How Light Regains its Velocity After Passing Through a Denser Medium?

Also, I once wrote a blog entry that touched on some of this stuff, if you're interested. You may come across things you don't understand in the post, but I try to give colloquial explanations along the way. At the very least it's an attempt at answering your question about particle/wave duality.

http://cr4.globalspec.com/blogentry/2237/Fermions-and-Bosons

ga. concise.

Lot of discussion already took place on the topic and off the topic. I am not an expert on light but in simple terms I want to explain "how does the light beam gets acceleration to achieve its original speed once it gets out of the glass surface" with following example:

Suppose I am going on a flat road in a car with a particular constant speed, say 100 km/h, keeping accelerator at constant position. Now suddenly on the road a uniform gradient of say 30 degrees came. Even though accelerator position is fixed, speed reduces because of more resistance from the gradient. After crossing the inclined road again flat road comes and car regains the same speed as earlier because resistance is over. I think the same analogy applies to light. Molecules of glass are offering resistance while light is passing through it, so speed is reduced. Experts pardon me, if wrong.

I gave you a GA, and I'd add (as explained by others on this thread)--the "gradient" is due to energy from the light beam causing electrons to vibrate (or vibrate faster).

Here is why your analogy doesn't work.

In your system you are providing a constant force in that your foot on the accelerator produces a constant stream of gas into your engine which produces torque to constantly accelerate your car. If your car isn't constantly being accelerated, it would stop.

Light isn't being accelerated. Light moves at c because it has no mass. This is a very important point of relativity. So when Engineer Artist asks us "how does the speed of light change" they are asking a profound question.

The answer is it doesn't. What happens is the light interacts with the solid which produces light that interferes with the original light and produces the illusion of slower light. When the light is out of the material that interference stops.

Google Book Explanation

An Analogy Using Double Slit Interference

Here's something comparable that I think people have a better handle on. What if someone asked you "why does light split up after passing through a slit?". The answer is it doesn't. The light is there at the locations that appear dark, even though you can't see it, it is just interfering with itself. (see diagram below)

This is incorrect. If one photon at a time is send to the slits, the same interference pattern is seen, so this explanation cannot be correct.

I'm not sure how accurate this is, but photons passing through non-vacuum medium would reflect off of or be deflected by the atoms of the medium, and thus travel in zigzag paths. Velocity along the zigzag paths would remain c, but aggregate motion in the "forward" direction would be slower. Upon emerging into vacuum, the velocity in the "forward" direction is still c.

Problem with that model is that there's no reason why they (or the majority of them) should all come out parallel with the incoming ones.

Same thing happens with electricity, travels down a wire at velocity X and is emitted from an antenna, it speeds up and if it travels to space it reaches the 299,999Km/sec or so. Antenna lengths change 5% between sea level and space.

Sooooooooo.......my question is, how can they accurately measure the distance to the moon within mm's when the speed of RADAR or even LASERs is not constant?

RCE,

I'm willing to continue. But if you are made uncomfortable by Kramarat's comment we can do it privately by CR4 mail. Or we can stop. Let me know.

Roger

As the two of you have probably deduced, despite my repeated claims to leave I still lurk in this thread. Before the two of you slip off into privacy mode there is a comment I wish to add in a much more sober state than I am now and with more rest. Work tomorrow will be a bear though so don't expect my comment until lunch time EDT.

This question, as well as many others, can only be answered easily with Ultrawave theory. Light is composed of two waves, an electrically charged wave and a magnetically charged wave. One of the waves always travels at c and the other travels at a velocity approx. equal to 8.935E+16 m/s, both in two dimensions. When traveling through a medium, the orientation of the waves changes and the propagation through three dimensions is altered, either slowing down or speeding back up as conditions warrant.

The ultrawave view of matter and energy answers the question of how light (energy)and matter are interchangeable. It also explains how light can be slowed down with a laser beam, or even stopped and restarted. If you would like to know more, visit ultrawavetheory.org.

Which one moves at 8.935+16?

OK, I did a quick scan of your link on this concept of Ultrawave. This theory seems to be at least a branch if not an oblique tangent of string theory. (Please, gently correct me if I'm wrong.) To answer RCE's question, this theory states that the Ultrawave moves at 8.935E+16 m/s (u) while the observed other wave of the photon propogates at the velocity known as c. u>>>c This is an absurdly faster velocity than light. Light takes about nine hours to travel the the average diameter of Neptune (about 1E13m) while the Ultrawave can travel this in less than a millisecond. Without studying this proposal, it seems obvious that the Ultrawave does not travel in a straight spacial path. If it did then it would very quickly dissociate with the speed of light wave.

