You seem to be thinking of light as a transverse wave, depicted as a wavy line through space. That depiction is certainly inaccurate. Light does not move back and forth from side to side as it propagates from point A to point B.Heretoignore said:A pond lies flat when there is no wind, a river runs flat unless obstructed , a wave is not a wave without interaction. So is light before it hits something not a wave and a straight line instead?
You need to be careful about proposing unsupported personal theories. Have you read the forum rules?Heretoignore said:Light has no net charge in space, light only has a net charge when interacting with matter, light can only have a frequency when it touches something.
Light is composed of photons, and a photon is defined as a quantum having energy of ##hf## with ##f## the frequency. So, by definition, light always has frequency.Heretoignore said:light can only have a frequency when it touches something.
The wave in water is not produced by "hitting something". First you need to have a source producing the wave, like wind or a boat or some object moving in the water.Heretoignore said:A pond lies flat when there is no wind, a river runs flat unless obstructed , a wave is not a wave without interaction. So is light before it hits something not a wave and a straight line instead?
Excellent first post. Welcome to the forum.Richmonder said:You can't thoroughly describe a quantum phenomenon (light) using classical analogies (wave, particle). You can say that in some situations light behaves as a wave and in other situations it behaves as a particle. But light is richer in properties - light is light and if you want to describe it precisely you need to use the language of quantum mechanics.
Drakkith said:Well, if I observe a wave in one location, and then I observe what I think is the same wave in another location, why would I think that it wasn't a wave between point A and point B?
So you imagine that to be a "wave", something has to be a patterned mechanical motion of some underlying substrate, e.g. of the luminiferous ether?Heretoignore said:Between point A and point B there is nothing to propagate EMR.
Heretoignore said:Between point A and point B there is nothing to propagate EMR.
Would you be referring to CBR?Nugatory said:There is such a thing. It is an observed fact that electrical and magnetic fields can and do exist in a vacuum, and electromagnetic radiation is waves in these fields.
No. It's easy to produce hard vacuums in laboratories on earth, and it's easy to create and observe electrical and magnetic fields in these vacuums. For example, you can evacuate the space between the plates of a parallel-plate capacitor and then charge the capacitor... and there are many many more examples. Stuff like this was routine even back in the 19th century.Heretoignore said:Would you be referring to CBR?
[WARNING: The description below relies on an analogy. It will help you form an intuitive picture of what's going on, but if you want more than an intuitive "OK, I see how that could work" picture, you have to write down and solve the differential equations involved. If you try building on the analogy without checking it against the math, you'll probably be misled]c also remains a constant in a vacuum , there is no propagation?
Thank you for the informative post, however this does not explain something traveling at a linear direction at the speed of c without any obstruction . Is it not true that light slows down in a medium such as a cloud, a propagation of light?Nugatory said:No. It's easy to produce hard vacuums in laboratories on earth, and it's easy to create and observe electrical and magnetic fields in these vacuums. For example, you can evacuate the space between the plates of a parallel-plate capacitor and then charge the capacitor... and there are many many more examples. Stuff like this was routine even back in the 19th century.[WARNING: The description below relies on an analogy. It will help you form an intuitive picture of what's going on, but if you want more than an intuitive "OK, I see how that could work" picture, you have to write down and solve the differential equations involved. If you try building on the analogy without checking it against the math, you'll probably be misled]
Let's go back to your very first post in this thread, the one in which you said that a pond lies flat if there is no wind. That's not quite right - even if there is no wind, you can toss a small pebble in the pond and ripples will propagate away from the point where the pebble splashed in. These ripples move horizontally across the surface even though the water itself is not moving horizontally (a cork floating on the surface will bob up and then down as the ripple passes by, but it won't be pushed sideways). Thus, those ripples have a propagation speed; it's the speed that they move across the surface of the water.
Now, if I have electrical and magnetic fields in a vacuum and I do something to disturb them, there will be ripples in these fields just as the disturbing the surface of the water with the tossed pebble created ripples. Just as the ripples in the surface of the water spread out from the point of disturbance at some speed, the ripples in the electrical and magnetic fields spread out from the point of disturbance at some speed... and that speed happens to be ##c##. The one difference that you have to keep in mind is that a horizontally moving ripple in water makes the vertical height of the water increase and decrease (the cork bobs up and down) as it passes by, while a ripple in the electrical and magnetic fields makes the field strength increase and decrease as it passes by.
Heretoignore said:Thank you for the informative post, however this does not explain something traveling at a linear direction at the speed of c without any obstruction
Heretoignore said:Is it not true that light slows down in a medium such as a cloud, a propagation of light?
Heretoignore said:Is it not true that on the surface of matter light propagates to reveal spectral content?
Heretoignore said:Is it not true that air has a low refractive index and is transparent to light, light does not propagate in air ?
