WEBVTT - What Is Light?

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<v Speaker 1>Welcome to brain stuff from how stuff works, Hey, brain

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<v Speaker 1>stuff loin Volga bamb here. Light, in addition to being

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<v Speaker 1>a bright patch of sunshine on your window sill, is

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<v Speaker 1>a metaphor for enlightenment and exploration, which is a bit

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<v Speaker 1>paradoxical for a phenomenon that, even after thousands of years

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<v Speaker 1>of inquiries and endless experiments, scientists still can't quite explain.

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<v Speaker 1>Is it a particle or a wave or both or neither?

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<v Speaker 1>Do we need a new word for it? Your eyes

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<v Speaker 1>tell you a lot about the way light behaves. It

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<v Speaker 1>travels so fast that it seems instantaneous, about a hundred

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<v Speaker 1>and eighty six thousand miles or three thousand kilometers per second.

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<v Speaker 1>It blazes through air and space and laser like straight lines,

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<v Speaker 1>but it also bounces, reflects, and refracts, and when it

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<v Speaker 1>interacts with the right medium, like a camera lens, it

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<v Speaker 1>may curve. We know that it's made up of tiny

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<v Speaker 1>units that we call photons, and we know that the

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<v Speaker 1>term waves can describe its movements, but neither of these

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<v Speaker 1>words really encompass lights oddities. In ancient times, the Greeks

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<v Speaker 1>used philosophy to attempt to address light's wide range of behaviors.

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<v Speaker 1>Perhaps they thought light is actually composed of little bits

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<v Speaker 1>of stuff that bounced to and fro. The idea never

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<v Speaker 1>really caught on. Then, in the sixteen hundreds, French philosopher

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<v Speaker 1>Renee de Cart became convinced that light was essentially a wave,

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<v Speaker 1>one that moved through a mysterious substance that he called plenum.

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<v Speaker 1>Isaac Newton thought that light was a particle, but he

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<v Speaker 1>was at a loss for a way to explain many

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<v Speaker 1>of its properties, like the way it refracted and could

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<v Speaker 1>be split by a prism from a single beam of

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<v Speaker 1>white light into a rainbow of many colors of light.

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<v Speaker 1>This was largely before the rise of empirical studies in science,

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<v Speaker 1>wherein we attempt to answer questions about the world around

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<v Speaker 1>us by designing experiments that demonstrate well how stuff works.

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<v Speaker 1>Back in the day, science was a matter of philosophy,

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<v Speaker 1>people coming up with ideas about how stuff works and

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<v Speaker 1>basically arguing about the idea's merit to be fair. Our

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<v Speaker 1>modern microscopes, computers, and other equipment help. Just for example,

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<v Speaker 1>light's behavior becomes more evident depending on where you're observing it.

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<v Speaker 1>In the vacuum of space, light zips along at the

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<v Speaker 1>aforementioned a hundred and eighty six thousand miles or three

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<v Speaker 1>thousand kilometers per second. But point a beam of light

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<v Speaker 1>at a very dense bit of matter, say a diamond,

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<v Speaker 1>and it can slow to only around seventy seven thousand

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<v Speaker 1>miles or a hundred twenty four thousand kilometers per second,

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<v Speaker 1>much easier to observe relatively. To try to explain in

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<v Speaker 1>these are modern times, what light is, Let's first remember

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<v Speaker 1>some science basics. Waves are not a thing or a substance.

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<v Speaker 1>They're a property of a thing. A wave is a

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<v Speaker 1>compressing and stretching of a particular medium, like an ocean

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<v Speaker 1>wave that drives towards the shore or the ripple that

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<v Speaker 1>spreads out across the surface of a pond. When you

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<v Speaker 1>toss in a rock, you can see the waves with

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<v Speaker 1>your eyes, feel them with your body, and sometimes when

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<v Speaker 1>a sound wave happens in the air, you can hear

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<v Speaker 1>them with your ears. Particles, on the other hand, are

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<v Speaker 1>not quite so easy to define. A particle can be

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<v Speaker 1>a tiny bit of matter, a matter broken down on

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<v Speaker 1>into its smallest and most basic units. Water, for example,

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<v Speaker 1>is made up of countless particles particles that are affected

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<v Speaker 1>by waves. What's really happening when you watch a wave

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<v Speaker 1>in the ocean or a ripple in a pond is

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<v Speaker 1>that each particle or molecule in this case of water

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<v Speaker 1>is being moved, and thus the medium of the ocean

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<v Speaker 1>or pond is being compressed and stretched in sequence, and

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<v Speaker 1>we see waves. But light, as experiments have proven, also

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<v Speaker 1>consists of particles that we call photons that behave like waves.

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<v Speaker 1>Let's unpack that. There was a famous nineteenth century double

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<v Speaker 1>slit experiment in which researchers beamed light through two slits

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<v Speaker 1>and observed the way the light struck a screen behind

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<v Speaker 1>the slits. What they saw was that the streams of

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<v Speaker 1>light affected each other like two hands splashing water in

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<v Speaker 1>the same sink, as if they were waves interfering with

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<v Speaker 1>one another. But then in the twentieth century, scientists began

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<v Speaker 1>their pioneering explorations into sub atomic particles like neutrons and electrons.

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<v Speaker 1>Albert Einstein wondered what would happen if you admitted light

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<v Speaker 1>one photon at a time. In the double slit experiment,

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<v Speaker 1>what scientists saw dumbfounded them. The single photons went individually

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<v Speaker 1>through the slits, but the way that they struck the

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<v Speaker 1>screen over time showed the same interference pattern that occurred

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<v Speaker 1>with full scale beams of light streaming through both slits.

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<v Speaker 1>This behavior can't be explained by the physics we use

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<v Speaker 1>to describe particles and waves in the macro world around us.

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<v Speaker 1>It's in the realm of quantum mechanics, the physics theories

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<v Speaker 1>that describe what goes on at the very smallest sub

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<v Speaker 1>atomic levels and which we humans still don't really understand.

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<v Speaker 1>So ultimately, if you want to answer the question what

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<v Speaker 1>is light, you could call it both a particle and

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<v Speaker 1>a wave and you'd be correct. But as for fully

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<v Speaker 1>explaining why and how it works, we're still working on it.

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<v Speaker 1>Today's episode was written by Nathan Chandler and produced by

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<v Speaker 1>Tyler Clang for i Heeart Media and How Stuff Works.

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<v Speaker 1>To learn more about the weird behavior of light and

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<v Speaker 1>the history of how humans have thought about it, check

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<v Speaker 1>out our sister podcast, Daniel mclae explained the universe. Their episode,

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<v Speaker 1>Is Light, a Particle or a Wave goes into lots

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<v Speaker 1>more details, and of course, for more on this and

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<v Speaker 1>lots of other lighthearted topics, visit our home planet How

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<v Speaker 1>Stuff Works dot com.