WEBVTT 1 00:00:03.399 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.960 --> 00:00:31.199 Imagine uh, stepping outside tonight, I assumeing it's a clear 8 00:00:31.280 --> 00:00:32.439 night wherever you happen. 9 00:00:32.240 --> 00:00:35.320 To be listening to this right, hopefully no clouds. 10 00:00:35.119 --> 00:00:37.679 Yeah, exactly, and you look up at the sky, you 11 00:00:37.719 --> 00:00:40.600 look past the street lights, past the airplanes, and you 12 00:00:40.640 --> 00:00:42.679 try to spot Elpha Centauri. 13 00:00:42.520 --> 00:00:45.000 Which is our nearest stellar neighbor. 14 00:00:44.920 --> 00:00:47.719 Right the closest star system to our own solar system. 15 00:00:48.039 --> 00:00:51.439 It just sits there in the darkness, glowing faintly. And 16 00:00:51.600 --> 00:00:54.200 because we call it the closest, it feels like it 17 00:00:54.280 --> 00:00:56.520 is just, you know, right next door in the grand 18 00:00:56.600 --> 00:00:57.759 cosmic scheme of things. 19 00:00:57.840 --> 00:00:58.640 It does feel that way. 20 00:00:58.719 --> 00:01:01.600 Yeah, But distance in space is just it's a really 21 00:01:02.200 --> 00:01:04.920 tricky concept to wrap your mind around because if you 22 00:01:04.959 --> 00:01:08.319 were to actually try to travel there right now, using 23 00:01:08.359 --> 00:01:12.439 the absolute pinnacle of our current rocket propulsion technology, the. 24 00:01:12.480 --> 00:01:14.040 Very best engines we've ever built. 25 00:01:14.040 --> 00:01:17.560 Exactly, you would be embarking on a journey that would 26 00:01:17.640 --> 00:01:20.400 take tens, if not hundreds of thousands of years. 27 00:01:20.719 --> 00:01:22.920 Hundreds of thousands, I mean, it is a timeline that 28 00:01:23.000 --> 00:01:26.879 completely defies human comprehension. Just to put that into perspective, 29 00:01:27.480 --> 00:01:32.959 human civilization as we know it, like recorded history, agriculture, cities, 30 00:01:33.159 --> 00:01:34.840 that's only about ten thousand years old. 31 00:01:34.959 --> 00:01:36.799 Yeah, yeah, so one hundred thousand years is. 32 00:01:37.079 --> 00:01:40.599 It's essentially forever. So a journey of one hundred thousand 33 00:01:40.640 --> 00:01:43.519 years means you aren't just sending a crew of astronauts, 34 00:01:43.519 --> 00:01:46.200 you are sending an entire civilization. 35 00:01:45.840 --> 00:01:47.040 A whole society in a can. 36 00:01:47.319 --> 00:01:50.079 Exactly, you would be launching a generationship where the people 37 00:01:50.079 --> 00:01:53.599 who actually arrive at Alpha centaury wouldn't even remember Earth. 38 00:01:53.920 --> 00:01:57.760 They would have to survive, evolve, and basically sustain themselves 39 00:01:58.000 --> 00:02:01.959 for countless generations in the void just to reach the closest. 40 00:02:01.439 --> 00:02:06.560 Star, which frankly makes interstellar travels seem practically impossible. 41 00:02:06.680 --> 00:02:07.480 It really does. 42 00:02:07.719 --> 00:02:10.080 It feels like this hard boundary drawn by the laws 43 00:02:10.120 --> 00:02:13.719 of physics. But today we're going to explore how that 44 00:02:13.879 --> 00:02:17.039 timeline is currently being challenged in a way that honestly 45 00:02:17.080 --> 00:02:18.400 sounds like pure science fiction. 46 00:02:18.680 --> 00:02:20.639 It really does sound like sci fi, but it's happening 47 00:02:20.680 --> 00:02:21.360 right now. 48 00:02:21.240 --> 00:02:25.479 Right because what if that mind boggling multimillennial journey could 49 00:02:25.479 --> 00:02:27.919 be compressed down to roughly twenty years. 50 00:02:28.120 --> 00:02:31.400 Twenty years a single human generation. 51 00:02:31.479 --> 00:02:35.840 Right, a single generation. A spacecraft launch today could actually 52 00:02:35.879 --> 00:02:39.360 be intercepted by the people who built it. We are 53 00:02:39.400 --> 00:02:43.879 talking about fundamentally escaping the limitations of traditional fuel heavy 54 00:02:44.000 --> 00:02:48.360 rocketry and entering an era where we propel objects through 55 00:02:48.360 --> 00:02:51.560 the vacuum of space using literally nothing but light. 