The Physics of Invisibility Cloaks (Science Out Loud S1 Ep3) - By MITK12Videos
Transcript
00:00 | every morning you see your reflection in the mirror , | |
00:03 | but every summer your friend looks quigley in the bottom | |
00:07 | of the pool , eh , But how can we | |
00:11 | use this to make invisibility cloaks , booth , What | |
00:16 | ? Or explain the shiny wings of a butterfly . | |
00:21 | The answer is photonics , which is all the crazy | |
00:25 | ways to mess with lights . Crazy Way # one | |
00:34 | bouncing . Take a look at yourself in a mirror | |
00:38 | . You probably do this often enough , but you | |
00:40 | were to get anyway . What do you see it | |
00:43 | yourself ? Of course . But have you ever wondered | |
00:46 | why this happens ? You may have heard that light | |
00:49 | travels like a wave sort of like these water waves | |
00:53 | . The water ripples have high parts and low parts | |
00:55 | that travel out and if they hit a wall they | |
00:57 | bounce right back . That's the same sort of thing | |
01:00 | going on with the mirror . Light coming from your | |
01:03 | cell phone is hitting your face and bouncing off of | |
01:05 | it . This bouncing is called reflection . A lot | |
01:08 | of that reflected light bounces off the mirror and goes | |
01:11 | into your eyes . Crazy Way . # two , | |
01:15 | bending Alice . Look at this pencil underwater . Why | |
01:19 | does the part of the pencil that's in the water | |
01:22 | look bent compared to the part above it ? Of | |
01:25 | course for you to see the pencil at all . | |
01:27 | Light needs to reflect off of it . But it | |
01:30 | also has to travel through different materials before it hits | |
01:33 | your eye . Like generally takes the fastest path to | |
01:36 | get between two points and that might not always be | |
01:39 | a straight line . Light travel slower in water than | |
01:42 | an air . So the fastest path is actually bank | |
01:46 | . It's just like when you travel from your house | |
01:48 | , the shortest path isn't always the fastest . Like | |
01:51 | here you could travel the shorter route along slower smaller | |
01:54 | roads or you could go a little farther and take | |
01:57 | the fast highway . Like does that to this bending | |
02:00 | is called refraction . That's why the pencil looked bent | |
02:04 | in the cup and your friend looks quickly in the | |
02:06 | pool . Crazy Way . # three . Mixing . | |
02:11 | Let's look at water waves which actually behave pretty similarly | |
02:14 | to light waves . I made these waves by dropping | |
02:17 | two droplets some distance apart . Each droplet forms a | |
02:20 | set of waves going out and these waves meet and | |
02:22 | mix with each other . This mixing is called interference | |
02:27 | . At some meeting points . The mixed wave is | |
02:29 | bigger than each of the original two waves at other | |
02:31 | meeting points the two waves cancel each other out . | |
02:36 | We can see the same thing happening with light waves | |
02:38 | . And this experiment where I shine light through two | |
02:41 | tiny slits with a small separation just like with water | |
02:45 | . There are some parts of light meeting where the | |
02:47 | mixed light is brighter and other parts where the mixed | |
02:50 | light is darker . But what does this have to | |
02:53 | do with invisibility , cloaks and butterflies ? Let's bring | |
02:57 | these crazy ways to mess with light together . How | |
03:01 | could this cloak make someone invisible ? Let's say this | |
03:04 | camera is your eye and this green fabric is the | |
03:07 | cloak we want to make invisible . You're probably thinking | |
03:11 | let's make the cloak itself invisible so that light would | |
03:14 | pass through it . But if we did that light | |
03:17 | would still be able to bounce off what the cloak | |
03:19 | covers pass through the cloak and get to your eyes | |
03:24 | and that's no good . What the cloak really needs | |
03:27 | to do is take light from the opposite side of | |
03:29 | the camera , channel it through the fabric and out | |
03:31 | the front , unchanged . No light would bounce off | |
03:34 | the cloak or what it covers inside . So you | |
03:37 | would just see what's on the opposite side of the | |
03:38 | cloak . Kind of like camouflage . And every other | |
03:43 | side of the cloak would just channel like to its | |
03:45 | opposite side . So none of the light would even | |
03:49 | get to what's inside the cloak . And none of | |
03:52 | the light hitting the cloak would be reflected into the | |
03:54 | camera lens . So there would be nothing to see | |
03:58 | . All . This depends on channeling light , which | |
04:01 | is not easy . But nature can help . I'm | |
04:05 | here with some morpho butterflies at the boston Museum of | |
04:08 | Science . Their wings are super shiny , bright blue | |
04:11 | color . The front of their wings are made of | |
04:13 | alternating layers of air and Keaton and Keaton is what | |
04:16 | lobster shelves are made of these alternating layers . Take | |
04:20 | advantage of how light bounces , bends and mixes to | |
04:23 | channel the reds , yellows , greens , oranges , | |
04:25 | basically every color of light except blue . All the | |
04:28 | way to the back of the wing . The blues | |
04:31 | don't get channeled through . So this is why you | |
04:33 | see blue on the surface , but no other color | |
04:36 | . If you could take the color channeling structures of | |
04:39 | a butterfly wing and weave them together into a fabric | |
04:43 | . You would have a cloak that would be invisible | |
04:45 | to every color of light except blue . If we | |
04:49 | lived in a world with no blue light , no | |
04:51 | blue could ever be reflected . So our cloak would | |
04:54 | work great . But if someone shined a blue light | |
04:58 | on you and your cloak , you would look kind | |
05:00 | of silly to work in our world . Your clerk | |
05:03 | would have to channel all colors including blue . So | |
05:08 | how do you invent a true photonic invisibility quote . | |
05:11 | Well , any photonic cloak should be possible , right | |
05:14 | ? Because you can mess with how light bounces , | |
05:16 | bends and mixes . All right . Well , I'm | |
05:18 | going to invent a photonic clip first . I already | |
05:24 | Mhm . You know that's just a green cloak . | |
05:28 | Uh huh . |
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