But this is not my real questions for you, but here they are:

• What phenomena does Ultrawave theory predict to happen that the Standard Model theory predicts will not happen?
• Can we observe this phenomena today with our technology? If we can observe this, have we observed this?
• Has this proposed theory been peer reviewed?

as an addendum, I would ask who peer reviewed it just for clarity?

Also, as he indicated that light is made of two wave components, electic field and magnetic field waves, and that one of the two waves move at 8.935E+16. Which one moves at that speed? which was leading toward the dissociation of the wave comment, once he explained soemthing more.

Light is considered to have dual character, as particles when considering photonics, and as an electromagnetic wave when studying phenomena such as refraction, reflection, and diffraction, and "interference" effects. The frequency of such waves is a constant (regardless of the medium), as is the energy of a photon of light. Since light slows down in a dense medium such as water, glass, etc., the wavelength actually decreases, while the frequency is constant. Once light exits the medium back into air or "vacuum", the wavelength reverts to its original. Maxwell's equations reveal the out of phase nature of the electric field and the magnetic field, and the progagation of the wave depends on the permeability of the medium. The slowing of light waves in a medium are responsible also for the phenomena of refraction (lens, prisms, etc.), as well as dispersion of the spectrum (due to changes of the refractive index with respect to various wavelengths).

Your synopsis is what I recall. As the frequency remains constant, there is no red or blue shift

Quote: ".. since light slows down in a dense medium"

Where can I find experiments which show that light slows down in dense media James? All I can find are experiments in which light appears to slow down. I think there may be some simple omissions of some experimental parameters. We can reduce the frequency of radiation, or limit its penetration in dense media until it is completely absorbed, but we cannot "slow it down". We can make it go around corners and reflect it, thereby increasing the effective distance it travels, and the time it takes to get from A to B, but light is not going any slower than before. Light is stripped of energy and maintain only the longer wavelengths, but it is still not going any slower!

I would love to see some experiments (to prove Albert wrong about C at last!)

Slow light, it ain't light. The opposite is also true ..

I don't know where you would find an experiment concerning light, but it is a common factor in radio communications.

My understanding is the frequency remains constant but the wavelength changes. If the frequency changed, the colors would also change.

I understand that if the frequency remains the same, so does the speed. Only the wavelenghts are changed , or stripped?

NO. The wavelength becomes shortened, meaning in one period the wave travels a shorter distance, hence the speed in the medium is less. I refer you to Maxwell's equations for the progagation of radiation.

There was an article where light had been slowed down to a rediculously slow speed of twenty some meters per second in a material or gas using lasers. You may find it if you search for slowing light with lasers. I haven't checked myself.

Bose-Einstein condensate. Seems to me light never slowed down, it only had a very long, convoluted bath to get from a to b. So it took longer.

The short answer is refraction, light will travel in a straight line until matter that is solid or less denser such that of glass. The light as passes through the glass the speed does not change but will travel a longer distance due its refractory as oppose to straight-line distance.

or until it passes near a local masive body such that the gravity well bends the light path.

According to the fiber optic folks, you are correct. They use a refractive index of approx 1.5 for a velocity of approx 200,000 KM/S

Light is light and to be so it always retains constant speed, because it is its nature, or it just would not be in the state we call "light"; a simile would be the difference between milk and cheese (lol), or helium and gold. When light travels through a theoretical vacuum it makes no adjustments to its trajectory (it does not take detours around the magnetic fields which bend its path). The denser the medium, the stronger and more tightly packed the fields, the more detours. The farther the distance through this mass of fields, the greater the energy is dissipated as heat. This is why lights bends within a lens (refraction). In conclusion: light does not slow down and then accelerates: it simply goes around more bends and it gets from A to B slower than if it had been travelling in a straight line. We just did not notice the path's complexity. The common description of "light slows down in a medium denser than vacuum" is deceiving and was probably originally coined as a metaphor.

The mathematics or the physical picture?
Ok, spare the math for a while. If you think of the dense medium as sand and the light beam as marbles, it does not make sense. If you think of the medium as a hill and plateu, then the marbles go up the hill, lose speed, but gain potential energy, travel at (lower) constant speed in the plateu, and then travel downhill to gain their initial speed. The energy (of the photon-marble) is always the same. But you must change your perception of solid matter and geometric dimensions.

To understand matter you must understand light, and the converse is true. Why impose primitive models for nature, when ultimately sophisticated models that accurately and precisely describe nature are already in place?

What you call "sophisticated models" I call "overcomplicated models". The physical models based on UT more accurately and more precisely describe nature.

Someone has obviously sold you a bill of goods. Sorry for that to be the case. Go read some physics, if you can read.

