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The Question

(Submitted March 03, 1999)

My question is, since the amount of matter and anti-matter is equal, why there is a such big different in the ratio of these two things?

The Answer

You are correct in that we do believe that equal amounts of matter and anti-matter were created in the big bang. However today we see no strong evidence for anti-stars or anti-galaxies. When matter and anti-matter meet they turn into energy, and we know what range of energy this energy should be seen. Although some anti-matter events are seen, they are not enough to assume that half the cosmos is anti-matter. The amount of anti-matter observed can be explained by processes that have occurred since the big bang.

So where is the anti-matter? There is no reason to think that they could have/would have separated at the time of the Big Bang, like you suggested. One theory states that anti-matter decays slightly faster than matter. Before the matter and anti-matter had a chance to recombine, some of the anti-matter decayed. So when they recombined, there was some matter left over which formed our universe.

Hope this helps,

Jeff Silvis, Allie Hajian and John Cannizzo
for Ask an Astrophysicist

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