Heretoignore said:Is it not true that we do not see any spectral content (frequency) in air?
Heretoignore said:Is it not true that light passing through air is not seen?
Yes, it is true. The behavior of the electrical and magnetic fields are influenced by interactions with nearby charged particles including the ones electrons and protons that make up the medium, and this can affect the speed with which the ripples propagate. If we're going to keep pushing the analogy (but please do remember the warning in my earlier post)... water waves change their speed if we pour oil on the surface of the water, and electromagnetic waves change their speed if we introduce something other than vacuum.Heretoignore said:Is it not true that light slows down in a medium such as a cloud, a propagation of light?
Some matter does, some doesn't. Clear air doesn't reflect much of anything, a mirror reflects just about everything at every frequency, and many other things fall in between. None of this has much to do with the behavior of light in a vacuum (although you might want to to consider that all matter consists of particles with vacuum in between).Is it not true that on the surface of matter light propagates to reveal spectral content?
It is true that air has a low refractive index, but that means that it doesn't interfere much with light propagating through it. It's obvious that light propagates through air - otherwise you wouldn't be able to see anything because no light would ever make it to your eyes.Is it not true that air has a low refractive index and is transparent to light, light does not propagate in air?
Not true. Have you ever seen a sunset? For that matter, the sky is blue because different wavelengths interact differently with air. The effect is subtle enough that you don't notice it in a room with artificial lighting, or even in a ship looking at a lighthouse fifty kilometers away, but it's there.Is it not true that we do not see any spectral content (frequency) in air?
If it hits your eyes you will see it, which is why drivers are supposed to dim their high beams for oncoming traffic. If the light isn't aimed directly at your eyes, you'll only see what's scattered by the air so that it reaches your eyes and this may be a lot or little depending on the conditions.Is it not true that light passing through air is not seen?
phinds said:Excellent first post. Welcome to the forum.
Astronauts are not ''blind'' in space, in space there is no air. It is not so obvious that light propagates in space, Universally we can see through all of space, space is ''transparent'' to sight, space has no opaqueness , in this space we do not observe colour or frequency or a wave. (By sight not device).Nugatory said:It is true that air has a low refractive index, but that means that it doesn't interfere much with light propagating through it. It's obvious that light propagates through air - otherwise you wouldn't be able to see anything because no light would ever make it to your eyes.
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Drakkith said:I'm not sure what this means. Are you referring to how reflected light gives us colors and such?
Yes compression and decompression.nasu said:I have the feeling that you assign an unusual meaning to the word "propagate".
Look here at number 9. Is this what you mean when you use the word?
http://dictionary.reference.com/browse/propagate
That would be a "no" then. Light does not propagate by compression and decompression of a medium.Heretoignore said:Yes compression and decompression.
That is not what I meant or said, the refractive index of a medium is what decreases the speed of light is it not?jbriggs444 said:That would be a "no" then. Light does not propagate by compression and decompression of a medium.
Heretoignore said:Astronauts are not ''blind'' in space, in space there is no air. It is not so obvious that light propagates in space
Heretoignore said:How do we know it is not only a wave when light is being interfered with?
Heretoignore said:How do we know that '''white light'' is really a mixture of frequencies?
Heretoignore said:Could a prism simply not just be a result of a Center of pressure (C.O.M) , offset, the angular displacement of the prisms surface having effect on the radiation pressures force by angular distance travelled?
Heretoignore said:What mechanism would a prism have to separate a mixture of incident frequencies to from individual outputs of a wavelength?
Heretoignore said:Yes compression and decompression.
Thank you , I now see my error and why I was asked about an aether.nasu said:No, read again the definition, the part that follows after the closing parenthesis.
"to travelt hrough space or aphysical medium"
The words between parantheses are just examples of waves, they are not part of the definition so they are not a requirement to have propagation.
Not all waves have to do with compression but they all propagate.
To propagate simply means to "go" from one point to another. But rather than referring to an object it refers to a collective phenomenon like a wave.
Heretoignore said:I would ask you if the CBMR is the aether?
And the answer would be ... HUH? The CMB is the surface of last scattering. I has nothing to do with any kind of aether. Is that another word where you are perhaps using a non-standard definition?Heretoignore said:Thank you , I now see my error and why I was asked about an aether.
If I was considering the now known proper use of the term propagation , I would ask you if the CBMR is the aether?
Drakkith said:Of course it is. That's what propagate means. To travel through something.
We don't. We just have no reason to think that light stops acting like a wave when we stop observing it.
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Would you consider the actions of a Prism to be of a temporal flux?Drakkith said:Because we know how a prism works, and it doesn't work that way.
