Wouldn't it be great if we could be invisible? Ha, right?
如果我们能隐身，这难道不好么？对么？
I mean, we could spy on people without being noticed and do whatever we want without being held responsible.
我是说，我们可以偷窥别人而且不会被发现，可以做我们想做的任何事而且不用负责任。
Now, magicians have figured out how to utilize full-sized mirrors to bend light in order to create disappearing illusions.
现在，魔术师研究出了如何让真实尺寸的镜子来弯曲光线来产生隐身的假象。
Scientists have created metamaterials to guide rays of light around tiny, two-dimensional objects.
科学家创造出了一种“超材料”，在极小的二维空间的物品中可以引导光线的方向。
Cameras can also film what is behind you and project the image so you appear invisible from the front.
相机可以拍到你身后的东西并映射出图片，所以，从前面是看不见你的。
However, none of these options can make an object as large as a person appear invisible for all angles and distances while its moving.
然而，这些方式都没办法让一个真人大小的物体，在移动的情况下从所有角度和距离看都保持隐形。
But if you are truly invisible, as in from within, here are a few problems you may not have thought about before.
即使你真的做到从内到外都隐形，这里还有一些问题你之前可能没列入考虑。
To move around undetected by other people, you would have to be totally naked.
要在别人无法察觉的情况下行动，你必须完全裸体。
Even if it's freezing outside! You can't carry anything, including your wallet and keys,
就算外面天寒地冻！你也不能携带任何东西，连你的钱包和钥匙都不能带，
otherwise people would just see your wallet and keys floating around.
否则人们就会只看到你的钱包和钥匙在空中飘浮移动。
Drivers and people on the street can't see you either, therefore they can and will run into you at some point.
路上的驾驶和行人也看不到你，他们可能会直接撞上你。
Oh, and you better not wear any perfume or make any noise breathing, otherwise they'll know you're there.
喔，你最好别用任何香水，呼吸也不能出声，否则人们会注意到你的存在。
And, just because you start off invisible, doesn't mean you'll stay that way.
而且就算你真的开始隐形，也不表示你可以一直如此。
What if someone accidentally spills scolding hot coffee on you? And what if it rains?
假使有人不小心把热咖啡泼到你身上？又或是下起雨了？
But if you think only liquid can make you visible, you're wrong.
如果你以为只有液体会让你现形，那你可就错了。
Dust consists of dead skin cells from humans, soil particles, and fibers from clothes made from cotton and other materials.
灰尘包含人体代谢的皮肤细胞，土壤颗粒，衣服上的棉絮纤维以及其它材质。
Dust sticks to the moisture on our skin when we sweat and the tiny hairs on our skin when we are dry.
我们流汗时，灰尘会附着在潮湿的皮肤上，而干燥时灰尘会附在毛发上。
So, even if you are invisible, dust would still land on every part of you.
所以就算隐形了，灰尘还是会落在你全身上下。

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.
我们通常不会注意到皮肤上的灰尘，是因为我们有肤色为底，所以看不到有薄薄的灰尘覆盖。
But, if you're invisible, people would see a human-shaped blob of dust walking around with extremely dirty soles. Gross!
但如果隐形了，大家就会看到一个覆满灰尘的人型到处走动还留下超脏的脚印。太恶心了！
What do you think the world looks like if you are invisible?
你有没有想过当你隐形的时候这世界看起来是什么样子？
Well, the answer is nothing. The reason you can't see in the dark is because there is no light.
答案是什么都没有。你在黑暗中看不到东西是因为没有光线。
To see an apple, light has to hit the apple and return it to your eyes.
你要能看到一个苹果，得要有光线照到这个苹果，再回到你的眼睛。
Then, the retinas in your eyes catch the light reflection for your brain to interpret into the image of an apple.
然后你眼睛里的视网膜会将这光线反射到你的脑中，转译为一个苹果的影像。
If you're invisible, then, by definition, light would travel through you or around you instead of bouncing off you for people to see.
如果你隐形了，在这定义下，光线会穿越你或是绕过你，并不会有任何反射让人们看到你。
But that means that retinas in your eyes are not catching the light, either.
但这意味着你的视网膜也无法捕捉到任何光线。
Therefore, your brain has nothing to interpret into an image.
所以你的大脑不会有任何东西能被转译为影像。
Can you see your reflection without a mirror to stop the light? No.
如果没有镜子阻挡光线前进，你能看到你自己的影像吗？不能。
So, when you can't be seen by others, you also cannot see. Ouch!
所以当你不能被其他人看到时，你自己也看不到。哎哟！
Now, have you given any thought as of whether the invisibility is permanent?
你有想过要不要永远隐形吗？
If it is, how can you receive medical treatment from a doctor if you're injured?
如果永远隐形，哪天你受伤了，医生要怎么为你治疗？
The doctor wouldn't know where to apply ointments or bandages because they cannot access your injury.
医生无法知道要在哪里涂药膏或是上绷带，因为他们看不到你的伤口。
For that matter, you can't see it either.
而且连你自己也看不到啊。
I mean, what if you have an illness or an infection?
如果你生病或是感染了呢？
How can the doctor diagnose you without being able to see the color change or inflammation?
医生看不到颜色的改变或是发炎的情况，要怎么帮你诊断？
And what if everyone is permanently invisible?
假如每个人都永远隐形了呢？
Well, think about how boring the world would be without seeing people on the streets,
你想想这世界会有多无趣，在街上看不到任何人
on TV, or at home on your computer like right now.
在电视里或者是在家里的计算机上也看不到，就像现在一样
It's lonely being invisible.
隐形是很寂寞的。
Now, which superpower physics lesson will you explore next?
接下来，你打算去研究哪门超能力物理课？
Shifting body size and content, super speed, flight, super strength, immortality, and invisibility.
是改变人体大小和成分，超级快的速度，飞行，神力，长生不老还是隐身。