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

Expanding Universe & Red Shift

  1. May 21, 2009 #1
    We hear that the universe is expanding, and this accounts for red shift as all objecsts are accellerating away from eachother.

    But I have also heard that it is the space itself, of which the universe made, that is expanding - not that things are moving in that space.
    If so, then the distances between objects as measured in this expanding space is presumably constant, since the "rulers" would also be expanding in that same space.
    And in this case, there would be no red shift.
    Clearly, I'm wrong, and I'm hoping someone can straighten my out on this.

    This might relate to another puzzle I have.
    I am told not only that things are moving away from eachother, but that things are accelerating away from eachother.
    Since these objects are isolated, what is the constant force which is causing this acceleration?
    Or, if we are way beyong Newton at this point, how is this accelleration caused?

    Thanks again, Chris
  2. jcsd
  3. May 21, 2009 #2


    User Avatar
    Science Advisor

    Rulers are not expanding.

    The acceleration of expansion (discovered about ten years ago) is due to something given the name "dark energy". No one knows what it really is, although it seems to be related to the "Cosmological Constant" in general relativity.
  4. May 22, 2009 #3


    User Avatar
    Science Advisor
    Gold Member

  5. May 24, 2009 #4
    Bound systems - held together by gravity or electromagnetic forces - can oppose the expansion so they don't change. At least for now.

    Newton still holds, but we presently don't know what is causing the observed acceleration. There are lots of theories, but no definite answers as yet. That's why we're still making bigger and better telescopes to study it further. If we knew why, then the need for the scopes would be less.

    Beware of physicists with too many answers. They might be trying to sell you something ;-)
  6. May 24, 2009 #5


    User Avatar

    universe is expanding. maybe not! think if the photons ,we see in Hables telescope, are with more or less energy they change colors spectre - so if in middle of universe is huge super-massive black hole , which evidence universe , then on its way photon loose energy and we see it as red or violet or blue..
  7. May 24, 2009 #6
  8. May 24, 2009 #7


    User Avatar

    uh thanks!!! thats help a lot....
    anyway - do we have thread - how universe is made?

    btw it was idea i made myself - that i liked ;(
  9. May 24, 2009 #8
    Last edited by a moderator: Apr 24, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook