Speaker 1: Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff,
Speaker 1: I'm Lauren vogel Bomb, and this is another episode from
Speaker 1: the Vault. This one goes into the history of how
Speaker 1: people have thought of light. After all, our planet runs
Speaker 1: on it. But it's actually a pretty weird phenomenon right
Speaker 1: up through today's scientific theories for how it works. Hey
Speaker 1: brain Stuff, Lauren vocal Bomb.
Speaker 2: Here, light, in addition to being a bright patch of
Speaker 2: sunshine on your windowsill, is a metaphor for enlightenment and exploration,
Speaker 2: which is a bit paradoxical for a phenomenon that, even
Speaker 2: after thousands of years of inquiries and endless experiments, scientists
Speaker 2: still can't quite explain. Is it a particle or a
Speaker 2: wave or both or neither? Do we need a new
Speaker 2: word for it? Your eyes tell you a lot about
Speaker 2: the way light behaves. It travels so fast that it
Speaker 2: seems instantaneous, about one hundred and eighty six thousand miles
Speaker 2: or three thousand kilometers per second. It blazes through air
Speaker 2: and space and laser like straight lines. But it also bounces, reflects,
Speaker 2: and refracts, and when it interacts with the right medium
Speaker 2: like a camera lens, it may curve. We know that
Speaker 2: it's made up of tiny units that we call photons,
Speaker 2: and we know that the term waves can describe its movements,
Speaker 2: but neither of these words really encompass light's oddities. In
Speaker 2: ancient times, the Greeks used philosophy to attempt to address
Speaker 2: light's wide range of behaviors. Perhaps they thought light is
Speaker 2: actually composed of little bits of stuff that bounced to
Speaker 2: and fro. The idea never really caught on. Then, in
Speaker 2: the sixteen hundreds, French philosopher Renee des Cartes became convinced
Speaker 2: that light was essentially a wave, one that moved through
Speaker 2: a mysterious substance that he called plenim Isaac Newton thought
Speaker 2: that light was a particle, but he was at a
Speaker 2: loss for a way to explain many of its properties,
Speaker 2: like the way it refracted and could be split by
Speaker 2: a prism from a single beam of white light into
Speaker 2: a rainbow of many colors of light. This was largely
Speaker 2: before the rise of empirical studies in science, wherein we
Speaker 2: attempt to answer questions about the world around us by
Speaker 2: design any experiments that demonstrate well how stuff works. Back
Speaker 2: in the day, science was a matter of philosophy, people
Speaker 2: coming up with ideas about how stuff works and basically
Speaker 2: arguing about the idea's merit to be fair. Our modern microscopes, computers,
Speaker 2: and other equipment help. Just for example, light's behavior becomes
Speaker 2: more evident depending on where you're observing it. In the
Speaker 2: vacuum of space, light zips long at the aforementioned one
Speaker 2: hundred and eighty six thousand miles or three hundred thousand
Speaker 2: kilometers per second. But point a beam of light at
Speaker 2: a very dense bit of matter, say a diamond, and
Speaker 2: it can slow to only around seventy seven thousand miles
Speaker 2: or one hundred and twenty four thousand kilometers per second,
Speaker 2: much easier to observe relatively. To try to explain in
Speaker 2: these are modern times, what light is, let's first remember
Speaker 2: some science basics. Waves are not a thing or a substance.
Speaker 2: They're a property of a thing. A wave is a
Speaker 2: compressing and stretching of a particular medium, like an ocean
Speaker 2: wave that drives toward the shore, or the rip that
Speaker 2: spreads out across the surface of a pond.
Speaker 1: When you toss in a rock.
Speaker 2: You can see the waves with your eyes, feel them
Speaker 2: with your body, and sometimes when a sound wave happens
Speaker 2: in the air, you can hear them with your ears. Particles,
Speaker 2: on the other hand, are not quite so easy to define.
Speaker 2: A particle can be a tiny bit of matter, a
Speaker 2: matter broken down into its smallest and most basic units. Water,
Speaker 2: for example, is made up of countless particles particles that
Speaker 2: are affected by waves. What's really happening when you watch
Speaker 2: a wave in the ocean or a ripple in a
Speaker 2: pond is that each particle or molecule in this case
Speaker 2: of water, is being moved, and thus the medium of
Speaker 2: the ocean or pond is being compressed and stretched in sequence,
Speaker 2: and we see waves. But light, as experiments have proven,
Speaker 2: also consists of particles that we call photons that behave
Speaker 2: like waves. Let's unpack that. There was a famous nineteenth
Speaker 2: century double slit experiment in which researchers beamed light through
Speaker 2: two slits and observed the way the light struck a
Speaker 2: screen behind the slits. What they say saw was that
Speaker 2: the streams of light affected each other like two hands
Speaker 2: splashing water in the same sink, as if they were
Speaker 2: waves interfering with one another. But then in the twentieth century,
Speaker 2: scientists began their pioneering explorations into subatomic particles like neutrons
Speaker 2: and electrons. Albert Einstein wondered what would happen if you
Speaker 2: emitted light one photon at a time in the double
Speaker 2: slit experiment. What scientists saw dumbfounded them. The single photons
Speaker 2: went individually through the slits, but the way that they
Speaker 2: struck the screen over time showed the same interference pattern
Speaker 2: that occurred with full scale beams of light streaming through
Speaker 2: both slits. This behavior can't be explained by the physics
Speaker 2: we use to describe particles and waves in the macro
Speaker 2: world around us. It's in the realm of quantum mechanics,
Speaker 2: the physics theories that describe what goes on at the
Speaker 2: very smallest subatomic levels and which we humans still don't
Speaker 2: really understand. So ultimately, if you want to answer the
Speaker 2: question what is light, you could call it both a
Speaker 2: particle and a wave and you'd be correct. But as
Speaker 2: for fully explaining why and how it works, we're still
Speaker 2: working on it. Today's episode is based on the article
Speaker 2: Ray of Enlightenment Is Light a wave or a Particle?
Speaker 1: On How Stuffworks? Dot Com? Written by Nathan Chandler, who
Speaker 1: drew from the podcast Daniel and Hlurge Explain the Universe,
Speaker 1: which is a pretty cool one. Brain Stuff is production
Speaker 1: by Heart Radio in partnership with how stuffworks dot com
Speaker 1: and is produced by Tyler Klang. Or more podcasts my
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