1 00:00:01,840 --> 00:00:07,600 Speaker 1: Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff, 2 00:00:07,600 --> 00:00:10,400 Speaker 1: I'm Lauren vogel Bomb, and this is another episode from 3 00:00:10,480 --> 00:00:13,720 Speaker 1: the Vault. This one goes into the history of how 4 00:00:13,760 --> 00:00:17,120 Speaker 1: people have thought of light. After all, our planet runs 5 00:00:17,120 --> 00:00:19,800 Speaker 1: on it. But it's actually a pretty weird phenomenon right 6 00:00:19,880 --> 00:00:25,400 Speaker 1: up through today's scientific theories for how it works. Hey 7 00:00:25,440 --> 00:00:26,720 Speaker 1: brain Stuff, Lauren vocal Bomb. 8 00:00:26,800 --> 00:00:30,000 Speaker 2: Here, light, in addition to being a bright patch of 9 00:00:30,000 --> 00:00:33,720 Speaker 2: sunshine on your windowsill, is a metaphor for enlightenment and exploration, 10 00:00:34,360 --> 00:00:37,120 Speaker 2: which is a bit paradoxical for a phenomenon that, even 11 00:00:37,200 --> 00:00:41,080 Speaker 2: after thousands of years of inquiries and endless experiments, scientists 12 00:00:41,120 --> 00:00:44,120 Speaker 2: still can't quite explain. Is it a particle or a 13 00:00:44,159 --> 00:00:47,120 Speaker 2: wave or both or neither? Do we need a new 14 00:00:47,159 --> 00:00:50,240 Speaker 2: word for it? Your eyes tell you a lot about 15 00:00:50,280 --> 00:00:53,040 Speaker 2: the way light behaves. It travels so fast that it 16 00:00:53,080 --> 00:00:56,400 Speaker 2: seems instantaneous, about one hundred and eighty six thousand miles 17 00:00:56,480 --> 00:00:59,840 Speaker 2: or three thousand kilometers per second. It blazes through air 18 00:00:59,880 --> 00:01:03,880 Speaker 2: and space and laser like straight lines. But it also bounces, reflects, 19 00:01:03,880 --> 00:01:06,760 Speaker 2: and refracts, and when it interacts with the right medium 20 00:01:06,880 --> 00:01:10,319 Speaker 2: like a camera lens, it may curve. We know that 21 00:01:10,319 --> 00:01:12,560 Speaker 2: it's made up of tiny units that we call photons, 22 00:01:12,600 --> 00:01:15,120 Speaker 2: and we know that the term waves can describe its movements, 23 00:01:15,360 --> 00:01:19,520 Speaker 2: but neither of these words really encompass light's oddities. In 24 00:01:19,600 --> 00:01:22,520 Speaker 2: ancient times, the Greeks used philosophy to attempt to address 25 00:01:22,600 --> 00:01:26,080 Speaker 2: light's wide range of behaviors. Perhaps they thought light is 26 00:01:26,080 --> 00:01:28,560 Speaker 2: actually composed of little bits of stuff that bounced to 27 00:01:28,640 --> 00:01:32,000 Speaker 2: and fro. The idea never really caught on. Then, in 28 00:01:32,000 --> 00:01:35,560 Speaker 2: the sixteen hundreds, French philosopher Renee des Cartes became convinced 29 00:01:35,600 --> 00:01:38,039 Speaker 2: that light was essentially a wave, one that moved through 30 00:01:38,040 --> 00:01:41,880 Speaker 2: a mysterious substance that he called plenim Isaac Newton thought 31 00:01:41,880 --> 00:01:43,600 Speaker 2: that light was a particle, but he was at a 32 00:01:43,640 --> 00:01:45,840 Speaker 2: loss for a way to explain many of its properties, 33 00:01:46,000 --> 00:01:48,040 Speaker 2: like the way it refracted and could be split by 34 00:01:48,040 --> 00:01:50,400 Speaker 2: a prism from a single beam of white light into 35 00:01:50,440 --> 00:01:54,400 Speaker 2: a rainbow