Latest / Daniel and Kelly’s Extraordinary Universe / Can we build an invisibility cloak?

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Can we build an invisibility cloak? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Kelly, is there a superpower you see inviction that
0:11
Speaker 1: you'd like to have like in real life? You know,
0:15
Speaker 1: I think I'd like to be like the Flash, but
0:17
Speaker 1: instead of running anywhere, because I'm not a big fan
0:19
Speaker 1: of running, I want to get through my to do
0:21
Speaker 1: list super fast. Well, the world is on pause. I
0:27
Speaker 1: love it the Flash, but for paperwriting and parenting and
0:30
Speaker 1: household errands. Yeah exactly. But you know, I don't think
0:35
Speaker 1: a comic book about that would sell very well. To
0:37
Speaker 1: be honest, I also don't think that technology is likely
0:40
Speaker 1: to actually, you know, come to fruition. Really, you should
0:43
Speaker 1: have more faith in scientists, Daniel, Well, I think the
0:45
Speaker 1: problem is scientists already have too much to do, so
0:48
Speaker 1: they don't have time to create the Flash technology. Yeah,
0:51
Speaker 1: but once we have it, it'll be a snap to
0:53
Speaker 1: reinvent it. Hi. I'm Daniel. I'm a particle physicist and
1:12
Speaker 1: I have an infinitely long to do list. Hi. I'm Kelly.
1:16
Speaker 1: I'm a parasitologist and I haven't infinitely long to do list.
1:19
Speaker 1: Plus one and Welcome to the podcast. Daniel and Jorge
1:25
Speaker 1: Explain the Universe, a production of I Heart Radio in
1:28
Speaker 1: which we explore the infinity plus one things we'd all
1:32
Speaker 1: like to understand about the universe. We take a tour
1:35
Speaker 1: of everything that's amazing and crazy, from the inside of
1:38
Speaker 1: neutron stars to the tiniest particles out there, and we
1:41
Speaker 1: try to make sure you understand all of it. And
1:44
Speaker 1: as you might have, guest Jorge is not joining us
1:46
Speaker 1: to down the podcast, but we have a wonderful guest host, Kelly.
1:50
Speaker 1: Would you introduce yourself? Sure? So, I'm Dr Kelly Weener Smith.
1:53
Speaker 1: I am running a small ecology research site in central
1:57
Speaker 1: Virginia and I'm adjunct with Race University and only study parasites.
2:01
Speaker 1: But as my side job, I co author books with
2:03
Speaker 1: my husband, Zach Weener Smith. We've recently wrote a book
2:05
Speaker 1: called soon Ish Ten Emerging Technologies that will improve and
2:09
Speaker 1: or ruin everything. It isn't you're stuck inside because it's
2:11
Speaker 1: a pandemic. You should go read it. You should totally
2:14
Speaker 1: read it. It's a wonderful book. It's super fun to read.
2:17
Speaker 1: The comics are hilarious, and the science is super interesting
2:21
Speaker 1: and it's very relevant. Actually. For today's episode of the podcast.
2:25
Speaker 1: On this podcast, we'd like to talk about the physics
2:27
Speaker 1: of the universe and what's the inside black holes and
2:29
Speaker 1: how tiny particles work. But we also like to break
2:33
Speaker 1: down the physics of everyday objects and future technology. Previously
2:37
Speaker 1: on the podcast, we've talked about how solar panels work,
2:40
Speaker 1: can fusion reactors be real? Wood space elevators actually work?
2:45
Speaker 1: And the thing I think is super fun about that
2:47
Speaker 1: is understanding sort of like what's on the forefront of science?
2:50
Speaker 1: How are people actually solving these problems? You know, there's
2:54
Speaker 1: a wonderful interplay between science fiction where like crazy ideas
2:58
Speaker 1: about how the world might work are written into fiction
3:01
Speaker 1: and then actual scientists making it happen. Does that happen
3:04
Speaker 1: a lot in parasitology, Kelly, Oh jeez, we hope not
3:09
Speaker 1: not yet. You know, if the what is the name
3:11
Speaker 1: of the parasite in the expanse that takes over people's behavior?
3:15
Speaker 1: The proto molecule, the proto molecule. Yeah, so hopefully James S. A.
3:20
Speaker 1: Corey was totally wrong about that. I bet somebody out
3:22
Speaker 1: there in their lab is thinking, I wonder if I
3:24
Speaker 1: could actually build the protomolecule, and they're starting to write
3:27
Speaker 1: grant proposals for that. I hope not. I hope that's
3:30
Speaker 1: not fundable by the NSF. Well, today we are not
3:34
Speaker 1: talking about the protomolecule or anything that we think will
3:38
Speaker 1: lead to a more rapid demise of all of humanity. Instead,
3:42
Speaker 1: we're going to tackle a really fun concept that comes
3:44
Speaker 1: up a lot in fiction. We're asking the question today
3:47
Speaker 1: on the podcast, could we build a cloak of invisibility? So?
3:57
Speaker 1: Are you a fan of Lord of the Rings and
4:00
Speaker 1: Ry Potter Kelly? Yes, I can't say I watched them regularly,
4:02
Speaker 1: but yeah, I'm a fan. Yeah. So this kind of
4:04
Speaker 1: stuff pops up all the time in fiction, this idea
4:08
Speaker 1: of being invisible, of like sneaking around and having nobody
4:12
Speaker 1: see you, being able to listen to people's conversations or
4:15
Speaker 1: Rob Banks. Why do you think it's so fascinating? I mean,
4:18
Speaker 1: I think we all love the idea of of knowing
4:21
Speaker 1: what's going on when we're not in the room, and like,
4:23
Speaker 1: as a naturalist, I would love to be able to
4:25
Speaker 1: just sit in nature and watch stuff happening, because you know,
4:28
Speaker 1: when you're there, you're you know, impacting what happens when
4:30
Speaker 1: you know the deer are going to act differently if
4:32
Speaker 1: you're there, and just being able to observe the world
4:34
Speaker 1: as though you're not there. I think that's appealing in
4:36
Speaker 1: a lot of ways. Well, that's actually like a real
4:38
Speaker 1: science application for invisibility. I never even thought about that.
4:42
Speaker 1: Ecologist would love it, college just would love it. I
4:45
Speaker 1: would be terrified, though, to like sneak into a room
4:47
Speaker 1: and hear people talking about me. I'm pretty sure I
4:50
Speaker 1: don't want to hear what they have to say. I
4:53
Speaker 1: don't think i'd want to hear it either. No, that's
4:54
Speaker 1: why it appeals to me from a nature perspective. But
4:56
Speaker 1: I'll leave the humans alone, I think. So. This kind
4:59
Speaker 1: of stuff appears in Harry Potter and in Lord of
5:02
Speaker 1: the Rings and in much much older writing. And it's
5:05
Speaker 1: interesting to me how it first starts in sort of
5:08
Speaker 1: like magic and fantasy based worlds, and then in like
5:11
Speaker 1: the last hundred and fifty years, it appeared in like
5:13
Speaker 1: science fiction stories as authors have tried to figure out, like,
5:17
Speaker 1: what is the mechanism for this? How could this actually happen?
5:20
Speaker 1: And it appeared first in an eighteen fifty story by
5:23
Speaker 1: Fitz James O'Brien where there was a monster in a
5:26
Speaker 1: house that was alive and you know, not a ghost
5:29
Speaker 1: but invisible, so you couldn't see it. Was it cloaked?
5:32
Speaker 1: It was it just straight up invisible? It was just
5:34
Speaker 1: straight up invisible. Yeah, the whole monster itself was invisible.
5:37
Speaker 1: And then maybe the most famous early appearance was of course,
5:40
Speaker 1: in The Invisible Man by H. G. Wells, And this
5:43
Speaker 1: was right around the turn of last century, and it
5:46
Speaker 1: was just after X rays were discovered, and so people
5:48
Speaker 1: were sort of like getting their minds around the concept
5:51
Speaker 1: that there was different kinds of light and different kinds
5:53
Speaker 1: of visibility, right, that our bodies are opaque to normal light,
5:57
Speaker 1: but they could be transparent to other kinds of light.
6:00
Speaker 1: That was like a mind blowing idea. That is pretty awesome. Yeah,
6:04
Speaker 1: and so I think this god science fiction writers thinking
6:06
Speaker 1: about what is visibility and what is invisibility? Then a
6:09
Speaker 1: transition to science fictions. And now today maybe we'll talk
6:13
Speaker 1: about how it could actually be science. And so today
6:17
Speaker 1: on the podcast we will be answering that question and
6:19
Speaker 1: digging into all the various ways that you could have invisibility.
6:23
Speaker 1: The technology is underdeveloped, it's not actually there yet, but
6:27
Speaker 1: you might be impressed by how far people have gotten. So,
6:30
Speaker 1: as usual, I looked for volunteers for people who were
6:33
Speaker 1: willing to speculate baselessly on how something worked or answer
6:36
Speaker 1: a difficult physics question. So thank you to everyone who
6:39
Speaker 1: was brave and lent your voice, And if you would
6:42
Speaker 1: like to volunteer for future episodes, please write to us
6:45
Speaker 1: two questions at Daniel and Jorge dot com. Here's what
6:48
Speaker 1: people had to say. People have made really micro scale
6:53
Speaker 1: invisibility cloaks. I think invisibility cliques can be built, and
6:59
Speaker 1: I think at least one already does exist. I think
7:03
Speaker 1: it works by making light bend around it. I'm not
7:07
Speaker 1: sure if we can build a cloak per se, but
7:09
Speaker 1: I know we can make invisibility happen by using fiber
7:13
Speaker 1: optic cables. I think that's got to be a definite yes.
7:17
Speaker 1: And I think it really depends on what you mean
7:19
Speaker 1: by invisibility. But I think if if you consider a
7:23
Speaker 1: chameleon to be invisible, then yeah, I've seen cases where
7:29
Speaker 1: using cameras and displays and creatively arranged we can come close. Um.
7:37
Speaker 1: I think it's an engineering problem more than a physics
7:40
Speaker 1: problem at this point. Camouflage is something that has been
7:43
Speaker 1: figured out in the animal kingdom. I mean, if you
7:46
Speaker 1: look at an octopus then and a cuttle fish the
7:49
Speaker 1: way that they can completely blend into their background. So
7:53
Speaker 1: it seems like it's possible. Probably at some level. I
7:59
Speaker 1: really don't think we can. The problem with the invisibility
8:03
Speaker 1: clock is that if the wearer of the cloak is
8:06
Speaker 1: invisible to anyone on the outside, then the wearer also
8:10
Speaker 1: cannot see anything outside of the cloak. Probably not, i'd say,
8:17
Speaker 1: mainly because I'm guessing anything that can bend light around
8:20
Speaker 1: something with that force will probably have quite a horrendous
8:24
Speaker 1: effect on anyone or anything that it is put around. No,
8:28
Speaker 1: I don't think it's possible to build an invisibility cloak.
8:32
Speaker 1: I would say not likely, just because you can build
8:37
Speaker 1: it maybe invisible from one direction, but from multiple directions. UM,
8:43
Speaker 1: I can't imagine it. I have heard of some invisibility
8:47
Speaker 1: technology where it basically bends the light around something so
8:53
Speaker 1: that it looks like you're seeing through it. UM. I
8:57
Speaker 1: thought that it depended on the perspective of the viewer.
9:02
Speaker 1: So what do you think of those answers, Kelly? I
9:05
Speaker 1: thought they were really interesting answers. As a biologist, I
9:07
Speaker 1: thought it was interesting that chameleons and cuttle fish came
9:09
Speaker 1: up pretty often. And to be honest, when you told
9:11
Speaker 1: me the topic of this, my first thought was, woh, well,
9:14
Speaker 1: chameleons and octopuses can do it. I guess I sort
9:17
Speaker 1: of matched up with some of these responses. What did
9:19
Speaker 1: you think? Yeah? I was impressed. There's a huge variety
9:22
Speaker 1: of possible ideas in here, and I love in these
9:24
Speaker 1: responses hearing people sort of think on their feet. They
9:28
Speaker 1: don't know the answer, they're thinking about it, they're wondering,
9:30
Speaker 1: and that's like people doing physics right there, like taking
9:33
Speaker 1: their understanding of the universe and trying to use it
9:35
Speaker 1: to solve problems. Though. I love hearing people figure it
9:38
Speaker 1: out and actually making some progress on the fly. I'm
9:41
Speaker 1: impressed we have smart listeners totally alright. So let's dig
9:45
Speaker 1: into it. And first, maybe the thing we should talk
9:47
Speaker 1: about is what do we actually want to accomplish? If
9:50
Speaker 1: we're like talking to DARPA about building an invisibility cloak,
9:53
Speaker 1: what do we really mean buying visibility? What are the
9:56
Speaker 1: specs that we want to achieve? So you talked about
10:00
Speaker 1: invisibility in biology, and I'm super interested in that but
10:03
Speaker 1: don't know a whole lot about it. Could you tell
10:04
Speaker 1: us a little bit about how do octopy or chameleon
10:07
Speaker 1: or cuddlefish achieve some sort of biological camouflage. Sure, so
10:11
Speaker 1: I can't say that I'm an expert on this topic,
10:13
Speaker 1: but my understanding is that they have these chromatophors, which
10:16
Speaker 1: are cells that can expand and contract, and the cells
10:19
Speaker 1: are always filled with pigments, and whether they're expanding or
10:23
Speaker 1: contracted determines how much of the pigment you get to see.
10:27
Speaker 1: And so by making more of this pigment visible, for example,
10:30
Speaker 1: an octopus can become more brown by allowing more of
10:33
Speaker 1: the brown pigment up to the surface. And really complicated
10:37
Speaker 1: animals like chameleons might have different layers of these pigmented cells,
10:42
Speaker 1: and by sort of turning on some layers and turning
10:45
Speaker 1: off other layers, they can come up with really complicated
10:48
Speaker 1: and complex color patterns. But usually what happens when they're
10:52
Speaker 1: doing these things is they're staying like dead still. They're
10:55
Speaker 1: not moving at all. And so I'm guessing that invisibility cloaks,
10:59
Speaker 1: people who are wearing them expect to be able to
11:02
Speaker 1: to move while they're wearing them. Is that true? What
11:04
Speaker 1: do you think? I definitely think you want to be
11:07
Speaker 1: able to sneak around. Yeah, I don't think you want
11:09
Speaker 1: to just have to like squat somewhere and stay fixed.
11:12
Speaker 1: But also does that really count as invisibility? In my mind,
11:15
Speaker 1: what's happening is like an octopus is like sitting on
11:18
Speaker 1: a coral, and then it makes itself look like a coral,
11:20
Speaker 1: which is super amazing and impressive and not something I
11:23
Speaker 1: could ever do. But it doesn't look like it's not there.
11:27
Speaker 1: It just looks like it's more coral, right, yeah, fair enough,
11:30
Speaker 1: which I think would be a cool trick for people
11:32
Speaker 1: who want to sneak around, But I agree that it's
11:34
Speaker 1: probably not the same thing as being invisible. Yeah, Like,
11:36
Speaker 1: you know, you can make yourself look like a bush
11:38
Speaker 1: or whatever, but if you want to walk into a
11:40
Speaker 1: room and have nobody see that you're there, you can't
11:42
Speaker 1: just like, oh, I'm gonna look like more chairs or something.
11:45
Speaker 1: You need to blend in some way. So I think
11:47
Speaker 1: that's awesome and impressive, but not technically invisibility, right yeah,
11:51
Speaker 1: fair enough? All right, And then maybe we should disentangle
11:53
Speaker 1: invisibility from another similar concept, which is stealth technology. A
11:58
Speaker 1: lot of airplanes out there, you know, we have like
12:00
Speaker 1: stealth airplanes that can't be seen by radar. That's a
12:03
Speaker 1: really cool technology, but it's not also the same thing
12:07
Speaker 1: as invisibility. It's more like being totally black or like
12:11
Speaker 1: not reflecting anything. The way like a stealth airplane works
12:15
Speaker 1: is that when you shoot radar at it, and radar
12:17
Speaker 1: is just like another form of light, it doesn't bounce
12:20
Speaker 1: anything back. Like a normal airplane, you can think of
12:23
Speaker 1: like as a sphere, and if you bounce radar at it,
12:25
Speaker 1: it's going to bounce some back at you. Has a reflection,
12:28
Speaker 1: but a stealth airplane is like all these weird angles
12:30
Speaker 1: and so it has the profile so that if you
12:32
Speaker 1: shoot radar at it, the radar always bounces off in
12:35
Speaker 1: another direction. It's all these like sharp edges. There's no
12:38
Speaker 1: smooth curves that would always reflects something back at you.
12:41
Speaker 1: And so that's also not invisibility, right, It doesn't reflect
12:45
Speaker 1: any light. But it's sort of like equivalent to you know,
12:47
Speaker 1: painting yourself black. That doesn't make people invisible, right, I mean,
12:51
Speaker 1: it's it's pretty amazing that we figured out how to
12:53
Speaker 1: do that, but yeah, I agree. Also not invisibility, Yeah,
12:56
Speaker 1: not invisibility, like if you ordered an invisibility cloak that
13:00
Speaker 1: just gave you like a black sheet, you'd be pretty disappointed. Yeah, yeah,
13:03
Speaker 1: I want my money back for sure. All Right, So
13:07
Speaker 1: we want something that's actually invisible, which means it looks
13:11
Speaker 1: like you're not there, right. I want to be able
13:13
Speaker 1: to see basically what's behind you. I want to get
13:16
Speaker 1: an image in my eyes that would be the same
13:18
Speaker 1: image as if you were not there. And this includes
13:22
Speaker 1: being able to move or is it just not look
13:24
Speaker 1: like you're there and you're just standing still? Like I
13:26
Speaker 1: guess I'm wondering if moving is part of the definition here. Now,
13:29
Speaker 1: I think moving is definitely part of the definition. I mean,
13:31
Speaker 1: let's be aspirational, right, we're setting the bar high. We
13:34
Speaker 1: want like, actual, real, useful invisibility, and so I think
13:37
Speaker 1: we want to be able to move. And also I
13:40
Speaker 1: think it's important that it works for different wavelengths of light. Right,
13:44
Speaker 1: it can't just be like, oh, you're invisible in red
13:46
Speaker 1: light or in green light, or in radio waves or
13:49
Speaker 1: in microwaves. Has to work broadband across the whole spectrum,
13:53
Speaker 1: otherwise you'd be pretty easy to detect. So more than
13:55
Speaker 1: just what humans and their machines can view, is what
13:58
Speaker 1: we're going for. Yeah, because other wrinkle, right, and that
14:01
Speaker 1: maybe people don't really appreciate or think about, is that
14:04
Speaker 1: humans are more than just visible. We actually glow like
14:07
Speaker 1: we give off light. Because every object in the universe
14:11
Speaker 1: that has a temperature is giving off infrared light. You're
14:14
Speaker 1: radiating heat, which is why, for example, night vision goggles,
14:17
Speaker 1: what they do is they see in the infrared, and
14:20
Speaker 1: like every object in the universe that has a temperature,
14:22
Speaker 1: you glow as some color. So the sun is super
14:25
Speaker 1: duper hot, which is why it glows. In the visible light.
14:27
Speaker 1: Where we take a piece of metal and heat it up,
14:29
Speaker 1: it glows red or blue or white or whatever. Your
14:32
Speaker 1: body is also glowing. So I think invisibility should mean
14:35
Speaker 1: not just that you look like the thing behind you,
14:38
Speaker 1: but that you don't give off any light also, so
14:40
Speaker 1: it has to somehow block your heat. I had not
14:43
Speaker 1: thought of that extra complication beforehand. That's really interesting. Yeah,
14:46
Speaker 1: it's complicated. And in addition, I think if we're gonna
14:49
Speaker 1: set the bar really high, it should be that you
14:52
Speaker 1: can't tell any difference in the light that comes to you,
14:55
Speaker 1: even like a time delay. Right, you can imagine, and
14:57
Speaker 1: we're gonna dig into this and talk about various solutions
15:00
Speaker 1: to invisibility. You don't want that the light that's coming
15:02
Speaker 1: from behind you is slowed down as it passes through
15:06
Speaker 1: you by your invisibility cloak, because then again, somebody could
15:09
Speaker 1: detect that right and then if you started moving around
15:12
Speaker 1: really fast, the image would be sort of flawed, sort
15:14
Speaker 1: of like the Predators camouflage and fix seen those movies totally,
15:18
Speaker 1: But I mean you can imagine if you're an early adopter,
15:20
Speaker 1: you can like get away with some of these things
15:22
Speaker 1: because people aren't expecting invisibility cloaks. But yes, as you
15:26
Speaker 1: go further on, I think you've got to fix all
15:28
Speaker 1: these problems first gen invisibility cloaks of lower standards. You know,
15:32
Speaker 1: I was thinking about this last night. I was talking
15:34
Speaker 1: to my thirteen year old about this, and he was thinking,
15:36
Speaker 1: invisibility would that even really be a good idea, you know,
15:40
Speaker 1: because could you even use it? He made this really
15:42
Speaker 1: interesting point I hadn't thought of, which is, if you're invisible,
15:46
Speaker 1: can you see the rest of the world. Because if
15:49
Speaker 1: light is like passing through you and not interacting with you,
15:52
Speaker 1: doesn't that mean that you're not seeing the rest of
15:54
Speaker 1: the world. So if you're invisible, are you also then blind? Oh? Well,
15:59
Speaker 1: that's an extra complicate ation. I mean, could there be
16:00
Speaker 1: like a little screen inside of your cloak that's showing
16:03
Speaker 1: you what's going on outside? Yeah, you need something like that, right,
16:05
Speaker 1: otherwise you'd be totally blind. And then I thought, hold
16:08
Speaker 1: on a second, even if you aren't blind, even if
16:11
Speaker 1: the world can't see you, but you can still see outside,
16:14
Speaker 1: you're probably not seeing yourself, right. You can't see your
16:17
Speaker 1: arms or your hands or anything. And I started thinking about, like,
16:20
Speaker 1: what is it like to walk up a flight of
16:23
Speaker 1: stairs if you can't see your own body? I mean,
16:26
Speaker 1: you're the biologists tell me, like, doesn't our brain rely
16:29
Speaker 1: on seeing where your feet are to be able to
16:31
Speaker 1: go upstairs? Like I can't walk up a flight of
16:33
Speaker 1: stairs with my eyes closed? Very well? Totally? Yeah, No,
16:36
Speaker 1: that's that's a great point. You. I guess you definitely
16:38
Speaker 1: need to do a lot of practice. So you know,
16:39
Speaker 1: like I think astronauts when they go into space, they
16:41
Speaker 1: sort of learned to live without some of the cues
16:43
Speaker 1: that they're used to on Earth. So I guess with
16:46
Speaker 1: enough practice, you could learn to stop relying on being
16:49
Speaker 1: able to see what your body is doing to accomplish
16:51
Speaker 1: that task. But I definitely think you'd be clumsy initially.
16:54
Speaker 1: You'd need some training in this cloak. You definitely would.
16:57
Speaker 1: So the first end click probably not super sophisticated, and
17:00
Speaker 1: the first and gen user probably pretty clumsy. I mean
17:04
Speaker 1: you'd be like banging around into stuff. And also like
17:07
Speaker 1: how would you walk through a crowd of people? Right,
17:09
Speaker 1: Nobody would see you, so they wouldn't know to avoid you,
17:12
Speaker 1: so they'd be like bumping into you all the time.
17:14
Speaker 1: The more I think about it, the more like complicated
17:17
Speaker 1: it would be to be invisible. Yeah, there might just
17:20
Speaker 1: be very specific situations where you can use it, and
17:22
Speaker 1: otherwise you're likely to get found out. Yeah, Like you
17:25
Speaker 1: can't stand in the rain if you're invisible. Right, we
17:27
Speaker 1: don't have invisibility cloth. That's gonna be like rain permeable. Also, anyway,
17:31
Speaker 1: it sounds really complicated. You need to carry a huge
17:33
Speaker 1: battery pack or a really long extension cord also invisible,
17:40
Speaker 1: which no one can trip over, so you need to
17:42
Speaker 1: make sure your path doesn't cross anyone else's all right,
17:45
Speaker 1: So I want to learn more about the technologies that
17:48
Speaker 1: have been developed so far. But first let's take a break,
18:04
Speaker 1: and we're back and we're talking about whether or not
18:06
Speaker 1: you could actually make an invisibility cloak Daniel, What do
18:10
Speaker 1: we know about how you can make invisibility cloaks? Has
18:13
Speaker 1: anyone done research on this? People have been doing this
18:15
Speaker 1: for a while, actually, and this is a really fascinating
18:18
Speaker 1: field where people had ideas like fifty years ago and
18:22
Speaker 1: then it's sort of lay dormant for a long time,
18:24
Speaker 1: nobody was doing anything. I think people sort of shrugged
18:26
Speaker 1: it off as basically impossible, like the flash technology. And
18:29
Speaker 1: then about fifteen years ago there was like a little
18:32
Speaker 1: renaissance where people had sort of like starting ideas for
18:35
Speaker 1: how you could actually tackle this and tried it and
18:38
Speaker 1: made some progress and now it's like a flourishing field again.
18:41
Speaker 1: So it's an exciting time actually to talk about invisibility.
