What Is Light?

tell you a lot about the way light behaves. It travels so fast that it seems instantaneous, about a 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 lights 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 de Cart became convinced that light was essentially a wave, one that moved through a mysterious substance that he called plenum. 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 designing 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 along at the aforementioned a hundred and eighty six thousand miles or three 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 a hundred 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 towards the shore or the ripple 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 on 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 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 sub atomic particles like neutrons and electrons.

Albert Einstein wondered what would happen if you admitted 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 sub atomic 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 was written by Nathan Chandler and produced by Tyler Clang for i Heeart Media and How Stuff Works. To learn more about the weird behavior of light and the history of how humans have thought about it, check out our sister podcast, Daniel mclae explained the universe. Their episode, Is Light, a Particle or a Wave goes into lots more details, and of course, for more on this and lots of other lighthearted topics, visit our home planet How Stuff Works dot com.