Why You Don’t Want Invisibility

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 turn invisible? Most of the responses I’ve heard to that question are less than heroic. Many of them come down
to sneaking into places you shouldn’t be or borrowing
stuff without asking. Of course, you could use the power of invisibility for good. It is one of the fundamental hero powers. But thinking about the scientific
reality of this ability, I don’t think invisibility
is something you’d even want. Like super strength and super speed, humans have fantasized about the power of invisibility for a long time. Suddenly disappearing is the subject of great novels like The
Invisible Man by H.G. Wells, the 1933 movie of the same name, and of course the masterpiece Hollow Man starring Kevin Bacon. Many of these stories have considered the consequences of turning invisible, but I think that 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 sciencey, to make something invisible
you have to change the way that something
interacts with light. Everything that you can
see interacts with photons, elementary particles that
are the basic units of light and electromagnetic radiation. Those photons of light are
flying around the universe, and they enter our eyes
and give our brains visual information based on the
properties of those photons, like frequency and phase. Now, everything that you can see, then, therefore is either emitting
light that reaches your eyes or is bouncing photons off
of itself and to your eyes. So to make yourself invisible, then, you have to change these paths. However your powers worked, they would have to redirect photons so that they would either go around you or an object so that those
didn’t bounce off of you or an object and make it into your eyes, or the photons would
have to go through you, kind of like you were transparent. Or a third option is
that you could project what is behind you in front
of you and into people’s eyes, kind of like how Predator’s
camouflage might work and look. But I don’t think that this is what we consider classic invisibility. Yeah, sorry, dude. Yeah, I don’t know. Oh, heads up! How invisibility might actually work is the first real problem with this power. The easiest way to make yourself invisible would be to reroute
photons around yourself so that they didn’t bounce off of you and into other people’s eyes, but if you were doing this successfully, no photons would be entering your eyes to give your brain visual information, and you would be blind. You might be invisible to
other people like Kevin Bacon, but they would be invisible to you too. Now, there is a solution
to this, but it is weird. The human eye is an incredibly
sensitive photon detector. Experiments have shown
that we can register the impact of a single photon
at the backs of our eyes. But that doesn’t mean we see
an image when that happens. Reportedly, it’s like a
feeling of seeing something without actually seeing it. So to see an image, we
need many, many photons hitting the backs of our eyes, especially considering that
upwards of 90% of photons that enter the front don’t make
it to the back of our eyes. They just bounce around
all over the place. So to be both invisible and able to see, you would not only have to
reroute photons around your body, you would have to route a lot
of photons into your eyes. Which would illuminate 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 is weird. And gross. And doesn’t really fit with
our conception of invisibility and it would give you away pretty quickly. Get outta here, Kevin! Cut loose, 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 make yourself invisible by rerouting photons around yourself, you’d probably want to do
this right above your skin or, better yet, at your skin,
because if you were making a large volume around you invisible, you might start to make objects around you look weird enough to give you away. But if just your physical
form was invisible, you also wouldn’t want any
objects or the environment interacting with it to
give away your shape. This would immediately limit your powers by making it impossible
to sneak through a world when it was either snowing or raining, and you wouldn’t be able to
stand in one spot for too long, because the dust and debris
that you would gather would also give away your shape. And in this conception of invisibility, you would have to be naked. So to be truly invisible, if you wanted to sneak around anywhere, you would have to be cold
and naked and uncomfortable. But at least you’d be invisible, right? Well, that depends on
what is trying to see you. Every second, the average human radiates 100 joules worth of heat energy out into the universe in all directions. Anything with a temperature does this. And so you are always emitting
light, but infrared light. Now, I know we don’t
think of infrared light like we do visible light, but
consider the term red hot. When something is red hot, it is radiating enough heat energy that its wavelengths of infrared light are being pushed up into red light. Visible light. It’s all on the same spectrum. And so even if you were invisible to people looking for
you with visible light, anyone that was looking