18:44
Speaker 1: Was there anything fifteen years ago that kicked it off,
18:46
Speaker 1: like some technology that made people think it might be
18:49
Speaker 1: feasible or was it just sort of random, probably some
18:52
Speaker 1: scientists staying up late reading some science fiction novel and
18:55
Speaker 1: then just having an idea. You know, it's cool the
18:58
Speaker 1: way these things happen, that there's like progress and then
19:00
Speaker 1: it's abandoned for thirty years, and then somebody has an
19:03
Speaker 1: idea and then it moves forward anyway. That's sort of
19:05
Speaker 1: like three different ways you might achieve invisibility. There's like
19:09
Speaker 1: projecting your image on something, there's like recreating your image
19:13
Speaker 1: like adaptive camouflage, and then when I think is the
19:15
Speaker 1: most promising of like bending an image around you. But
19:19
Speaker 1: let's talk about them in turn. So the first idea
19:21
Speaker 1: of this idea of image projection is pretty hokey, but
19:24
Speaker 1: I got a lot of attention In like two thousand
19:26
Speaker 1: and three, you win a lab in Tokyo put out
19:28
Speaker 1: a video showing how it would work, and the idea
19:30
Speaker 1: here it's basically, you have a camera behind you that's
19:33
Speaker 1: taking an image of what's going on behind you, and
19:36
Speaker 1: then you have a projector in front of you that's
19:38
Speaker 1: like shining that image onto your invisibility cloak. So then
19:42
Speaker 1: somebody standing basically next to the projector is technically seeing
19:47
Speaker 1: through you because they're seeing an image of what's behind
19:49
Speaker 1: you projected onto this cloak you're wearing. How smooth is
19:53
Speaker 1: the image, Like if there's any wrinkle in the cloak?
19:56
Speaker 1: Is there a wrinkle in the image, do you need
19:57
Speaker 1: to like stand there like a scarecrow. Yeah, you basically
20:00
Speaker 1: need to stand there like a scarecrow because you're right,
20:03
Speaker 1: like you're projecting this and so the image doesn't lie
20:06
Speaker 1: smoothly on the cloak, right, but it sort of works.
20:09
Speaker 1: If you stand there and hold your cloak pretty flat,
20:12
Speaker 1: then you basically look like a movie screen and it's
20:15
Speaker 1: sort of cool. It gives this sense of invisibility. You
20:17
Speaker 1: could definitely tell like, oh, where's the edge of the cloak,
20:20
Speaker 1: and you can see the guy's face because your face
20:22
Speaker 1: doesn't make a very good screen. But if you look
20:24
Speaker 1: at this video from this Tokyo experiment, it's invisibility ish,
20:28
Speaker 1: you know. It gives you that like the flavor of it.
20:30
Speaker 1: So you might be able to like stand still as
20:32
Speaker 1: somebody passes by and maybe they won't see you if
20:35
Speaker 1: they're not looking too hard. Yeah. Maybe. And also they
20:38
Speaker 1: have to like not pay attention to the fact that
20:40
Speaker 1: there's a projector they're showing this image onto you, and
20:44
Speaker 1: they have to be an exactly the right angle for
20:45
Speaker 1: this to work. So it's sort of like a cool
20:47
Speaker 1: demonstration that like maybe you could use to film a
20:50
Speaker 1: movie about invisibility to make that special effect, But it's
20:53
Speaker 1: never going to be like what we talked about, an
20:56
Speaker 1: actual invisibility cloak. You could us to walk around and
20:58
Speaker 1: do stuff. Yeah, right, if fails a lot of the
21:00
Speaker 1: criteria we were talking about. Yeah, but it's sort of
21:02
Speaker 1: like got people excited, and you know, there are some
21:05
Speaker 1: actual applications of it, Like it could be useful in
21:08
Speaker 1: some ways now when you want to sneak around in
21:10
Speaker 1: the faculty meeting and here where people really think about
21:12
Speaker 1: your work. But you know, you could imagine using in
21:14
Speaker 1: some scenarios, Like people have talked about using it for airplanes,
21:18
Speaker 1: Like if you can make the floor of the cockpit
21:21
Speaker 1: basically invisible, then a pilot would have like a better
21:24
Speaker 1: sense for where they are. It might be easier to
21:26
Speaker 1: fly if you like projected an image of the ground
21:29
Speaker 1: onto the floor of the cockpit, sort of a similar application.
21:32
Speaker 1: Do pilots have a lot of problems with that? I
21:36
Speaker 1: don't think pilots too much to the landing anymore. I
21:38
Speaker 1: think it's mostly AI these days, and AI doesn't care
21:41
Speaker 1: at all these images. But maybe it'd be cool, like
21:44
Speaker 1: for passengers, you know, if like the floor the airplane
21:48
Speaker 1: looked like it wasn't there, but they think i'd be
21:50
Speaker 1: cool with that would be like terrifying. I think it
21:52
Speaker 1: might be terrifying. It might depend on the person or
21:56
Speaker 1: the person you're sitting next to you. I think i'd
21:58
Speaker 1: be cool with it, but if the person next to
21:59
Speaker 1: me started to get nervous, that would make me nervous. Well.
22:02
Speaker 1: I remember Odd airplanes when they first had this feature
22:05
Speaker 1: that they had a bunch of cameras and you could
22:07
Speaker 1: do yourself like cycle through them and like look down
22:09
Speaker 1: or back or outside. I thought that was super cool,
22:12
Speaker 1: like connect to you with what's going on outside the airplane,
22:15
Speaker 1: because otherwise you feel like you're in this bubble. You
22:17
Speaker 1: get on it in l A, you get off it
22:19
Speaker 1: in New York. You don't really see experience the transition much.
22:22
Speaker 1: So I think it's cool to be connected to what's
22:24
Speaker 1: going on outside. But I think that would be pretty terrifying.
22:27
Speaker 1: When was that a thing that does sound awesome? Yeah,
22:30
Speaker 1: I think it's you know, in the last ten or
22:32
Speaker 1: fifteen years or so, when they you had like your
22:34
Speaker 1: own little screen that you could control yourself rather than
22:36
Speaker 1: like everybody watching the same movie, and so you could
22:39
Speaker 1: look at these cameras. It's like a camera in the
22:41
Speaker 1: nose and a camera in the tail. I thought that
22:43
Speaker 1: was pretty cool. I guess I've been flying the cheap airlines.
22:45
Speaker 1: I gotta I gotta upgrade. That does sound fun. You
22:48
Speaker 1: gotta get some of that government funding. There are other applications,
22:51
Speaker 1: like you could imagine painting the inside of your car
22:54
Speaker 1: with a view of what's going on outside, like, hey,
22:56
Speaker 1: maybe no more blind spots, right, Or you could look
22:59
Speaker 1: out of your car and actually see what's behind you.
23:01
Speaker 1: We have sort of a version of this already where
23:03
Speaker 1: people have like cameras on their license plates and you
23:06
Speaker 1: can just look at a screen in front of you
23:08
Speaker 1: and see what's behind you. But it would be sort
23:10
Speaker 1: of cool if the car didn't block your view at all. Yeah,
23:13
Speaker 1: that would be awesome. I bet that would save some lives. Yeah,
23:15
Speaker 1: And I read about some applications where in surgery, for example,
23:20
Speaker 1: you could paint an image of what's behind the surgeon's
23:23
Speaker 1: hand on his hand so he can hear she could
23:25
Speaker 1: see what they were doing better, like make their own
23:28
Speaker 1: hands invisible. So that would be I mean, if you
23:30
Speaker 1: got your hand inside a body, there's gotta be a
23:32
Speaker 1: lot of things getting in the way of the projection
23:34
Speaker 1: getting to the hands. So would it be like the
23:36
Speaker 1: gloves projecting, like would you have fancy gloves? Yeah, I
23:40
Speaker 1: guess if the body is opened, then you'd want, just
23:43
Speaker 1: like the gloves to have a projection on them. But
23:46
Speaker 1: if it's closed and you're doing it like laparoscopically, maybe
23:49
Speaker 1: you could like project an image of what's going on
23:51
Speaker 1: inside the body, like on the torso that would be
23:53
Speaker 1: kind of cool. So it would like look like you're
23:55
Speaker 1: opened up, even if you're not. That would be super cool.
23:58
Speaker 1: That does sound super cool, you know, that's fun. That's interesting,
24:01
Speaker 1: But it's definitely not real invisibility, right, and it's not
24:04
Speaker 1: a cloak, and it's not a cloak, right. And so
24:07
Speaker 1: moving on from that is a second category, which I
24:09
Speaker 1: think is closer to what we're trying to do, and
24:11
Speaker 1: this is like image recreation. So it's the same idea
24:15
Speaker 1: where you're like gathering the image on one side and
24:17
Speaker 1: creating it on the other side, but instead of using
24:19
Speaker 1: like a projector has to be like far away from
24:22
Speaker 1: you and then the image only works at one angle,
24:24
Speaker 1: you have basically like adaptive camouflage. Imagine like the cloak
24:28
Speaker 1: being made out of pixels. And it has cameras all
24:31
Speaker 1: over the place and pixels, and so it's taking pictures
24:34
Speaker 1: of what's behind you and creating that image on the
24:38
Speaker 1: pixels on the outside of the cloak. Well, and so
24:41
Speaker 1: you still have the problem with needing to make sure
24:43
Speaker 1: you're not bending or folding anywhere, right, Yeah, maybe, I
24:46
Speaker 1: mean it's potentially with like fancy computation and AI, you
24:50
Speaker 1: could imagine that the cloak would sort of know how
24:53
Speaker 1: it's arranged, and so it could know like where the
24:56
Speaker 1: cameras are pointed and how the cloak is folded to
25:00
Speaker 1: create the image in just the right way. A simpler version,
25:03
Speaker 1: which is like painting image on the cloak, assuming it's flat,
25:05
Speaker 1: but that might not always work. But if you knew
25:08
Speaker 1: how it was curved, you might be able to adjust
25:10
Speaker 1: how you're painting the image to still make it work.
