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

Dark Energy, Space Expansion

  1. May 15, 2015 #1
    Dear PF Forum,
    Thanks readers for giving me so many explanations about space expansion in my previous thread.
    However, I've forgot to ask 2 things that I'd like to know the answer.
    Space is expanding. According to Hubble Law?
    What cause space expands?
    1. Dark Energy?
    2. Does space its own have property to expand at certain rate?

    Thanks for any explanation. :smile:
  2. jcsd
  3. May 15, 2015 #2


    User Avatar
    Science Advisor

    Space expands because it was expanding before now. It retains the inertia of the previous expansion. Gravity determines how that expansion changes over time, and dark energy is a factor in influencing how gravity operates on the expansion.

    But what caused the expansion to start in the first place? That we don't know.
  4. May 16, 2015 #3
    Thanks Chalnoth for your answer.
    But I'd like to ask further,
    What do you mean by "space RETAINS its inertia"?
    Or do the GALAXIES retain their inertia?
    According to Hubble Law, it's space that expand. 67km/3ly/second if I'm not mistaken.


  5. May 16, 2015 #4


    User Avatar
    Science Advisor

    You can describe it either way. The two descriptions, "space is expanding," and, "objects in the universe are moving away from one another," are two different ways of describing the same underlying phenomenon.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook