<human>:  How does light travel through glass?      
<bot>: Light travels through glass by refraction. When light passes from air into glass it is bent, causing the light to change direction. This is known as refraction and it is due to the fact that the speed of light is different in the two materials. When passing from a less dense material like air into a more dense material such as glass, light is bent and so it follows a different path through the glass than it would if it were in air.