Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Newtonian Dark Energy

  1. Jul 15, 2010 #1
    A very simple way to explain the observable universe expanding:
    Perhaps there is just a bunch of matter surrounding the observable universe and all the observable stars/galaxies are moving per the gravitational field created by matter outside that we have not yet seen. Thoughts?
    Last edited: Jul 15, 2010
  2. jcsd
  3. Jul 16, 2010 #2


    User Avatar

    Staff: Mentor

    A uniform spherical shell of matter exerts a net gravitational force of zero on any object inside it:


    Considering that, how would you distribute your "outside" matter so as to produce a net outward force on all the "inside" matter?
  4. Jul 16, 2010 #3
    The outside matter could be distributed to pull the star/galaxies away as we see it. Just cause we havent seen all matter yet, we cant get zero
  5. Jul 16, 2010 #4


    User Avatar
    Science Advisor

    It's clear this is true of Newtonian gravity. Is it clear that this still holds in an expanding universe that obeys general relativity?
  6. Jul 16, 2010 #5


    User Avatar
    Science Advisor

    Yes, that's proven.
  7. Jul 16, 2010 #6
    On the other hand, how do we know that the area outside the observable universe obeys general relativity?
  8. Jul 16, 2010 #7


    User Avatar
    Science Advisor

    That was not the question.
  9. Jul 17, 2010 #8
    yeah, the question is does this outside matter affect our universe(if it exists without us seeing), off course it does
  10. Oct 12, 2010 #9
    Or are we certain we've seen all matter? to make the net zero.
    perhaps matter outside 'not our observable" is moving opposite direction
    Last edited: Oct 12, 2010
  11. Oct 13, 2010 #10


    User Avatar
    Science Advisor
    Gold Member

    Er, no. jtbell already explained why this does not work. Furthermore, we see distant galaxies [the ones receeding the 'fastest'] as they were billions of years ago, so it us, not them, that is closest to this hypothetical unseen matter surrounding the observable universe. Apparently no one notified the Andromeda galaxy because it is on a collision course with the Milky Way.
  12. Dec 8, 2010 #11
    Could the outside matter's distribution be determined by where matter would most likely agglomerate in multiverses? I assume we have not seen all matter since any dark matter outside our line of sight to another observable galaxy/object would be difficult to detect.
  13. Dec 23, 2010 #12
    but if there is already matter outside the observable universe that means tha the Universe is not expanding only the amount of the Universe we can actually see is increasing. also does that mean that there is a finite point to which te Universe can expand??
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook