Why You Don't Want Invisibility

- This episode of Because Science is sponsored by LightStream. You don't actually

want

the power of

invisibility

. What would you do if you could become invisible? Most of the answers I've heard to that question are anything but heroic. Many of them boil down to sneaking into places you shouldn't be or borrowing things without asking. Of course, you could use the power of

invisibility

forever. It is one of the hero's fundamental powers. But thinking about the scientific reality of this ability, I don't think invisibility is something you would

want

. Like super strength and super speed, humans have long fantasized about the power of invisibility.

Sudden disappearance is the theme of great novels such as The Invisible Man by H.G. Wells, the 1933 film of the same name and, of course, the masterpiece Hollow Man starring Kevin Bacon. Many of these stories have considered the consequences of becoming invisible, but I think science has even more to say. So why wouldn't you want this classic superpower? First, what is invisibility? Well, whether the source of the power is magical or scientific, to make something invisible you have to change the way something interacts with light. Everything you can see interacts with photons, elementary particles that are the basic units of light and electromagnetic radiation.

Those photons of light fly around the universe, enter our eyes, and give our brain visual information based on the properties of those photons, such as frequency and phase. Now, everything you can see, then, emits light that reaches your eyes or bounces photons off of itself and back to your eyes. So to become invisible, you have to change these paths. Regardless of how your powers worked, they would have to redirect the photons to surround you or an object so that they wouldn't bounce off you or an object and into your eyes, or the photons would have to pass through you, as if you were transparent.

Or a third option is that you could project what's behind you, in front of you, and into people's eyes, kind of like what Predator camouflage might work and look like. But I don't think this is what we consider classical invisibility. Yeah, sorry, buddy. Yes, I don't know. Attention! How invisibility could actually work is the first real problem with this power. The easiest way to become invisible would be to redirect the photons around you so they don't bounce off you and other people's eyes, but if you did this successfully, no photons would enter your eyes to give your brain vision. information and you would be blind.

You may be invisible to other people like Kevin Bacon, but they will be invisible to you too. Now there is a solution for this, but it's strange. The human eye is an incredibly sensitive photon detector. Experiments have shown that we can record the impact of a single photon on the back of our eyes. But that doesn't mean we see a picture when that happens. It is said to be like the sensation of seeing something without actually seeing it. So to see an image, we need many, many photons reaching the back of our eyes, especially considering that more than 90% of the photons entering from the front do not reach the back of our eyes.

They just bounce everywhere. So, to be invisible and able to see, you would not only have to redirect photons around your body, but you would have to direct many photons towards your eyes. That would enlighten them. Apparently this is what Marvel's Invisible Woman does, but if you did this, your eyes would be visible while your body was invisible, and that's weird. And disgusting. And it doesn't really fit with our conception of invisibility and would give you away pretty quickly. Get out of here, Kevin! Let go, man! Even if you weren't blind, even if you weren't just a pair of disembodied eyes, another reason you wouldn't want the power of invisibility is that you wouldn't be truly invisible.

If you can become invisible by redirecting photons around you, you'll probably want to do it right above your skin or, better yet, on your skin, because if you were making a large volume around you invisible, you could start to become invisible. The objects around you look strange enough to give you away. But if only your physical form were invisible, you also wouldn't want any objects or the environment that interacts with it to reveal your form. This would immediately limit your powers by making it impossible to sneak through a world when it's snowing or raining, and you wouldn't be able to stay in one place for long, because the dust and debris you'd accumulate also gives away your form.

And in this conception of invisibility, one would have to be naked. So to be truly invisible, if you wanted to sneak anywhere, you would have to be cold, naked, and uncomfortable. But at least you'd be invisible, right? Well, that depends on what's trying to see you. Every second, the average human being radiates 100 joules of thermal energy into the universe in all directions. Anything that has a temperature does this. And so you are always emitting light, but infrared light. Now, I know we don't think of infrared light the way we think of visible light, but let's consider the term red hot.

