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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.
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