Scientists are now focusing their most powerful technologies on an effort to figure out exactly what happened. Our understanding of cosmic history hangs on the question: how did matter as we know it survive? And what happened to its birth twin, its opposite, a mysterious substance known as antimatter?
A crew of astronauts is making its way to a launch pad at the Kennedy Space Center in Florida. Little noticed in the publicity surrounding the close of this storied program is the cargo bolted into Endeavor’s hold. It’s a science instrument that some hope will become one of the most important scientific contributions of human space flight.
It’s a kind of telescope, though it will not return dazzling images of cosmic realms long hidden from view, the distant corners of the universe, or the hidden structure of black holes and exploding stars.
Unlike the great observatories that were launched aboard the shuttle, it was not named for a famous astronomer, like Hubble, or the Chandra X-ray observatory.
The instrument, called the Alpha Magnetic Spectrometer, or AMS. The promise surrounding this device is that it will enable scientists to look at the universe in a completely new way.
Most telescopes are designed to capture photons, so-called neutral particles reflected or emitted by objects such as stars or galaxies. AMS will capture something different: exotic particles and atoms that are endowed with an electrical charge. The instrument is tuned to capture “cosmic rays” at high energy hurled out by supernova explosions or the turbulent regions surrounding black holes. And there are high hopes that it will capture particles of antimatter from a very early time that remains shrouded in mystery.
The chain of events that gave rise to the universe is described by what’s known as the Standard model. It’s a theory in the scientific sense, in that it combines a body of observations, experimental evidence, and mathematical models into a consistent overall picture. But this picture is not necessarily complete.
The universe began hot. After about a billionth of a second, it had cooled down enough for fundamental particles to emerge in pairs of opposite charge, known as quarks and antiquarks. After that came leptons and antileptons, such as electrons and positrons. These pairs began annihilating each other.
Most quark pairs were gone by the time the universe was a second old, with most leptons gone a few seconds later. When the dust settled, so to speak, a tiny amount of matter, about one particle in a billion, managed to survive the mass annihilation.
That tiny amount went on to form the universe we can know – all the light emitting gas, dust, stars, galaxies, and planets. To be sure, antimatter does exist in our universe today. The Fermi Gamma Ray Space Telescope spotted a giant plume of antimatter extending out from the center of our galaxy, most likely created by the acceleration of particles around a supermassive black hole.
The same telescope picked up signs of antimatter created by lightning strikes in giant thunderstorms in Earth’s atmosphere. Scientists have long known how to create antimatter artificially in physics labs – in the superhot environments created by crashing atoms together at nearly the speed of light.
Here is one of the biggest and most enduring mysteries in science: why do we live in a matter-dominated universe? What process caused matter to survive and antimatter to all but disappear? One possibility: that large amounts of antimatter have survived down the eons alongside matter.
In 1928, a young physicist, Paul Dirac, wrote equations that predicted the existence of antimatter. Dirac showed that every type of particle has a twin, exactly identical but of opposite charge. As Dirac saw it, the electron and the positron are mirror images of each other. With all the same properties, they would behave in exactly the same way whether in realms of matter or antimatter. It became clear, though, that ours is a matter universe. The Apollo astronauts went to the moon and back, never once getting annihilated. Solar cosmic rays proved to be matter, not antimatter.
It stands to reason that when the universe was more tightly packed, that it would have experienced an “annihilation catastrophe” that cleared the universe of large chunks of the stuff. Unless antimatter somehow became separated from its twin at birth and exists beyond our field of view, scientists are left to wonder: why do we live in a matter-dominated universe?