Speed of Light Question.......VERY Difficult.

[Ring]

@Deeg

I’m confused too because if electromagnetic “waves” don’t have a 2D space how do they create interferences patterns?

It doesn’t seem like anyone answered your question.

You don’t need any physical extension to get interference because interference requires at least two wave fronts that intersect.

The interference evident in Young’s experiment (double slit) is due to Huygens principle and diffraction.

Huygens principle: All points on a wavefront serve as point sources of spherical secondary wavelets.

When a wave front reaches the slits the light is diffracted and acts as a point source of light that emits semicircular wavefronts. These wavefronts then intersect and when a point has a minimum field strength from one wave and a maximum from the other there is destructive interference and vice versa.

In QM the electromagnetic wave is the wavefunction (probability wave) for the photon and the same thing happens.

[Napier]

>amplified the intensity of my curiosity … explanation of polarization

Here’s an appetizing direction to head off in:

Radio antennas, which serve to move charge back and forth to cause electromagnetic radiation to occur, are a great way of thinking simply about polarization. That these have something to do with light is clear, when you consider the development of what are technically called “eentsy teentsy teeny tiny bitty little antennas” in semiconductor chips, that act as antennas to convert light into electricity without any photoelectric or photon effects.

Polarization can be linear, in the simplest case, but a slightly more complicated situation is circular polarization. If you can make vertically polarized radio waves by bouncing charge up and down, you can also make circularly polarized radio waves by spinning positive and negative blobs of charge around each other like ends of a baton. You can also do it with an antenna shaped like a “+” and giving the vertical arms and the horizontal arms signals that are 90° out of phase.

Lasers generally make polarized light. In the simplest case, which is called TEM00, all the field direction throughout the beam is alternately one way and then the opposite way. So-called randomly polarized lasers, like some HeNe tube lasers, also have this going on but the direction is not controlled and often flips and swivels about. Some lasers have more complicated modes, for example in a grid that is 3 regions by 4 regions the directions will alternate, which has other numbers after the TEM (I think it’s something like TEM34 but maybe a little more complicated).

Laser diodes, AFAIK, always make stably linearly polarized light in the TEM00 mode.

To turn linearly polarized laser light into circularly polarized light, you shine it through a wave plate, which is a thin flat piece of something like quartz that has certain electromagnetic properties. Gradually a secondary beam of light appears that has 90° different polarization, and it grows as strong as the first one, which is growing weaker. Now the light has circular polarization.

What is insight-giving about this is that the crystalline behavior of the quartz, which includes the stiffness and quantity of charge that repeats its organization periodically, is what causes this secondary beam to appear.

By the way, the index of refraction of a material, which represents the speed of “sound” only using electrical potential rather than pressure, and charge rather than air, can be approximately predicted from the dielectric constant and the density of the material.

[nd_n8]

@Napier

Lotta great questions and I want to interfere constructively with many of them.

Three big statements that will send some of the questions into new directions all at once: Photons aren’t balls and they don’t have surfaces with surface velocities with spin. And, observers can’t move at c. And, there is no real wave-particle duality. Well, let me reword that last one: when we refer to a wave-particle duality, though we may say radiation sometimes behaves as waves and sometimes behaves as particles, it would be more correct to say that radiation always does exactly the same thing, and we have two ideas, “waves” and “particles”, such that sometimes one seems more correct and sometimes the other does, but the problem is with the ideas.

Now, then, polarization. The drawings that illustrate how a wavy shaped sturdy rigid bent wire would fit through a wire grating are very irritating. They share several features with the real situation but also with the incorrect picture of two dimensional wave shapes being involved in polarization. This is most misleading. In polarized light there is some kind of order or organization to the direction in which the electromagnetic field is changing. Most simply, linearly polarized light, like what you see through Polaroid sunglasses, has all the field fluctuation happening in the same direction.

In radio, charge moving back and forth in an antenna creates the electromagnetic field radiating away from it. If the charge moves up and down, like it does in an AM radio station whose entire tower is a conductor, then the radio emission is vertically polarized.

