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  • Hey, Vsauce. Michael here. But you are

  • actually right there. Well, at least

  • the camera is. Mirrors are amazing.

  • In fact, the word "mirror" comes from Latin "mirari",

  • meaning "to wonder at, to admire."

  • It's also where we get the word miracle. Mirror-

  • -acle. Like when mirrors face each other and transform a toilet room

  • into infinity. I love this kind of stuff.

  • But what if instead of a rectangular prism,

  • the room was a sphere, mirrored

  • all the way around? What would it look like?

  • What would you see floating around in such a room? The first question we should

  • ask involves

  • the light source. If you were in this room using a flashlight and you turned the

  • flashlight off,

  • would the light keep bouncing around off of the mirrored walls,

  • illuminating the room until your body absorbed all of it?

  • Or if you left the flashlight on, would light continue

  • bouncing around, building up, getting brighter and brighter until you lost

  • your vision and cooked?

  • Probably not. Every time light

  • hits a mirror and reflects off, a tiny tiny amount

  • is absorbed. Even if your mirror spherical room was the size of a

  • giant stadium and its walls reflected

  • 99.99% of light

  • on each reflection, light speed is just too fast,

  • meaning that the reflections will happen rapidly, a little bit of light being lost

  • each time.

  • The room will go dark in a fraction of a fraction of a second. To you and me,

  • it would seem instantaneous. As for what it would look like,

  • let's pretend you begin with your face up against a wall of

  • the sphere and float backward toward and past the centre.

  • At first, you would see your face quite clearly.

  • The surrounding reflections would be very distorted. As you moved away,

  • at a certain point your face would cease to shrink away in appear smaller

  • in mirror and instead would grow larger and become magnified

  • until you reach the center at which point your face would fill

  • your field of view. As you continued on past the center, your image would flip

  • upside down and continue receding away.

  • It would look a bit like this. But don't get too enamoured

  • with your reflection because mirrors don't show you

  • as you really are.

  • Have you ever wondered why you liked the way you look in a

  • mirror but don't like how you look in photographs or

  • video? It might be because of the

  • mere-exposure effect. You prefer what you are used to

  • and most mirrors you look into don't show

  • the real you, the you that other people in cameras

  • see. Instead, a mirror shows you a reversed

  • version of yourself and you've become more comfortable with that version

  • of you. A version of you that is flipped left to right.

  • Mirrors reverse along axes perpendicular to their surfaces,

  • like left and right. They don't also flip things upside down, they don't also

  • reverse up and down because those directions

  • are parallel to the surface of the mirror. When it comes to the way you and

  • other people look,

  • the difference can be startling. NPR pointed out that Abraham Lincoln

  • looked like

  • this. Mirrored he would have looked like

  • this. Now to us, something seems noticeably strange about it but it is

  • the Lincoln

  • Lincoln would have preferred. It's what he saw every day

  • in the mirror. But here's something really cool.

  • You can take a flexible mirror and

  • unreverse its image by folding the mirror

  • into a cylindrical shape. Take a look at this.

  • Here I am with a reflective material and there

  • is the camera with some text taped underneath, as you can see everything is

  • flipped left to right. But as I fold the sheet into a cylindrical shape

  • the image separates, revealing an unreversed

  • version. It becomes a true mirror.

  • Finally, here is one last piece

  • of every day mirror trickery. When you look into a mirror,

  • how big is your reflection, your image

  • on the surface of the mirror to you? Surely,

  • it depends on how far away you are from the mirror. But it doesn't.

  • When you look into a mirror your reflection on the surface of that mirror

  • is

  • always the exact same size. In fact, it is always

  • about half of your actual size. This is because

  • when light reflects off a mirror, it comes in

  • and reflects back out at the same angle, which means that

  • in order to reach your eyes at the top of your body,

  • light from your feet at the bottom must hit the mirror

  • halfway between the two. The triangles you form

  • with a mirror are similar, regardless of

  • where you stand. You can demonstrate this effect by

  • outlining the size of your own head as it appears on the surface of a mirror

  • using a bar of soap. Now, because you aren't here

  • let's pretend that this phone is your head and its camera

  • is your eye. We begin up close. The camera looks

  • really big from this perspective. Let me just

  • carefully trace around the outside, so we can compare later.

  • Good, good, good. Okay. Now, I'm going to pull away from the mirror. Clearly

  • the phone is smaller, right? Well,

  • if I reach out and once again carefully trace the edges.

  • There we go. I will find that I have drawn a

  • rectangle that is the exact same size.

  • Your image on the surface of a mirror

  • from your own perspective is always the same size, whether you are a few

  • centimeters away from the mirror

  • or a few kilometres away. Your image on the surface of a mirror in fact is

  • always half your actual size.

  • Okay, enough about light returning to our eyes. What about light

  • that never returns?

  • Could we use a telescope to resolve individual

  • aliens on a planet light years away? Well, over on Vsauce3,

  • Jake investigates this question with Star Wars.

  • And my friend Rusty investigates the potential for Star Wars

  • becoming real in his episode of Science Friction. And

  • Vsauce2 has a brand new lüt all about cool

  • Star Wars stuff. Check them all out.

  • And as always,

  • thanks for watching.

Hey, Vsauce. Michael here. But you are

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B1 中級

球面鏡の内側 (INSIDE a Spherical Mirror)

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    林宜悉 に公開 2021 年 01 月 14 日
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