56 00:02:51.800 --> 00:02:54.360 And that is the paradigm shift we are witnessing right now. 57 00:02:54.360 --> 00:02:56.960 We are basically moving away from the brute force of 58 00:02:57.120 --> 00:02:58.759 chemical explosions. 59 00:02:58.240 --> 00:02:59.800 Which is really all the traditional rocket is. 60 00:03:00.000 --> 00:03:02.919 Oh yeah, exactly, a highly controlled explosion, and we're stepping 61 00:03:02.960 --> 00:03:08.039 into this entirely new realm of optical propulsion and microscopic levitation. 62 00:03:08.439 --> 00:03:11.400 It's a shift from fire to photons. 63 00:03:11.719 --> 00:03:14.080 I want to frame this properly because the timing of 64 00:03:14.120 --> 00:03:16.599 this shift is just incredible to watch unfold. I mean, 65 00:03:16.680 --> 00:03:20.319 just recently, the world has been celebrating some absolutely massive 66 00:03:20.360 --> 00:03:22.520 milestones in the traditional space flat arena. 67 00:03:22.639 --> 00:03:24.400 Oh, absolutely huge achievements. 68 00:03:24.520 --> 00:03:27.280 Right, Like, we watched the Artemis the Second Mission preparations 69 00:03:27.400 --> 00:03:29.680 getting ready to send humans back around the Moon, and 70 00:03:29.759 --> 00:03:32.800 we saw Blue Origin making headlines by reusing the new 71 00:03:32.840 --> 00:03:37.280 Glenn booster. Down Florida. We are watching these colossal, towering 72 00:03:37.360 --> 00:03:42.879 metal skyscapers filled to the brim with volatile, highly explosive chemicals, 73 00:03:43.199 --> 00:03:45.919 roaring into the sky on pillars of fire. It is 74 00:03:46.080 --> 00:03:49.080 on spiring, it shakes the ground. It's an event. But 75 00:03:49.159 --> 00:03:53.039 at the exact same time, a quiet, almost totally invisible 76 00:03:53.159 --> 00:03:56.120 revolution is happening in a laboratory at Texas A and 77 00:03:56.240 --> 00:03:59.120 M University Texas A and M. Right scientists, there are 78 00:03:59.240 --> 00:04:04.039 literally level vitating and steering microscopic devices using lasers, using 79 00:04:04.080 --> 00:04:07.280 just light right, they call the metajets, and the underlying 80 00:04:07.280 --> 00:04:10.280 physics of these tiny metajets could ultimately render those massive 81 00:04:10.319 --> 00:04:14.400 chemical rockets completely obsolete for deep space exploration. 82 00:04:14.680 --> 00:04:17.360 The contrast there is just brilliant. I mean, you have 83 00:04:17.399 --> 00:04:20.439 the deafening roar and the massive thermal exhaust of the 84 00:04:20.480 --> 00:04:22.839 new Glenn booster on one side, yeah, pure power, and 85 00:04:22.879 --> 00:04:25.560 on the other you have complete silence and the invisible 86 00:04:25.560 --> 00:04:28.959 push of a laser beam in a pristine clean room. 87 00:04:29.360 --> 00:04:30.120 It's wild. 88 00:04:30.360 --> 00:04:32.920 The work coming out of the J. Mike Walker sixty six, 89 00:04:32.959 --> 00:04:36.040 Department of Mechanical Engineering at Texas A and M is 90 00:04:36.079 --> 00:04:40.360 fundamentally redefining how we even think about motion, momentum, and 91 00:04:40.399 --> 00:04:41.279 travel in space. 92 00:04:41.800 --> 00:04:42.800 So who is leading this? 93 00:04:43.600 --> 00:04:46.319 So there's doctor Schuffing Lawn. He's an assistant professor there 94 00:04:46.360 --> 00:04:49.160 and the director of the Lab for Advanced Nanophotonics. He 95 00:04:49.199 --> 00:04:52.079 recently published a groundbreaking study with his team in the 96 00:04:52.160 --> 00:04:52.920 journal Newton. 97 00:04:53.120 --> 00:04:53.839 The Journal Newton. 98 00:04:53.879 --> 00:04:57.399 Oukay right, And the paper is titled Optical Propulsion and 99 00:04:57.480 --> 00:05:01.120 Levitation of metajets, and it out lines exactly how they're 100 00:05:01.160 --> 00:05:05.079 achieving this controlled three dimensional motion using only laser light. 