The speed of light and a straight line?

[jajrussel]

This is basically a question, but it deals with speculation, so I am not sure that this is the proper place to ask the question, but here goes.

 

I was watching a math video that said that when considering the orbital path of an electron we should consider the orbital motion more like a wave than a nice clean elliptical.

 

Other comments in SFN dealing with time and motion kind of made this question come to mind, which I will eventually get around to asking. I am assuming that the speed of light is a straight line measurement, with the assumption continuing that the photon is moving in a straight line path. We know that the path itself can curve and the photon can follow it. I believe the term is geodesic and we can see the effect through what I have read is called gravitational lensing. This happens on a scale that is easily observed.

 

There were the comments in another thread about light moving through a medium that has the appearance of slowing it down, but the actual reason being that the photon is interacting with the medium and that interaction takes time, the whole while light never ceasing to move at C, so the appearance is that it has slowed when it has not.

 

Then there is the photons particle and wave like qualities.

 

I am not sure if this clears up why the question entered my mind, and the truth is I had the explanation worked out better in my mind than I have presented it, but now to the question.

 

How do we know that a photon is moving straight? How do we know that it is not constantly changing direction, but much too fast for us to see it as anything but a straight line?

 

If it were constantly changing direction its actual path would be longer than than the straight line distance which I am assuming that c is based on, and this seems intriguing, but I could be wrong about the whole thought including how they have determined what c is.

[Endercreeper01]

It depends on if you are thinking of light as a wave or a particle. In a vacuum, as a wave, the wave is not a straight line, but as a particle, it would be straight. In a vacuum, there is nothing for it to interact with as a particle. As a particle, it wouldn't be like that because of special relativity. If the path was longer, then c would be greater then 299,792,458 m/s. This s not true because we have made measurements with special relativity and the Lorenz factor. If c was different, then the Lorenz factor would be different in the measurement, and therefore, special relativity (sing the value of c we have measured) would not be 100% accurate, and we would have to use a different c.

[md65536]

Not an expert but I'll try...

 

 

When we describe how light behaves it's not meant as a description of what it is "really doing", only the best description of how its behavior can consistently be measured. If we say it behaves as a wave or as a particle depending on how it's measured, it's because it consistently does either, and we don't have any better description of what it is doing that explains both at once.

 

As a wave it behaves not as though traveling on a line but as a wave front (spherically shaped), which is how you can get descriptions like "the wave seems to go through both slits in a double-slit experiment." Measurements consistent with it being a particle are consistent with it traveling in a straight line (or null geodesic as you mentioned, to be precise) and at an invariant speed c along that line.

 

So the reason we wouldn't say that its actual path is zig-zagged and faster than c, is that...

1) there's no theoretical prediction that it should, but there is a prediction from electromagnetic theory that it should travel at c

2) there's no measurement of light as a particle that is inconsistent with it traveling along the straight line path. There's no evidence that it does otherwise.

 

 

 

If you hypothesized that it traveled off of a straight line, and then were able to come up with a test that would have different results if it did vs didn't, then it might be tested and the answer decided. But unless there's such a test, there's simply no reason to describe light's behavior as a particle except that it travels along null geodesics, and adding anything to that would no longer be describing how its behavior is measured, but guessing about what it's "really doing", which is useless unless it's simpler or better than the current description, or has measurable evidence.

Edited November 12, 2013 by md65536

[jajrussel]

Thank you both for your replies. I haven't had time to consider the full implications of your answers, and considering that when it come to just about anything I am in a constant learning mode I have to look up just about everything. It would help If I had a better memory. One of the first things I looked up was the Lorenz Factor. In its description there is this explanation that I have included in brackets in order to help single it out, and it come from Wikipedia (β is the ratio of v to the speed of light c) this seems to indicate that the Lorenz Factor is factoring in a reference other than c. I realize that I still have a lot to learn, and that I may be taking part of the equation out of context since I have not entirely figured out why the Lorenz factor is necessary.

 

So, my first question does the Lorenz factor need apply to a particle of zero mass? Second, does the Lorenz Factor have anything to do with mass, as in have I taken the bracketed potion out of context, or is it a dimensional tool?

Edited November 12, 2013 by jajrussel

[DimaMazin]

Lorentz factor has no thing to do with quantity of mass.

[jajrussel]

I wasn't exactly thinking in terms of zigging and zagging. That is somewhat to two dimensional. I might little better reference it to a marble moving through a long straight tube. Our best observation says that it’s path is straight, but the marbles own qualities and other variances would show that the path where the marble makes contact with the surface of the tube is not straight and we might have to assume that there are points along its path where there might be no direct contact between the two surfaces.

But, even this references is poor for obvious reasons and the fact that the scale is much to large. With a photon we would have to divide time into very small increments in order to magnify and observe a minute direction change, so a direct observation would seem to fall into uncertainty. Mathematically it might be somewhat more easily predicted, but prediction does not make it so.