When light goes through a transparent solid, it generally actually behaves as vibrations in the electrons and to a much lesser extend the nuclei of the atoms of the structure. This is why the nature of the solid influences the transmission of light. The electrons are very light and their connection to the rest of the solid gives them a high stiffness to mass ratio so the vibrations pass very rapidly. When light shines perpendicularly on a glass face, the vibrations it creates also create their own light headed back the other way, which is why you see a bit of a reflection. If you start angling the light further and further from perpendicular, at some point the vibrations in the surface caused by field strength variation in the plane of the incoming and reflecting beams will be aligned with the direction of the reflected light beam; that is, they will be trying to push and pull on the reflected light beam, if you will, and won’t have any transverse motion. At further angles their transverse motion is in the opposite transverse motion for the reflected beam. At the angle where we go through this minimum, none of the light waves whose field direction are in the plane of the beams have a transverse component in the reflected beam, and they aren’t reflected at all, and so only the perpendicularly oriented field waves are part of the reflected beam, which makes it polarized.

Hmm. This is hard to say well, and even harder when I should be going and am worried about the SDMB timing out. Maybe I’ll try again when there’s more time.

Hmm… Let’s see if I get this.

Non-polarized light travels away from the source in, lets say, a hemisphere of 180 degrees of the source. This range of this hemisphere is determined by the medium through which the light travels but let’s say the original medium allows for a 180 degree range.

When light passes through a lens of different properties of the original medium, some of the light passing through is coming directly from the source (although altered by the medium of the lens) and some of the light is reflected off of the surface back at the direction of the source. This reflected light changes the properties of the medium and alters the light coming from the source passing into the lens. The altered light passing through the lens has it’s own apparent point of origin separate from the original source and the interference it causes is commonly called glare.

Polarized lenses have properties on their surface to minimize or eliminate the light reflected from the surface and eliminate the multi-source interference thus the light passing through the lens is altered only by the original medium and the lens itself. So a visual representation would be less like the standard filtering representation (because without adding the reflected light there would be nothing to filter out) and more like this.

I guess my question then is: would light traveling through a perfectly void atmosphere already be polarized or would it be randomized somehow by itself? I think my diagram answers this but I just wanted to make sure.

[nd_n8]

Upon reflection of my diagram, it seems to me that the mechanism involved to inhibit reflection doesn’t actually stop reflection but instead phases it out with the wave reflected counter to itself so it has no impact on the incoming light. Is the angle of this phase the angle of polarization? Is this why two polarized lenses appear to darken when rotated one behind the other?

Ok, so if it is, then that is why as the angle of polarization approaches 90 degrees the light that does come through seems more and more purple (presuming a non-tinted lens). As the lenses become less penetratable only the slower, wider and stronger wavelengths squeeze through, thus near IR is filtered out almost all but completely and near UV is all that is able to penetrate.

[1010011010]

@GayIthacan

The speed of light is (roughly) 186,000 MPS from point to point. This is a straight line measurement.

But if light is a waveform - and waves contain varying degrees of VERTICAL movement within them - then does not this vertical component have to travel FASTER than 186,000 MPS? A wave, after all, is NOT a straight-line phenomenon.

And since different wavelengths of light have higher or lower vertical components to them, how can ALL of them be said to travel the same distance in the same period of time?

Because electromagenetic radiation isn’t a wave. It also isn’t a particle. We’ve discovered we can predict the behaviour of EMR with math that also deals with the behaviour of waves or particles, but light isn’t a wave or a particle… it’s something else entirely that we aren’t very good at conceptualizing because it has no macroscale equivalent.

[wevets]

Thanks! I think I understand it a little better now.

[Napier]

>Because electromagenetic radiation isn’t a wave.

1010011010, you miss the point here. It’s because the wave doesn’t involve motion perpendicular to the line of travel. Nothing in this picture travels faster than c.

The wiggles in the lines drawn while discussing light are graphs of electrical field strength, in volts per meters or some multiple thereof. Or, actually, they’re magnetic field strength graphs, in teslas. Either one, as the two are linked. But they aren’t geometric shapes.

Waves radiate through the surface of water, and if you look through a fishtank with waves, you see a wiggly line at any moment representing the water’s surface touching the graph. This is a real wave phenomenon and you can see it with your eyes. There actually IS a wiggly geometric shape, as well as its being a graph of the height of water. But this is one of the only wave situations in which there is actually a wiggly line involved. In the context of light, the fishtank analogy would be a confusing distraction. In the context of light, there are no objects or physical agencies that have wiggly shapes. It is only the human idea of drawing graphs that creates a wiggly shape.