101 00:05:05.439 --> 00:05:08.000 Okay, before we get into the microscopic engineering of an 102 00:05:08.040 --> 00:05:11.279 actual metajet, I think we really need to establish why 103 00:05:11.319 --> 00:05:12.360 this research is so. 104 00:05:12.480 --> 00:05:15.040 Absolutely necessary, why we need it at all? 105 00:05:15.240 --> 00:05:18.319 Right, Like, why are we looking to completely abandon the 106 00:05:18.399 --> 00:05:21.879 chemical rocket technology that took us to the moon and 107 00:05:21.879 --> 00:05:22.839 it is taking this to Mars. 108 00:05:23.160 --> 00:05:24.079 It's a fair question. 109 00:05:24.399 --> 00:05:26.560 If you're listening to this on your commute right now, 110 00:05:27.040 --> 00:05:30.120 think about the engine in your car. It runs because 111 00:05:30.160 --> 00:05:33.000 you carry a heavy tank of gas with you. As 112 00:05:33.040 --> 00:05:35.680 you drive, you burn the gas and your car gets 113 00:05:35.680 --> 00:05:40.800 slightly lighter. But rockets take that concept to a pretty 114 00:05:40.839 --> 00:05:42.399 punishing extreme, don't they. 115 00:05:42.560 --> 00:05:45.560 They really do, and it is honestly a trap. Traditional 116 00:05:45.639 --> 00:05:49.000 rocketry is bound by this mathematical paradox known as the 117 00:05:49.079 --> 00:05:51.120 Siolkovsky rocket equation. 118 00:05:50.959 --> 00:05:52.480 The Silkowsky rocket area. 119 00:05:52.720 --> 00:05:55.800 Yes, in aerospace circles they often just refer to it 120 00:05:55.839 --> 00:05:57.800 as the tyranny of the rocket equation. 121 00:05:58.120 --> 00:06:00.800 The tyranny that sounds dramatic, well. 122 00:06:00.600 --> 00:06:03.439 It dictates a very harsh reality. It says that if 123 00:06:03.480 --> 00:06:05.959 you want to move a payload through space, you need fuel. 124 00:06:06.439 --> 00:06:09.759 But fuel has mass. It is heavy, right, So to 125 00:06:09.839 --> 00:06:12.600 push your payload and your heavy fuel, you need even 126 00:06:12.639 --> 00:06:13.240 more fuel. 127 00:06:13.439 --> 00:06:14.920 Oh, I see where this is going. 128 00:06:14.839 --> 00:06:16.879 And then you need more fuel to push that extra fuel. 129 00:06:16.959 --> 00:06:19.399 It's like, okay, it's like trying to plan a cross 130 00:06:19.439 --> 00:06:22.360 country road trip where there are absolutely no gas stations, 131 00:06:22.600 --> 00:06:23.920 so you have to bring all the gas for the 132 00:06:23.920 --> 00:06:24.920 whole trip in your trunk. 133 00:06:25.000 --> 00:06:26.319 That's a great way to think about it. 134 00:06:26.639 --> 00:06:29.480 But the weight of all that gas means your car 135 00:06:29.519 --> 00:06:32.839 gets terrible mileage, so you have to tow a trailer 136 00:06:33.000 --> 00:06:36.439 full of more gas which lowers your mileage even further. Exactly, 137 00:06:36.519 --> 00:06:39.680 you end up in this incredibly punishing cycle. You build 138 00:06:39.720 --> 00:06:42.360 a massive vehicle where ninety nine percent of the weight 139 00:06:42.439 --> 00:06:45.040 is just the explosive liquid required to get the remaining 140 00:06:45.120 --> 00:06:48.639 one percent, like the actual payload or the astronauts to 141 00:06:48.720 --> 00:06:49.519 where they need to go. 142 00:06:49.879 --> 00:06:52.759 That is a perfect way to visualize it, and that equation, 143 00:06:53.040 --> 00:06:55.560 as brutal as it is, works fine. 144 00:06:55.319 --> 00:06:57.720 For our local neighborhood, right going to the moon or whatever. 145 00:06:57.920 --> 00:06:59.680 Yeah, we can use it to get to Earth, orbit, 146 00:06:59.879 --> 00:07:01.720 can use it to get to the moon. We can 147 00:07:01.759 --> 00:07:04.360 even use it to send rovers to Mars, provided we 148 00:07:04.480 --> 00:07:06.480 are a patient and willing to wait months for them 149 00:07:06.519 --> 00:07:09.360 to arrive. Sure, but the moment you want to go 150 00:07:09.480 --> 00:07:13.120 incredibly fast, say a significant fraction of the speed of light, 151 00:07:13.120 --> 00:07:15.519 which is roughly one hundred and eighty six thousand miles 152 00:07:15.519 --> 00:07:18.319 per second, the math completely breaks. 153 00:07:18.079 --> 00:07:19.480 Down because the fuel gets too heavy. 