why does light have a finite speed

@cheeser,

cheeser wrote:

actually i am going to pull a u-turn, can someone please verify this, i think that radio wave photons as a for instance, are intrinsically different from gamma ray photons so i think the photon must have a frequency associated to it.

Kind of. It's electromagnetic waves that have a frequency. And you're right, gamma radiation does have a different frequency than radio waves. But photons, as particles, have an energy and a momentum associated with them. Quantum mechanics tells us how to translate between the wave's frequency and the particle's energy and momentum. But since you said you want to keep things simple, you should ignore quantum mechanics for now. Instead, you should focus on understanding light as an electromagnetic wave, which is the way classical physics treats it. Forget about photons for now.

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@Thomas,

Quote:

Instead, you should focus on understanding light as an electromagnetic wave, which is the way classical physics treats it. Forget about photons for now.

Tom thanks but to save me a half hour scrolling Google don't these waves travel as an oscillating concentration of photons

The concept has always baffled me. Isn't the only diff between gamma and radio waves their frequency

And to get back to the original q, isn't there an intuitional notion why the speed of light has to be c and not some other value; also, has it yet been settled whether the photon has mass

In the foregoing connection, if it's no trouble could you review

http://able2know.org/topic/187876-1

Evidently I didn't get the idea across, but I wanted to show a means by which the otherwise peculiar behavior of a moving object could easily satisfy the intuition. It has met resistance where the typical respondent assumes I'm trying to refute relativity whereas I'm only offering another way of looking at it

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@cheeser,

First, in quantum mechanics EVERYTHING has an associated wavelength, even you!

To the original question:
You are really into territory where you need a more substantial background in science to be able to understand what is happening. For example, strictly speaking the qualitative way to answer via Special Relativity is that light DOES have an infinite velocity – according to the photon. As someone told you the photon doesn’t experience time. WE see it as moving at c. What you observe depends on your frame of reference. So in relativity if you want to say the photon is moving infinitely fast, it is assumed you are talking from the position of the photon and we plug a “c” into our equations (if not Relativity can’t play your game, and is mute). Relativity doesn’t decide which is the “correct” reference frame it is simply a method for being able to convert calculations to and from the different frames of reference.

So there are much deeper levels to this question than it may seem to you.

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@Zarathustra,

Quote:

…..you need a more substantial background in science…...

You can say that again
However at 81 by the time I've absorbed what I need it will be dime to doon and dee so I keep hoping somebody will explain the whole thing in short sentences and common words suitable to the Average Clod (me)

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…….. light DOES have an infinite velocity – according to the photon.

It was exactly my assertion that to understand shrinking, slowing, mass gain, and the apparent limitation c, we assume the viewpoint of the moving subject; that is, that the stationary observer back home is merely underestimating his speed; so your reply is encouraging

However the idea of an infinite velocity is intuitively troublesome--at least to me--and so I propose instead that the speed of light instead be viewed as many (many) times c. This way of looking at it allows for slightly faster velocities--eg neutrino

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As someone told you the photon doesn’t experience time.

I was thinking of the moving object as a fellow in a rocket ship. Everything of course seems perfectly normal to him

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…...if you want to say the photon is moving infinitely fast, it is assumed you are talking from the position of the photon……

Exactly the viewpoint of my "crazy" concept that I called "relative relativity". But it met much resistance from those who insisted c was absolute

Yet being able to assume the Photon's frame easily satisfies the intuition's need to explain for those apparent relativistic effects. I deviate only slightly from your interpretation by imagining each of us in his own concentric universe (see my post #…099 above)

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Relativity doesn’t decide which is the “correct” reference frame…...

But doesn't your (our) viewpoint somewhat contradict the usual interpretation.

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So there are much deeper levels to this question than it may seem to you.

