Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff, I'm Lauren vogel Bomb, and this is another episode from the Vault. This one goes into the history of how people have thought of light. After all, our planet runs on it. But it's actually a pretty weird phenomenon right up through today's scientific theories for how it works. Hey brain Stuff, Lauren vocal Bomb.
Here, light, in addition to being a bright patch of sunshine on your windowsill, is a metaphor for enlightenment and exploration, which is a bit paradoxical for a phenomenon that, even after thousands of years of inquiries and endless experiments, scientists still can't quite explain. Is it a particle or a wave or both or neither? Do we need a new word for it? Your eyes tell you a lot about
the way light behaves. It travels so fast that it seems instantaneous, about one hundred and eighty six thousand miles or three thousand kilometers per second. It blazes through air and space and laser like straight lines. But it also bounces, reflects, and refracts, and when it interacts with the right medium like a camera lens, it may curve. We know that it's made up of tiny units that we call photons, and we know that the term waves can describe its movements,
but neither of these words really encompass light's oddities. In ancient times, the Greeks used philosophy to attempt to address light's wide range of behaviors. Perhaps they thought light is actually composed of little bits of stuff that bounced to
and fro. The idea never really caught on. Then, in the sixteen hundreds, French philosopher Renee des Cartes became convinced that light was essentially a wave, one that moved through a mysterious substance that he called plenim Isaac Newton thought that light was a particle, but he was at a loss for a way to explain many of its properties, like the way it refracted and could be split by a prism from a single beam of white light into
a rainbow of many colors of light. This was largely before the rise of empirical studies in science, wherein we attempt to answer questions about the world around us by design any experiments that demonstrate well how stuff works. Back in the day, science was a matter of philosophy, people coming up with ideas about how stuff works and basically arguing about the idea's merit to be fair. Our modern microscopes, computers, and other equipment help. Just for example, light's behavior becomes
more evident depending on where you're observing it. In the vacuum of space, light zips long at the aforementioned one hundred and eighty six thousand miles or three hundred thousand kilometers per second. But point a beam of light at a very dense bit of matter, say a diamond, and it can slow to only around seventy seven thousand miles or one hundred and twenty four thousand kilometers per second,
much easier to observe relatively. To try to explain in these are modern times, what light is, let's first remember some science basics. Waves are not a thing or a substance. They're a property of a thing. A wave is a compressing and stretching of a particular medium, like an ocean wave that drives toward the shore, or the rip that spreads out across the surface of a pond.
When you toss in a rock.
You can see the waves with your eyes, feel them with your body, and sometimes when a sound wave happens in the air, you can hear them with your ears. Particles, on the other hand, are not quite so easy to define. A particle can be a tiny bit of matter, a matter broken down into its smallest and most basic units. Water, for example, is made up of countless particles particles that
are affected by waves. What's really happening when you watch a wave in the ocean or a ripple in a pond is that each particle or molecule in this case of water, is being moved, and thus the medium of the ocean or pond is being compressed and stretched in sequence, and we see waves. But light, as experiments have proven, also consists of particles that we call photons that behave
like waves. Let's unpack that. There was a famous nineteenth century double slit experiment in which researchers beamed light through two slits and observed the way the light struck a screen behind the slits. What they say saw was that the streams of light affected each other like two hands splashing water in the same sink, as if they were waves interfering with one another. But then in the twentieth century, scientists began their pioneering explorations into subatomic particles like neutrons
and electrons. Albert Einstein wondered what would happen if you emitted light one photon at a time in the double slit experiment. What scientists saw dumbfounded them. The single photons went individually through the slits, but the way that they struck the screen over time showed the same interference pattern that occurred with full scale beams of light streaming through both slits. This behavior can't be explained by the physics we use to describe particles and waves in the macro
world around us. It's in the realm of quantum mechanics, the physics theories that describe what goes on at the very smallest subatomic levels and which we humans still don't really understand. So ultimately, if you want to answer the question what is light, you could call it both a particle and a wave and you'd be correct. But as for fully explaining why and how it works, we're still working on it. Today's episode is based on the article Ray of Enlightenment Is Light a wave or a Particle?
On How Stuffworks? Dot Com? Written by Nathan Chandler, who drew from the podcast Daniel and Hlurge Explain the Universe, which is a pretty cool one. Brain Stuff is production by Heart Radio in partnership with how stuffworks dot com and is produced by Tyler Klang. Or more podcasts my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.