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I How can Andromeda collide with the Milky Way?

  1. Oct 16, 2016 #1
    If everything in the universe is moving away from everything else in the universe, how can Andromeda collide in the distant future with the Milky Way?
     
  2. jcsd
  3. Oct 16, 2016 #2

    Borg

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    Because this part isn't true. Locally, galaxies interact with each other.
     
  4. Oct 16, 2016 #3
    So, what exactly do people mean when they say 'everything is moving away from everything else'?
     
  5. Oct 16, 2016 #4

    Borg

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    You have to keep in mind the scales. Galaxies at distances of billions of light years away are all moving away from each other at significant speeds due to the expansion of space. However the Andromeda Galaxy is only 2.5 million light years away. The magnitude of its speed away from us that is due to the expansion of space is far smaller than the magnitude of its speed toward us due to its existing momentum and gravitational attraction between the Milky Way and Andromeda.

    If someone is telling you that everything includes local galaxies in this case, then they don't know what they're talking about.
     
  6. Oct 16, 2016 #5
    Alright, that makes sense.
    I think it is my own ignorance, when I watch YouTube channels like Vsauce and MinutePhysics that is what I understand from it.
    Thanks for clarifying!
     
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