[ELI5] Why does light oscillate?

1.13K views

Maybe this is a stupid question, but I dont understand what force is driving photons in light beams to go up and down, making a sine wave. How often in which it oscillates determines the frequency yeah, but why does it do that in the first place? And why is it that when light is emitted, instead of scattering like individual particles, the photons stay in a line. Like there’s a force that is keeping them in a straight line, and theres a force causing them to oscillate. Maybe they arent forces, but I just don’t get it.

In: Physics

10 Answers

Anonymous 0 Comments

Well the reason they stay in line is because if you throw a baseball forward, its not gonna go and do a couple loop de loops and 360s because the force is making go in one direction.

Anonymous 0 Comments

Light behaves like any other EM wave. They have a Magnetic Field and an Electric Field that interact with each other. This allows each wave to vary, but everything sticks together.

The same principles at work in Radio waves, Microwaves, infrared, ultraviolet, visible light, X-rays, and gamma waves. We test for diffraction, reflection, refraction, and polarization to prove these are EM waves. This means, when it goes through an opening it moves similarly to a water wave, bounces back from some materials, changes direction through different materials, and have an orientation (Vertical or Horizontal).

Reference:

* [Star Gazer: What allows EM waves to oscillate?](https://stargazerslounge.com/topic/168496-what-allows-an-electromegnetic-wave-to-oscillate/)
* [Physics Classroom: Wave like behaviors of light](https://www.physicsclassroom.com/class/light/Lesson-1/Wavelike-Behaviors-of-Light)

Anonymous 0 Comments

The latest theory of our universe is not very intuitive (in fact, downright weird). Everything (and that is literally everything) is made out of waves. What we see as “matter”, atoms, etc are built out of things that are essentially waves. And these are not tangible or physical waves – these are waves of probability.

So there are a lot of things that are difficult to really understand. Photons are waves, so are electrons, and protons and neutrons are made out of quarks which are described by their wave functions.

Ultimately, it isn’t only light that is described by a wave but EVERYTHING is described by a wave function.

Anonymous 0 Comments

The oscillation of photons does not stem from a force. The oscillation is not movement as you would normally think of it. What happens is, an electric field collapses and forms a magnetic field next to it as it collapses. This magnetic field then collapses and forms an electric field next to it. This then collapses, and it goes on… There is nothing physically jiggling around – just fields popping into and out of existence in a sine wave pattern.

Anonymous 0 Comments

No photons don’t oscillate. There are 2 distinct ways of looking at light

1) Particle(photon)

2) Wave

When you consider light as a group of photons they do not exhibit any property of waves.

When you consider light as a wave they do not exhibit any property of particle.

Light is not photon and wave both. But in some cases it acts a particle and in some cases as a wave.

In some cases where light acts as a particle you might think that light can’t do this as waves can’t do this but light still does that totally not acting at all like a wave. But in other cases it will start acting like a wave and won’t show any characteristics of a particle.

Anonymous 0 Comments

The short version is that a photon is a travelling oscillation of electric and magnetic fields. **The key is that a changing electric field produces a magnetic field and a changing magnetic field produces an electric field**. The fields themselves are at right angles to each other a well as the direction of travel so lets say the electric field is up and down and the magnetic field is left and right while the direction of travel is forward. In this case the cycle looks something like this:

1. When the electric field is increasing upwards, it pushes the magnetic field to the right.
2. When the magnetic field is increasing to the right, it pushes the electric field down.
3. When the electric field is increasing downwards, it pushes the magnetic field left.
4. When the magnetic field is increasing to the left, it pushes the electric field up.

and you’re back at 1 so the cycle repeats.

This cycle of the electric and magnetic fields pushing each other back and forth as they travel forward together is fundamentally what light and all other forms of electromagnetic radiation is. All is needed is some event to cause a change in either the electric or magnetic field to start the cycle and the interaction between the two will take care of the rest.

Anonymous 0 Comments

The photon travels in straight lines and isn’t wiggling around like you see in some animations. That’s just a bad way of showing the wave nature of it.

For imagination purposes don’t think of waves in the ocean that have motion up and down as they travel across the surface. Think of light more like sound waves. Sound waves are oscillations just like ocean waves, but nothing is moving across the direction of travel because the sound wave is just a pressure front. It’s not a perfect analogy since sound travels in something, but light does not. The light is just the electric and magnetic fields alternately collapsing and inducing the creation of the other field which then collapses and induces…etc.

Anonymous 0 Comments

> And why is it that when light is emitted, instead of scattering like individual particles, the photons stay in a line.

Here photons behave similarly to particles – neither will scatter unless they collide with something. A particle in a vacuum will just keep traveling in the same direction.

Anonymous 0 Comments

Consider a guitar string. You pluck it. It oscillates at a certain frequency. That oscillation has has other properties unique to that particular frequency. The “force” that keeps it oscillating is its disruption from the linear state, the zero-energy point. It has energy, and until it converts that energy into some other form, that energy will keep it perturbed from the restful state, and it will keep oscillating. It wants to go back to zero, but can’t, so long as it has energy. This is like a particle.

Now consider a moving wave. For example, if you’re making your bed, you might send a ripple down your sheets as you toss them over your bed. That traveling ripple is a moving wave, transferring energy from one position to another in space. This is like a moving particle.

When a photon is emitted, it is literally a ripple in the field of space, transferring energy (the disruption from rest) from place to another.

Anonymous 0 Comments

Consider a [Mass-Spring System](https://thumbs.gfycat.com/GaseousPoliticalAlaskajingle-size_restricted.gif)

It oscillates back and forth. How and why? Gravity and the such right? But lets not worry about what makes it move and instead consider the energy balance.

At the peak, we have maximum potential energy, zero kinetic. In the middle we have maximum kinetic, zero potential. And at the bottom again max potential, zero kinetic.

Lets try to [Graph This](https://upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Simple_Harmonic_Motion_Orbit.gif/260px-Simple_Harmonic_Motion_Orbit.gif)

We see the position as it moves up and down on the Y axis, and we see the speed/velocity on the X axis. Notice that at max position (top or bottom) we have no speed, and at max speed we are at position zero (origin).

What the circle illustrates is the conservation of energy, and the X and Y coordinates indicate how that energy is being distributed between potential and kinetic energy.

Light behaves in the sane manner. Electrostatic energy is just a form of potential energy, and magnetic energy is just the kinetic form of electrostatic energy.

If youve seen maxwells equations, this should make sense. Why is there no such thing as a magnetic monopole? Because magnetism can only exist as electrons *in motion*.

So to answer your question, light oscillates because it is exchanging a set amount of energy between potential and kinetic energies in exactly the same way a mass-spring system does.

[Bonus Gif](https://i.redd.it/4tt857no9xr01.gif) heres how light really travels, and why people say it possesses “wave-particle duality”. Also shows what Eulers identity actually means