Antimatter

Because of that heat, the early universe was a simpler place. Its extreme heat enforced homogeneity, or what physicists refer to as symmetry. In the first moment after the big bang, the symmetry was perfect: Only energy filled the universe. But by the time the universe was less than one nanosecond old it was cooling, and the primordial energy began to coalesce, symmetrically, into perfectly equal amounts of matter and antimatter.


Herein lies the problem. If matter and antimatter destroy each other, and there were equal amounts of the two in the earliest moments of the universe, then everything should have been promptly annihilated, leaving behind only light. But what if immediately after the big bang, some of the antimatter spontaneously changed into matter? It's conceivable; after all, radioactive elements in the periodic table can randomly change into other elements. If even a small fraction of the primordial antimatter morphed into matter, then there would have been an imbalance, and after all the pyrotechnics, some matter would have survived-potentially enough to cool and coalesce, eventually bunching into stars and galaxies.


FAITH IN THE MACHINE
Stew Smith, my guide inside the particle accelerator, is one of the leaders of the team at SLAC that's searching for the subtle differences, or asymmetries, in the way matter and antimatter behave. In principle, it's a simple process: Just make lots of matter and lots of antimatter, then compare the two. The challenge is perfecting it in practice.


Every particle has an equivalent antipartner-the proton has the antiproton, the electron has the positron, and so on-but it takes a very special kind of particle-antiparticle pair to reveal the variations that scientists are looking for.


Back in 1964, physicists experimenting with a particle known as the K meson and its antimatter equivalent, the anti-K meson, showed for the first time that antimatter can decay more rapidly than matter. (What scientists mean when they talk about a particle decaying is that it changes into something else. Most elementary particles are unstable, and within a fraction of a second after coming into existence they undergo a series of changes before finally reaching a stable form.)
Today, physicists believe a rare particle called the B meson, or B for short, is best suited to reveal the differences between matter and antimatter. Particles shed mass as they decay, with heavy particles turning into lighter ones. B mesons are especially heavy, which makes them ideal for asymmetry research. Think of it this way: Let's say you're planning a European vacation, starting from London and ending in Athens. If money is limited, you'll travel directly, making few stops in between. But if your budget is vast and you must spend it all, you'll visit a dozen countries along the way. Similarly, the B meson's abundant mass, and need to shed it, creates a range of disintegration pathways. Scientists watch the various ways in which it decays, then compare the end results, checking and cross-checking their findings for consistency.