The Physics of Invisibility Cloaks (Science Out Loud S1 Ep3) - Free Educational videos for Students in K-12

The Physics of Invisibility Cloaks (Science Out Loud S1 Ep3) - By MITK12Videos

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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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