Why There’s More Matter Than Antimatter in the Universe

by Fraser Cain on March 28, 2008

KEK accelerator. Image credit: KEK
In the first few moments of the Universe, enormous amounts of both matter and antimatter were created, and then moments later combined and annihilated generating the energy that drove the expansion of the Universe. But for some reason, there was an infinitesimal amount more matter than anti matter. Everything that we see today was that tiny fraction of matter that remained.

But why? Why was there more matter than antimatter right after the Big Bang? Researchers from the University of Melbourne think they might have an insight.

Just to give you an idea of the scale of the mystery facing researchers, here’s Associate Professor Martin Sevior of the University of Melborne’s School of Physics:

“Our universe is made up almost completely of matter. While we’re entirely used to this idea, this does not agree with our ideas of how mass and energy interact. According to these theories there should not be enough mass to enable the formation of stars and hence life.”

“In our standard model of particle physics, matter and antimatter are almost identical. Accordingly as they mix in the early universe they annihilate one another leaving very little to form stars and galaxies. The model does not come close to explaining the difference between matter and antimatter we see in the nature. The imbalance is a trillion times bigger than the model predicts.”

If the model predicts that matter and antimatter should have completely annihilated one another, why is there something, and not nothing?

The researchers have been using the KEK particle accelerator in Japan to create special particles called B-mesons. And it’s these particles which might provide the answer.

Mesons are particles which are made up of one quark, and one antiquark. They’re bound together by the strong nuclear force, and orbit one another, like the Earth and the moon. Because of quantum mechanics, the quark and antiquark can only orbit each other in very specific ways depending on the mass of the particles.

A B-meson is a particularly heavy particle, with more than 5 times the mass of a proton, due almost entirely to the mass of the B-quark. And it’s these B-mesons which require the most powerful particle accelerators to generate them.

In the KEK accelerator, the researchers were able to create both regular matter B-mesons and anti-B-mesons, and watch how they decayed.

“We looked at how the B-mesons decay as opposed to how the anti-B-mesons decay. What we find is that there are small differences in these processes. While most of our measurements confirm predictions of the Standard Model of Particle Physics, this new result appears to be in disagreement.”

In the first few moments of the Universe, the anti-B-mesons might have decayed differently than their regular matter counterparts. By the time all the annihilations were complete, there was still enough matter left over to give us all the stars, planets and galaxies we see today.

Original Source: University of Melbourne News Release


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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