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Why galaxies are rushing apart

  1. Jul 10, 2012 #1
    in weinberg's first three minutes he wrote:
    I'm starting to regret reading this book. he came out with an updated edition in 1993 but it looks like he didn't correct his mistakes. it looks like he just put a small forward at the end of the book because clearly there are some things that were known in 93 but not in 79 that should have forced him to correct some passages. in any case dark energy was not known until 1998, so i just want to make sure that galaxies are rushing apart due to dark energy and that the above passage is wrong.
  2. jcsd
  3. Jul 10, 2012 #2


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    Quite a bit of the book is outdated, as is the issue you are concerned about, and you are correct that his "updates" were inadequate, but it is still a book worth reading.

    EDIT: and yes, in direct answer to your specific question, he didn't know about dark energy, which IS the name we give to WHATEVER it is that is causing the ACCELERATION of the expansion of the universe (but not the expansion itself). See:

    www.phinds.com/balloonanalogy for a small amount of further discussion.
  4. Jul 10, 2012 #3
    No, dark energy is not causing the expansion if the universe. It's causing the acceleration of the universe. The concept of an expanding universe is an effect of general relativity, and has been well understood since Friedman proposed an expanding universe. In general relativity, distance is defined in terms of the metric. When we say the universe is expanding, we mean the metric is changing - the distance between galaxies is changing. If you held rulers in between every galaxy, you would find that, after time, these rulers no longer measured the full distance.

    This effect of expansion is caused by the presence of any matter or energy in a particular space-time. This was Einstein's dilemma - he tried to introduce the cosmological constant to avoid this fact. But, you know how the story goes from there.

    However, Weinberg's statement that galaxies were driven apart by an explosion is also incorrect.
  5. Jul 13, 2012 #4
    What I think the shape of the universe before the big bang was a few millions giant stars each star equals to a billion times of the size of earth .......
    Last edited: Jul 13, 2012
  6. Jul 13, 2012 #5


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    You really should not post nonsense on a serious physics forum. It doesn't go over well here.
  7. Jul 14, 2012 #6


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