of many colors of light. This was largely 36 00:01:54,400 --> 00:01:57,200 Speaker 2: before the rise of empirical studies in science, wherein we 37 00:01:57,200 --> 00:01:59,680 Speaker 2: attempt to answer questions about the world around us by 38 00:01:59,680 --> 00:02:04,200 Speaker 2: design any experiments that demonstrate well how stuff works. Back 39 00:02:04,200 --> 00:02:07,480 Speaker 2: in the day, science was a matter of philosophy, people 40 00:02:07,480 --> 00:02:10,080 Speaker 2: coming up with ideas about how stuff works and basically 41 00:02:10,240 --> 00:02:15,320 Speaker 2: arguing about the idea's merit to be fair. Our modern microscopes, computers, 42 00:02:15,320 --> 00:02:19,600 Speaker 2: and other equipment help. Just for example, light's behavior becomes 43 00:02:19,639 --> 00:02:22,760 Speaker 2: more evident depending on where you're observing it. In the 44 00:02:22,800 --> 00:02:25,520 Speaker 2: vacuum of space, light zips long at the aforementioned one 45 00:02:25,600 --> 00:02:27,960 Speaker 2: hundred and eighty six thousand miles or three hundred thousand 46 00:02:28,000 --> 00:02:31,000 Speaker 2: kilometers per second. But point a beam of light at 47 00:02:31,040 --> 00:02:33,720 Speaker 2: a very dense bit of matter, say a diamond, and 48 00:02:33,760 --> 00:02:36,800 Speaker 2: it can slow to only around seventy seven thousand miles 49 00:02:36,880 --> 00:02:39,320 Speaker 2: or one hundred and twenty four thousand kilometers per second, 50 00:02:39,800 --> 00:02:44,120 Speaker 2: much easier to observe relatively. To try to explain in 51 00:02:44,160 --> 00:02:47,480 Speaker 2: these are modern times, what light is, let's first remember 52 00:02:47,560 --> 00:02:51,560 Speaker 2: some science basics. Waves are not a thing or a substance. 53 00:02:51,600 --> 00:02:54,320 Speaker 2: They're a property of a thing. A wave is a 54 00:02:54,360 --> 00:02:57,600 Speaker 2: compressing and stretching of a particular medium, like an ocean 55 00:02:57,600 --> 00:03:00,240 Speaker 2: wave that drives toward the shore, or the rip that 56 00:03:00,280 --> 00:03:01,960 Speaker 2: spreads out across the surface of a pond. 57 00:03:02,000 --> 00:03:03,360 Speaker 1: When you toss in a rock. 58 00:03:03,960 --> 00:03:06,080 Speaker 2: You can see the waves with your eyes, feel them 59 00:03:06,120 --> 00:03:08,840 Speaker 2: with your body, and sometimes when a sound wave happens 60 00:03:08,880 --> 00:03:12,280 Speaker 2: in the air, you can hear them with your ears. Particles, 61 00:03:12,320 --> 00:03:15,000 Speaker 2: on the other hand, are not quite so easy to define. 62 00:03:15,400 --> 00:03:18,000 Speaker 2: A particle can be a tiny bit of matter, a 63 00:03:18,040 --> 00:03:21,680 Speaker 2: matter broken down into its smallest and most basic units. Water, 64 00:03:21,760 --> 00:03:24,560 Speaker 2: for example, is made up of countless particles particles that 65 00:03:24,600 --> 00:03:28,160 Speaker 2: are affected by waves. What's really happening when you watch 66 00:03:28,160 --> 00:03:29,680 Speaker 2: a wave in the ocean or a ripple in a 67 00:03:29,720 --> 00:03:32,600 Speaker 2: pond is that each particle or molecule in this case 68 00:03:32,639 --> 00:03:35,640 Speaker 2: of water, is being moved, and thus the medium of 69 00:03:35,640 --> 00:03:39,000 Speaker 2: the ocean or pond is being compressed and stretched in sequence, 70 00:03:39,160 --> 