Ahhh... How do you think the light of distant stars makes it to your eyes, if that light did not propagate through the empty space between star and earth? Electrical and magnetic fields can exist in a vacuum, in air, or in any other matter, and where the fields exist there can be waves in them.Heretoignore said:Astronauts are not ''blind'' in space, in space there is no air. It is not so obvious that light propagates in space
We don't. We do know that the laws of electricity and magnetism, which were formalized in Maxwell's equations more than 150 years ago, say that there will be waves in the electrical and magnetic fields even when nothing is interacting with the propagating waves. We do know that centuries of observations of the behavior of light agree with the answers we get when we calculate what would happen if light is in fact a wave as described by these laws of electricity and magnetism. We do know that no one has ever been able to come up with any alternative that correctly describes the observed behavior of light. Putting all that together... The only sensible theory we have says that light is a wave in the electrical and magnetic fields and all the available evidence supports this explanation. That's as good as it ever gets in science.How do we know it is not only a wave when light is being interfered with?
You construct a light source that generates electromagnetic radiation with an appropriate mixture of frequencies, activate it, and see if the light that comes out is white. It is. Then you suppress some of the frequencies to get a different mixture, see if the light is still white. It isn't. That doesn't prove that white light is a mixture of frequencies, but it does support that hypothesis and it shifts the burden of proof to people who claim that they have some plausible alternative explanation.How do we know that '''white light'' is really a mixture of frequencies?
Can we use that model to correctly calculate the deflection of light of different colors (don't forget the stuff outside the visible spectrum, from radio waves to hard x-rays) when it encounters materials of different composition? And that agrees with all the other observations of light that we've been able to make over the centuries? The wave theory does all those things, and a lot more besides. For example...Could a prism simply not just be a result of a Center of pressure (C.O.M), offset, the angular displacement of the prisms surface having effect on the radiation pressures force by angular distance travelled?
Set up the wave equation for waves of various frequencies intersecting an angled surface, solve it, see you get. If you do the calculation right, you'll get a result that says the waves of different frequencies are deflected by different angles. Now check those calculated results against the behavior of a real prism. The results will agree to within the limits of your measurement accuracy.What mechanism would a prism have to separate a mixture of incident frequencies to from individual outputs of a wavelength?
Nugatory said:Set up the wave equation for waves of various frequencies intersecting an angled surface
Thank you for the interesting post, but what if we considered that the Sun releases an isotropic outward quanta ''stream''? a continuous flow of quanta with no spacing between quanta, would this not give an illusion of a wave and a speed?ogg said:@Nugatory. I'm doubtful that "hard vacuum" has EVER been created in the lab. Its a trivial point, but last I heard (long ago, admittedly) our very best lab vacuums were orders of magnitude dirtier than space. Your statement of course isn't false (whether I'm correct or not) since you didn't define "hard" vacuum. Last I heard, we need to get 100,000 miles or so away from Earth, to get a reasonably "clean" vacuum, and go out a hundred+ AU to get away from the Solar Wind, and then tens of thousands of lightyears to get to intergalactic space, and finally out millions of lightyears to get into space having density below the average density of the Universe (the Void).
The OP has been well answered, but I'd like to try to address the question in a different way: Thinking "Light is a particle" is wrong. Thinking "Light is a wave" is wrong. Light is light. We can DESCRIBE light AS IF it were a wave in some situations, and AS IF it were a particle in other situations (and as neither or both in others). We usually think of groups of photons as a wave or waves and single photons as particles (or quanta) (photons are the quanta of emr - we don't call them particles of emr (usually) because calling them 'quanta' helps distinguish them from the mathematical point-like particles in beginning Physics texts, and distinguishes them from the macroscopic stuff we see (and touch) all around us. A quantum mechanical particle is very very different from a rock or a grain of sand.) So, here is the question: if thinking "light is a wave/particle" is wrong, why do we describe it that way? The answer is: It is useful to think of light as a wave/particle in some situations because the mathematical treatment becomes much simpler. Its not clear, but is seems as if the OP thinks that the wave nature of light involves the path of a quanta to be wavy in space, moving to the left, then to the right (or up and down, or backwards and forwards). This is wrong. The wave nature of light is about the electric field and magnetic field oscillations and the way their change with time (or distance). Think of the pressure in a car's piston chamber. The pressure is a periodic function (a wave, although not a sine wave). So describing the pressure profile as a wave is accurate, but doesn't mean the car or the piston chamber or the gasses in the chamber are weaving down the road like a wave. So, I point out two errors: one: the MOTION of a photon is not ever "wave" motion; two: thinking of light at anyone instant as either a wave or a particle is wrong. Light is light. I also want to add that "light" is a word with many meanings. In physics it may mean "a photon", it may mean a group of photons, or it may mean a (very large) stream of photons. The (mathematical) models we use to deal with these different meanings are often quite different. We usually choose the model so that whatever problem we are working with can be handled most easily.