Mr. Stewart:

Here are two places to you may look.

www.transition.com/transitionnetworks/resources/en/PDF/fiber_wp.pdf

www.madsci.org/posts/archives/2001-02/983369337.ph.r.html

If you do a search for "velocity of light in fiber optic cable" you can find more.

But they say the phenomena is the result of refraction.

In the communications field we use a piece of equipment called a TDR used to be HP, now Agilent. One of the settings deals with velocity factor in the media you are testing. They come in several flavors, Optics and conductor. You must enter the velocity factor as provided by the manufacturer to get valid readings.

I realize you are in Lubbock, did you ever work in Coral Gables or Chicago suburbs? With your attitude, you would be a perfect fit.

Typical response from someone who does not know anything about the subject matter. Ultrawave theory can make sense of any aspect of nature I have attempted to explain. It can even account for the NASA tech brief concerning "optical batteries". I have no more time to devote to this thread, so don't bother to reply. If anyone wants to learn a simpler and more logical way of looking at the universe then I recommend they look at UT rather than the Standard Model.

I have no more time to devote to this thread, so don't bother to reply.

Typical response from a narcissist

as if you are the only one reading or participating in this discussion

Just an observation 200 odd post on;

If you disregard how light got into the 'denser medium' and the whole traveling through part - and just ask 'at what speed does light radiate from any emitting surface?" (into air or vacuum) - the answer is rather self evident.

Light remains a paradox. Ripples on a pond, sounds through a media and light...? are manifestations of the harmonic movement of tiny particles. IMHO if something has zero mass it doesn't exist. So matter is also a paradox.

Bobguz

Your theory, thoughts, words, and attitude have no mass. Therefore they do not exist. Since your thoughts do not exist, you do not think. Now taking the obverse of René Descartes famous quote "Cogito ergo sum" this then means that you do not exist. Since you do not exist, you have no mass. Congratulations, you've just achieved the Weight Watchers record of complete weight loss.

Smug, arrogant and ignorant describe most science in most ages. Bobguz

I like the idea of resonance as it may be applied to light. I suspect that resonance could help to describe why light appears to slow down as it transverses a medium denser than vacuum, and why the trajectory changes when it enters the medium at an angle different to 90° and why there is a change in wavelength depending on the medium elements composition.

In fibre optics the refractive index of 1.5 is inversely proportional to the estimated speed (200.000 m/s through glass cable?), with some wavelength change (color) from origin, hence the need for medium purity. The light travels through the cable at a constant speed; if it was "slowing down" the speed would gradually decrease; this does not happen. Provided the energy is not completely absorbed the light travels at a constant speed caracteristic to that medium (all elements have a caracteristic wavelength) .

The wavelength changes could be called immediate upon entry into the medium and scatter and absorption dependent on impurities and molecular geometry (reflection). Does the wavelength change? Resonance could explain how this could happen. Or should we say that some wavelengths are absorbed and others pass through because the orbits are wider or smaller that the element's atomic field? I propose that the "orbit" of the wave (I see the energy propagating as an helix, multiple helices in a variety of wavelengths,) becomes captured by same size "orbits", while others are unaffected and pass through the medium. Impurities in the medium would imply other elements (different atomic structure) which would absorb other "orbits", because they are present in its structure. In my mind we should also consider how gravity fits into this, but I don't want to go that way here.

"At the microscale, an electromagnetic wave's phase speed is slowed in a material because the electric field creates a disturbance in the charges of each atom (primarily the electrons) proportional to the permittivity of the medium."

I can see nothing wrong with the above and we don't need another esoteric model to explain it, just some experiments to get rid of the "light slows down" expression which seems to be so stuck in so many statements from this discussion and media science reportage.

When I first posted the comment below, I had two "Off topic" marks; they seem to have now disappeared (#184). I would abolish the off topic system, as it is rife with missuse and it does not add anything to the debate: to declare any statement off topic, members should provide their explanation.

"Light is light and to be so it always retains constant speed, because it is its nature, or it just would not be in the state we call "light"; a simile would be the difference between milk and cheese (LOL), or helium and gold. When light travels through a theoretical vacuum it makes no adjustments to its trajectory (it takes no detours around the magnetic fields which bend its path). The denser the medium, the stronger and more tightly packed the fields, the more detours. The farther the distance through this mass of fields, the greater the energy is dissipated as heat. This is why lights bends within a lens (refraction). In conclusion: light does not slow down and then accelerates: it simply goes around more bends and it gets from A to B slower than if it had been travelling in a straight line. We just did not notice the path's complexity. The common description of "light slows down in a medium denser than vacuum" is deceiving and was probably originally coined as a metaphor."

