• Question: how many particles are there in the universe

    Asked by SPEC BOY to Christie, Dan, David, Dawn, Sian on 14 Jun 2016.
    • Photo: Christie Waddington

      Christie Waddington answered on 14 Jun 2016:

      There’s a number called the Eddington Number, named after the astrophysicist Arthur Eddington, that is an estimate of the number of protons in the observable universe (and atoms are made up of protons, neutrons and electrons). The Eddington number (NEdd) is estimated to be around 1.57×10^79 protons i.e.:
      15747724136275002577605653961181555468044717914527116709366231425076185631031296.

      In terms of how many particles there are in the whole universe is impossible to say, because we don’t know how big the universe is!

    • Photo: Dawn Lau

      Dawn Lau answered on 14 Jun 2016:

      The universe that is visible to us is estimated to have about 10^80 atoms, assuming most of the atoms in the universe are hydrogen.

      But then dark matter is also unaccounted for in this number (I think). Maybe David knows a bit more about this?

    • Photo: Sian Thomas

      Sian Thomas answered on 20 Jun 2016:

      Looks like Christie has done some work here :-).

      Great answer, and of course, if we don’t know how big something is then it is difficult to estimate other things in relation to this.

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