Theories are important. The time that it takes for something to get from point A to point B is important, but does this rule out vector changes? It simply says that in a straight line something has to move at a specific velocity to get from point A to point B. Since we can not make the observation we can only say that so far as we can tell it is moving in a straight line. So, if we can not rely on direct observation to give us an exact answer then we have to look for effects that might be more easily explained if a zero mass particle was constantly changing direction. If a zero mass particle were constantly changing direction our best direct observation would only indicate that it got from point A to point B at c, but then c is based on a vacuum which is a calculated existence which is to say it can not be observed.

Please note that I am not arguing with you here. Everything I am stating here are simply questions that have risen in my mind based on your answers. My questions seem reasonable to me, but that does not mean that my reasoning is right, and it certainly does not mean that your reasoning is in anyway wrong. It just means that for now I am having difficulty with it.

[swansont]

 

I wasn't exactly thinking in terms of zigging and zagging. That is somewhat to two dimensional. I might little better reference it to a marble moving through a long straight tube. Our best observation says that it’s path is straight, but the marbles own qualities and other variances would show that the path where the marble makes contact with the surface of the tube is not straight and we might have to assume that there are points along its path where there might be no direct contact between the two surfaces.

But, even this references is poor for obvious reasons and the fact that the scale is much to large. With a photon we would have to divide time into very small increments in order to magnify and observe a minute direction change, so a direct observation would seem to fall into uncertainty. Mathematically it might be somewhat more easily predicted, but prediction does not make it so.

Theories are important. The time that it takes for something to get from point A to point B is important, but does this rule out vector changes? It simply says that in a straight line something has to move at a specific velocity to get from point A to point B. Since we can not make the observation we can only say that so far as we can tell it is moving in a straight line. So, if we can not rely on direct observation to give us an exact answer then we have to look for effects that might be more easily explained if a zero mass particle was constantly changing direction. If a zero mass particle were constantly changing direction our best direct observation would only indicate that it got from point A to point B at c, but then c is based on a vacuum which is a calculated existence which is to say it can not be observed.

Please note that I am not arguing with you here. Everything I am stating here are simply questions that have risen in my mind based on your answers. My questions seem reasonable to me, but that does not mean that my reasoning is right, and it certainly does not mean that your reasoning is in anyway wrong. It just means that for now I am having difficulty with it.

 

 

If there were random direction changes that averaged out, you would then expect there to be distribution of arrival times of photons that started at the same instant. If the photons were in phase at the start, they would not be in phase at the end; there would be pulse dispersion not related to having a frequency width of the light. That puts a limit on how much "bouncing" there could be.

[jajrussel]

The marble and tube reference was poor.

 

Why random directional changes? Wouldn't that imply an uneven distribution of space that might be obvious if the photons were a large distance apart at the start but less obvious when closer to point A and in phase at the start?

 

Oh well, I have to take a nap and then go to work then I should have time to have a better understanding of what you mean by pulse dispersion.

 

Thank you.

[studiot]

What do you mean by 'a straight line' and why is it important to you?

[jajrussel]

I am interested in answering your questions, but for now I have to go to work.

[swansont]

The marble and tube reference was poor.

 

Why random directional changes? Wouldn't that imply an uneven distribution of space that might be obvious if the photons were a large distance apart at the start but less obvious when closer to point A and in phase at the start?

 

Oh well, I have to take a nap and then go to work then I should have time to have a better understanding of what you mean by pulse dispersion.

 

Thank you.

 

"Why random directional changes?" Um, you are the one who brought up changes in direction, and your analogy implied these were random. Why would they not be random?

[jajrussel]

 

"Why random directional changes?" Um, you are the one who brought up changes in direction, and your analogy implied these were random. Why would they not be random?

 

If this is the only problem you had with my reply I am a little puzzled?

 

 

 

If there were random direction changes that averaged out, you would then expect there to be distribution of arrival times of photons that started at the same instant. If the photons were in phase at the start, they would not be in phase at the end; there would be pulse dispersion not related to having a frequency width of the light. That puts a limit on how much "bouncing" there could be.

 

You answered my question which was, " How do we know that a photon is moving straight? How do we know that it is not constantly changing direction, but much too fast for us to see it as anything but a straight line? "

 

Thank you...

 

I do not consider the question to be speculative, but the thought that provoked the question I do. I could only allow myself to disagree with answers using none speculative points. I tried to remain within that boundary. Your answer was like a stop sign that I should have seen but did not because I was looking to far down the road. I was still tempted to charge full speed ahead, but the nagging thought of if you cant get past this answer that swansot has given, then the road ahead is not only going to be speculative it is going to zig zag, and bounce all over the place. So, once again thank you for pointing out the stop sign.

 

 

 

What do you mean by 'a straight line' and why is it important to you?

 

I found the idea to be intriguing and interesting. I still do. The only thing important to me about the thought is fixing the problems that arise because of the thought. By straight line; I meant as opposed to a geodesic. Though I may have been willing to play loose with the definition of geodesic by flirting with different possible causes.