154 00:07:19.879 --> 00:07:23.279 Exactly, to reach Alpha Centauri in twenty years, you need 155 00:07:23.319 --> 00:07:25.519 to travel at about twenty percent the speed of light. 156 00:07:26.079 --> 00:07:28.720 The amount of chemical fuel you would need to accelerate 157 00:07:28.759 --> 00:07:33.040 a traditional spacecraft to that speed is physically impossible. 158 00:07:32.639 --> 00:07:34.800 Like impossible, impossible. 159 00:07:34.279 --> 00:07:37.360 Yeah, possible, impossible. There isn't enough chemical energy in the 160 00:07:37.360 --> 00:07:40.839 known universe to make that equation balance out. The ship 161 00:07:40.879 --> 00:07:43.160 would be too massive to ever even move. 162 00:07:43.480 --> 00:07:48.360 Wow. Okay, so light powered propulsion completely sidesteps this tyranny. 163 00:07:48.480 --> 00:07:49.639 It completely ignores it. 164 00:07:49.720 --> 00:07:52.920 Yes, why doing what? Just leaving the gas station behind. 165 00:07:52.759 --> 00:07:55.959 In a manner of speaking, Yes, by leaving the power 166 00:07:56.040 --> 00:07:56.879 source behind. 167 00:07:57.160 --> 00:07:58.560 Okay, unpack that for me. 168 00:07:59.040 --> 00:08:01.920 Well, if you're an engine is a massive laser array 169 00:08:02.000 --> 00:08:04.560 sitting on Earth or maybe sitting in orbit around the Earth, 170 00:08:05.000 --> 00:08:07.319 your spacecraft doesn't have to carry a single drop of 171 00:08:07.360 --> 00:08:08.959 fuel to power its journey. 172 00:08:09.160 --> 00:08:09.680 Oh I see. 173 00:08:09.720 --> 00:08:12.319 It doesn't carry the engine, and it doesn't carry the propellant. 174 00:08:12.639 --> 00:08:15.639 It is just a payload and a sail riding the beam. 175 00:08:15.879 --> 00:08:18.480 I just love the elegance of leaving the heavy machinery 176 00:08:18.519 --> 00:08:21.439 at home. It totally solves the math problem. 177 00:08:21.480 --> 00:08:22.120 It really does. 178 00:08:22.519 --> 00:08:24.800 But I have to admit I struggle with the actual 179 00:08:24.800 --> 00:08:25.920 physical mechanics of this. 180 00:08:26.160 --> 00:08:28.600 That's fair. It's very counterintuitive. 181 00:08:28.000 --> 00:08:31.439 Because if I shine a really bright, high powered flashlight 182 00:08:31.680 --> 00:08:34.559 at a piece of paper sitting on my desk, the 183 00:08:34.600 --> 00:08:35.600 paper doesn't. 184 00:08:35.320 --> 00:08:36.720 Move, No, it doesn't. 185 00:08:36.799 --> 00:08:38.799 It might get warm if the flashlight is bright enough, 186 00:08:38.799 --> 00:08:42.360 but it doesn't like slide across the wood. How on 187 00:08:42.440 --> 00:08:45.360 Earth does light which is just photons? Right? And photons 188 00:08:45.399 --> 00:08:48.399 have zero rest mass? Correct, How does something with no 189 00:08:48.600 --> 00:08:51.840 mass actually push a physical object? 190 00:08:51.919 --> 00:08:56.120 It is highly counterintuitive because we don't experience the physical 191 00:08:56.159 --> 00:08:59.480 force of light in our daily macroscopic lives. Right, we 192 00:08:59.519 --> 00:09:02.200 don't feel We feel the heat of the sun absolutely, 193 00:09:02.360 --> 00:09:05.159 but we don't feel it pushing us down into the sidewalk. 194 00:09:05.480 --> 00:09:07.200 But to understand this, we have to look at the 195 00:09:07.240 --> 00:09:08.120 dual nature. 196 00:09:07.879 --> 00:09:09.840 Of light, a wave particle duality. 197 00:09:09.960 --> 00:09:13.159 Exactly, light is both a wave and a particle. The 198 00:09:13.440 --> 00:09:16.559 particles photons don't have mass in the traditional sense of 199 00:09:16.559 --> 00:09:18.919 a rock or a bowling ball, but according to the 200 00:09:19.000 --> 00:09:22.919 laws of quantum mechanics and relativity, they do possess momentum. 201 00:09:23.159 --> 00:09:27.759 Wait. Wait, if momentum is mass times velocity and a 202 00:09:27.799 --> 00:09:31.440 photon has zero mass, how does it have momentum? 