25:12
Speaker 1: So that is totally epic, and it sounds like it
25:15
Speaker 1: would require a lot of computing ability, So like to
25:18
Speaker 1: do this, do you need to have like a big
25:21
Speaker 1: battery or carrying a computer inside the cloak with you.
25:25
Speaker 1: I'm gonna imagine you're carrying like one of those old
25:27
Speaker 1: tower computers from like the year two thousand inside and
25:30
Speaker 1: people are like, I hear the fan worrying on your computer, man,
25:33
Speaker 1: Like that would give you away. Yeah, you need sound
25:38
Speaker 1: canceling something. Yeah. But you know, in terms of like
25:41
Speaker 1: the general possibility, you could imagine maybe solar power and
25:45
Speaker 1: super micro computers of the future could potentially pull this off.
25:49
Speaker 1: And I think this is the basis of the Predators
25:52
Speaker 1: invisibility in this sort of like adaptive camouflage that projected
25:56
Speaker 1: the image behind him. It created the image on his
25:59
Speaker 1: surface so that you could see it. And I think
26:01
Speaker 1: one cool thing about that is that I think it
26:03
Speaker 1: should work from any angle. Right. It shouldn't matter necessarily
26:07
Speaker 1: what direction you're looking at the cloak from. It should
26:10
Speaker 1: still be able to work as long as you create
26:12
Speaker 1: the right image. You've got from all sides you need
26:15
Speaker 1: cameras looking out, and then from all sides you need
26:17
Speaker 1: pixels so that if somebody walks behind you, you're still invisible.
26:21
Speaker 1: So is that the idea. That's the idea. Yeah, And
26:24
Speaker 1: people are actually working on this, and there's a lab
26:27
Speaker 1: I've seen one of their papers where they have these
26:29
Speaker 1: thermo chromic liquid crystals. Liquid crystals are these things that
26:34
Speaker 1: are very cool. A lot of people have l c
26:36
Speaker 1: D displays on their computers or on their calculators or whatever.
26:39
Speaker 1: But these can be flexible, so they can be like
26:40
Speaker 1: woven into fabric and they can respond, of course, you know,
26:44
Speaker 1: to computation, and so you can create basically any image.
26:47
Speaker 1: And these are thermo chromic, which means that they change
26:50
Speaker 1: their color based on the temperature. Remember those mugs that
26:53
Speaker 1: if you poured hot water into them, an image appeared
26:56
Speaker 1: or disappeared or something. I have one that says best
26:58
Speaker 1: daughter in law. Wait, and what happens when you pour
27:01
Speaker 1: water into it changes to worse daughter in law or something.
27:04
Speaker 1: You know it's black, and then it says best daughter
27:06
Speaker 1: in law. But yeah, maybe there's a secret message in there.
27:09
Speaker 1: If you pour hot enough water in there, you see
27:12
Speaker 1: the secret message. I know how they really feel. Then yeah, no,
27:17
Speaker 1: I don't want to get you in trouble with your family.
27:20
Speaker 1: So I've seen an example of this. They have a
27:21
Speaker 1: small patch like a few inches by a few inches
27:25
Speaker 1: that can effectively create an image of what's behind the user.
27:29
Speaker 1: But you're already takes a lot of computation, and if
27:31
Speaker 1: you want it to be very effective, it has to
27:33
Speaker 1: work quickly, right, has to like really quickly update the image,
27:36
Speaker 1: otherwise it will be obvious if you move or somebody
27:38
Speaker 1: changes their perspective. So if this depends on temperature, if
27:41
Speaker 1: somebody had like a temperature sensing device, would they be
27:45
Speaker 1: able to detect your cloak? No, because the cool thing
27:48
Speaker 1: is that this thing can also cloak your temperature. These
27:51
Speaker 1: pixels can create an arbitrary color, but they can also
27:54
Speaker 1: heat up or cool down to cloak your temperature. For example,
27:58
Speaker 1: if you're in a warm environment, you want to give
28:00
Speaker 1: off a lot of heat. If you're in a cold environment,
28:03
Speaker 1: you want to not give off a lot of heat.
28:04
Speaker 1: So that's actually a really cool application of this sort
28:07
Speaker 1: of like adaptive camouflage that it can cloak you not
28:10
Speaker 1: just in terms of visible light, but also in terms
28:13
Speaker 1: of infrared light, effectively your temperature. What is the largest
28:17
Speaker 1: size of one of these that they've been able to make.
28:19
Speaker 1: Are we talking about cloaks? Are we talking about, you know,
28:22
Speaker 1: postage stamps where this has been tried out so far.
28:24
Speaker 1: We're talking about like basically a napkin. So it's an
28:27
Speaker 1: invisibility napkin, so you might be able to like hide
28:30
Speaker 1: a small road in behind it, you know, but you're
28:32
Speaker 1: definitely not squeezing behind this napkin. But you know it's
28:34
Speaker 1: also chunky, Like the pixels are not very small, they're
28:38
Speaker 1: like a centimeter and by a centimeter. But you know,
28:40
Speaker 1: these are engineering problems, and so as I often like
28:44
Speaker 1: to say, you know, the physics has been figured out,
28:46
Speaker 1: the idea is there, and we just hand it off
28:48
Speaker 1: to the engineers and they can make the pixels smaller
28:50
Speaker 1: and make it the battery more efficient, and make the
28:52
Speaker 1: cameras better and you know, it's a it's a tech
28:54
Speaker 1: problem now exactly. There'll be an app for it eventually,
28:59
Speaker 1: no doubt. So that's image projection, which I think is
29:01
Speaker 1: pretty hokey, and then like image recreation or adaptive camouflage,
29:05
Speaker 1: which I think has some promise, but also there's definitely
29:08
Speaker 1: some issues. They're like the one that you identified, all
29:10
Speaker 1: this computation that's happening inside the cloak that would get
29:13
Speaker 1: pretty warm. I'm joking around, but that's not a small
29:16
Speaker 1: tech problem to solve. This seems like a good place
29:19
Speaker 1: to stop, So let's take a quick break and we're back. Okay, So, Daniel,
29:37
Speaker 1: you said that there were three different sort of types
29:39
Speaker 1: of technologies for invisibility cloaks. Let's tackle the third, all right,
29:43
Speaker 1: and this is I think the one that might actually
29:45
Speaker 1: one day achieve like actual invisibility and real cloaking, so
29:49
Speaker 1: I'm pretty excited about it more. The idea here is
29:54
Speaker 1: basically image bending. Instead of projecting the image onto you
29:58
Speaker 1: or recreating the image, interrupting it, digesting and computing and
30:02
Speaker 1: recreating it, it's like, just take the light that was
30:04
Speaker 1: gonna hit you and instead of having it hit you,
30:07
Speaker 1: have it flow around you instead. So the common analogy
30:10
Speaker 1: that's used is think about a rock that's in a river.
30:13
Speaker 1: The water is flowing, it flows around the rock, and downstream,
30:17
Speaker 1: it's not easy to tell that the rock was there
30:19
Speaker 1: all the water is flowing basically in the same direction
30:21
Speaker 1: as it was before. So if you could somehow get
30:24
Speaker 1: light to bend around you and then reform the original
30:28
Speaker 1: image that was behind you, you could effectively be invisible.