[studiot]

 

What do you mean by 'a straight line' and why is it important to you?

 

I found the idea to be intriguing and interesting. I still do. The only thing important to me about the thought is fixing the problems that arise because of the thought. By straight line; I meant as opposed to a geodesic. Though I may have been willing to play loose with the definition of geodesic by flirting with different possible causes.

 

 

I asked because we gloss over the question 'what is a straight line'.

 

It is interesting to note that Newton, for instance, did not actually mention straight lines, although N1 and N2 are often couched in terms of a 'straight line'.

 

N1

 

Every body continues in its state of rest or uniform motion in a right line, unless it is compelled to change its s tate by forces impressed upon it.

 

N2

 

The change of motion is proportional to the motive force impressed, and is made in the direction of the right line in which the force is impressed.

 

 

 

[jajrussel]

 

I asked because we gloss over the question 'what is a straight line'.

 

 

 

 

Can I assume that when you say "we" you are not speaking of yourself in plural?

 

 

 

 

It is interesting to note that Newton, for instance, did not actually mention straight lines, although N1 and N2 are often couched in terms of a 'straight line'.

 

N1

 

Every body continues in its state of rest or uniform motion in a right line, unless it is compelled to change its s tate by forces impressed upon it.

 

N2

 

The change of motion is proportional to the motive force impressed, and is made in the direction of the right line in which the force is impressed.

 

 

 

 

Newton was a Mathematician. I can not read his work. It is in a language I can not understand. I can rely on translations and hope that they are correct and that the translator has no agenda in the translation. Then I can try to make sense of what is being said. If one has an agenda one might accept and present a view that is not true because the presentation is not in agreement with the original statement. It starts at a point somewhere in the middle of the original meaning then transcends.

 

I would guess that Newton was using language that he knew would be understood by the ones most interested in his work at the time. If he did not use the word straight I can only assume that he had no reason to do so. Perhaps he used a word that made a better, or similar presentation of his meaning knowing that those reading his work would know his meaning.

 

With N1 I see a straight line. With N2 I see three straight lines. I realize that it is more complex than what I have stated and the number of straight lines I see for both N1, and N2 can increase if I want to consider different perspectives, and points of view, and now that I am thinking about it I am convinced that a straight line is more complex than a right line, so it seems to me that what you are saying is that the meaning of a right line is what has been glossed over and that you think the term straight line is a poor substitution, but I do realize that this is not what you wrote. I admit that I am easily confused and I apologize for having read something into what you have written other than your intent.

 

I see lots of points of interest, would you care to expand on the ones you have mentioned, and perhaps doing so eliminate some of my confusion.

Edited November 14, 2013 by jajrussel

[jajrussel]

I have been thinking about it , and I might be coming across as flippant and rude. If I am I am sorry, because I do not mean to. I have been told that my communication skills are lacking, and I know for a fact that I would not make a very good cheer leader. One look at my face and the interviewer would say, " yeah right, next.."

[studiot]

I have had problems with the comments of some here, but not with any of yours that I've seen. No need for apology there mate.

[decraig]

jajrussel,

 

On electron orbitals: The modern idea of an electron orbital is more like the vibrations of a drum skin.

 

You hit the center of the drum, and the whole skin vibrates up and down. If you hit the drum off-center, the half you hit goes down. Then it oscillates. Half the drum head goes down while the other half is going up. These are fairly good models of the lowest energy states of an electron orbital (yes, they are still called 'orbitals') corresponding to the S1 and a P orbital. More complicated arrangements of these standing wave vibrations are possible.

 

An even better model of an orbital would be air vibrating inside a hollow sphere.

 

----------------------------------

 

The idea of photons as propagating particles doesn't work very well in quantum mechanics. 1) Things propagate as waves and 2) display a particle nature only on interacting or being measured. The one exception is an interpretation of quantum mechanics known as Bohmian mechanics. Even in this model, particles are guided by extended fields filling up all space.

 

As for taking zigzag paths, swansont may have been hinting at a theory called quantum field theory. In this theory, in getting from point A to point B, a photon takes all possible paths. So our 'photon' is a field spread-out everywhere. Added up, and averaged out, it can look like a classical straight line trajectory.

 

 

Despite the almost universally held belief, the speed constant, 'c' is not the speed of propagation of light in a vacuum, but an idealization. Take an ordinary beam of laser light so we get some simple and well behaved waves. We measure the wave velocity, called the phase velocity, by how long it takes for a peak or trough to pass from one point to another over an interval of time. We measure the "group velocity" (a group of oscillations), by measuring how long a group takes to go from one point to another.

 

Only in one direction, along the axis of the beam, do both the group and phase velocities have a speed of c. In any other direction the phase velocity exceeds c and the group velocity is less than c. A wave guide is a good example of this variation and for the very same reason.

 

Velocity is multivalued function of direction.

Edited November 19, 2013 by decraig