• Question: If the big bang produced equal numbers of quarks and antiquarks then why didn't they all annihilate each other back into radiation? And why was it matter not antimatter that survived?

    Asked by Newell to Jackie, Michele, Oliver, Vicky, Yelong on 16 Mar 2015.
    • Photo: Jaclyn Bell

      Jaclyn Bell answered on 16 Mar 2015:

      This is an interesting question and one scientists are still looking into. The big bang should have created equal amounts of both matter and antimatter particles, which are always produced in pairs and destroy one another when they meet, leaving behind a lot of energy but nothing more. I am glad something went wrong otherwise we wouldn’t be here today!

      During the big bang all of the matter and antimatter should have annihilated each other – However a tiny bit of matter managed to survive. The symmetry in the universe between matter and antimatter has gotten lost at some point and so now we live in a universe which is asymmetric. Some research suggests that some particles oscillate between being matter and anti-matter millions of times a second just before they are about to decay, and so maybe more particles decayed as matter than antimatter? This would give a reason to why there is more of one than the other – but it is still a hot topic in research and may take many more years to be understood.

    • Photo: Michele Faucci Giannelli

      Michele Faucci Giannelli answered on 16 Mar 2015:

      As Jaclyn said this is still a very open question in particle physics and be sure that anyone providing an answer will be awarded the Nobel prize.

      Just to reiterate, in Nature there are several symmetries, like the charge symmetry which explain the existence of particles and anti-particles. Most of these symmetries are exact symmetries, meaning that going from one value to the other in one direction (from + to -) or in the other (from – to +) they preserve the number of particles. We know that some symmetries are broken, for example the Weak force breaks the charge symmetry and interactions mediated by this force will lead to more matter than antimatter. For the weak force this asymmetry, which is a measure of how much the symmetry is broken, is a very small number and would not justify the excess of matter we observe in the Universe. Therefore there must exist another symmetry that is broken in a similar way that could justify the excess we observe. So far we have not found an answer so we are still looking and designing experiments to try found out.

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