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Posted by Richard Ruquist on March 15, 2003 15:43:38 UTC

I think it was Tim who forced me to look at why matter was not totally annihilated by anti-matter in the early universe. It turns out that anti-matter decays faster than matter, at least according to the NASA Goddard site. So equals amounts of matter and anti-matter are produced by pair production and same for annihilation. This always happens.

But by the time that the universe cooled enough that there was not enough energy for pair production, more anti-matter had decayed than matter. This meant that although equal amounts of matter and anti-matter get annihilated, there is an excess of matter, to the tune of one part in one billion. That is, one billion protons annihilated one billion negative protons, with one proton left over.

However, this creates a puzzle in my mind. electron-positron pairs continued to be produced down to much lower energies, a factor 1836 lower, if I remember correctly, the ratio of the electron mass to the proton mass. But then neither had mass at that time. The Higgs particle came into play at about the electro-weak breaking energy. Guess I have to admit I do not know what is going on. Good question for some physics FAQ forum.

Wrong again. According to the big bang table at,
the electro-weak broke into weak and EM at 10^-12 sec, whereas the end of annihilation was at 10^-6 sec. So the particles already had mass. Then electron-positrons stopped annihilation much later than proton-anti-protons. We would then expect a different number of protons and electrons in the universe. Could that be?

Another puzzle is how can so much anti-proton decay happen in just 10^-6 sec. The proton lasts for 10^32 years according to GUT theory. Its decay has never been measured, its so long. Strange that the anti-proton behaves so differently. Wish I were still in school and could ask someone these questions.


yanniru aka DummerDick and feelin' it.

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