00:03:43,680 Speaker 2: and we see waves. But light, as experiments have proven, 71 00:03:44,000 --> 00:03:46,960 Speaker 2: also consists of particles that we call photons that behave 72 00:03:47,320 --> 00:03:51,760 Speaker 2: like waves. Let's unpack that. There was a famous nineteenth 73 00:03:51,840 --> 00:03:55,440 Speaker 2: century double slit experiment in which researchers beamed light through 74 00:03:55,440 --> 00:03:57,840 Speaker 2: two slits and observed the way the light struck a 75 00:03:57,880 --> 00:04:00,560 Speaker 2: screen behind the slits. What they say saw was that 76 00:04:00,560 --> 00:04:03,320 Speaker 2: the streams of light affected each other like two hands 77 00:04:03,360 --> 00:04:05,680 Speaker 2: splashing water in the same sink, as if they were 78 00:04:05,720 --> 00:04:09,800 Speaker 2: waves interfering with one another. But then in the twentieth century, 79 00:04:09,880 --> 00:04:14,240 Speaker 2: scientists began their pioneering explorations into subatomic particles like neutrons 80 00:04:14,240 --> 00:04:17,440 Speaker 2: and electrons. Albert Einstein wondered what would happen if you 81 00:04:17,480 --> 00:04:20,159 Speaker 2: emitted light one photon at a time in the double 82 00:04:20,160 --> 00:04:25,159 Speaker 2: slit experiment. What scientists saw dumbfounded them. The single photons 83 00:04:25,200 --> 00:04:27,520 Speaker 2: went individually through the slits, but the way that they 84 00:04:27,600 --> 00:04:31,000 Speaker 2: struck the screen over time showed the same interference pattern 85 00:04:31,040 --> 00:04:33,520 Speaker 2: that occurred with full scale beams of light streaming through 86 00:04:33,600 --> 00:04:37,280 Speaker 2: both slits. This behavior can't be explained by the physics 87 00:04:37,360 --> 00:04:39,800 Speaker 2: we use to describe particles and waves in the macro 88 00:04:39,960 --> 00:04:43,160 Speaker 2: world around us. It's in the realm of quantum mechanics, 89 00:04:43,360 --> 00:04:45,560 Speaker 2: the physics theories that describe what goes on at the 90 00:04:45,720 --> 00:04:49,200 Speaker 2: very smallest subatomic levels and which we humans still don't 91 00:04:49,240 --> 00:04:53,039 Speaker 2: really understand. So ultimately, if you want to answer the 92 00:04:53,080 --> 00:04:55,320 Speaker 2: question what is light, you could call it both a 93 00:04:55,360 --> 00:04:58,560 Speaker 2: particle and a wave and you'd be correct. But as 94 00:04:58,600 --> 00:05:01,880 Speaker 2: for fully explaining why and how it works, we're still 95 00:05:01,880 --> 00:05:08,640 Speaker 2: working on it. Today's episode is based on the article 96 00:05:08,839 --> 00:05:11,359 Speaker 2: Ray of Enlightenment Is Light a wave or a Particle? 97 00:05:11,440 --> 00:05:14,000 Speaker 1: On How Stuffworks? Dot Com? Written by Nathan Chandler, who 98 00:05:14,120 --> 00:05:16,960 Speaker 1: drew from the podcast Daniel and Hlurge Explain the Universe, 99 00:05:17,040 --> 00:05:19,839 Speaker 1: which is a pretty cool one. Brain Stuff is production 100 00:05:19,920 --> 00:05:22,240 Speaker 1: by Heart Radio in partnership with how stuffworks dot com 101 00:05:22,279 --> 00:05:25,040 Speaker 1: and is produced by Tyler Klang. Or more podcasts my 102 00:05:25,160 --> 00:05:28,520 Speaker 1: heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever 103 00:05:28,520 --> 00:05:30,000 Speaker 1: you listen to your favorite shows.