The document discusses how light acts as the carrier of images, allowing humans to see objects. It explains that light travels at a very fast speed of 300 million meters per second, but that there is still a delay in the delivery of images due to the time it takes light to travel from the object to the eyes. This delay means that what we see is actually from the past - the more distant the object, the longer ago the light was emitted. For example, light from the moon takes 1.28 seconds to reach Earth, while light from stars billions of light years away was emitted billions of years in the past. Due to this finite speed of light, the universe can be thought of as consisting of layers of different time periods