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A stupid question

  1. Sep 29, 2005 #1
    the universe is expanding. The space between particles of an object is also expanding. So will the force of expanding eventually break the attractive force between particles?

    stupid question.. help me plz anyway
  2. jcsd
  3. Sep 29, 2005 #2
    According to the mathematics, any two particles will always be attracted unless they are an infinite distance aways from each other. That will never happen so there will always be some force attracting different particles in the Universe.
  4. Sep 29, 2005 #3
  5. Sep 29, 2005 #4
    How about if the attractive force become very weak since the distance between particles is getter longer? Will the particles of an object move apart from each other?
  6. Sep 29, 2005 #5

    Doc Al

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  7. Sep 29, 2005 #6
    Um didn't they recently discover that the rate of expansion was not only increasing but accerlating? Doesn't that throw some of that expanation out the window so to speak?
  8. Sep 29, 2005 #7
  9. Sep 29, 2005 #8
  10. Sep 29, 2005 #9


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    Expansion is, at least at present, an extremely feeble force. It's effects are only apparent over cosmological distances, at which point it is sufficient of overcome the also very weak force of gravity. This causes clusters of galaxies separated by many millions of light years to move apart, rather than together as would be the case if only gravity was acting upon them. In the case of unchecked, accelerating expansion, the force pushing apart galactic clusters increases in strength to the point the clusters themselves would not have enough gravity to hold them together. And then it gets ugly. Ultimately individual galaxies would fall apart, planets fly away from their parent stars, stars stop burning, etc. This is called the 'Big Rip':


    As if we don't already have enough things to worry about.
  11. Sep 30, 2005 #10
    What type of force you are talking about ?

    There is no meaning of force unless you specify it i.e., gravitational, electromagnetic...
  12. Sep 30, 2005 #11


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    Phantom energy... also known as the cosmological constant.
  13. Sep 30, 2005 #12
    There's a lot of confusion about this, and you need to be sure what derivative of the distance between galaxies you're talking about.

    Positive 0th derivative: Space is what prevents everything from being in the same place.

    Positive 1st derivative: (Zero cosmological constant). The universe is expanding, but this is because it started out that way - there's no force acting to make the distance between objects increase if it isn't doing so already (Newton's 1st law)

    Positive 2nd derivative (Positive cosmological constant). The expansion is accelerating. There will be a repulsive force between objects, acting as a sort of antigravity, but it will be tiny on most scales - it will mean that orbits are slightly larger than they would have been without it, but doesn't mean that the distance between objects is increasing over time.

    Positive 3rd derivative (Increasing cosmological constant). The acceleration is increasing. Thus the repulsive force will increase and so the distance between objects will increase over time. Eventually you will get the 'Big Rip'
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