the travelings of a photon


So I know that photons travel in waves, but is that like a straight up and down wave? Or is it more like a cork screw?

Why not just straight? I’m guessing the rudimentary answer has something to do with energy?

How do we know this?

In: 6

It doesn’t *actually* travel in waves. It just *acts* like it does when there’s a bunch of them.

A single photon will go in a straight line.

So photons aren’t “just” waves. They are something called a “wave-particle duality”, and that’s not a great scale to talk about wave motion. Where you actually get the single direction wave behavior is when you aggregate photons together, then they exhibit wave behavior quite a lot, which is where we get the descriptions of light as a wave.

It’s funny, because it can actually be *both*. The term for the “direction” that the waving happens in is called “polarization”. Light can be up/down polarized, left/right polarized, any angle in-between the two, and also it can be the corkscrew, also called “circular polarized light”.

If you’ve ever seen “polarized filter sunglasses”, you’ve seen how we can measure this.

It can’t be “just straight” because then you wouldn’t have any oscillation, and wouldn’t be a wave. An electric charge moving just straight does exist, but it’s an electron, and electrons aren’t light.

The corkscrew can happen because the direction of the polarization can change if you have multiple electric fields perpendicular to each other. And if it’s just right, you end up with the circular corkscrew.

A photon is a localized disturbance of the electromagnetic field.

What does this mean?

Well, when magnetic force builds in one direction, electrical field strength wanes in another direction, one which is normal to the magnetic field’s line of force. When magnetic field strength peaks, electric field strength is nil, the cycle reverses, with magnetic and electric fields bouncing energy back and forth between the electric and magnetic fields, kind of like two adjacent layers of frictionless Jello, each occupying a
its own distinct domain within the electromagnetic field.

Though instantaneous in origin, the photon propagates as a wave-front, a discrete series of oscillations (Jello wiggles) of both finite amplitude and frequency.

A photon could be a short but powerful gamma ray of a length not bigger than a proton. Or a photon could be a kilometers’ long radio wave.

A good analogy for the photon would be a packet of wiggles. In other words: a particle.

Photons come into existence instantaneously as if someone were to pluck the center of a Jello-filled swimming pool.

Each wiggle packet conveys a finite amount of energy to whatever it interacts with, according to how much wiggle the packet has. More packets deliver more wiggles, and thus more energy.

As a field disturbance, the photon propagates in all directions, like the wave from a stone thrown into a pond.

When this wave encounters the double slit for instance, it forms two beams of new origin. Light which diffracts off the sides of each slit interferest with itself to create an interference pattern on a target screen. Attempting to measure photonic energy as it passes through a slit disrupts the photon’s characteristics, eliminating it’s potential to interfere with the version of itself which transited the other slit.

This is why you get a diffraction pattern, even when you send just one photon at a time. And this why when you try to measure a photon’s passage through the double slit, its interference pattern disappears.

It isn’t a wave any any direction like a wave of water. It’s a wave of *probability* which we visualize as a wave of stuff. At the quantum scale, location isn’t really a *thing* for particles most of the time. They don’t occupy one place, they are kind of in all places they could possibly be, at the time time. They’re only in one place when you go looking for their location and measure that.

The top of the wave is the place where you’re most likely to find that particle when you go looking for it. I *can* be anywhere else, it’s just more likely to be in some places than in others. It’s kind of like the wave seen in a [probability graph of rolling dice]( You can see that certain sums are more likely with two dice, so you get that nice bell curve. That’s the wave you see for a photon: at any particular point in space, you’re more or less likely to find a photon in that space.

Now, it gets a bit more complicated when you start talking about *polarity* but it’s still not a physical wave of *stuff*, just a measure of the probability of finding a photon.

> So I know that photons travel in waves, but is that like a straight up and down wave? Or is it more like a cork screw?

Both can happen. The technical term is _polarization_, where we call the up-down (or left-right, diagonal, etc) one _linear_, and the corkscrew one _circular_. The basic ones are vertical, horizontal and circular, and if you “combine” any two in the right way, you can end up with the third. For example, if you have something waving left-right, and now add up-down movement to it, you either get diagonal movement, or a circular pattern, or more generally an elliptical one (like a quenched circle).

One can even filter for the photons of a certain kind in a rather naive way: make some minute opening only such photons should pass through. If you have lots of very fine vertical slits, you filter for that polarization. Same with horizontal. If you want to filter for circular, you can use tiny corkscrews.

Note that corkscrews come in two kinds, or _chiralities_, clockwise and counter-clockwise turning. Those are different polarizations as well, and you have to consistently use the same type for the filter.

As a side effect of combining the waving motions, those corkscrews also slightly turn vertically polarized light a bit in their direction. Some basic molecules such as sugar are famous for this, you can measure the sugar content of water by how much it “turns” light.