A question about light speed.

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Originally Posted by Hired_Goon

Irrelevant. It has taken longer to get there, therefore, it has been slowed.

It is of course slowed by something, but the definition of a detour is then up for debate.

A perfect pane of glass will slow light down in a direct line, Therefore not a detour. A detour would be through a series of prism's or mirrors.

It's the same as the term Vacuum loosely used in previous posts. A vacuum doesn't really exist in reality. The term vacuum is used to define a lower pressure area that is created by the higher pressure of matter outside it. The terms of definition can always be argued, as can the interpretation.

But in reality, your simple question of "Can light move slower than the speed of light?" is Yes. It can. But not by itself.

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If Rota's right, it only really appears to still be travelling in a straight line; the changes in direction would all average out to that result; the changes would be tiny and many. And the fact of a "detour" is important. There's a big distinction between instantaneous speed and average velocity.

Has anyone considered the effects of 'Dark Matter' on light? Im an economics major but i took an astrophysics course last year for the fun of it, and i seem to recall the prof talking about a theroy stating that the mass of the 'dark matter' affects the wavelengths of light. This could be the friction that was mentioned earlier, and could also be responsible for bending light.

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Originally Posted by Bree Fletcher

If Rota's right, it only really appears to still be travelling in a straight line; the changes in direction would all average out to that result; the changes would be tiny and many. And the fact of a "detour" is important. There's a big distinction between instantaneous speed and average velocity.

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If you drive directly through a pane of glass, you will lose velocity, therefore speed. You are not being detoured from your original direction.

All glass is doing to light is slowing down the velocity of it's travel.

Not detouring.

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Originally Posted by Lucas101

Has anyone considered the effects of 'Dark Matter' on light? Im an economics major but i took an astrophysics course last year for the fun of it, and i seem to recall the prof talking about a theroy stating that the mass of the 'dark matter' affects the wavelengths of light. This could be the friction that was mentioned earlier, and could also be responsible for bending light.

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Anything with mass will create at least a minor gravitational field. That will bend light, even if it is very slight. Dark matter will bend light, as well as planets, and stars, and asteroids, and comets, and ANYTHING the light might pass by. :)

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Originally Posted by Hired_Goon

If you drive directly through a pane of glass, you will lose velocity, therefore speed. You are not being detoured from your original direction.

All glass is doing to light is slowing down the velocity of it's travel.

Not detouring.

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That analogy... isn't really valid... for so many reasons...

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Originally Posted by Hired_Goon

If you drive directly through a pane of glass, you will lose velocity, therefore speed. You are not being detoured from your original direction.

All glass is doing to light is slowing down the velocity of it's travel.

Not detouring.

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LOLWUT??

:duh:

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Originally Posted by Hired_Goon

Irrelevant. It has taken longer to get there, therefore, it has been slowed.

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Incorrect. Speed = Distance/Time, what you are thinking of is velocity. The distance is how far the light travels, which counts all the little bumps/detours/refractions that the light goes through. Velocity is Displacement/Time, and displacement only counts the distance between the end and beginning points.

So basically, the speed never changes while velocity does.

k i haz 1..
youre in space (a vacuum) straight in front of you theres a mirror, you can see yourself.
then you both start accelerating (at the same rate) up to the speed of light.
what do you see in the mirror?

good luck sleepin tonight rota ;)

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Originally Posted by lkmus

k i haz 1..
youre in space (a vacuum) straight in front of you theres a mirror, you can see yourself.
then you both start accelerating (at the same rate) up to the speed of light.
what do you see in the mirror?

good luck sleepin tonight rota ;)

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Actually, that one's pretty simple. First, you'd never get to the speed of light. Second, you'd always see yourself in the mirror, so long as you have a light source.

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Originally Posted by Bree Fletcher

That analogy... isn't really valid... for so many reasons...

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A hell of a lot simpler than quoting passages from the 100 odd wikipedia passages the basicaly say the same thing.

Light is matter, matter can travel at a certain velocity, velocity can be slowed by passing through different matter.

Semantics can be argued to keep a point of debate going, but basically, the question has been answered:).