There must be events in the stock market that make it bounce up and down a bit before things settle. So we draw wiggly lines. But it’s people fretting and fussing and counting their money and yelling at each other. The wiggly lines aren’t real, they are only a way of expressing ideas.

When air pressure fluctuates rapidly, you have sound, and it travels, and ears detect it, and you could graph pressure as a function of distance or graph pressure as a function of time and you would draw a wiggly line. But there are no wiggly objects at work. It is only our conventions of drawing graphs that generate anything wiggly.

When electrical field strength fluctuates rapidly, you have light, and it travels, and eyes detect it, and you could graph field strength as a function of distance or graph field strength as a function of time and you would draw a wiggly line. But there are no wiggly objects at work. It is only our conventions of drawing graphs that generate anything wiggly.

When gravitational field streng fluctuates rapidly, you have gravity waves, and… well, damn, you see the pattern here. 'Nuf said.

[Napier]

nd_n8, is that diagram actually yours? It’s visually stunning, for a quick discussion illustration. If we could pair that with some kind of correctness, the combination would be wonderful.

So, I didn’t make the polarization thing very sensible at all, and you didn’t get it.

http://physics.bu.edu/~duffy/semester2/c27_brewster.html does a better job. The point they are making is that reflection that involves the field vector being aligned along the direction of the reflecting beam will not work.

The Wikipedia article at Brewster's angle - Wikipedia also states things clearly.

How do these grab you?

[Napier]

By the way, common polarizing filters, like in Polaroid sunglasses and the ones you attach to a camera, are made by orienting molecular having the correct properties so that they are parallel to each other. This kind of polarizing film was invented by Edwin Land, who founded Polaroid around his invention, and then worked out instant photography (when they came out, I stupidly thought the Land cameras were supposed to be used on land).

Land made his first successful batch of polarizing film while he was friends with a fellow who later became a good friend of mine. Through our intermediate friend, I inherited a small roll of the film from this batch. It still works. From time to time I cut pieces from this roll and make gifts of them to technical people I work with who impress me especially favorably and whom I appreciate.

[nd_n8]

Napier - Yes sir, thank you sir, the diagram and all of it’s misconceptions are mine (maybe not misconceptions, but oversimplifications). I read both of your links and stepped outside for a quick smoke to think about them (and to look at light).

The sun was bouncing off of my car windshield and fenders with a dynamic glair pattern similar to the patterns I represented in my drawing. If I understand things correctly I was seeing a combination of reflected unpolarized and polarized light from the shiny objects, and mostly reflected polarized light (p-polarized if I understand correctly) from the duller objects (rubber on the tires). The reason that I am seeing mostly p-polarized light reflecting off of the less reflective surface is because of the irregularity of the surface on a molecular level, the light that is reflected back at me is parallel to the plane of incident but on a molecular level the plane of incident varies so there is less unpolarized light able to reflect back to the observer. On the surfaces with less variation on a molecular level more of the light is reflected and there is a combination of p-polarized light and unpolarized light bouncing back at me.

This connection occured to me as I turned to walk into the building and noticed that the image reflected off of the window had considerably less glare than the original image. My thoughts here were that the light bouncing back at me from the window was still a combination of p-polarized light and unpolarized light, but there was more p-polarized light visable due, again, to molecular irregularities in the glass causing more of the light to bounce back at me from the window at an angle of 2(θB). I stood there for a moment looking back and forth between my car windshield and the reflection of the windshield compairing the image and the light reflected by each source. Looking in the window was almost like looking through a polarizing lens due to a lack of glare. Once inside I found a mirror and held it up to look at the light bouncing off of my car again. The glare was more pronounced than the reflection in the window but still not as much as the glare off of the original source. So again I was seeing more doubly reflected light from the source than I was in the plate glass window (not doubly reflected exactly, it was a single reflection of light from a single source but two different visualizations of light affected by the surfaces).

If I am even close with this then I think I have an idea on how to visually represent the physical shape (or lack thereof) of light waves using a more correct (???) diagram of polarized light than the standard parallel lines gateing the light wave but requiring less technical background than the explaination of Brewster’s Angle. The parallel lines still gate the light waves and filter out the non-polarized light, allowing p-polarized light to pass through, but only when they are (roughly) perpendicular to the plane of reflection on the original source (I say roughly, pun intended, because molecular irregularities in the surface would make it next to impossible to filter out all unpolarized light).

Unless I’m still way off base here.