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B Why are only hydrogen and helium created

  1. Jul 31, 2017 #1
    in the beginning the big bang only created hydrogen and helium.

    why is that?

    was there just not enough time to create heavier elements or is there another reason?

    thx.
     
  2. jcsd
  3. Jul 31, 2017 #2
    A small amount of Lithium as well.
    The problem after that is the next element, Beryllium, cannot be made by fusion of Lithium with Hydrogen or Helium.
    (If it did happen, that would be an unstable isotope which would quickly decay back to lighter elements)
    After Lithium, the next sustainable fusion reaction is fusion of 3x Helium to 1 Carbon.
    This occurs in stars, which have a stable high temperature and density in the core, and it is a more lengthy process than H to He,.
    Immediately after the big bang conditions were not like that, the Universe was rapidly expanding and temperature falling.
    https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
     
    Last edited: Jul 31, 2017
  4. Jul 31, 2017 #3
    thank you very much for the answer.

    I will dive into the info you gave me.

    cheers
     
  5. Jul 31, 2017 #4

    kimbyd

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    Gold Member

    Yes. The universe became too cool for nucleosynthesis after only about 20 minutes. It takes much longer to fuse heavier elements, as they need long chains of sequential reactions to produce. So elements heavier than helium were only produced in trace quantities.
     
  6. Jul 31, 2017 #5
    wow, that is very very short.
     
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