What Even is Light?

We know for sure it's not dark. How do light bulbs work? Are they small suns inside a glass circle? James and special guest Greg stumble around as they try to explain light fundamentally. Kat and John enjoy their struggle. How can we explain light to a five year old? In order to handle the the complex question about what light is, it is best to start by exploring what light does.

What Does Light Do?

Mirrors are weird. We know light can reflect or bounce off things. So is light made up of bouncy stuff? We also know light refracts or it's path can bend. Imagine a straw in a glass of water. The water half of the straw looks disconnected from the top half. This is because light bends as it travels from water to air (or vice versa).  Light has to bounce and bend. What kind of thing does this?

History of Our Understanding of Light

Always starting with the Ancient Greeks. They understood light as straight lines called "rays". But how do these rays move? Some Greeks (example: Pythagoras) thought that rays left your eyes, bounced off the object, and came back to your eyes to be detected. Other Greeks thought light rays only came into our eyes after it bounced off an object. Here, John goes on a quick tangent to discuss the fact that researchers have slowed down light to 38 MPH (about 61 km/hr).

The discussion then moves to Ancient Arab times and all the work they did with geometric optics. This is where pinhole cameras were invented. Lenses and all their weirdness are also briefly explored. Our history of light then fast forwards to Isaac Newton and all the work he did with light. He thought that light was made up of a stream of particles called corpuscles based on his experiments. However, Newton's contemporary Christiaan Huygens thought light was a wave based on his own observations! The basics of waves are briefly discussed at this point. So we have options here. That is until Thomas Young came along.

Young conducted the famous double slit experiment which definitively showed that light is a wave. So that's it right? Episode over? It would be if it wasn't for cha boi Einstein and the photoelectric effect. It order to explain how electrons come off some metals when light is shined at it, Einstein had to use the particle description of light! So what is light? A wave? A particle? Both? Neither? Today we describe light as having both particle characteristics and wave characteristics. This is known as wave-particle duality! From here, each "picture" of light is explored separately. First light waves are explored then later, light particles.

Light as Waves and Light as Particles

So alright cool, light is a wave. But what is waving? In order to understand what's going on, electromagnetism is briefly discussed. The work of Ørsted, Faraday, and Maxwell are all touched upon to show that light is an electromagnetic wave! The electromagnetic field is what's waving to create light! From here, different wavelengths of light are explained. Radio waves, microwaves, infrared, visible, ultraviolet, x-rays, and gamma rays are all presented, explained, and discussed. In order to discuss the particle picture of light, black-bodies and the ultraviolet catastrophe were discussed along with Max Planck's solution. The episode concludes by talking about the finite speed of light and it's implications.