When something is red hot, it radiates enough thermal energy that its infrared light wavelengths are pushed toward red light. Visible light. Everything is on the same spectrum. And so, even if you were invisible to people looking for you in visible light, anyone looking for your heat signature could see you just as easily as if you weren't invisible at all. Warning! Ha ha, I missed it by six degrees. Kevin! No! So while classic invisibility would hide visible light, anyone with something as simple as a thermal camera could easily detect it. This wasn't a problem in 1933, when the movie The Invisible Man was released, but today we have technology that would make it almost impossible to go unnoticed in most places you'd like to go unnoticed.

A motion or thermal camera, the most common security measure in homes and banks, could easily detect it. Which would be nice, because I know what you'd do if you were invisible, you bunch of creepos. I know. You don't have to say it. We all know. Even if you weren't blind, even if you didn't have to be naked, even if you were somehow completely undetectable, you still wouldn't want to be invisible, because of your own brain. I want you to try something with me, okay? Close your eyes, everything will be fine. Close your eyes and extend one of your arms.

Now extend your index finger over that arm and now bring the tip of your finger to touch the tip of your nose. Good, now he opens his eyes. Easy, right? Most people can get within 20 millimeters of their nose on the first try, without problem. But how can we do this? How can we precisely position something in space that we cannot see? Well, it's thanks to a sense we have but may not have heard of called proprioception. It is the sense of movement of our body. This is how our brain knows how our limbs are positioned in space without visual information.

Without proprioception, we couldn't drive without looking at where our feet are on the pedals. We couldn't write without looking at our fingers. And we wouldn't even be able to walk without keeping our feet on the ground. We couldn't dance either. I'm sorry. Proprioception is based on the information that your body is constantly generating. Your inner ear tells your brain how your body moves and its orientation. Your muscles and ligaments tell your brain how your limbs are positioned in space in relation to the rest of your body. All of this information is combined in the brain with visual information to give you an idea of ​​where you are and how you are moving.

Or not. The incredibly smart kid and neuroscientist Oliver Sacks once told a story of how important proprioception is in our everyday lives in his fantastic book, The Man Who Mistook His Wife for a Hat, which I highly recommend. In it, he describes a patient, Christina, who actually lost her sense of movement thanks to a viral spinal infection. After that, she could not walk, she could not control the volume of her voice, and she could not manipulate or grasp objects properly. Now, Christina partially recovered, but only because she learned to rely completely on visual information and not her sense of movement.

For example, she was able to pick up a fork to eat, but when she did, she had to grip the fork so hard that she hurt her hands and turned white. As Oliver Sacks said, Christina could have had a possible life, but not a normal one. The sensation of her own body, combined with visual information, is essential for normal functioning. Let us now imagine what it would really be like to be classically invisible. Which is invisible but unable to see your own body. It would be the other version of what happened to Cristina. Think about how difficult it would be to walk down a flight of stairs if you couldn't see your own feet.

You could just feel where they were. Imagine how difficult it would be to manipulate and grasp objects without any visual information. Here we go. It's not impossible, but it's not very great either. Being invisible would be an incredible hassle. Simply walking down the street would be very difficult. No, people wouldn't be able to see your strange, naked body, but you wouldn't be able to see where your body was in space either. And then you'd be stumbling down the street, bumping into other people and obstacles, cold and confused the whole time. It would be miserable. So why wouldn't you want the classic superpower of invisibility?

Well, it wouldn't make you feel very super powerful at all. Quite the opposite. You would be blind or have a strange pair of floating eyes. You would be cold and naked. You would be completely visible to anyone with thermal technology widely available. And without the visual information your brain needs, along with your sense of movement to make movement in life possible and bearable, doing anything while invisible would be frustrating at best and impossible at worst. . If you could really get out of sight, that would drive you crazy. Because science. Oh! Damn, Kevin, you took off your Sunday shoes and I tripped over them!

Basically, for invisibility to work, you have to do a lot of weird things. You could send photons into your eyes and then take them out of your eyes after they bounce back into your eyes, or you could completely disconnect from the electromagnetic spectrum, but then you'd fall through the earth and stuff. Then you would have to go through many obstacles. Anyway, classical invisibility, I don't think, is that cool, or nearly as cool, if you think about it scientifically. Although some have thought about its consequences, like Hollow Man, where he sees through his eyelids making it difficult for him to sleep, but why can't we see his eyeballs then?

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