Transparent materials are ones that light passes straight through like glass, air and water. One way to become invisible would be to turn yourself into a transparent material like glass. You’d be like a statue, though – dead. Oops.
The Invisible Man
In the book ‘The Invisible Man’ the solution was a potion that made the scientist transparent … Even if that worked you would have to hide after eating until the food was digested as it would be seen (Yuk!) … You would also be blind! Light would pass through your eye too, but the job of your eye is to catch light so it can tell your brain about the light from other things.
A Transparent Invisibility Cloak?
Instead, perhaps you could make an invisibility cloak out of a transparent material. Well yes. But when you hid under it everyone would be able to see you. The light from you would pass straight through the cloak to their eyes of course! It is only the cloak itself that is invisible, not things behind it.
Transparency is a way to make simple objects invisible, though. Say you want an invisible key. Make it out of a transparent material, like glass. Drop it in water and watch it disappear.
This is a bit trickier than you might hope though. Light changes direction as it passes from one material to another. Take the glass of water. The air, glass and water are all transparent. You can still see the glass, though. That is because light changes direction at the surfaces of things it passes through. It is called refraction.
Put a straw in the water and it will appear to bend or be broken at the surface of the water (try it and see). That is because the air and water that the different ends of the straw are in, send the light off in different directions as it passes from them to the glass.
This is also why its hard to catch fish looking from above. The light from the fish changes direction as it passes from water to air. Your brain assumes light travels in a straight line (as it mostly does). So the fish isn’t where you think it is. When you reach for it, it is actually somewhere else, not where you see it!
You can get round this by engineering a material that has exactly the same light directing properties as the water. It really will then disappear. Tip away the water and you will be able to see it again (just).
We need to try something else if we are to make an invisibility cloak though.