Although the above uses pretty simple metaphors, I still believe it describes what happens without complicated and exclusive terminology, or maths. Given that this discussion include participants from a number of disciplines and just interested individuals, I see as a fair deal containing the maths to an absolute minimum, or at least translating it into something like diagrams for everyone to see with an opportunity to understand.

Re: (it takes no detours around the magnetic fields which bend its path)

The first time you posted that I pisted to ask if the "no detours" was a typo, and you said yes (iirc)--you haven't changed your mind, have you? (I don't expect that you have--I just think you ought to correct it here, also ;-)

It should read: "it takes detours" I haven't changed my mind it is still taking detours.

Thanks!

I guess the explanation that resonates most with me at the moment is the one that talks about some of the energy from the light beam increasing the energy of the electrons in the material as light goes in, and then being restored to the light beam as it leaves the material. But, I'm not sure. And, there doesn't seem to be a clear consensus in this thread (or one definite convincing right answer)--of course, I may not know enough to recognize the one right answer if it is presented to me.

And, as I think someone else suggested in this thread, there could be more than one answer, e.g., one answer for light as a wave and one answer for light as a particle ;-)

I considered the dual aspect of light for awhile, but, like many others, I have come to being dissatisfied with it's description. I have been looking for ways in which I can dismiss the hypothesis of photons being diverted from a straight path in dense media (relative to a vacuum trajectory, therefore increasing distance), but I cannot come up with any experiment that proves otherwise, and instead, every experiment seems to support the idea, provided we get rid of the preconception of light actually slowing down and we replace it with "appears to slow down". I realise that if we measure a piece of optic fibre and time the travel of light through it, the time increases compared to its travel in a vacuum. I only have a problem with the "light slows down, then accelerates", because slow light does not exists as light, react as light, illuminate as light! We already know that light can bend around gravitational fields, geometry should then suffice for the explanation of distance/time.

"some of the energy from some of the energy from the light beam increasing the energy of the electrons in the material as light goes in, and then being restored to the light beam as it leaves the material as light goes in, and then being restored to the light beam as it leaves the material"

Your above it's probably a more attractive proposition, but maybe the less elegant idea is all we need for an explanation.There is no evidence that light somehow regains any of the energy lost though the medium: whether the loss was towards ultraviolet, or infrared. What is left over is what could pass through, the rest is gone into the medium. "some of the energy from the light beam increasing the energy of the electrons in the material" as you pointed out (you are half right). This is particularly clear in light-induced chemical reactions and in the practical optical applications.

We are almost back to the questions of: "what is energy?" Is it simply matter accelerated to C, and the inverse also true? It is certainly implied in Einstein's famous formula and evident in nuclear fission! But is it? The dual nature pops up again because of these questions. What actually happens in black holes? I think that the answer is the same: speed of light the same, larger scale. Is there a mini-black hole in every atom? How big is "mini"? It is calculable, that's how big, but not visible (of course; it's a black hole!).

Our sensory apparatus, and even the most sophisticated test equipment, is composed of larger particles than what we are trying to measure, so we have to choose how we interpret data, and use our imagination to see which possible (not just probable) parameter has been left out, as we CANNOT include them ALL.

I am quite happy for anyone to show me were I may be missing something, and I appreciate any comment.

Maths translations can be made later; ideas is where it all begins.

So how fast is the light going into the tungsten filament, given it comes out at the speed of light?

"So how fast is the light going into the tungsten filament"

I would say it is going at the speed of light going into it. As for how fast it is going while inside the filament that is the debate here.

I don't think there is any light going into the filament. When you burn a candle and light starts getting emitted, did light enter the candle (or wick, or wax, or even the incandescent gases)?

I reckon the electrons whizzing along the wire warmed it up enough to squeeze the phlogiston out. Don't know how it got there in the first place.

In theory, some form of energy raises the electrons into a higher quantum state, when they collapse back they release light.

"that is the debate here"

And strangely, it is. Whereas the question is clearly; "How Light Regains its Velocity After Passing Through Guinea Pigs"

I do not understand your point, can you please clarify?

You said you wanted to deal in "concepts" so I gave you one. Think of it this way; take 1 excited atom emitting photons - how do the photons know which way is 'out', so go 'faster', as opposed to which way is 'not out', so go slower?

Or is there something about 'not out' that means they take longer?

I think photons are emitted in all directions permitted by the molecular structure of the medium. The escaping photons, the ones which are generated on the surface, or reach the surface, radiate within the restrictions of the molecular structure of air/vacuum, or whatever.

I thought the speed was 200,000 Km/s or 200,000,000 m/s in fiber cable.

You are correct. My error.