22 September 2010

Cosmic accidents: Tipping the antimatter balance

These things really do matter

Read more: Cosmic accidents: 10 lucky breaks for humanity

Why isn’t the cosmos a sea of bland radiation? The triumph of matter suggests that the laws of physics are biased

Still unimaginably hot and dense, the post-inflationary universe was a melange of particles – electrons, positrons, quarks, antiquarks and the like – buzzing around to no particular end. Stable unions between particles that might create stars, planets and life were still far away. One obstacle was the near-equal numbers of matter and antimatter particles. For us to be here, one of them had to give.

You can’t make a planet or a person out of light. You need matter – heavy, stable particles such as protons and neutrons. And yet it seems an extraordinary accident that matter exists at all. Standard theories say that matter and antimatter were created in equal amounts after the big bang. Since the two annihilate each other on contact, generating pairs of high-energy photons, all there should be in today’s cosmos is a sea of restless and rather bland radiation.

This is not the case. Something seems to have favoured the creation of matter at a crucial moment within the first instants after the big bang.

A surplus of just one extra matter particle per billion would have been enough to lead eventually to today’s convenient mattery residue. But how would such an imbalance arise? While there is a pro-matter bias in some particle reactions, it is far too slight to create an advantage even this small. So physicists assume that a stronger bias, the consequence of unknown processes beyond the standard model of …


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