You're saying the mirror is accelerating at the speed of light toward me, while I am speeding at the speed of light toward it?

The mirror will be speeding toward me at the speed of the light energy which showed me the where mirror was when the whole thing started. I will see the mirror as being still in it's original position (with the original image of me standing still), until we collide.

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Originally Posted by lkmus

k i haz 1..
youre in space (a vacuum) straight in front of you theres a mirror, you can see yourself.
then you both start accelerating (at the same rate) up to the speed of light.
what do you see in the mirror?

good luck sleepin tonight rota ;)

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Answer: Nothing. You would die from the lack of air and cold then the speed of moving your body at lightspeed would generate heat that would vaporise your physical form. The Mirror would be broken and you would have 7 years bad luck too.

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Originally Posted by Bree Fletcher

Actually, that one's pretty simple. First, you'd never get to the speed of light. Second, you'd always see yourself in the mirror, so long as you have a light source.

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soz! meant to say the only light source was behind you.. and forget about turnin to energy as you get to the speed of light. purely a theoretical question

and no rota.. you and the mirror are moving in the same direction

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Originally Posted by Hired_Goon

A hell of a lot simpler than quoting passages from the 100 odd wikipedia passages the basicaly say the same thing.

Light is matter, matter can travel at a certain velocity, velocity can be slowed by passing through different matter.

Semantics can be argued to keep a point of debate going, but basically, the question has been answered:).

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With most forms of matter, this is true. Mometum will be transferred from one to another (such as a car transferring momentum to a large number of glass shards.) To decrese the momentum, the car has to slow down. Completely correct.

Light, however, acts differently. When it transfers momentum in some way, it decreases its own by decreasing wave frequency, not slowing down.

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Originally Posted by Bree Fletcher

Light, however, acts differently. When it transfers momentum in some way, it decreases its own by decreasing wave frequency, not slowing down.

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Sorry, But that appears to be an oxymoron.

It decreases, but doesn't slow down?

Drecreased wave frequency is slowing down.
You are, in a way, confirming my point.

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Originally Posted by lkmus

soz! meant to say the only light source was behind you.. and forget about turnin to energy as you get to the speed of light. purely a theoretical question

and no rota.. you and the mirror are moving in the same direction

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We are moving at the speed of light forward, and the mirror is facing me as I face forward in the direction we are traveling. No light can hit the mirror, since it is outpacing the light beams it would reflect. I will simply see the mirror as a black nothingness blocking out the starlight behind it. When we slow down even the slightest bit below the speed of light, it will appear to me again complete with a reflection of me.

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Originally Posted by imnothere

you know we dont really know a whole lot about what we know.

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And that officially seals the deal folks. This poster is now on my awesome list.

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Originally Posted by Hired_Goon

Sorry, But that appears to be an oxymoron.

It decreases, but doesn't slow down?

Drecreased wave frequency is slowing down.
You are, in a way, confirming my point.

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The frequency is not intrinsically related to speed. In fact, you can keep the speed constant (and this is actually what happens) by increasing wavelength. (The equation: speed = wavelength x frequency) Therefore, keeping speed constant, wavelength of light increses as frequency decreases, all brought about by a decrease in momentum of the photon. No change in speed.

A good description of the Compton Effect, which I am describing: http://dev.physicslab.org/Document.a...ptonEffect.xml (Note that for speed, the constant c is always used. As in, the speed of the photons never changes.)

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Originally Posted by Rota

We are moving at the speed of light forward, and the mirror is facing me as I face forward in the direction we are traveling. No light can hit the mirror, since it is outpacing the light beams it would reflect. I will simply see the mirror as a black nothingness blocking out the starlight behind it. When we slow down even the slightest bit below the speed of light, it will appear to me again complete with a reflection of me.

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But if that mirror were to be slowed down to just below the speed of light you would probably see a very outdated reflection of yourself, lol.:D

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Originally Posted by Rota

I accept the speed of light is approximately 300 million meters per second. I am willing to hear the argument that the speed of light is the "speed limit" of the universe. But, that's not what this thread is about. My question is...

Can light move slower than the speed of light?

