In the beginning, there was light. Under the intense conditions of the early universe, ionized matter gave off radiation that was trapped within it like light in a dense fog. But as the universe expanded and cooled, electrons and protons came together to form neutral atoms, and matter lost its ability to ensnare light. Today, some 14 billion years later, the photons from that great release of radiation form the cosmic microwave background (CMB).
Tune a television set between channels, and about 1 percent of the static you see on the screen is from the CMB. When astronomers scan the sky for these microwaves, they find that the signal looks almost identical in every direction. The ubiquity and constancy of the CMB is a sign that it comes from a simpler past, long before structures such as planets, stars and galaxies formed. Because of this simplicity, we can predict the properties of the CMB to exquisite accuracy. And in the past few years, cosmologists have been able to compare these predictions with increasingly precise observations from microwave telescopes carried by balloons and spacecraft. This research has brought us closer to answering some age-old questions: What is the universe made of? How old is it? And where did objects in the universe, including our planetary home, come from?
This article was originally published with the title The Cosmic Symphony.