203 00:09:31.720 --> 00:09:34.480 That is the exact question physicists wrestled with over a 204 00:09:34.519 --> 00:09:35.080 century ago. 205 00:09:35.120 --> 00:09:36.279 Okay, good, so it's not just me. 206 00:09:36.519 --> 00:09:39.120 No, not at all. The answer comes from James Clerk 207 00:09:39.159 --> 00:09:42.840 Maxwell and later Albert Einstein. While a photon has no 208 00:09:43.000 --> 00:09:47.080 rest mass, it has energy okay, and Einstein's extended equations 209 00:09:47.080 --> 00:09:50.240 show that energy and momentum are intrinsically linked. So even 210 00:09:50.279 --> 00:09:54.039 without mass, a photon carries a tiny discrete packet of momentum. 211 00:09:54.080 --> 00:09:55.240 A packet of momentum. 212 00:09:55.320 --> 00:09:59.200 Yeah, doctor Lan uses a very helpful tangible analogy in 213 00:09:59.240 --> 00:10:02.120 the research to explain and how this momentum actually transfers 214 00:10:02.159 --> 00:10:04.919 to an object. Imagine you are throwing ping pong balls 215 00:10:04.960 --> 00:10:05.559 at a surface. 216 00:10:05.639 --> 00:10:07.879 Okay, I am picturing throwing a bucket of ping pong 217 00:10:08.000 --> 00:10:11.799 balls at like a wooden board hanging from a string. 218 00:10:11.639 --> 00:10:13.720 Right exactly now, Even though a ping pong ball is 219 00:10:13.799 --> 00:10:16.440 very light, when it strikes the board and bounces off, 220 00:10:16.519 --> 00:10:19.519 it transfers a tiny bit of its forward momentum to 221 00:10:19.559 --> 00:10:22.679 the board before it redouns oh, I see, it physically 222 00:10:22.720 --> 00:10:25.759 pushes the board, making it swing slightly. Now, just scale 223 00:10:25.759 --> 00:10:29.399 that down. When a photon strikes an object and reflects 224 00:10:29.399 --> 00:10:33.039 off of it, it transfers its tiny packet of momentum 225 00:10:33.039 --> 00:10:33.840 to the object. 226 00:10:34.039 --> 00:10:36.840 So the light from a laser is essentially a continuous, 227 00:10:37.200 --> 00:10:42.159 highly focused brage of trillions upon trillions of microscopic pingkong 228 00:10:42.240 --> 00:10:44.799 balls bouncing off the surface of the spacecraft. 229 00:10:44.840 --> 00:10:48.799 That is the exact mechanism. It is an incredibly tiny 230 00:10:48.960 --> 00:10:52.200 microscopic force, which is why your flashlight doesn't move the 231 00:10:52.200 --> 00:10:53.000 paper on your. 232 00:10:52.879 --> 00:10:54.399 Desk right, because it's friction. 233 00:10:54.759 --> 00:10:58.080 Exactly. Yeah, the push of those photons from your flashlight 234 00:10:58.159 --> 00:11:00.639 is completely overwhelmed by the gravity of the Earth pulling 235 00:11:00.679 --> 00:11:02.799 the paper down, by the friction of the wood holding 236 00:11:02.840 --> 00:11:05.000 it in place, and even by the air pressure in 237 00:11:05.039 --> 00:11:07.080 the room pushing against it from all sides. 238 00:11:07.320 --> 00:11:10.279 But if you remove that friction, Yes, if you place 239 00:11:10.320 --> 00:11:12.559 an object in the vacuum of space, where there is 240 00:11:12.600 --> 00:11:16.000 absolutely no air resistance, no friction, and eventually no significant 241 00:11:16.039 --> 00:11:20.039 gravitational pull, that microscopic force becomes cumulative. 242 00:11:20.159 --> 00:11:21.679 Cumulative exactly because in. 243 00:11:21.600 --> 00:11:25.440 A vacuum, an object in motion stays in motion. So 244 00:11:25.519 --> 00:11:28.399 every single photon that bounces off at a tiny fractional 245 00:11:28.399 --> 00:11:28.759 bit of. 246 00:11:28.679 --> 00:11:30.799 Speed a tiny push. 247 00:11:30.320 --> 00:11:33.360 And because there is no drag, it never slows down. 248 00:11:33.960 --> 00:11:39.840 Over days, weeks, and years of continuous laser illumination, that continuous, 249 00:11:39.960 --> 00:11:44.320 gentle push accelerates the object to unbelievable speeds. 250 00:11:44.600 --> 00:11:49.679 Exactly, it's continuous acceleration. A chemical rocket burns all its 251 00:11:49.720 --> 00:11:52.720 fuel in a few minutes, giving the ship one massive 252 00:11:52.720 --> 00:11:55.200 shove and then it coasts for the rest of the journey. 253 00:11:55.240 --> 00:11:57.360 It's basically coasting on that one explosion. 