Does a little electron of light-energy ALWAYS travel at the speed of light? Can a beam of light-energy travel at a paltry 100 million meters per second? If energy is moving slower than the speed of light, then is it no longer considered to be "light?" Is it now some other kind of radiated energy?

The speed of light is a constant (c) in many physics and math equations. But, is the speed of light constant? Or is (c) really just the maximum speed of light?

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According to modern physics, the speed of light is determinate on its' medium. Light moves faster in a vacuum, slower in air, slower still in a liquid or a solid. This backs up the fundamental theory that light behaves not only as a wave, but also as a particle, as it encounters an assumed resistance to a specified medium.

We can see evidence of this in situations such as the refraction of light upon entering a body of water. The beam of light appears distorted and transformed to follow a new angular path, away from the perpendicular of the waters surface, rather than its' angle of incidence.


Fig. 1
http://hyperphysics.phy-astr.gsu.edu...ic/brokpen.jpg

This is due to water having a refractive index of 4/3, meaning that light travels 3/4 its' relative speed in air, in water.

So if your question is simply; "Does the speed of light have a definite value?". Then, no, it doesn't. The speed of light changes depending on its' medium. Theoretically, if you could find a medium with less resistance than what we currently know as a vacuum, then the speed of light would increase, conversely in media thicker than a vacuum the speed is decreased.

That aside, the speed of light does have a definitive value for a medium. Meaning, if you were asking; "Is the speed of light only a maximum value?". Then, no, the speed of light is a constant figure for a medium, and has never been measured at a different speed other than 'v'. Which in a vacuum is 'c' (299,792,458 M/s), and at a speed of c / 1.0003 in air. (Where 1.0003 is the refractive index for air) Due to this value being so small, we rarely find the need to state the difference between air and a vacuum in calculations, as it is assumed that this is a negligible figure.

To quote, and I feel dirty doing so, Wikipedia;

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The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is very close to c.

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Does that answer your question?

(Citation; My A-Levels in Physics, and AQP (Advancing Quantum Physics), respectively)

If you slow light down from light speed to walking speed, you'll see its really just a guy in a gorilla suit.

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Originally Posted by The Midnight Walker

Does that answer your question?

(Citation; My A-Levels in Physics, and AQP (Advancing Quantum Physics), respectively)

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If you'd actually read through the thread, then you'd realize that we've been down this path about five seperate times. Every time we've come across this same problem:

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Originally Posted by Rota

But, the example I gave earlier about the route between two cities... Does refraction truly slow down the light? or just detour it? Is light still moving at the same speed, but taking a longer route to get to it's destination (thus it only "appears" to go slower)?

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Originally Posted by Bree Fletcher

If you'd actually read through the thread, then you'd realize that we've been down this path about five seperate times. Every time we've come across this same problem:

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And if you'd care to drop the high and mighty persona, we'll continue.

Light travelling through a medium is not 'detoured' but slowed down.

If you subscribe to the quantum theory of light, you'd know that light does not travel a single path, but all possible paths imaginable, and selects its' path based on a determinable probability. So if this theory of a detour was the case, then it would be a result of a probability. However due to experimentation it is shown that, despite the predicted anomalies, the prior is true.

Also explained in this theory is the law of refraction, which although is a change in direction, does not fulfil the theory that the light has taken longer because it has gone a different way, but the inverse. Refraction occurs as a part of the light wave hits the incidence of medium before another, therefore part of a beam is slowing down before another, giving the effect of an altered angle. Meaning, that light has taken a different route because it has been slowed down.

You can try and argue the opposite if you'd like, but to remind you; Much smarter men than you, the world over, throughout hundreds of years have come to this conclusion through experimentation, calculation and observation. If I were you, I'd believe them, they seem to know a thing or two.

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Originally Posted by The Midnight Walker

And if you'd care to drop the high and mighty persona, we'll continue.

Light travelling through a medium is not 'detoured' but slowed down.

If you subscribe to the quantum theory of light, you'd know that light does not travel a single path, but all possible paths imaginable, and selects its' path based on a determinable probability. So if this theory of a detour was the case, then it would be a result of a probability. However due to experimentation it is shown that, despite the predicted anomalies, the prior is true.

