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

Cosmic horizon of 42-billion light-years?

  1. Jul 27, 2011 #1
    I recently read the new Scientific American and in one of the articles it says that the observable universe can see a distance of 42 billion light-years away but my question is that the big bang is predicted to have occurred at approximately 14 billion years ago, so how can the observable universe be 42 billion light-years?
     
  2. jcsd
  3. Jul 27, 2011 #2
    There is a well written FAQ on this:

    https://www.physicsforums.com/showthread.php?t=506987 [Broken]

    In mathematical terms, the radius of the observable universe is (REF: Introduction to Modern Cosmology, Eqn. A1.12):

    ro = 3 c to

    ro = radius of observable universe
    c = speed of light in vacuum
    to = age of universe

    This formula will match your numbers.
     
    Last edited by a moderator: May 5, 2017
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook