A small advance guard of hydrogen atoms acted as a moderator, intercepting the photon emitted by one helium atom before it could destroy another. What is more, they avoided the crab bucket syndrome. With twice the electric charge of protons, helium nuclei had more latching power and formed atoms earlier, catching their first electron at about 15,000 years and their second at 100,000 years. The second nuance is that although the universe consisted mostly of hydrogen, it also had a fair amount of helium. The commonly cited time frame of 400,000 years is just a convenient milestone recombination actually took as long as a couple of million years to run to completion. What overcame their mutual antagonism was cosmic expansion, which sapped the photons’ energy and gradually tilted the balance in favor of atom formation over destruction. Like crabs in a bucket, atoms thwarted one another. Further complicating matters, a photon from one atom tended to knock the electron off another. To tighten up, a newly formed atom had to lose energy by emitting photons, and it did so in its own good time. First, it took a while for protons to get a firm hold on electrons. Yet this picture glosses over two nuances. The pachinko had thoroughly mashed their spectrum, and the only thing cosmologists can glean from it is the overall density of matter. So the photons began to stream across space in more or less straight lines. Being electrically neutral, the atoms were less prone to scatter photons. They scattered off protons and electrons in a game of cosmological pachinko until everything cooled enough for protons to latch onto electrons and form hydrogen atoms-a process known as recombination. In the conventional picture, the background radiation consists of photons produced in the earliest moments of the big bang. At the American Astronomical Society meeting this past January, renowned astrophysicist Rashid Sunyaev of the Max Planck Institute for Astrophysics in Garching, Germany, argued that a successor to Planck might pick up similar fingerprints in the background radiation, the spectrum of which currently seems completely featureless and generic.
But cosmologists looking beyond Planck say the radiation has a barely explored aspect that, if it could be observed with enough precision, would reveal new details about the early universe: its spectrum.Īstronomers routinely use the rainbow of colors emitted by the sun and other stars to determine their composition. After all, the European Space Agency intends for its new Planck satellite to extract “essentially all the information available” in the radiation’s spatial patterns. Cosmologists talk about the cosmic microwave background radiation, their snapshot of the universe at the tender age of 400,000 years, so much that it might seem pretty well mined out by now.