Also explained in this theory is the law of refraction, which although is a change in direction, does not fulfil the theory that the light has taken longer because it has gone a different way, but the inverse. Refraction occurs as a part of the light wave hits the incidence of medium before another, therefore part of a beam is slowing down before another, giving the effect of an altered angle. Meaning, that light has taken a different route because it has been slowed down.

You can try and argue the opposite if you'd like, but to remind you; Much smarter men than you, the world over, throughout hundreds of years have come to this conclusion through experimentation, calculation and observation. If I were you, I'd believe them, they seem to know a thing or two.

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Now see, this explanation could have served earlier, so that your first post wouldn't have been a repeat of what has been said...

Now, not to be rude or stubborn, but I honestly haven't read anything about what you are saying. Sounds like there is something, though, so I'd much like to see it if you could find it for me. :D

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Originally Posted by Bree Fletcher

Now see, this explanation could have served earlier, so that your first post wouldn't have been a repeat of what has been said...

Now, not to be rude or stubborn, but I honestly haven't read anything about what you are saying. Sounds like there is something, though, so I'd much like to see it if you could find it for me. :D

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Here is a diagram illustrating my point;

http://farside.ph.utexas.edu/teachin...es/img1319.png

Found on a page detailing Snell's Law (The Law of Refraction)

Does this help?

EDIT: Thinking about it, the whole page may explain more than just the image, so here you go :)

http://farside.ph.utexas.edu/teachin...s/node128.html

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Originally Posted by The Midnight Walker

Here is a diagram illustrating my point;



Found on a page detailing Snell's Law (The Law of Refraction)

Does this help?

EDIT: Thinking about it, the whole page may explain more than just the image, so here you go :)

http://farside.ph.utexas.edu/teachin...s/node128.html

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Well, I already knew how refraction worked as a general principle, but my problem was always how every explanation I've found says it slows, but then fails to explain why. What did help on that website, however, is where it said the light's wavelength decreases. If that's true, then I suppose there's no other conclusion then to say that the speed of light decreased.

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Originally Posted by Bree Fletcher

Well, I already knew how refraction worked as a general principle, but my problem was always how every explanation I've found says it slows, but then fails to explain why. What did help on that website, however, is where it said the light's wavelength decreases. If that's true, then I suppose there's no other conclusion then to say that the speed of light decreased.

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Correct. I completely forgot to mention that in my first post. Would have saved a lot of hassle. :)

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Originally Posted by Rota

I accept the speed of light is approximately 300 million meters per second. I am willing to hear the argument that the speed of light is the "speed limit" of the universe. But, that's not what this thread is about. My question is...

Can light move slower than the speed of light?

Does a little electron of light-energy ALWAYS travel at the speed of light? Can a beam of light-energy travel at a paltry 100 million meters per second? If energy is moving slower than the speed of light, then is it no longer considered to be "light?" Is it now some other kind of radiated energy?

The speed of light is a constant (c) in many physics and math equations. But, is the speed of light constant? Or is (c) really just the maximum speed of light?

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yes, yes you can.. it has to do with refraction or something if i remember correctly...
also light speed is a fixed speed... time is relative... so you can slow down light by slowing down time... yeah, i know.. thats cheating

This might help :)

http://abcnews.go.com/Technology/story?id=99111&page=1

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Originally Posted by Sooria

This might help :)

http://abcnews.go.com/Technology/story?id=99111&page=1

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Good find! I heard a rumour that something like this had been done, yet I found no evidence of it when I searched. Thanks, and +rep

Agreed. That is an excellent find.

+rep from me as well.

Thanks :) And being an engineer helps a bit :p

what practical uses can be made from slowing light down, also would it be possible to give light density since they were able to slow it down? if they can give it some sort of density or good use then ill acknowledge it as a worthwhile experiment

Light has different properties and has to be looked at from a scientific point of view in order to understand its behavior and properties. I have posted a website below that explains it well without the scientific mumbo jumbo that sometimes we get lost in, however, remember that this is just an overview not with the latest in discovery :) Hope it helps!

http://www.play-hookey.com/optics/what_is_light.html
http://science.howstuffworks.com/light.htm