254 00:11:57.480 --> 00:12:01.600 Right, A laser driven sail gets pushed constantly, second after second, 255 00:12:01.679 --> 00:12:02.399 year after year. 256 00:12:02.519 --> 00:12:05.480 Okay, that definitely helps clarify the physics of the push. 257 00:12:05.639 --> 00:12:09.039 The vacuum of space allows that tiny cumulative force to 258 00:12:09.120 --> 00:12:10.039 just keep building. 259 00:12:10.200 --> 00:12:11.559 Yes, it's all about the vacuum. 260 00:12:11.559 --> 00:12:14.759 But that brings up an entirely new, incredibly complex problem 261 00:12:14.799 --> 00:12:15.279 in my mind. 262 00:12:15.320 --> 00:12:16.360 Oh I bet, what's that. 263 00:12:16.559 --> 00:12:19.120 Well. Understanding that light can push an object is one thing, 264 00:12:19.519 --> 00:12:21.759 but how do you keep it from just tumbling wildly 265 00:12:21.759 --> 00:12:22.360 out of control? 266 00:12:22.480 --> 00:12:24.360 The stability issue, right, Because, to. 267 00:12:24.360 --> 00:12:27.240 Use another analogy, if I take a fire hose which 268 00:12:27.279 --> 00:12:29.879 is shooting a very powerful stream of water, and I 269 00:12:30.039 --> 00:12:32.720 blast a piece of cardboard with it, the cardboard doesn't 270 00:12:32.720 --> 00:12:34.399 fly perfectly straight away from. 271 00:12:34.240 --> 00:12:35.600 Me, No, it definitely wouldn't. 272 00:12:35.799 --> 00:12:38.200 The water hits it, the cardboard tilts slightly, the water 273 00:12:38.240 --> 00:12:41.039 catches an edge, and suddenly the cardboard is flipping and 274 00:12:41.080 --> 00:12:44.200 spinning and getting blasted off to the side, completely out 275 00:12:44.240 --> 00:12:44.759 of the stream. 276 00:12:44.919 --> 00:12:47.399 It just flies out of control exactly. 277 00:12:47.320 --> 00:12:51.159 And a laser beam is narrow If the spacecraft tilts 278 00:12:51.360 --> 00:12:54.639 even a fraction of a degree, Won't it just slide 279 00:12:54.720 --> 00:12:56.720 right off the beam and get lost in the dark. 280 00:12:56.919 --> 00:12:59.000 That is the million dollar question. 281 00:12:59.240 --> 00:13:01.240 So how are the sign scientists at Texas A and 282 00:13:01.360 --> 00:13:02.960 M actually controlling this motion? 283 00:13:03.360 --> 00:13:06.879 That exact question is what makes this research so revolutionary. 284 00:13:07.919 --> 00:13:10.519 The stability problem you just described is one of the 285 00:13:10.519 --> 00:13:14.360 biggest hurdles in all of optical propulsion. Okay, the answer 286 00:13:14.440 --> 00:13:17.639 to how they solve it lies in the specific materials 287 00:13:17.720 --> 00:13:20.679 these metajets are made of. They aren't just using flat, 288 00:13:20.879 --> 00:13:24.559 shiny mirrors. They are composed of what are called metasurfaces. 289 00:13:24.600 --> 00:13:27.120 Metasurfaces. Okay, we definitely need to break that down. What 290 00:13:27.240 --> 00:13:29.200 exactly are we looking at here? If I were holding 291 00:13:29.240 --> 00:13:31.320 a metajet in my hand, what would it look like? 292 00:13:31.639 --> 00:13:33.279 Well, honestly, you wouldn't be able to see it in 293 00:13:33.279 --> 00:13:36.159 your hand. Wait, really, really, to understand a metajet, you 294 00:13:36.200 --> 00:13:39.200 first have to understand the scale. We are talking about 295 00:13:39.240 --> 00:13:42.399 devices that are only tens of microns in size. 296 00:13:42.440 --> 00:13:44.720 Tens of microns. Just to give a listeners some real 297 00:13:44.759 --> 00:13:48.080 world context for that, a single human red blood cell 298 00:13:48.440 --> 00:13:52.320 is about eight microns across, right. A single human hair 299 00:13:52.519 --> 00:13:56.440 is roughly seventy to one hundred microns thick. So these 300 00:13:56.720 --> 00:14:01.120 entirely engineered functional devices are literally smaller than the width 301 00:14:01.159 --> 00:14:01.559 of a hair. 302 00:14:01.840 --> 00:14:05.639 They are truly microscopic. They are manufactured in specialized clean 303 00:14:05.720 --> 00:14:08.879 rooms like the aggifab Nanofabrication facility. 304 00:14:08.480 --> 00:14:10.399 At Texas A and m okay what goes on in there? 