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Big Crunch. What happens at the moment the universe changes direction?

  1. Apr 14, 2010 #1
    According to my minimal understanding, a universe with the fate of the "Big Crunch" theory, has to come to a complete stop before it begins its journey in reverse. My understanding of slowing down, then stopping, is this. No matter how slow and delicate you proceed in doing so, at that moment when you actually stop, there is a measurable jerk, where the matter wants to keep going. On such a large scale (such as our universe), is it possible this might offset the universe greatly, and possibly upset everything in the universe, resulting in pure uncertainty of what will happen next? Think of the possibility of everything in the universe being pushed to one side, not knowing exactly where the partials end up could prevent us from knowing if indeed the universe would then collapse. Or maybe, the universe will decrease in speed, at such a gradual rate, that this above effect will be so minuet it will be almost undetectable.

    I have difficulty imagining the universe stopped, even for a small amount of time. And something must stop in order to change direction.

    Which logic is the case in this scenario? Or is there too much uncertainly to be exact?
  2. jcsd
  3. Apr 14, 2010 #2


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    The only reason the Universe's expansion would come to a stop would be due to gravity. The gravity of every object pulls on every other object. Our current observations indicate that gravity is not enough to slow the expansion to a stop.

    Assuming that it was, there would be no "jerk" anymore than a ball tossed up into the air feels a jerk when it stops moving up and starts to fall back down. You can actually demonstrate this to yourself. Jump up. Do you feel any jerk at the top of your jump?
  4. Apr 14, 2010 #3
    Thanks for that analogy. The concept makes more sense now. So what do resent observations conclude to be the ultimate fate of the universe? Big rip, or heat death?
  5. Apr 15, 2010 #4
    according to our current knowledge the universe is flat [that's why we are able to do geometry]. Dark energy which opposes gravity, from supernovae(carbon detonation) spectral line is seems that the universe is accelerating. Dark energy overrides the effect of gravity so gravity can't stop the expansion [Dark energy violates the conservation of energy, just seems to grow, but its accepted, because that's the only way we can explain the expansion].
  6. Apr 17, 2010 #5
    Thank you for the responses. It's a very fasinating topic for me. I spend much time studying this and wanted to knOw the most resent accepted theory. So all in all, we are likely to be headed into a big freeze, correct?
  7. Apr 17, 2010 #6
    That seems to be the currently favored theory by most physicists today, if my perception didn't fool me too badly.
  8. Apr 23, 2010 #7
    Of course I don't know; but when something comes to a halt, gradually, it looses its kinetic energy, gradually and doesn't "want to keep going". Inertia isn't an issue. So there [PROBABLY] wouldn't be a 'jerk'. If there were, it might only be a jerrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrk. Of course I'm just guesssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssing.
  9. May 16, 2011 #8
    Just a side note on the moment of the stop as you had described it, most of the univerase from what I have seen seems to bellow out in spirals of some kind, not always the large structures themselves, but the galaxies might not have a stopping point for the point as they spiral out, if we spiral in what would happen we would never feel an adjustment because of the sheer scale of the path we are on, There would never actually be a stop but just a mild course adjustment from rotating out to rotating in...
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