for your heat signature could see you just as easily as if you were not invisible at all. Heads up! Ha ha, missed me by six degrees. Kevin! No! So while classic invisibility
would hide your visible light, anyone with something as simple as a thermal camera
could pick you up easily. This wasn’t a problem back in 1933, when The Invisible Man movie came out, but today we have the
technology which would make it almost impossible to sneak
undetected through most of the places that you would
want to be undetected in. Anyone with a motion or thermal camera, the most common security
measure in homes and banks, could pick you up easily. Which would be good, because
I know what you would 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 invisibility, because of your own brain. I want you to try something with me, okay? Close your eyes, it’ll be fine. Close your eyes, and
extend one of your arms. Now extend the pointer finger on that arm, and now bring the tip of your finger to touch the tip of your nose. Okay, now open your eyes. Easy, right? Most people can get within 20 millimeters of their nose first try, no problem. But how can we do this? How are we able to position something accurately in space that we cannot see? Well, it is thanks to a sense that we have but you may not have heard
of called proprioception. It is our body’s movement sense. It’s how our brains know how our limbs are positioned in space
without visual input. Without proprioception, we
wouldn’t be able to drive without looking where our
feet are on the pedals. We wouldn’t be able to type
without looking at our fingers. And we wouldn’t even be able to walk without watching our feet on the ground. We wouldn’t be able to dance either. I’m sorry. Proprioception relies on information that your body is constantly generating. Your inner ear tells your brain how your body is moving
and its orientation. Your muscles and your ligaments tell your brain how your
limbs are positioned in space relative to the rest of your body. All of this information
combines in the brain with visual information
to give you an idea of where you are and how you are moving. Or not. Incredibly smart boy and
neuroscientist Oliver Sacks once told a story of just how
important proprioception is to 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 movement sense, thanks to a viral infection in her spine. After that, she wasn’t able to walk, she wasn’t able to control
the volume of her voice, and she couldn’t manipulate
or grasp objects correctly. Now, Christina made a partial recovery, but only because she
learned to rely entirely on visual information and
not her movement sense. For example, she was able to
grasp a fork again to eat, but when she did so, she
had to grab the fork so hard that it hurt her hands
and they turned white. As Oliver Sacks put it, Christina was able to
have a possible life, just not a normal one. The sense of your own body, combined with visual information, is critical to normal functioning. So now imagine what it
would really be like to be classically invisible. That is invisible but
unable to see your own body. It would be the other version
of what happened to Christina. Think of how hard it would be to walk down a flight of stairs if you
couldn’t see your own feet. You could only feel where they were. Imagine how hard it would be to manipulate and grasp objects with zero visual input. There we go. It’s not impossible, but
it’s not very super either. Being invisible would
be an incredible hassle. Just walking down the
street would be so hard. No, people wouldn’t be able
to see your naked, weird body, but you wouldn’t be able to see where your body was in space either. And so you’d be stumbling down the street, bumping into other people and obstacles, cold and confused all the while. It would be miserable. So why wouldn’t you want the classic superpower of invisibility? Well, it wouldn’t make you
feel very superpowered at all. Quite the contrary. You would either be blind or
a weird pair of floating eyes. You would be cold and naked. You would be completely visible to anyone with widely available thermal tech. And without the visual
information that your brain needs, along with your movement sense to make movement through life
possible and bearable, doing anything while invisible would be, at best, frustrating and,
at worst, impossible. If you really could go out of sight, it would drive you out of your mind. Because science. Ow! Dang it, Kevin, you kicked
off your Sunday shoes, and I tripped over them! Basically, to make invisibility work, you have to do a lot of weird stuff. You could route photons into your eyes and then out of your eyes after they bounced off of your eyes, or you could make yourself
completely disconnected from the electromagnetic spectrum, but then you’d fall through the earth and stuff. So you’d have to jump
through a lot of hoops. Regardless, classic
invisibility, I don’t think, is as 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 so it’s hard to sleep, but why can’t we see his eyeballs then? See? Same problem. That’s… That’s new. Hm. Hey, when do you want to start paying less interest on
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