30:32
Speaker 1: Out of all the technologies you've talked about so far,
30:34
Speaker 1: this one seems the most sci fi to me. Really
30:37
Speaker 1: hard for me to wrap my brain around this being
30:39
Speaker 1: a thing that we could actually do in a lab. Well,
30:43
Speaker 1: it's really cool and there's a lot of people working
30:45
Speaker 1: on this kind of stuff, and there's a few different
30:47
Speaker 1: technological approaches that people are taking, but it's the one
30:50
Speaker 1: that while most science fiction e actually I think is
30:53
Speaker 1: most realistic. So while I'm a physicist, I'm not an
30:56
Speaker 1: expert in optics. So I reached out to an expert,
30:59
Speaker 1: Greg word, and asked him to talk to us about
31:02
Speaker 1: this new promising technology. My name is Greg Gaboram, a
31:06
Speaker 1: professor of optical science and engineering at the University of
31:10
Speaker 1: North Carolina and Charlotte, and my specialty is theoretical classical optics. Basically,
31:18
Speaker 1: light is a wave. So I was really grateful to
31:21
Speaker 1: Greg for giving us some time and talking about the
31:23
Speaker 1: prospects of invisibility. So I asked him what he thought
31:26
Speaker 1: was the most promising technology. The approach that really gained
31:30
Speaker 1: prominence starting with some papers in two thousand six is
31:34
Speaker 1: the idea of of invisibility cloak. That it's not like
31:37
Speaker 1: a Harry Potter cloak, where it's a flexible material that
31:40
Speaker 1: you can strape over yourself. It's a structure, probably a
31:44
Speaker 1: rigid structure made of some very specialized material that we
31:48
Speaker 1: don't completely know how to make yet, that would guide
31:51
Speaker 1: light around some hidden interior region and send it along
31:55
Speaker 1: its way as if it had encountered nothing at all.
31:58
Speaker 1: One analogy that was used by those original authors in
32:02
Speaker 1: two thousand six was like water going around a rock
32:05
Speaker 1: and a stream, which, amusingly is also a description that
32:08
Speaker 1: a science fiction author used in the nineteen thirties used
32:11
Speaker 1: exactly the same analogy. I think the best way to
32:14
Speaker 1: understand this is to think about the way you might
32:17
Speaker 1: see this otherwise in your life, Like if you're on
32:20
Speaker 1: a road on a hot day, you can see this
32:23
Speaker 1: reflection on the horizon. It's sort of like the desert
32:26
Speaker 1: mirage effect, where it looks like there's a puddle of
32:29
Speaker 1: water in the desert, and what's happening there is just
32:31
Speaker 1: that light is bending, Like you're not actually seeing water
32:34
Speaker 1: on the highway or water in the desert. Where you're
32:37
Speaker 1: seeing is a reflection of the sky because the air
32:40
Speaker 1: that's just above the hot sand creates this effect where
32:43
Speaker 1: light from the sky gets bent towards your eye. What
32:46
Speaker 1: you're seeing is an image. You're not actually seeing the reality,
32:48
Speaker 1: so it fools your eye into thinking there's a puddle
32:51
Speaker 1: of water on the ground. So the same basic idea
32:54
Speaker 1: of finding a way of bending the light around something.
32:57
Speaker 1: Is the physics behind this approach, and so why and
33:00
Speaker 1: we do this in a lab, it won't have the
33:02
Speaker 1: like wibbly look that you get over, you know, a
33:04
Speaker 1: highway on a hot day. It'll it'll be a lot
33:07
Speaker 1: more controlled than crisp. Is that the idea, that's the goal.
33:10
Speaker 1: And people are doing this in several different ways, which
33:13
Speaker 1: I think is pretty cool. There's like really three or
33:15
Speaker 1: four totally different approaches to bending the light around you.
33:19
Speaker 1: Number one, which is sort of science fictionally cool but
33:22
Speaker 1: probably not very practical, is using nanotubes. Nanotubes are these
33:27
Speaker 1: really weird constructions of carbon that were invented a couple
33:30
Speaker 1: of decades ago. These carbon nanotubes have lots of really
33:33
Speaker 1: interesting electrical and other kinds of effects, and they're very
33:36
Speaker 1: very thin, and they're very very strong. Actually, they're like
33:39
Speaker 1: one candidate for how you could build a space elevator. Right.
33:42
Speaker 1: They're super strong and thin and they can hold a
33:44
Speaker 1: lot of weight. But also they have weird optical properties
33:48
Speaker 1: and when you heat them just right, light bends around them.
33:51
Speaker 1: And just this way that we're talking about that blows
33:54
Speaker 1: my mind. Because they're just carbon, it seems like such
33:55
Speaker 1: a simple molecule, but yeah, it would be very cool
33:58
Speaker 1: if it could do this. Yeah, and that's the base principle.
34:00
Speaker 1: It's a simple molecule, but complex arrangements of simple molecules
34:04
Speaker 1: can have really interesting optical effects. I think the best
34:08
Speaker 1: example is like silver. Take a piece of silver and
34:11
Speaker 1: you polish it. What do you get? You get a mirror, right,
34:13
Speaker 1: silver makes like some of the best mirrors out there.
34:16
Speaker 1: But take that same silver, chop it up into nanoparticles
34:20
Speaker 1: and suspended in water. What does it look like? It's
34:23
Speaker 1: jet black. In fact, a lot of the negatives that
34:25
Speaker 1: you see the black in that comes basically from suspended
34:28
Speaker 1: silver nanoparticles and so like the same materials, just the
34:32
Speaker 1: same silver can have very different optical properties based on
34:35
Speaker 1: how you build it because the optical effects depend on
34:38
Speaker 1: how light interacts with it and the surfaces inside and
34:41
Speaker 1: exact arrangement of electromagnetic fields can really change how that happens.
34:45
Speaker 1: So that's the key idea. Yeah, but nanotubes aren't really
34:48
Speaker 1: very practical. They did a little demonstration where they have
34:50
Speaker 1: a really small bit of it and it kind of works,
34:53
Speaker 1: which is cool sort of in principle, but you've got
34:55
Speaker 1: to heat this thing up and only really works for
34:57
Speaker 1: like a very very thin sheet. So if you want
35:00
Speaker 1: to wear a very hot, thin sheet of nanotubes, then
35:04
Speaker 1: you know, maybe you could look a little invisible, but
35:07
Speaker 1: it's not something that can easily be scaled up about
35:09
Speaker 1: how hot are we talking. We're talking like a hundred
35:11
Speaker 1: degrees celsius. Yeah, that's probably know, that's not gonna work out.
35:15
Speaker 1: It reminds me of that Nathan for You episode where
35:18
Speaker 1: he puts on the chili suit and then he realizes
35:20
Speaker 1: he doesn't want to walk around in a suit of
35:22
Speaker 1: hot chili. And now there's another approach which has gained
35:27
Speaker 1: a lot of attention on the internet, probably because they
35:30
Speaker 1: put the name quantum in it for no good reason.
35:33
Speaker 1: And that's this thing called the Quantum stealth invisibility cloak.
35:37
Speaker 1: And if you just google invisibility technology, probably the top
35:40
Speaker 1: ten videos you'll see are people demonstrating this stuff. And
35:44
Speaker 1: at first glance, it looks pretty cool. It's like a
35:47
Speaker 1: sheet of stuff and if you stand behind it, people
35:49
Speaker 1: can't see you. And he's like a guy and he's
35:51
Speaker 1: holding a sheet of the stuff. It's like a real
35:53
Speaker 1: size sheet of it. And when you look at the sheet.
35:55
Speaker 1: You only see the thing behind him, the wall behind him.
35:57
Speaker 1: You don't see his body, so it's like you see
35:59
Speaker 1: the top of his body and then the middle of
36:01
Speaker 1: its invisible, and then you see his legs. So it
36:03
Speaker 1: appears pretty impressive at the beginning, So it's not actually
36:08
Speaker 1: really invisibility in my mind, because the way it works
36:11
Speaker 1: is that actually has like a grooved surface. It's sort
36:14
Speaker 1: of like you know holograms that have these grooves on
36:17
Speaker 1: them and they give you like a weird image as
36:19
Speaker 1: you look at them, or you know, like a wall
36:21
Speaker 1: of glass that has like a rough edge to it,
36:23
Speaker 1: so it doesn't project the image behind it very clearly.
36:26
Speaker 1: These have these lenticular lenses. He's like very narrow grooves.
36:30
Speaker 1: So it happens is that when the light passes through it,
36:32
Speaker 1: it gets spread out, but only in one direction. So,
36:35
Speaker 1: for example, the light that from his body he's standing
36:38
Speaker 1: behind this invisibility shield, the light from his body gets
36:41
Speaker 1: smeared out in one direction, and so you actually still
36:44
Speaker 1: can see him through the invisibility shield. It's just that
36:47
Speaker 1: his body has been smeared out, so you don't really
36:49
Speaker 1: notice him anymore. It's like diluted his effect by smearing
36:53
Speaker 1: it in one direction. So it sounds like for some
36:55
Speaker 1: of these ideas, it really sounds like if they're used
36:57
Speaker 1: very rarely, you might be able to get away with
36:59
Speaker 1: it people aren't expecting it. But if it becomes a
37:02
Speaker 1: popular tech, it's just not going to work because you've
37:04
Speaker 1: noticed the smeared guy. If you need to look out
37:05
Speaker 1: for him, that's right. And then once people know that
37:08
Speaker 1: it's out there, they'll be on the lookout for it,
37:09
Speaker 1: and it wouldn't work very well anymore. And this, for example,
37:12
Speaker 1: it's pretty easy to fail. It works at some levels,
37:15
Speaker 1: but if you're looking at it from the right angle
37:17
Speaker 1: or actually from the wrong angle, then it actually makes
37:19
Speaker 1: what's behind the cloak look bigger and larger. It amplifies it. Awkward, Yeah,
37:25
Speaker 1: awkward if you're like sneaking up on your enemy, you know,
37:28
Speaker 1: for military applications, and all of a sudden like boom,
37:31
Speaker 1: you know, they can see you. That could be embarrassing.
