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Dark Energy, Distance to Galaxies and Distance in time.

  1. Feb 21, 2009 #1
    I've read that Dark Energy was invented to explain why galaxies really far away are moving away from us faster than ones closer to us. Now I'm sure they did this, but did they take into account that if they look at 2 galaxies A and B. Galaxy A is 500 million ly away and B is 5billion ly away, so, galaxy B would also be 4.5 billion ly older than galaxy A and therefore receding from us at a faster rate since according to bing bang the galaxy was expanding faster 4.5 billion years ago than it was 500 mililon years ago? or do they take this into account and still find that the universe is accelerating?

    Also. is there a website I can go to to find the reletive speeds of galaxies that have been observed and measured and what not?
  2. jcsd
  3. Feb 21, 2009 #2


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    What is ordinarily listed is a galaxy's redshift.

    You should learn how to calculate the recession rate (the rate the distance is increasing) from the redshift. There is a calculator for that. the URL is in small print in my signature.
    Or google "cosmos calculator". Morgan's calculator will be the first hit.

    We observe galaxies with a big range of redshifts from low numbers like 0.5 to 1.0 to 1.5, to 2 to 3 up to 6.5 or 7.

    The redshift of the microwave background is 1090, larger than that of any galaxy.

    Why don't you try Morgan's calculator and see if you can get it to work.
    If you have any questions, ask!

    When you first open the calculator you need to type in three numbers, over on the left:
    From the top down, the three numbers are .27, .73, and 71
    These are the parameters of the standard model.
    Then all you do is type in some redshift like, say, 5, or 6. and press calculate.

    If it doesn't respond when you put in a new redshift and press calculate again, please let me know. I will back up your calculation and make sure it's giving the right answer.
  4. Feb 22, 2009 #3


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    Dark energy was not 'invented', it was necessary to explain observational evidence. No scientist desired this solution, it was an evil they could not refute. The DE hypothesis is very fragile. Almost any stray observation could kick the stool out from under it, but, it still stands.
    Last edited: Feb 22, 2009
  5. Feb 22, 2009 #4


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    Bear in mind that there still remains the possibility that it's explained by modified gravity, but for theoretical reasons this seems rather less likely. Investigations are underway...hopefully we'll understand something about the cause of the accelerated expansion within a decade or so.
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