How did the universe begin? What makes up the universe? Why does the sky look the way it does? Humankind has been asking these kinds of questions for millennia, but these questions are now subject to direct observational measurements. Measurements have revealed that we live in an expanding universe and that the expansion is becoming faster and faster.
It is now firmly established that our universe has been expanding and cooling for billions of years, ever since the Big Bang. To be precise, the Wilkinson Microwave Anisotropy Probe (WMAP) space mission has determined that the age of the universe is thirteen billion, seven hundred million years. This has been recognized by the Guinness Book of World Records as the most accurate determination of the age of the universe.