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When Dark Energy 'Turned On' in the Universe

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  • derhexer@aol.com
    URL to an interesting article in The Daily Galaxy http://tinyurl.com/76oqqtk When I was younger (not quite halfway to the Big Bang) the universe was going to
    Message 1 of 1 , Mar 31 7:51 PM
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      URL to an interesting article in The Daily Galaxy
      http://tinyurl.com/76oqqtk


      When I was younger (not quite halfway to the Big Bang) the universe was
      going to exp[and, then contract. Now it looks like it will expand and
      expand. Sounds dark and lonely.

      First few paragraphs
      "
      Some six billion light years distant, almost halfway from now back to the
      big bang, the universe was undergoing an elemental change. Held back until
      then by the mutual gravitational attraction of all the matter it contained,
      the universe had been expanding ever more slowly. Then, as matter spread
      out and its density decreased, dark energy took over and expansion began to
      accelerate.


      Accelerating expansion was announced less than 14 years ago by both the
      Supernova Cosmology Project (SCP) based at Berkeley Lab and the competing
      High-z Supernova Search Team, a discovery that resulted in 2011 Nobel Prizes
      for the SCP's Saul Perlmutter and High-z Team members Brian Schmidt and Adam
      Riess. Acceleration may result from an unknown something dubbed "dark
      energy" – or, dark energy may be just a way of saying we don't understand how
      gravity really works.
      The first step in finding out is to establish a detailed history of
      expansion. Unlike supernova searches, which depend on the brightness of exploding
      stars, BOSS uses a technique called baryon acoustic oscillation (BAO) to
      determine the distances to faraway _galaxies_
      (http://www.physorg.com/tags/galaxies/) .
      Baryon acoustic oscillation measures the angle across the sky of structures
      of known size, the peaks where galaxies cluster most densely in the
      network of filaments and voids that fill the universe. Since these density peaks
      recur regularly, the angle between appropriate pairs of galaxies as
      precisely measured from Earth reveals their distance – the narrower the apparent
      angle, the farther away they are.
      Knowing the distance to an object tells its age as well, since its light
      travels from there to here at known speed. And the redshift of the light
      reveals how the universe has expanded since that time, as expansion stretches
      space itself; the wavelength of light traveling through space toward Earth
      stretches proportionally, becoming redder and revealing the _expansion of
      the universe_ (http://www.physorg.com/tags/expansion+of+the+universe/) since
      the light left its source."
      Chris


      [Non-text portions of this message have been removed]
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