37:34
Speaker 1: But maybe this could work in like the animal Kingdom,
37:36
Speaker 1: you know, where you like try to look bigger than
37:38
Speaker 1: your enemies. Maybe you could give like small chickens this, uh,
37:42
Speaker 1: this device, and then they could be you know, top
37:44
Speaker 1: of the pecking order. Yeah, exactly. So in my mind,
37:47
Speaker 1: this is basically just the same thing that like a
37:49
Speaker 1: fuzzy shower door does. You know, like somebody's taking a
37:52
Speaker 1: shower and the door is fuzzy, you can't really see them, right,
37:55
Speaker 1: It basically blurs them out. This is that, but it
37:57
Speaker 1: just sort of like maximized like maximum blurs. You don't
38:00
Speaker 1: really noticed that they're there. But again, anybody who's really
38:03
Speaker 1: on the lookout is going to tell. So this guy
38:05
Speaker 1: has been trying to sell his quantum stealth technology to
38:08
Speaker 1: the military for like a decade, and they have been
38:11
Speaker 1: buying it, I guess for a reason. Yeah, yeah, and
38:14
Speaker 1: so now he's offering it to the general public. So anyway,
38:18
Speaker 1: it's cool. It's definitely not something I could have invented.
38:20
Speaker 1: It's pretty simple stuff, you know, achieves something of what
38:23
Speaker 1: you want to do. But again, it's not real invisibility.
38:26
Speaker 1: It's not really bending the image around the person. Yeah,
38:30
Speaker 1: I certainly wouldn't want to go to war with a
38:32
Speaker 1: sort of smudgy mirror in front of me, smugy piece
38:36
Speaker 1: of glass. So the most promising approach came after a
38:40
Speaker 1: breakthrough in two thousand and six when people realize that
38:44
Speaker 1: if you made a really weird new kind of material,
38:48
Speaker 1: a substance called a meta material, then you could use
38:51
Speaker 1: that to bend the light around an object because had
38:54
Speaker 1: a really strange optical property of having a negative index
38:59
Speaker 1: of ref action. What does that mean? So index with
39:02
Speaker 1: refraction tells you how a material bends light. So, for example,
39:05
Speaker 1: you know that when light hits glass, it passes through,
39:08
Speaker 1: but it also gets bent. Right, that's how prisms work.
39:11
Speaker 1: Or if you look at somebody who's half in the
39:13
Speaker 1: pool and half out of the pool, the bottom half
39:15
Speaker 1: looks like shifted in one direction. That's because the light
39:18
Speaker 1: bends a little bit as it passes through the material. Well,
39:21
Speaker 1: that's an index of refraction. It's usually measures like one
39:25
Speaker 1: or above. But if you had a negative index of refraction,
39:28
Speaker 1: the light would do something really weird. Instead of entering
39:31
Speaker 1: at an angle and just changing its angle a little bit,
39:34
Speaker 1: it would enter and then go the other direction, so
39:36
Speaker 1: it would make like more than a ninety degree turn
39:38
Speaker 1: and bend really weirdly inside the material. Well this is
39:42
Speaker 1: cool because if you wrap an object in this negative
39:46
Speaker 1: index of refraction material, then it basically bends the light
39:49
Speaker 1: in such a way that it passes around the object,
39:52
Speaker 1: and then when it comes back out, it's going in
39:54
Speaker 1: exactly the direction was originally. So the idea was, oh,
39:58
Speaker 1: maybe if you had this negative index of refraction material,
40:01
Speaker 1: it could actually achieve this invisibility. Yeah. Well, the coolest
40:06
Speaker 1: part of the story is that the idea comes from
40:08
Speaker 1: like the sixties. Somebody wrote a paper in the sixties
40:11
Speaker 1: being like, hmm, this seems impossible, but if you could
40:14
Speaker 1: make a material that had this weird property nobody's ever
40:16
Speaker 1: seen before, then you could achieve invisibility. Ignored for four
40:20
Speaker 1: decades until in two thousand and six, people realized if
40:23
Speaker 1: you could create this meta material, and a meta material
40:26
Speaker 1: is a material that has a property that you don't
40:29
Speaker 1: usually find in nature, like negative index of refraction. They
40:32
Speaker 1: realized there might be a way to do it by
40:34
Speaker 1: constructing a really strange material. And so, for example, to
40:37
Speaker 1: have this material with really thin layers of silver and
40:40
Speaker 1: then really thin layers of magnesium fluoride. And there's another
40:44
Speaker 1: way to do it, making these like silver nano wires.
40:47
Speaker 1: And the way to understand it and to think about
40:48
Speaker 1: it is to remember that light is just an electromagnetic wave.
40:52
Speaker 1: So what we're talking about is bending light. We're talking
40:55
Speaker 1: about electromagnetic interactions. So you just create these atoms in
40:58
Speaker 1: a special arrange mints, so they have these weird electromagnetic
41:02
Speaker 1: properties that bend light in whatever way you want. And
41:05
Speaker 1: this is possible now and it wasn't fifty years ago,
41:08
Speaker 1: because now we're much better like building these nano materials,
41:11
Speaker 1: like engineering super duper small structures and then making a
41:14
Speaker 1: large sample of them. So has anyone tried making a
41:17
Speaker 1: cloak out of this or is this still pretty preliminary?
41:20
Speaker 1: It's still pretty preliminary. Like they got it to work,
41:22
Speaker 1: and where they built basically was like a cylinder of
41:25
Speaker 1: this stuff, and you can't see the cylinder, Like you
41:28
Speaker 1: shine a bunch of light at it, and the light
41:29
Speaker 1: comes out the other side going exactly the same direction
41:33
Speaker 1: that it entered. Yeah, it's like basically invisible, but it
41:37
Speaker 1: only works in certain wavelengths. So far it works in microwaves,
41:42
Speaker 1: or maybe it works in radio waves. It doesn't work
41:44
Speaker 1: in visible light. You can still see this thing in
41:46
Speaker 1: the visible light, but you know, if somebody shines a
41:48
Speaker 1: microwave laser at it or shoots radio waves at it,
41:51
Speaker 1: then it's invisible to that kind of radiation. So this
41:55
Speaker 1: would not require the like giant batteries and computers that
41:58
Speaker 1: we were talking about for the other one. But would
42:00
Speaker 1: it cover your own heat or is that another problem? Yeah?
42:03
Speaker 1: That is another problem. But you're right, this thing is
42:06
Speaker 1: like static. It doesn't need to be powered. It's just
42:08
Speaker 1: like a structure of material that bends light in a
42:10
Speaker 1: certain way. And if you're inside of it, you're like
42:13
Speaker 1: walking around with this cylinder of meta material. Then imprinciple,
42:16
Speaker 1: people can't see you in the microwave or the radio wave.
42:19
Speaker 1: But you're right, it doesn't mask your heat, right, doesn't
42:22
Speaker 1: like absorb all of your heat. I don't know how
42:24
Speaker 1: you could do that, right, because you're putting out a
42:26
Speaker 1: lot of heat and if there's no way to vent it,
42:28
Speaker 1: you're just going to basically roast inside this thing. Yeah,
42:31
Speaker 1: and is that the state of the art right now?
42:33
Speaker 1: Is that the fanciest solution we have? And that is
42:36
Speaker 1: basically what we've achieved. And by we, I mean you know,
42:38
Speaker 1: the whole physics community actually working hard on it, and
42:41
Speaker 1: me just sort of like reading articles about it. But hey,
42:43
Speaker 1: that's a contribution. And people are trying to think about
42:46
Speaker 1: how to make it work for visible light. Also, like,
42:49
Speaker 1: is it possible to build a material which could do
42:52
Speaker 1: this for all kinds of frequencies? And that's sort of
42:55
Speaker 1: the next generation. That's what people are working on now.