Not at all, I think we're on the same track though I concede yours is deeper by far than mine

Still the OPq remains why the specific distance between concentric spheres

1 Reply

@dalehileman,

dalehileman wrote:

Tom thanks but to save me a half hour scrolling Google don't these waves travel as an oscillating concentration of photons

No, they don't. You're confusing light with sound. Sound waves do travel as an oscillating concentration of air molecules, or water molecules, or whatever the carrier material is. Lightwaves, by contrast, do not need any carrier material. An oscillating electro-magnetical field is all it takes to propagate one.

dalehileman wrote:

Isn't the only diff between gamma and radio waves their frequency

Yes it is.

dalehileman wrote:

And to get back to the original q, isn't there an intuitional notion why the speed of light has to be c and not some other value;

Not really. We know why it's finite --- because it takes time for the electrical field in one location to induce a magnetic field a little further down the path, and vice versa. But given that it's not infinite, it has to have some finite value. Why 300,000,000 meters per second? I can only answer that with a question: Why not? It has to be something.

dalehileman wrote:

also, has it yet been settled whether the photon has mass"

No. And if the photon does not, indeed, have a mass, it will never be settled, because no experiment can establish that. All an experiment can establish is an upper limit to its mass.

dalehileman wrote:

In the foregoing connection, if it's no trouble could you review

It's nonsense --- sorry to break it to you. You have failed to articulate an intelligible physical theory. And to make a more general point about intuition: Human intuition has evolved to deal with medium-sized objects moving at medium speeds. Trying to reconcile relativistic phenomena with intuition will almost always mislead you.

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@dalehileman,

Let me try to be diplomatic and say that I see your posts as philosophy not science. When viewed in that way I can kind of follow some of the things you are saying but I can’t determine the importance or any noted consequences of any of it.

How does your infinite velocity idea handle the fact that it is just as correct to say from the photon’s point of view it is not moving at all, or to say that it is everywhere on its entire world-line at once. All of these are just as valid interpretations for the photon. What point of "concentric circles" when nothing moved i.e. zero velocity?

I’ll pass on attempting to explain the world-line reference but zero velocity is easy to understand. By definition velocity is distance covered in unit time. For the photon t=0 always so any velocity you want times zero is zero and hence no movement at all let alone infinite velocity AS EXPERINCED by the photon.

What is the correct answer: it is RELATIVE to the frame of reference. Personally I have never done a calculation involving light where I was in any way concerned how the light felt about it :-)

Also, a strong understanding of scince doesn't require credentials in any way but training certainly can help.

1 Reply

@Thomas,

Quote:

Lightwaves, by contrast, do not need any carrier material.

You're evidently 'way beyond me as I don't consider space a "carrier material"

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because it takes time for the electrical field in one location to induce a magnetic field a little further down the path, and vice versa

Yes, no, Tom, that's in fact very interesting

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It's nonsense --- sorry to break it to you.

Quite all right, very common reaction

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You have failed to articulate an intelligible physical theory.

I wasn't trying to. I was attempting merely to articulate another way of looking at it

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Trying to reconcile relativistic phenomena with intuition will almost always mislead you.

It's worth a try

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@Zarathustra,

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Let me try to be diplomatic and say that I see your posts as philosophy not science.

Relativity is a sort of philosophy, no need for diplomacy

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How does your infinite velocity idea handle the fact that it is just as correct to say from the photon’s point of view it is not moving at all, or to say that it is everywhere on its entire world-line at once.

That's one reason I backed off its velocity as infinite and suggested instead that is much much greater than c

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What point of "concentric circles" when nothing moved i.e. zero velocity?

It gives us a point of view, satisfying the intuitive puzzlement of otherwise strange behavior of the moving object, eg, it appears to be shorter because the light from its front and rear end arrive here simultaneously

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I’ll pass on attempting to explain the world-line reference……..no movement at all let alone infinite velocity AS EXPERINCED by the photon.

Instead Joe is driving a very fast rocket ship. Yes he's entitled to consider himself stationary with the rest of the Universe flying past

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Personally I have never done a calculation involving light where I was in any way concerned how the light felt about it :-)

No, yes, Zara but it's instructive to look at things from Joe's viewpoint

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Also, a strong understanding of science doesn't require credentials in any way but training certainly can help.

