Invisibility is an overlong word that contains far to many I’s. We’ll see another problem about eyes in just a minute, but first, what is invisibility? There are many different definitions and applications, but here we’re talking about the special super-ability, intrinsic or extrinsic, to not be seen.
How is this achieved? First, we must understand that light does not pass through humans in the same way it passes through, say, the air. Obviously. Humans absorb some colors of light, and reflect other colors; that’s what gives us different skin colors. Clothing acts the same way.
Invisibility overcomes this, by simply allowing light to pass unhindered through the body, right? We shall see…
Problem 1: Blindness
Remember? You are invisible because the light passes unhindered through you. But there’s a problem, because in order to see, the light entering your eye needs to stop at the retina—the thing at the back of your eye that detects light, and sends information about it to the brain—not to pass through the retina.
So when you become invisible, and light passes freely through you, light passes through the retina, which is unable to detect it. So when you’re invisible, you’re blind. End of story—or maybe just the beginning.
Solution 1.1, Problem 1.1: Exclusion
Light does stop at the retina. It’s so simple, right? Simply exclude the retina from invisibility, or wait… if light did stop and register at your retina, then people can see it! Wouldn’t it be really creepy and alarming to see a couple of little balls floating around through the air? The cover is up!
Of course, we could just say that only light coming from the front of the body stops at the retina, but light from behind passes through. So as long as you are facing someone, they can’t see you, but if someone approaches from behind…
Solution 1.2: Magic
You have got to be kidding me. Seriously, magic? That is so unscientific. Or is that the point? Whatever. We can’t just appeal to magic to fix all of our problems, now, can we? Or can we…
Problem 2, Solution 2.1: Clothes
This is a very serious problem, and a scary reality for invisible people. If they existed. The question being, is it, or is it not, only the body of a person that becomes invisible? In H.G. Well’s story, The Invisible Man, it was. But in many other works, not only the body, but the clothes, and things being carried are invisible as well. That’s the obvious solution.
Solution 2.2, Problem 2.2:
If only the body were invisible, you couldn’t wear clothes, or carry anything, without being seen. And that is a solution, unpleasant as at sounds. But if you tried to rob the cookie jar, people would notice the lid floating through the air, and a cookie slowly being eaten. Which brings up another problem. At what point does the cookie become part of the body? When it enters the mouth? Or the stomach? I’m sure scientists would be delighted if they could see The Complete Digestion of a Cookie, but the rest of us would find it just plain gross. At best. And your mom would know you’ve been sneaking cookies, anyway.
Problem 2.1: Disappearance
And if things you wear and hold become invisible with you, we still have a problem. When you tried to rob the cookie jar, the lid would immediately disappear. And if people saw this strange phenomenon, you probably wouldn’t have time to make the cookie disappear too.
But it gets even worse. What if something accidentally falls on you? The guy on the roof might be slightly alarmed when his ladder falls down and disappears, accompanied by a scream from an unknown source. Or what if you were climbing the ladder itself? You would need to be very careful not to wrap your hand around the rungs, because then the ladder would flash invisible for a moment. On the other hand, if you didn’t hold the rungs, you’d fall, and the ladder with you, and it would all end up invisible anyway.
Problem 2.1.1: Limit Disappearance
So what if you were wearing gloves? They’d be invisible, no problem yet. But what if you tried to pick something up? The only thing worse than misty CO2 floating through the air (scientific inaccuracy alert), is the actually block of dry ice floating around! Or what if you hold tongs? The tongs are invisible, but the salad isn’t. It’s awfully scary to see lettuce leaves flying through the air and falling onto an invisible plate.
Solution 2.1.1: Extend Disappearance
That’s the obvious solution, right? If you extend disappearance beyond things your body is touching, then all is well. Or is it? What if your body made the air invisible? Everything would become invisible, since it’s touching the air!
Problem 2.1.2: Gardening
So, you’re invisible, and you’re weeding the garden. Why you didn’t go invisible to avoid weeding the garden, I’ll never know, but the fact is, you didn’t. What happens when you stick your hand into the ground? That’s right, the earth disappears. Pretty scary.
In Conclusion…
But none of this matters, since it's impossible anyway! Obviously, I think too hard sometimes.
There is another paragraph that I wrote, which I removed since it seemed so anticlimactic. But if you want to read it, here it is:
Impossibility 1: Shadows
This is certainly not a universal problem, unique, as far as I know, to Tolkien’s works (and as I now know, Rick Riordan's). When you put on the One Ring to rule them all, you become invisible, but in daylight, you will still cast a faint shadow. But what is a shadow? It is darkness caused by something—or someone—standing between the area where the shadow is, and a light source. The thing casting the shadow is blocking the light. But that goes against the very concept of invisibility! If you cast a shadow, then necessarily, whatever you’re casting the shadow on can detect, if it has eyes, your form. Otherwise, there’d be no shadow.