By Lambda

2016-09-07 00:23:01 8 Comments

I'm new to the forum. So I'm not sure how a question like this will be received, but it's a sincere question that I have wonder about often.

Let's say on a nice summer evening I shine a red laser across my backyard. What if I could freeze time and walk up to a portion of the wave as it traversed the yard. What if I could really examine it, say enlarge the beam so all its components down to the photon level were visible or measureable. Would I see textbook looking sine waves. Would it be billions of little waves. Would each wave have width and height. Would I be able to identify its parts. "Oh, look, there's a wave. Look there's a photon".


@Gordon McDonald 2017-02-16 10:32:08

Some researchers in Austria decided to take a picture of the electric field of a short pulse of light. They took an image of the electric field of light going up and down as a short pulse of light went past, by looking at how it deflected nearby electrons.

Image of Light Pulse

Source: Goulielmakis et. al. "Direct Measurement of Light Waves", Science, Vol. 305, Issue 5688, pp. 1267-1269, 2004. DOI: 10.1126/science.1100866

@HolgerFiedler 2016-09-07 19:36:33

How your laser works

It is common sense that electrons get pushed into higher energy levels and synchronous falling back in lower energy level and by this synchronous somehow emit photons. This photons get reflected between two mirrors, but one of them let some amount of this photons through. This artful designed device creates a beam of photons with nearly the same frequency and focused in parallel directions. So you get a coherent (more or less) stream of photons

How a radio wave is created

To recognise this is important, because this type of EM radiation often is called an EM wave. In reality it happens something that is in the result similar to the lasers emission of photons. A lot of electron get accelerated in the antenna rod and by this more or less synchronous emit photons, but this time in a broad range of wavelengths. Since the electrons get accelerated for- and backwards in the rod the intensity of the emission is swelling and the electric as well as the magnetic component of the EM radiation has the properties of a wave. It is well understood that in the nearfield of the antenna the electric component is perpendicular to the magnetic component and both are perpendicular to the direction of propagation of the emitted photons. It has to be underlined that the two components are shifted by 90° to each other.

What is a photon

To explore the full behaviour of a single photon is until now impossible because of the slowness of the observation instrument. But it is possible to conclude from behaviour of the nearfield of the radio wave to the behaviour of single photons. Each of the emitted photons has the same properties as the whole emission:

  • two field components, an electric and a magnetic
  • both 90° staying on each other (in vacuum)
  • both shifted by 90° to each other
  • both ( in vacuum) directed 90° to the direction of the photons propagation

enter image description here

So if you are able to "float" with the photon through space you will see a swelling electric and a swelling magnetic field component.

@Lambda 2016-09-08 00:38:38

Thank you for that complete response. I can picture that in my mind, two alternating spheres, electro and magnetic, each one gaining a radius in distance as it grows out of the prior dying field. I guess the questions are endless, but please allow me one more. Is that process all together the photon. In other words, is the light wave a photon or does the photon live within the wave perhaps at the wave crests or along the k axis? Maybe the photon is just the sum of the energy in the wave so the energy of the photon rises and falls with the fields?

@HolgerFiedler 2016-09-08 04:58:24

An electric bulb emits photons of different wavelengths. This we call an electromagnetic radiation. What behave like a wave with moving crests are radio waves where an antenna generator periodically induces EM radiation. In the far field of the antenna this periodical radiation is approx. a plane wave, but again is made of zillions of photons. Photons are indivisible units with swelling electric and magnetic field component.

@user108787 2016-09-07 00:37:05

No, unfortunately you will not be able to see what is purely a math description of something that is impossible to visualize. I can't tell you what you would see, because I can't visualize it either.

Here is one common example of how we use mental pictures:

enter image description here

It's a graph/picture of time versus velocity, but you know it's only a representation, that the 45 degree line at the start represents acceleration, and is really not a hill.

Imo, because I am not an expert, it would be exactly the same as if I told you I knew exactly what an electron "looked" like. Would you believe me? What questions would you ask me before you made up your mind? I would be telling you that I could see a "thing," that mathwise needs to go around twice before it gets back to its starting point, that can be linked with another electron and change its properties, as soon as the first electron changes, no matter how far away it was and completely ignore the speed of light. Also, mathwise only, it can be in more than one place at the same time.

enter image description here

Now here is a picture of an electromagnetic wave. The fields are shown as plane surfaces, at right angles to each other, but the real electric field is not a bit like that. It has depth and it weakens when you move away from the plane of the arrows, but we can't really draw pictures like that, especially in 2 D. A 3 D model would be better, but it's still not the proper picture, because there really is no full representation of the quantum world, using classical pictures.

These are just analogies so we can work more easily with the math that really describes them. We need mental pictures, in order to try and understand the quantum world better, and we can't resist thinking of things in 3 D terms because that's what we are used to.

@user12029 2016-09-07 01:53:21

If you got a tiny van de graff generator and turned it on for a bit so that it was charged, and went around measuring the force on it, you would see and feel the electromagnetic field. Saying it is a "mental picture and we can't really understand it" is throwing in the towel way prematurely.

@user108787 2016-09-07 02:05:24

@NeuroFuzzy hey, I am not a quitter :). I meant we can't really understand in pictures, as the OP wanted to know.. I worded it badly perhaps, but I won't pack my bags on trying to understand. Btw where did I say mental picture and we can't really understand it, I can't see it in my post. A bit unfair to quote something I didn't actually say or even imply.

@Burrito 2016-09-07 01:11:41

Great question. I'm a junior undergrad physics major, and I know it's one thing to take what teachers tell you and understand it well enough to solve problems, but quite another to understand it well enough to satisfy one's own curiosity.

Let's begin with "Look there's a photon." This sounds fishy to me, since you see objects when photons emitted or reflected from them enter your eye. You could say you never actually see objects, just photons (but then you're talking philosophy, as Feynman says). Thus to see a photon it has to be in your eye. You can't point it out to someone. That said, if you are small enough and appropriately calibrate your retinas, you would see the light one photon at a time (Can a Human See a Single Photon?). I suspect it might look like a red dot, but of course, what it looks like to us is probably more a question of biology than physics. Suppose your laser were ultraviolet instead of red, then you wouldn't see anything at all, but it's still there.

As for the waves, you wouldn't actually see them since these are oscillating electric and magnetic fields. However, if you have the proper equipment, you could plot their strength at every point and see them this way.

@Lambda 2016-09-07 03:39:44

Thanks to everyone for your answers. I read each response several times. It would have been nice if there was a clear answer to the question, but that's not the case. At least now when I ponder the question I'll know there is just not an easy answer, but then, unfortunately, I will say to myself, but, nevertheless, I would see something. What would it be?

@user108787 2016-09-07 04:50:19

@Lambda If it was all easy answers, you would have nothing to ponder : ). Personally, I like physics just the way it is, not too easy, but not impossible, just knowing a bit more so you can go " oh, yeah, so that's how it works", every so often. Thanks for a good question.

@Lambda 2016-09-07 04:54:58

I agree 100%. Well said.

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