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B How can we see Background radiation

  1. Apr 11, 2017 #1
    CMB was created 380k years after big bang. Then photons were released in the creation of hydrogen.
    How can we still see them today?

    Would they not travel fairly straight forward out of our universe and never return again?
  2. jcsd
  3. Apr 11, 2017 #2


    Staff: Mentor

    Because they were released everywhere in the universe. The CMB radiation we are seeing now was released just far enough away that it is reaching us now. In the future we will see CMB radiation that was released still further away.

    There is no "out of our universe". Our best current model is that the universe is spatially infinite. That does mean that a particular bit of CMB radiation, once it passes us, won't ever return to us again. But there will always be more, from places more and more distant when the CMB radiation was released.
  4. Apr 11, 2017 #3
    What does that mean?, what outside?
    Outside what is observable to us at the present moment?
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