Based on what you know about how light travels, explain why you can't see the back of your own head without using a mirror, camera or other device.

Light travels in straight lines, a principle known as rectilinear propagation. This is the fundamental reason why we can't see the back of our own head without the aid of a mirror or other device.

Here's a step-by-step explanation:

1. When light hits an object, it bounces off in all directions. Some of this light enters our eyes, which is how we see the object.

2. The back of our head is an object that light hits and bounces off from. However, because light travels in straight lines, the light bouncing off the back of our head travels away from our eyes, not towards them.

3. Therefore, without something to redirect the light (like a mirror or camera), the light rays bouncing off the back of our head will never reach our eyes. As a result, we can't see the back of our own head.

4. A mirror or camera works by reflecting or capturing the light that bounces off the back of our head and redirecting it towards our eyes. This is why we can see the back of our head using these devices.