Telescopes are time machines. Light that is emitted or reflected by objects takes time to travel, and the vast distances it must cross to reach us from the farthest parts of the universe means that we see the most distant galaxies as they were billions of years ago. That light is stretched beyond the red end of the visible light spectrum into infrared wavelengths by the expanding universe, making it visible only to infrared-detecting telescopes like Webb.
The Webb telescope will capture this long-traveling light to see the universe's infancy, early stars and galaxies flickering to life after the Big Bang. It will investigate why galaxies produced stars so much faster in the past; 10 billion years ago, the rate of star birth was 10 times higher. We're accustomed to seeing stately spiral and shining elliptical galaxies, but we don’t know how groups of stars evolved into these familiar shapes. Webb will uncover whether the process is something internal to galaxies or affected by outside events, such as galaxy collisions.
Shortly after the Big Bang, the universe went through a period known as the dark ages, when no light sources were available. Webb will look for the bright objects that transformed this dark universe to the one we see today, ablaze with the glow of stars, gathered into immense galaxies.