Redshift

Cosmological redshift is a change in the color of light that occurs when a wave of light is apparently stretched by the expansion of the universe.

All white light can be broken into a rainbow of component colors called a spectrum – we see this happen every time a beam of light hits a prism. When a bright object is moving away, we see its colors shift toward the red end of the spectrum – thus the name, “redshift.”

Since the universe has been expanding since the Big Bang, the galaxies that formed in its aftermath are also moving away from each other. The farther a galaxy is from us, the faster it is receding and the redder its light appears. Light from objects very far away can shift so much that the light moves out of the visible range and becomes infrared light, which humans cannot see but can perceive as heat. The Webb telescope will be able to detect this infrared light, allowing it to “see” the light from objects that are extremely distant, light that would have left those objects only 130 million years after the Big Bang.