42:58
Speaker 1: And I read a paper from lad Ear that has
43:01
Speaker 1: a really cool title on it. It talks about developing
43:04
Speaker 1: a tachyonic invisibility cloak. What the heck is that? Yeah,
43:08
Speaker 1: attack eon is something that travels faster than the speed
43:13
Speaker 1: of light. So we talked in the podcast once about
43:15
Speaker 1: like what is a tacky on It's a hypothetical particle
43:17
Speaker 1: that might travel fast than the speed of light. We
43:19
Speaker 1: don't think it exists. It violates special relativity. But the
43:22
Speaker 1: phrase tachi on it, it doesn't just exist in star
43:25
Speaker 1: trek is referred to anytime something moves faster than the
43:28
Speaker 1: speed of light. And so that's pretty cool. And the
43:30
Speaker 1: idea behind this was they did a bunch of theoretical
43:33
Speaker 1: calculations to figure out could you make a material which
43:37
Speaker 1: number one passes all frequencies of light through it in
43:41
Speaker 1: the same way that the meta material does, right, having
43:43
Speaker 1: a negative index of refraction, but works for all kinds
43:46
Speaker 1: of frequencies, not just microwave or radio wave. And number two,
43:50
Speaker 1: and this is an important and tricky bit that also
43:53
Speaker 1: didn't have a time delay. One problem with bending the
43:57
Speaker 1: image around you is that then the path length of
43:59
Speaker 1: the image is longer. It takes more time for the
44:02
Speaker 1: light to travel around you than if it had flowed
44:05
Speaker 1: through you. Somebody with like really sensitive devices might be
44:08
Speaker 1: able to measure that time difference and deduce that you're there.
44:11
Speaker 1: So they wanted to develop a cloak that was take
44:14
Speaker 1: ionic so that the light traveled on that longer path
44:18
Speaker 1: was going faster effectively than the speed of light, in
44:21
Speaker 1: such a way that it emerged on the other side
44:23
Speaker 1: of the material exactly the same time it otherwise would
44:26
Speaker 1: have if you weren't there. And is that possible? Well,
44:29
Speaker 1: they claim that it is, and they do all these calculations,
44:31
Speaker 1: and your first thought must be like, hold on a second,
44:33
Speaker 1: what about special relativity? Right? Doesn't that violate causality? How
44:38
Speaker 1: could you possibly get from one side of material to
44:40
Speaker 1: the other and do it faster than the speed of light. Well,
44:42
Speaker 1: as usual in physics, there are loopholes, and if you
44:46
Speaker 1: read the rules really really carefully, you can discover that
44:49
Speaker 1: there might be ways around them. For example, what actually
44:52
Speaker 1: is the rule about traveling faster than the speed of light,
44:56
Speaker 1: it's that no piece of information can go through space
45:00
Speaker 1: faster than light travels through space. So, for example, we've
45:03
Speaker 1: talked in the podcast before about how that doesn't mean
45:05
Speaker 1: that you can't get from one place to another faster
45:08
Speaker 1: than light could if you could like bend space itself. Right,
45:12
Speaker 1: That's like how warp drives and wormholes work. So the
45:14
Speaker 1: spirit there is to look for loopholes, and the loophole
45:17
Speaker 1: here is to think about how the wave propagates through
45:20
Speaker 1: this stuff. And there's two actually different velocities to think
45:23
Speaker 1: about when you think about the wave. There's the phase velocity.
45:27
Speaker 1: That's like how an individual piece of the stuff is moving,
45:30
Speaker 1: like the thing that's doing the waving. How fast is
45:33
Speaker 1: that being actually moving? And that can't move fast in
45:36
Speaker 1: the speed of light because it's the thing and moves
45:37
Speaker 1: through space. But then there's the group velocity. The group
45:40
Speaker 1: velocity tells us about like how the speed of the
45:43
Speaker 1: whole wavefront is moving. Is not actually a requirement for
45:47
Speaker 1: the group velocity to move slower than the speed of light.
45:50
Speaker 1: So this is pretty tricky. So I asked our friend
45:53
Speaker 1: Greg Gaber to see if he could explain it to us.
45:56
Speaker 1: If you have a material that has optical gain that
45:59
Speaker 1: you can pump so has energy built into it, you
46:02
Speaker 1: can basically have a wave that effectively moves faster than
46:05
Speaker 1: the vacuum speed of light, kind of like an avalanche.
46:08
Speaker 1: That the center of gravity of an avalanche can move
46:10
Speaker 1: faster than the front of the avalanche because it's picking
46:13
Speaker 1: up extra rocks as it goes and leaving some behind.
46:18
Speaker 1: So the shape of the wave itself is moving, so
46:20
Speaker 1: you're sort of like losing the back edge of the
46:22
Speaker 1: wave and adding new stuff to the front edge of
46:25
Speaker 1: the wave, which effectively makes the wave move faster. So
46:28
Speaker 1: there's a lot of technical stuff in this paper. If
46:30
Speaker 1: you're really interested, I suggest you look it up. But
46:32
Speaker 1: the basic idea is that you use some loopholes and
46:35
Speaker 1: trickery to try to get that light to pass through
46:38
Speaker 1: the material in such a way that it appears with
46:40
Speaker 1: no time delay on the other side. So is this
46:43
Speaker 1: something that is working on a computer but not working
46:47
Speaker 1: in real life yet. Yeah, this is just a calculation
46:51
Speaker 1: and they've done in simulation, and they say, if you
46:53
Speaker 1: could build this thing and it has these properties, then
46:55
Speaker 1: you could actually achieve that that's exciting, and the people
46:58
Speaker 1: I've talked to you said, wow, this is a cool idea.
47:01
Speaker 1: And in the paper they don't actually build it, right,
47:03
Speaker 1: they just talk about how you might be able to
47:05
Speaker 1: and to do that you need this thing called a
47:07
Speaker 1: semiconductor optical amplifier, and that's what Bird was talking about.
47:11
Speaker 1: It needs some energy, like requires a little bit of
47:14
Speaker 1: optical pumping. So this is a technology that people are
47:16
Speaker 1: working on, have developed. They haven't quite made it do
47:19
Speaker 1: this thing yet, but it's sort of like, you know,
47:21
Speaker 1: at the theoretical stage, like, hey, this idea might be possible.
47:24
Speaker 1: Let's get some folks in the lab and try to
47:26
Speaker 1: actually build this thing. Awesome. I hope it gets funded.
47:30
Speaker 1: Probably dark, but would be all about it. So I
47:34
Speaker 1: think that covers most of the topics of like how
47:36
Speaker 1: you could do invisibility and what people are doing and
47:38
Speaker 1: the progress that's been made. And I'm pretty excited that
47:42
Speaker 1: people are making progress. Like we've gone from this is
47:44
Speaker 1: a ridiculous thing in science fiction to hey, here's how
47:47
Speaker 1: you might actually be able to do it, to like, look,
47:50
Speaker 1: we have some basic working prototypes that you know, don't
47:53
Speaker 1: satisfy all the requirements, but satisfy some of them. I'm
47:56
Speaker 1: torn between thinking it's totally awesome that we're making progress
47:59
Speaker 1: on this, being excited about seeing the world of sci
48:01
Speaker 1: fi come to real life, and also being a little
48:04
Speaker 1: bit uncomfortable about a world where this technology exists and
48:07
Speaker 1: people can go sneaking around. So I guess, I guess
48:09
Speaker 1: I can see the good and bed of this well.
48:12
Speaker 1: As Professor Gooberg what he thought the prospects were for
48:15
Speaker 1: invisibility in the future, if you want to make a
48:17
Speaker 1: device that would work very well to hide things from
48:21
Speaker 1: visible light, you would need to design something that has
48:25
Speaker 1: a controllable structure on the order of the wavelength of light,
48:29
Speaker 1: which means very very small sizes, and we don't quite
48:33
Speaker 1: know how to do that yet. So we might start
48:35
Speaker 1: seeing interesting applications not in visible light. But something that
48:41
Speaker 1: I've noticed is there's a trend of looking at how
48:44
Speaker 1: can we use this same cloaking technology for other types
48:47
Speaker 1: of waves. People have talked about making earthquake cloaks or
48:51
Speaker 1: cloaks that guide water waves around structures, And I love
48:56
Speaker 1: his idea there that we could use invisibility for more
48:59
Speaker 1: than just like sneaking around and snooping on people, but
49:02
Speaker 1: for like making objects invisibles to other kinds of waves,
49:05
Speaker 1: like earthquakes or water waves or sound waves. That's a
49:08
Speaker 1: really cool idea. So maybe one day the whole Bay
49:12
Speaker 1: Area will be cloaked in some sort of earthquake invisibility device. Alright,
49:18
Speaker 1: So that's the science of invisibility. Thanks for taking this
49:22
Speaker 1: trip with us to understand how people are pushing the
49:24
Speaker 1: forefront of physics to make science fiction real. Thanks tune
49:28
Speaker 1: in next time and don't forget. If you have something
49:31
Speaker 1: you'd like us to break down, send it to us
49:33
Speaker 1: to questions at Daniel and Jorge dot com. Thanks for listening,
49:44
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explained.
49:47
Speaker 1: The Universe is a production of I Heart Radio or
49:50
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