Original subtitles

Wouldn't it be great if we could be

invisible?

Ha, right?

I mean, we could spy on people without being noticed

and do whatever we want

without being held responsible.

Now, magicians have figured out

how to utilize full-sized mirrors to bend light

in order to create disappearing illusions.

Scientists have created metamaterials

to guide rays of light

around tiny, two-dimensional objects.

Cameras can also film what is behind you

and project the image

so you appear invisible from the front.

However, none of these options

can make an object as large as a person

appear invisible for all angles and distances

while its moving.

But if you are truly invisible,

as in from within,

here are a few problems

you may not have thought about before.

To move around undetected by other people,

you would have to be totally naked.

Even if it's freezing outside!

You can't carry anything,

including your wallet and keys,

otherwise people would just see

your wallet and keys floating around.

Drivers and people on the street can't see you either,

therefore they can and will run into you at some point.

Oh, and you better not wear any perfume

or make any noise breathing,

otherwise they'll know you're there.

And, just because you start off invisible,

doesn't mean you'll stay that way.

What if someone accidentally spills

scolding hot coffee on you?

And what if it rains?

But if you think only liquid can make you visible,

you're wrong.

Dust consists of dead skin cells from humans,

soil particles,

and fibers from clothes made from cotton

and other materials.

Dust sticks to the moisture on our skin when we sweat

and the tiny hairs on our skin when we are dry.

So, even if you are invisible,

dust would still land on every part of you.

We usually don't notice the dust on our skin

because we can't see a thin layer of dust

on top of our skin color.

But, if you're invisible,

people would see a human-shaped blob of dust

walking around with extremely dirty soles.

Gross!

What do you think the world looks like

if you are invisible?

Well, the answer is nothing.

The reason you can't see in the dark

is because there is no light.

To see an apple,

light has to hit the apple

and return it to your eyes.

Then, the retinas in your eyes

catch the light reflection for your brain

to interpret into the image of an apple.

If you're invisible,

then, by definition, light would travel

through you or around you

instead of bouncing off you for people to see.

But that means that retinas in your eyes

are not catching the light, either.

Therefore, your brain has nothing

to interpret into an image.

Can you see your reflection

without a mirror to stop the light?

No.

So, when you can't be seen by others,

you also cannot see.

Ouch!

Now, have you given any thought

as of whether the invisibility is permanent?

If it is, how can you receive medical treatment

from a doctor if you're injured?

The doctor wouldn't know

where to apply ointments or bandages

because they cannot access your injury.

For that matter, you can't see it either.

I mean, what if you have an illness or an infection?

How can the doctor diagnose you

without being able to see the color change or inflammation?

And what if everyone is permanently invisible?

Well, think about how boring the world would be

without seeing people on the streets,

on TV,

or at home on your computer

like right now.

It's lonely being invisible.

Now, which superpower physics lesson

will you explore next?

Shifting body size and content,

super speed,

flight,

super strength,

immortality,

and

invisibility.