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  • 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.

Wouldn't it be great if we could be

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B1 TED-Ed invisible dust skin invisibility apple

【TED-Ed】If superpowers were real: Invisibility - Joy Lin

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    Zenn posted on 2013/08/27
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