305 00:14:10.720 --> 00:14:14.399 They use advanced lithography techniques. These are environments where even 306 00:14:14.440 --> 00:14:17.440 a single speck of dust is a massive boulder that 307 00:14:17.440 --> 00:14:18.879 could ruin the entire device. 308 00:14:18.960 --> 00:14:21.320 Oh wow, so it has to be perfectly clean exactly. 309 00:14:21.799 --> 00:14:25.159 The researchers wear full protective bunny suits, working under special 310 00:14:25.200 --> 00:14:28.399 yellow lights to avoid exposing the photosensitive chemicals used in 311 00:14:28.440 --> 00:14:29.639 the manufacturing process. 312 00:14:29.759 --> 00:14:32.559 That is intense. And what are they actually manufacturing at 313 00:14:32.559 --> 00:14:35.000 that tiny scale? Like? What makes it a metasurface and 314 00:14:35.080 --> 00:14:36.440 not just a tiny piece of oil? 315 00:14:36.759 --> 00:14:39.799 So a metasurface is an ultra thin material that has 316 00:14:39.840 --> 00:14:44.559 been engineered with incredibly tiny, complex geometric patterns on its 317 00:14:44.559 --> 00:14:50.519 surface patterns. Yes, imagine a landscape of microscopic pillars, ridges, antennas, 318 00:14:50.519 --> 00:14:54.519 and valleys, all spaced apart at distances smaller than the 319 00:14:54.519 --> 00:14:55.559 wavelength of light. 320 00:14:55.399 --> 00:14:57.960 Itself, wait smaller than the wavelength of light. 321 00:14:58.159 --> 00:15:02.320 Yes, incredibly small when these patterns are explicitly designed to 322 00:15:02.399 --> 00:15:06.559 interact with electromagnetic waves, in this case, the incoming laser 323 00:15:06.639 --> 00:15:08.759 light in highly specific ways. 324 00:15:08.840 --> 00:15:10.919 So it's not just bouncing the light back like a 325 00:15:10.960 --> 00:15:14.360 dumb mirror. The physical shape of the material is doing 326 00:15:14.360 --> 00:15:16.279 something complex to the light. Yes. 327 00:15:16.480 --> 00:15:19.039 When we talk about manipulating light, we usually talk about 328 00:15:19.039 --> 00:15:22.200 manipulating its phase, its amplitude, and its polarization. 329 00:15:22.720 --> 00:15:25.039 Okay, let's pause unpack those terms for those of us 330 00:15:25.080 --> 00:15:28.159 who aren't optical physicists. Sure, when you say the metasurface 331 00:15:28.279 --> 00:15:31.039 changes the phase of the light, what does that actually 332 00:15:31.120 --> 00:15:33.600 mean in practice? Or we're talking about shifting the wave itself. 333 00:15:33.919 --> 00:15:35.720 Yeah, so think of light as an ocean wave. It 334 00:15:35.720 --> 00:15:38.480 has peaks and valleys. The phase refers to where you 335 00:15:38.559 --> 00:15:41.320 are in that wave cycle. Are you at the crest 336 00:15:41.679 --> 00:15:42.759 or are you in the trough? 337 00:15:42.919 --> 00:15:43.960 Okay, that makes sense. 338 00:15:44.240 --> 00:15:48.639 By engineering these microscopic pillars of varying heights and widths 339 00:15:48.720 --> 00:15:52.720 on the metasurface, you can actually slow down certain parts 340 00:15:52.720 --> 00:15:55.279 of the incoming LightWave just a tiny fraction of a 341 00:15:55.279 --> 00:15:58.879 second more than others. Oh, this shifts the peaks and valleys, 342 00:15:58.960 --> 00:16:00.559 altering the phase okay. 343 00:16:00.320 --> 00:16:01.879 And amplitude and polarization. 344 00:16:02.279 --> 00:16:05.480 So amplitude is essentially the intensity or the height of 345 00:16:05.519 --> 00:16:08.360 the wave, basically how bright it is right, and polarization 346 00:16:08.480 --> 00:16:11.440 refers to the orientation of the wave's oscillation. Is it 347 00:16:11.440 --> 00:16:13.639 waving up and down or left and right or maybe 348 00:16:13.639 --> 00:16:14.120 in a spire? 349 00:16:14.279 --> 00:16:17.519 Oh, like polarized sunglass is blocking certain ways exactly. 350 00:16:17.720 --> 00:16:21.679 A metasurface can change all of these properties simultaneously. Upon reflection, 351 00:16:22.320 --> 00:16:26.080 think about how a traditional glass magnifying lens works. Okay, 352 00:16:26.279 --> 00:16:28.840 it relies on the physical curvature and the thickness of 353 00:16:28.840 --> 00:16:31.919 the glass to bend and focus the light passing through it. 354 00:16:32.120 --> 00:16:34.200 Right, the glass itself bends it right. 