. Nov 13, 2011 #4
    I don't understand how any of that answered my questions. Maybe I'm missing both of your points.
  6. Nov 13, 2011 #5


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    One point is that your question is not specific to gravity or general relativity. The exact same scenario would occur if the stadium was receding from you at great speed, purely due to special relativity. If you can see this, then think whether you have a problem understanding special relativity. Confusion should be easier to clear up in this context before worrying about gravity.
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