I am trying to get a few key points correct regarding expansion and dark energy...

  1. Expansion: the Universe has been expanding continuously at different rates since the singularity that caused the Big Bang. This expansion continued to take place during the interval between the inflation period and the beginning of the dark energy period, so expansion appears to be independent from dark energy. The Universe would continue to expand even if it was not experiencing a force accelerating this expansion.

  2. Dark energy: Theoretically the force that began to dominate gravity about 7 billion years ago and believed to be the reason expansion began accelerating again.

Are these descriptions accurate? Feel free to respond to either


closed as too broad by Brandon Enright, ACuriousMind, Danu, Void, Kyle Kanos Oct 4 '14 at 11:35

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  • $\begingroup$ Dark energy may be responsible for the acceleration of the expansion. It's not clear why you are trying to separate inflation from dark energy. If it's an energy term that causes inflation and acceleration of expansion, it may be the same energy term. At current we have no way of distinguishing between these phenomena. It is further not clear that any of this can be physically separated from gravity, at all. As to 4): the expansion has been observed from the scale of galaxy clusters to all the way to the entire visible universe. 5) doesn't make any sense, whatsoever. There is no "void". $\endgroup$ – CuriousOne Oct 4 '14 at 2:45
  • $\begingroup$ @CuriousOne: Thanks for your comments. This is the wiki page where I read about the void en.wikipedia.org/wiki/Void_%28astronomy%29, but maybe I have misunderstood the information. $\endgroup$ – curiousGeorge119 Oct 4 '14 at 13:53

One. The inflationary period is thought to have lasted from around $t = 10^{-36}$ seconds to $t = 10^{-33}$ seconds after the Big Bang. So while you're technically correct to say it lasted less than a second that's a bit of an understatement.

Two. See my answer to What was the density of the universe when it was only the size of our solar system? for the factors that determine the expansion rate. Dark energy is not solely responsible but it does contribute to driving the expansion.

Four. Galaxy clusters are gravitationally bound structures, that is the mutual gravitational attraction of the galaxies within a cluster is greater than the forces caused by the expansion of spacetime. The expansion is not observed between galaxies within a galaxy cluster.

  • $\begingroup$ Thank you very much...especially for clarifying number 4. This was a very helpful answer. $\endgroup$ – curiousGeorge119 Oct 4 '14 at 14:05

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