I admit to skimpy credentials

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@dalehileman,

dalehileman wrote:

You're evidently 'way beyond me as I don't consider space a "carrier material"

Neither do I. That's my point. Light does not need one.

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It should also be pointed out, for the sake of this discussion, that even though light *behaves* like a particle and a wave, it is neither. It is something entirely different which simply *behaves* like those two things. We just don't have a word for the concept of what this might be, so we try to pigeonhole it into either of those two categories, even though neither of them is entirely accurate.

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@dalehileman,

"Relativity is a sort of philosophy..."

This is one thing that is absolutely incorrect. Relativity is quantitative physical science. You may choose to opine philosophically about Relativity, but it is, in no way of common usage of the term, a philosophy.

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@Zarathustra,

So what defines velocity, why exactly does mass, energy, space and velocity have the relationship it has. Is there an answer?

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@Thomas,

"But since you said you want to keep things simple"
When did I say that?

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@cheeser,

cheeser wrote:

"But since you said you want to keep things simple"
When did I say that?

You didn't. I inferred it from what you said here:

http://able2know.org/topic/200238-2#post-5141980

which seemed to imply you're a bit overwhelmed. Ignoring the quantum-mechanical side of light is one way of not getting yourself overwhelmed, because it helps keep things simple.

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@Thomas,

Fair enough

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@dalehileman,

Quote:

You're evidently 'way beyond me as I don't consider space a "carrier material"

Light used to be thought to be propagated through something called the aether. It was also said to be a light carrying medium. Kind of how sound is propagated through a medium - air. Alot of testing was done in the 19th century to try to verify how the medium worked. One theory of the aether was even assumed by Maxwell and he was probably thinking about it when he published his papers on electromagnetic radiation. It is pretty much a dead theory now but is very interesting to read about. It was disproven by experiments that tried to detect different speeds of light as the Earth moved through the aether(see Michelson Morley Experiment).

We think of light now as being able to propagate itself through space and other materials which is probably how you are thinking of it.

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@Thomas,

Quote:

Not really. We know why it's finite --- because it takes time for the electrical field in one location to induce a magnetic field a little further down the path, and vice versa. But given that it's not infinite, it has to have some finite value. Why 300,000,000 meters per second? I can only answer that with a question: Why not? It has to be something.

I don't think it is fair to say we know that it takes time for an electric field to generate a magnetic field in an electromagnetic wave. I have never heard that. What experiment could we do to verify that? I have heard the that electric and magnetic fields generate each other in maxwell's theory but I always took this to be instantaneous since their vectors are perpendicular to the line of em wave propagation at any point on that line.

But I am with you on the speed of light. It cannot be infinite. To many things would have to happen. There would be no explanation for the delay of a signal over long distances.

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@tomr,

tomr wrote:

I don't think it is fair to say we know that it takes time for an electric field to generate a magnetic field in an electromagnetic wave. I have never heard that.

Then you need to learn the Maxwell equations and how to solve them for an electromagnetic field in a vacuum.

1 Reply

@Thomas,

Solving for Maxwell's equations does not give us a relationship for a time delay when generating a magnetic field from electric fields or vice versa on the same point in space where they both exist. See the following link:

http://www.scribd.com/doc/32880088/Electromagnetic-Waves

See page 1082, the optional section for the derivation of c. Where do we come across a delay in the creation of either a magnetic or electric field?

See page 1081, in the bold text the equation E/B =c says that the ratio of E to B always equals the speed of light at any instant in time. If there were a delay the ratio would not hold at the point where you are generating the E or B fields.

1 Reply

@Thomas,

Quote:

Light does not need one.

I'm not sure, Tom, that's been conclusively decided. Don't some thinkers still maintain a strong case for light as an oscillation of space (See Tomr #…565)

After all gravity waves seem to travel that way

2 Replies

why does light have a finite speed

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