Welcome to an Exciting Science Match!
This time, we've got 2 teams lined up for the game- the Purely Particles and the Wild Waves. These 2 amazing teams have prepared their best players for this big league game, which is going to decide what light actually is. We're going to play throughout history until we have a winner! That's right folks, get all the action right here, right now!
First up- the ancient moves
The whistle's blown, and they're off!
First up are the particles, and they start off strong. With such ancient philosophers as the Indian Dharmakirti and the Greek Euclid, they're covering the play field with preliminary theories and ideas. The early Indians view light as tiny entities equivalent to energy. The Greeks think that light is rays of particles.
But now the Greeks make an early mistake! They seem to think light rays come from our eyes… oh wait, no. Euclid corrected this- he states that unless light's speed is infinite, light can't originate from the eyes, since we can see the stars immediately after we blink even though they're very far away. Great save by Euclid!
The ancients proceed to study reflection. Reflection dials with light rays striking reflective surfaces and bouncing back… but is that all?
Next up is the Muslim scientist, Ibn al-Haytham, nicknamed Alhacen by his team. He can explain reflection a lot better- light rays come from a source, say the sun, and they're radiated in all directions. Each point from an illuminated area reflects the light ray into our eyes, allowing us to see objects. Alhacen held light rays to be streams of minute energy particles that travelled at a finite speed, and this is a point for the particles.
Alhacen is about to make another move… he's taking on refraction. Refraction is the phenomena that occurs when light moves from one medium to another- the angle changes. Alhacen explains this by saying that light changes speed.
Round 2- Renaissance time
Our first quarter of ancient times was dominated by the particles team.
But wait! Here comes René Descartes, the famous philosopher and scientist. He's trying to find a better explanation for refraction… it looks like Descartes believes light travels faster in denser mediums, just like sound waves. This analogy between sound and light is the first successful move by the wave team, and now things are getting exciting.
It's time for the particles to throw in their star player, Sir Isaac Newton. He states that light is made of corpuscles (particles of matter) which were emitted in all directions from a source. He explains reflection (particles bounce back) and refraction (particles change speed due to a greater gravitational pull), and colours (represented by particles of different masses).
Newton's play is challenged by the waves. They claim that the particle theory can't explain diffraction- the phenomena that shows how light spreads out when it faces a small opening. Newton responds by attributing diffraction to particles bumping on the edges of the opening, and proceeds to deliver a major blow to the wave team- light doesn't bend around corners like most waves!
Newton's reputation allows him to keep the particles team on the lead throughout the 18th century. But the wave team is throwing in some of their heavier names now- Hooke, Euler and Frensel. But it's young Huygens who grabs the ball.
Huygens suggests that light is emitted in all directions as a series of waves in a medium. He is able to explain interference and interactions between different light waves, as well as diffraction, much better than Newton's idea. He even explains polarization!
But wait… the particles are closing in for a hit. If light are waves, they have to pass through a medium… but there's no medium in outer space, so how can light waves reach here from the sun? Great question, this is a major point!
This game is getting very intense!
Final rounds- 19th century, and beyond
We start off with Leon Foucault. He successfully measures the speed of light (approximately) using rotating mirrors. His findings help determine that light moves slower, not faster, in a denser medium, the opposite of what Newton thought! This comes as a serious blow to the particles.
The wave team continues to fight, this time using electromagnetic waves. First up will be Michael Faraday, who discovers that the angle of polarization of light can be altered by a magnetic field. So light relates to electromagnetism!
Faraday passes the ball to Maxwell, who discovers that electromagnetic waves can travel through space without a medium at a speed that is equal to the speed of light that's already been calculated. Yes, it fits! Hertz now uses experiments to show that radio waves act just like light waves, displaying the reflection, refraction, diffraction and polarization properties. The waves now take the lead!
But the game's not over yet. Albert Einstein gets on the field now. He's going to try and explain the photoelectric effect- light striking a metal surface ejects electrons from the surface, and the energy of individual ejected electrons is proportional to the frequency, rather than the intensity, of the light. This is a point against the wave team.
Particle scores this one, but the waves are also a part of it. Einstein explains that light is composed of particles called photons, which have energy proportional to their frequency. In essence, light has both a particle nature and a wave nature, and various experiments can be done to bring out one or the other. Einstein calls this wave-particle duality!
And the whistle is blown!
The game is now over! Thanks for watching
This was quite the exciting match-up. The particles took an early lead, but then the wave team joined the fray and battled it out. Just when it looked like one team was winning, the other team took a swing back in. And at the end of the day, it looks like a tie game- light is both a particle and a wave!
And the Winner is: A tie! Wave-Particle Duality of Light!
Image Credit:Shreski, Allison91, Thomas Faivre-Duboz, guanno
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