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B Are all galaxies moving away from the Milky Way?

  1. Nov 27, 2016 #1
    Once again I am reading and trying to understand more about the different theories of the beginning of time/space. I don't know why I never thought about this, but they say that galaxies are moving further and further away. One day we will not be able to see them because they moved so far. My main question is how is everything moving away from us? In retrospect wouldn't some galaxies be getting closer, or does that make us the center of the universe, or is it an optical illusion?

    Thank you for your time to reply.

  2. jcsd
  3. Nov 27, 2016 #2


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    Regarding galaxies there are two factors. Space everywhere is expanding. This means that distant objects get further and further away from each other. We see all distant galaxies receding from us, but so would someone in another galaxy. To them, our Milky Way would be receding.

    No galaxy, therefore, is at the centre of the universe. It has no centre.

    But, galaxies that are not so far away are attracted gravitationally to each other and move towards each other faster than space is expanding between them. These local clusters of galaxies will eventually collide and merge. For example, the Milky Way will eventually collide and merge will the Andromeda galaxy.
  4. Nov 27, 2016 #3
    Just in theory,what if we were on a planet looking at the sky but we were on the most distant galaxy the one that is approximately 14 billion years old would everything look like it was still moving away, or coming towards us? As I am doing my research I have noticed a relentless amount of information about other theories outside of the big bang, and the information just keeps expanding like the universe seems to. Other than mathematics where to start seems crazy, just the definitions and explanations in all of this leave me with more questions than answers. I love it, where should I put down all of my questions so I don't flood out the forum board? Any ideas?


  5. Nov 27, 2016 #4


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    If we consider one of the most distant galaxies that we can see - that is at the limit of our observable universe. We will be at the limit of the observable universe for someone in that galaxy, but their observable universe will extend as far again in all directions, including galaxies outside our observable universe.

    Each galaxy therefore is at the centre of its observable universe and, in this respect, no galaxy is special.
  6. Nov 27, 2016 #5
    The overall picture should look the same for any galaxy anywhere in the Universe.
    The most distant galaxies from them will seen to be receding increasingly fast, less distant ones not so fast, and closeby ones hardly receding at all, some of them actually getting closer, like Andromeda is to the Milky way.
    Last edited: Nov 27, 2016
  7. Dec 3, 2016 #6
    Well. once i've heard that Andromeda is coming to colide with us.
  8. Dec 3, 2016 #7


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    yeah ... post #2 of this thread
  9. Dec 3, 2016 #8
    Consider a balloon, fill some air and mark two dots. Draw a line joining the two dots. Now enter more air into the balloon. As the balloon expands, the dots separate more and the line between them extends. This is happening with the galaxies. As the universe itself is expanding like the balloon, we see other galaxies in every direction moving away from us.
  10. Dec 3, 2016 #9


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    @Pbody101 you might find it informative to read the one-page discussion provided by the link in my signature
  11. Dec 6, 2016 #10
    500 galactic years from now, all galaxies outside of the Milky Way local group will disappear behind the cosmic horizon.
  12. Dec 7, 2016 #11
    Thank you Jack, for your reply. That is a very simple and easy to understand way of looking at it.

    I will definitely read it! Awesome, thank you.

    Crazy when you think about it, it makes me wonder if our galaxy is expanding as well.
  13. Dec 7, 2016 #12
    My understanding is that the gravitational force in our galaxy and galaxy cluster and supercluster is sufficient to nullify the expansion of space within it/them.
  14. Dec 7, 2016 #13


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    No, it is not. This is explained in the link I gave you.

  15. Dec 9, 2016 #14
    Cool, I am sorry I haven't been here with stupid questions I have been on a journey from the begging in Mesopotamia. It all began with what we understand now, and strangely led me to the past. Ironically the ancient past, perhaps it is because I can understand it clearer @phinds I read the article and it was wonderfully written. It explains a lot that didn't make sense to me.

    although it is still hard for me to grasp the fact that the universe is expanding pulling against things at a rate that is crazy, and it would have no effects on galaxies. That is why I am an idiot, and I ask questions.

    I will re-read the article.

    sorry if I sound crazy tonight I had a little to drink
  16. Dec 9, 2016 #15
    We've established that the cosmic light horizon exists due to space between galaxies expanding at a speed that is faster than light. Does this horizon apply to gravity as well since gravity propagates at the speed of light? If so, this should mean that the particle horizon is also the point after which the gravity of matter can no longer have any effect whatsoever on Earth. Is this correct?
    Last edited: Dec 9, 2016
  17. Dec 20, 2016 #16
    How do we know that our Big Bang was not just a local big Bang of an infinite number of other far off Big Bangs?
  18. Dec 20, 2016 #17
    We don't and there are a number of theories which conclude that there could be a 'multiverse'.
    However there is no evidence of that being a fact, and unlikely there will be since these other universes are not causally connected with the one we are in.
    That means there is no way of obtaining any information about them (if they do indeed exist)
    What *might* happen in the future is that we find a way to peer further back than the CMB radiation.
    That could rule out multiverse proposals, or maybe it could strengthen the case, but at present the idea is only a hypothesis based on mathematical speculations.
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