355 00:16:34.320 --> 00:16:38.320 A metasurface does the exact same thing. It shapes, bends, focuses, 356 00:16:38.360 --> 00:16:40.840 and steers the light, but it does it on a 357 00:16:40.960 --> 00:16:44.480 vastly smaller, thinner, and perfectly flat. 358 00:16:44.200 --> 00:16:45.879 Scale without the curved glass. 359 00:16:46.240 --> 00:16:51.080 Exactly. It uses those nanoscale geometric patterns to manipulate the light. 360 00:16:51.360 --> 00:16:54.679 The level of nanoscale fabrication required to build something like 361 00:16:54.720 --> 00:16:56.039 that is just mind bending. 362 00:16:56.200 --> 00:16:57.679 It is an engineering marvel. 363 00:16:57.799 --> 00:17:00.919 It's almost like building a macroscopic p ball machine, or 364 00:17:00.960 --> 00:17:04.000 like a pachinko board where you carefully place all the 365 00:17:04.000 --> 00:17:07.200 bumpers and pegs so that when a ball or in 366 00:17:07.200 --> 00:17:10.039 this case, a photon drops in, you know exactly which 367 00:17:10.039 --> 00:17:11.319 direction it's going to bounce out. 368 00:17:11.519 --> 00:17:14.200 That is a highly accurate way to visualize it. You 369 00:17:14.240 --> 00:17:17.519 are engineering the microscopic bumpers to dictate the bounce. 370 00:17:17.599 --> 00:17:18.039 I love that. 371 00:17:18.359 --> 00:17:20.559 And here is the crucial distinction that really stood out 372 00:17:20.559 --> 00:17:23.640 about the Texas A and M approach. Historically, when people 373 00:17:23.680 --> 00:17:27.240 talked about moving things with lasers, the prevailing idea was 374 00:17:27.279 --> 00:17:30.160 that you had to perfectly shape and aim a highly 375 00:17:30.240 --> 00:17:34.039 complex adaptive laser beam to keep the object balanced right 376 00:17:34.079 --> 00:17:34.680 to stop. 377 00:17:34.400 --> 00:17:36.519 It from sliding off like my cardboard example. 378 00:17:36.720 --> 00:17:39.960 Huh exactly. The idea was if the object started to tilt, 379 00:17:40.240 --> 00:17:43.000 the laser beam on Earth would have to instantly detect 380 00:17:43.000 --> 00:17:45.799 that tilt and change its own shape to correct it. 381 00:17:46.240 --> 00:17:48.039 You had to do all the complicated work at the 382 00:17:48.119 --> 00:17:49.039 light source. 383 00:17:48.839 --> 00:17:51.079 Which sounds like a nightmare. If your spacecraft is a 384 00:17:51.160 --> 00:17:53.920 light year away, it would be impossible, right because the 385 00:17:53.960 --> 00:17:56.200 signal delay would be a year. If it tilts, you 386 00:17:56.200 --> 00:17:58.240 won't know for a year, and your correction won't reach 387 00:17:58.279 --> 00:18:00.920 it for another year. By then the ship is totally gone. 388 00:18:01.039 --> 00:18:04.920 Exactly the problem. But doctor Land's team flipped that entire 389 00:18:05.000 --> 00:18:08.519 paradigm on its head. Instead of trying to dynamically control 390 00:18:08.559 --> 00:18:12.079 the laser beam from afar, they built the control mechanism 391 00:18:12.200 --> 00:18:14.279 directly into the material itself. 392 00:18:14.440 --> 00:18:17.039 Oh wow, so the smarts are in the sail not 393 00:18:17.119 --> 00:18:17.559 the wind. 394 00:18:17.799 --> 00:18:22.799 Yes, yes, beautifully said. By carefully designing the shape, the orientation, 395 00:18:23.119 --> 00:18:27.000 and the placement of every single nanoscale feature on that metasurface, 396 00:18:27.400 --> 00:18:30.440 the scientists are dictating exactly how the light will bounce off, 397 00:18:30.519 --> 00:18:32.799 regardless of minor fluctuations in the beam. 398 00:18:33.240 --> 00:18:36.160 So if the laser hits a specific pattern of microscopic 399 00:18:36.240 --> 00:18:38.759 pillars on the left side of the metajet, the light 400 00:18:38.839 --> 00:18:42.359 is purposely deflected at a specific angle, say down into 401 00:18:42.400 --> 00:18:46.240