Unlocking the early universe
To reveal those secrets, cosmologists study the pattern of hot and cold spots frozen into the CMB and decompose those spots into their constituent sizes. While most of the hot and cold spots are about 1° on the sky, they are overlaid on fluctuations with larger sizes.
“Imagine looking at a smooth pond of water that we might drop pebbles into,” says Dunkley. “If you drop a whole bunch of pebbles in, the ripples will sort of combine together, and you see a whole pattern of ripples across the water. We think of this pattern of slightly different temperatures of this light on the sky a little bit like the pond after it’s covered in ripples.”
The size breakdown of the CMB’s temperature spots, or fluctuations, is like a cosmic Rosetta Stone. The strength of the fluctuations’ signals at different scales is associated with the universe’s age, its ingredients, its expansion rate, and when the first stars lit up the cosmos. By comparing computer models to the signal strengths (which astronomers obtained from analyzing WMAP and Planck data), researchers can piece together what the early universe looked like and how it has evolved.
Thanks to these three cosmic probes, we know the universe began in a Big Bang, and around 380,000 years later, electrons and protons combined, letting light roam free. We know our cosmos is 13.8 billion years old and how fast it is expanding. We know that 31 percent of the universe is matter, but only 5 percent is made of ordinary matter like you and me, while 26 percent is invisible dark matter. Much more of the cosmos is composed of a mysterious, repulsive dark energy — 69 percent.
And perhaps most importantly, astronomers now have a way to find out pieces of information not literally encoded in the CMB itself. That’s because the CMB maps and their statistics have led to the so-called standard model of cosmology.
“We now have a really simple model that describes basically all of our observations,” says Dunkley. “We can track from the very first moments of time all the way through today and make predictions about how large-scale structure evolved. And it has remarkable success. That’s the big thing these satellite missions have given the community.”